geo and gmes - ecmwf...systems (geoss) by achieving comprehensive, coordi-nated and sustained...

ECMWF Newsletter No. 104 – Summer 2005

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In this issue

EditorialGEO and GMES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

NewsChanges to the operational forecasting system. . . . . . . . 2New items on the ECMWF web site . . . . . . . . . . . . . . . . 2New ECMWF data sets and services . . . . . . . . . . . . . . . . 2Tenth Workshop onMeteorological Operational Systems . . . . . . . . . . . . . . . . 3Long-term co-operation established with ESA . . . . . . . . . 3Meeting of the Scientific Advisory Committee on3–5 October 2005 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463rd Council session on 13–14 June 2005. . . . . . . . . . . . 4

MeteorologyA preliminary survey of ERA-40 users developingapplications of relevance to GEO(Group on Earth Observations) . . . . . . . . . . . . . . . . . . . . . 5EPS skill improvements between 1994 and 2005 . . . . . 10CO2 from space: estimating atmospheric CO2within the ECMWF data assimilation system. . . . . . . . . 14Improved prediction of boundary layer clouds. . . . . . . . 18

ComputingDeveloping and validating Grid Technology forthe solution of complex meteorological problems. . . . . 22

GeneralECMWF Calendar 2005/2006 . . . . . . . . . . . . . . . . . . . . . 24Index of past newsletter articles. . . . . . . . . . . . . . . . . . . 25ECMWF publications. . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Useful names and telephone numbers within ECMWF . 28

European Centre for Medium-Range Weather ForecastsShinfield Park, Reading, Berkshire RG2 9AX, UKFax: . . . . . . . . . . . . . . . . . . . . . . . . . . . .+44 118 986 9450Telephone: National . . . . . . . . . . . . . . . .0118 949 9000

International . . . . . . . . .+44 118 949 9000ECMWF Web site . . . . . . . . . . . . . .http://www.ecmwf.int

The ECMWF Newsletter is published quarterly. Its purposeis to make users of ECMWF products, collaborators withECMWF and the wider meteorological community aware ofnew developments at ECMWF and the use that can bemade of ECMWF products. Most articles are prepared bystaff at ECMWF, but articles are also welcome from peopleworking elsewhere, especially those from Member Statesand Co-operating States. The ECMWF Newsletter is notpeer-reviewed.

Editor: Bob Riddaway

Typesetting and Graphics: Rob Hine

Front coverPartial illustration of the scope of GEO (Group on EarthObservations). The full scope of GEO is presented inFigure 1 on pages 6 and 7.

Editorial

GEO and GMESThis quarter was marked by several events which togetherconstitute new milestones for the involvement of ECMWFin earth observation and environmental monitoring.

On 13 May 2005 the European Commission signedthe contract for the GEMS (Global and regional Earth-sys-tem Monitoring using Satellite and in-situ data) project.The signing of this contract constitutes a major milestonefor ECMWF as this project will allow the development ofthe assimilation and forecasting system towards environ-mental monitoring (see the article by Tony Hollingsworthin the last Newsletter, No. 103). It is also an importantstep in the involvement of ECMWF in the GMES initiative(Global Monitoring for Environment and Security)launched a few years ago by the European Union andthe European Space Agency (ESA). GMES has severalcomponents such as atmosphere, marine and land serv-ices, and the development of risk analysis and warningservices. ECMWF is primarily involved in the atmosphericcomponent (i.e. GEMS) as coordinator. However, as aconsequence of its development of an earth-system mod-elling facility, ECMWF is also involved as a participant inall of the other components.

On 3 and 4 May 2005, the first plenary meeting of thenew GEO (Group on Earth Observations) organisationwas held in Geneva, with ECMWF as one of the partici-pants. This organisation is a follow-up to the discussionswhose origin can be traced back to the Johannesburgsummit on sustainable development in 2002. The goal ofGEO is to develop a Global Earth Observation System ofSystems (GEOSS) by achieving comprehensive, coordi-nated and sustained observations of the earth system, andallowing the development of applications benefiting soci-ety in various areas including disaster mitigation, energy,health and weather (see the article by Hollingsworth andPfrang in this issue). A key aspect of this new organisationis that it involves States and International Organisations.ECMWF has been involved since the first Earth Observa-tion summit in 2003, thus recognising its role in theprocess of transforming observation data into useful infor-mation. It is not surprising that GMES is usually presentedas the major European contribution to GEO.

On 31 May 2005, a Co-operation Agreement wassigned in Paris between ESA and ECMWF. Again, this is aconfirmation of our role in earth observation which, asfar as ESA is concerned, was particularly successful withERS and will now continue with ADM-Aeolus.

Last but not least, an important characteristic of thesedevelopments is that ECMWF is involved in close part-nership with its Member States. Together they contributeto the whole European Meteorological Infrastructure(EMI) which is required to address the challenge of GEOand GMES.

Dominique Marbouty

ECMWF Newsletter No. 104 – Summer 2005NEWS

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François Lalaurette

Changes to the operational system

A new version of the model, Cy29r2, was implementedon 28 June 2005.

The main changes included in this version are:� Assimilation of rain-affected SSM/I radiances.� Set of changes to the AIRS assimilation (including retuned

bias correction).� Use of Meteosat-8 (MSG) winds.� Jb statistics from the latest ensemble data assimilation.� Refinement of the surface-pressure bias correction.� Humidity analysis changes: reduced spin-up and strato-

sphere increments.

Andy Brady

Updated User Guide to ECMWF Forecast Products

The User Guide to ECMWF Forecast Products is not like mostother "user guides", which provide clear and straightfor-ward instructions how to "plug in", "get started", "execute"and "switch off". Nor is this Guide a handbook in NWP,dynamic meteorology or weather forecasting; the aim ofthe Guide is to facilitate the use of traditional ECMWFmedium-range forecast products, and encourage the use ofnewer, more advanced products such as the wave forecasts

Alfred Hofstadler

New data sets disseminated on GTS

ECMWF has added some new data sets to its GTS dissemination.� ECMWF seasonal sea surface temperature (SST) fore-

cast anomalies. Global SST forecast anomalies from theECMWF seasonal prediction system are encoded in FM92 GRIB edition 2 at 2.5 degree lat/long resolution.Theforecast runs once a month with a basetime of 00 UTCon the first day of the month.The fields are produced andsent to the GTS on the fifteen day of each month.

� ECMWF Tropical Cyclone Tracks.Tropical Cyclone Tracksfrom the ECMWF deterministic forecast and the ensem-ble prediction systems are encoded in FM 94 BUFR andare made available from 00 and 12 UTC basetime. Thetracks delineate the positions of tropical cyclones from theanalysis to 120 hours into the forecast in 12 hourly timesteps.Products will only be generated and inserted onto the GTSif there are some observed positions of tropical cyclones orTropical Cyclone Tracks have been detected in the forecast.

� Use of the SMHI Baltic sea-ice analysis.� Convection changes (winds).� Revised Gaussian sampling for the EPS perturbations.

Planned changes — major upgrade

A major upgrade in resolution is planned for the autumn,with T511L60 to become T799L91 and the Ensemble Predic-tion System (EPS) to increase in resolution from T255L40 toT399L62.The data assimilation will benefit from the higherresolution model and the iterations (inner loops) will be runwith T255.More details (including test data) allowing MemberStates to prepare for this change can be found at:

www.ecmwf.int/products/changes/high_resolution_2005

Changes to the operational forecasting system

New items on the ECMWF web siteand the ensemble forecasts in the medium-range (EPS), andthe monthly and seasonal forecasts.

www.ecmwf.int/products/forecasts/guide/

Workshop on representation of sub-grid processes

A workshop on the representation of sub-grid processesusing stochastic-dynamic models was held from 6 to 8 June2005.The workshop explored new ideas on the represen-tation of sub-grid processes in weather and climate models,using computationally-cheap stochastic-dynamic systems.

www.ecmwf.int/newsevents/meetings/workshops/2005/Sub-grid_Processes/

New ECMWF data sets and servicesMore information about these new products and all other

ECMWF GTS products can be found by going towww.ecmwf.int/products/additional/

and then following the links at the bottom of the page.

New ECMWF services on the web

Two new ECMWF services are available via the web.Theseservices are restricted to the WMO community.� ECMWF EPSgrams for WMO Members. Epsgrams are

available for the capital city of each WMO Member.Theseare updated twice daily and are sorted by alphabeticalorder.The database of capital cities is still being constructed,particularly for islands. Please let us know about possibleinaccuracies.The new service can be accessed at:www.ecmwf.int/products/forecasts/d/charts/medium/epsgramswmo/

� ECMWF GTS dissemination data on the web.As a newservice ECMWF is providing access to its medium-rangeGTS dissemination data in FM92 GRIB on the web.Moreinformation about this new service can be found at:www.ecmwf.int/products/about/wmo_nmhs_access/


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NEWS

Horst Böttger

The biennial Workshop on Meteorological OperationalSystems, to be held at ECMWF on 14–18 November 2005,will be the tenth in the series.The workshop will review thestate of the art of meteorological operational systems andaddress future trends in the use of medium-range forecastproducts, data management and meteorological visualisationson workstations.

Use and interpretation of medium- and extended-range forecast guidance

The ECMWF forecasting system provides the users withoperational forecast guidance twice daily out to day ten, oncea week out to 31 days and once a month out to six months.Both the monthly and seasonal forecasts are based on acoupled ocean-atmosphere forecasting system.The Centreplans to implement major upgrades to the forecasting systembefore the end of 2005.The deterministic model will moveto the finer resolution of T799 (linear grid, 25 km reducedGaussian) with 91 levels in the vertical, while the EnsemblePrediction System (EPS) will be run at T399 (linear grid,50 km reduced Gaussian).There are also plans to upgradethe monthly forecasting system and integrate it into a unifiedmedium- to monthly-range forecasting system. A multi-model seasonal forecast system has been implemented andproducts are under development.These changes to the fore-casting system will be discussed at the workshop and firstexperiences will be reported. It is expected that users of theECMWF forecasts will report on the use and application ofthe products and on their approach to medium- andextended-range weather forecasting. Contributions address-ing the prediction and verification of severe weather eventswill be welcome.

With the planned extension of the medium-range fore-casts to 15 days and the introduction of a unified forecastingsystem out to a month it is planned to address the userrequirement for products from such a unified system in aworking group.

Operational data management systems

Users of meteorological data often find that data sets ofinterest are scattered around and that data access is cumber-some.Web services and Grid technologies are to an increasingextent finding their way into meteorological informationsystems, as well as other environmental disciplines, facilitat-ing the access to distributed data sets through user-friendlyapplication portals.

Developing technologies and applications will be presentedat the workshop together with user experience. Futurerequirements will be discussed in a working group, focussingon issues of interoperability (between centres and betweendisciplines), data catalogues, discovery mechanisms and meta-data standards.A working group will also address the servicesthat could be offered and ways to convert or abstract vari-ous data formats.

Meteorological visualisation applications

As the number of graphics file formats continues toincrease, more choices are becoming available regardingfunctionality but also more issues arise concerning softwareand hardware compatibility. Developments in this area forinteractive and batch production of meteorological plotswill be presented and demonstrated at the exhibition. Newmeteorological visualisation applications and updates toexisting applications will also be presented.

A working group will discuss the issues surrounding thedifferent file formats as they relate to meteorological plots,including static and animated formats for on-screen displaysuch as GIF and JPEG, formats for printing such as PostScriptand PDF, and interactive formats such as SVG and Flash. Fileformats suitable for interfacing with GIS systems will alsobe examined.

Further information

A registration form for the workshop is now available from:www.ecmwf.int/newsevents/meetings/workshops/2005/MOS_10/Further information about the workshop will be put on

this website, including the programme once it becomesavailable in the autumn.

Tenth Workshop on Meteorological Operational Systems

Manfred Kloeppel

On 31 May 2005 Dominique Marbouty, Director ofECMWF, and Jean Jacques Dordain, Director-General of theEuropean Space Agency (ESA), signed a Co-operationAgreement on exchange of information and expertise,whichwill establish long-term co-operation between these twoEuropean organisations.

Intended as an umbrella to cover activities already in placeas well as future activities, the agreement pledges the exchangeof information and expertise between ECMWF and ESA.

In addition it establishes regular bi-lateral meetings, educa-tional and fellowship exchanges, and fixed points of contact.

In practical terms, ECMWF is not only a leading opera-tional user of results from ESA-developed satellites but alsohelps ensure data quality control, instrument calibration andvalidation as well as providing estimates of the performanceof climate-related satellite sensors planned for the future.

ECMWF routinely assimilates near-real time data fromERS-2 and Envisat into its weather forecasts. It also validatesresults from these satellites’ instruments on an ongoing basis,comparing their data on meteorological events to other ground

Long-term co-operation established with ESA

ECMWF Newsletter No. 104 – Summer 2005NEWS

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Philippe Bougeault

The Scientific Advisory Committee (SAC) normally meetsonce a year to consider the draft programme of activities ofthe Centre and to submit to Council is opinions and recom-mendations.The 34th session of the SAC will take place on3–5 October 2005. Included in the agenda will be thefollowing topics.� Progress Report by the Head of the Research Department� Progress Report by the Head of the Operations Department� Verification statistics and evaluations of ECMWF forecasts� Impact of forecast system upgrades (1995–2005)� Progress in ocean wave forecasting

� Linearization and convergence issues in the 4D-Var� ECMWF Strategy 2006–2015� Consideration of the updated Four-year Programme of

Activities and ceilings of expenditure for the years 2006-2009

� Detailed Research Plan 2006-2009� Consideration of the budget including options� Requests from ECMWF Member States for allocation of

computer resources for Special Projects� ECMWF Workshops and Seminar

The SAC is composed of 12 members appointed in theirpersonal capacity by Council.The present Chairman is ProfErland Källén from Stockholm University.

Meeting of the Scientific Advisory Committee on 3–5 October 2005

and space-based sources and their numerical model outputs.In turn, the Centre uses archived ESA datasets as benchmarksto assess and improve the performance of its numerical models.

ECMWF is set to play a key role in future ESA EarthExplorer missions.The Centre has the task of processing verti-cal wind fields from the ADM-Aeolus mission and will beemploying climate-related data from the SMOS (SoilMoisture and Ocean Salinity) mission.

ECMWF is also a major user of the Meteosat series ofweather satellites, developed and built by ESA in co-oper-ation with EUMETSAT, the European Organisation forthe Exploitation of Meteorological Satellites. In additionECMWF is currently preparing for launch of MetOp

expected in April 2006.This is the first polar-orbiting jointventure between ESA and EUMETSAT.

The two organisations will also cooperate and share infor-mation on their activities for the Global Earth ObservationSystem of Systems (GEOSS) - an international effort settingup a system to share environmental information - as well asGlobal Monitoring for Environment and Security (GMES),a joint initiative between ESA and the European Union toestablish an independent global monitoring capability for thecontinent, also serving as a European contribution to GEOSS.

More information about ECMWF co-operation agree-ments can be found at:

www.ecmwf.int/about/basic/volume-1/cooperation_agreements/index.html

Manfred Kloeppel

Chaired by Adérito Vicente Serrão from Portugal, theECMWF Council held its 63rd session in Readingon 13–14 June 2005. Besides several decisions onfinancial matters, such as the use of the Budget surplus2004, and staff matters, such as approval of Reports fromthe Co-ordinating Committee on Remuneration (CCR),the main results of this session were as follows.

� Co-operation Agreements.The Director was autho-rised by Council to negotiate agreements for scientific andtechnical co-operation with Israel and Morocco.

� Building Programme. The Council authorised theDirector to negotiate and conclude, within the approvedfinancial framework, a contract for a new office building.

� Financial Matters. The Council took note of theAuditor’s Report regarding the financial year 2004 andgave discharge to the Director in respect of the imple-mentation of the budget for 2004.

63rd Council session on 13–14 June 2005


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NEWS / METEOROLOGY

Anthony Hollingsworth and Christian Pfrang

It has been recognised that there is a need for a morecomprehensive and coordinated approach to developingEarth observation systems.This led to the Group on EarthObservations (GEO) being established to implement a Systemof Systems to be known as GEOSS (Group on EarthObservation System of Systems).

It is expected that the ERA-40 re-analysis data for theperiod 1957–2003 will play an important role in achievingthe objectives of GEO. Consequently an investigation wasundertaken into current and future applications of the ERA-40 re-analysis data to provide a preliminary assessment of thecurrent status of development of GEO-relevant applica-tions. Initially we did an Internet search which identifiedmore than 100 projects involving ERA-40 data. Subsequently,we performed a web survey of ERA-40 users and received127 replies,with the majority of these providing positive feed-back about the quality and accessibility of the ERA-40data.These studies revealed that the ERA-40 data is beingused in a wide range of areas relevant to GEO.However, thereappears to be potential for more extensive use of this datain particular in areas associated with ecosystems and bio-diversity.

The background and goals of GEO- and GEOSS-relatedactivities will now be described. We will also present theresults of the web survey and discuss the feedback receivedfrom numerous ERA-40 users.

GEO and GEOSS

Thirty-three nations plus the European Commissionadopted, at the Earth Observation Summit I in July 2003,a Declaration of political commitment to move towardsdevelopment of a comprehensive, coordinated, and sustainedEarth observation system(s).There was also affirmation ofthe need for timely, quality, long-term, global informationas a basis for sound decision making.To further these goals,

they launched the intergovernmental ad hoc Group onEarth Observations (GEO) to develop a 10-Year Imple-mentation Plan.The group, co-chaired by the United States,the European Commission, Japan, and South Africa andjoined by more than 21 international organizations, beganpreparatory work immediately.The GEO observation systemwill be built as a System of Systems to be known as GEOSS(Group on Earth Observation System of Systems).

Ministers met at the Earth Observation Summit II inTokyo, Japan, on 25 April 2004, where they adopted theFramework Document for a 10-Year Implementation Planfor this initiative.

In February 2005 in Brussels some sixty countries adoptedthe GEOSS Implementation Plan and created a new inter-national entity, the Group on Earth Observations to executethe plan.They are supported in this undertaking by aboutforty international organisations with a mandate in EarthObservations.The GEO Framework Document, the GEOSSImplementation Plan and the Resolution creating GEOSSmay be found at: http://earthobservations.org.

GEO aims to create a System of Systems to achieve“Comprehensive, Coordinated, and Sustained Earth Obser-vations for the benefit of humankind”. In the words of theGEO Framework Document “Understanding the Earthsystem — its weather, climate, oceans, land, geology, natu-ral resources, ecosystems, and natural and human-inducedhazards — is crucial to enhancing human health, safety andwelfare, alleviating human suffering including poverty,protecting the global environment, and achieving sustain-able development”. Data collected and information createdfrom Earth observations constitute critical input for advanc-ing this understanding.

Comprehensive, coordinated and sustained Earth Obser-vations for understanding the Earth system more completelyand comprehensively will expand worldwide capacity. Inaddition they will provide the means to achieve sustainabledevelopment and will yield advances in many specific areas

A preliminary survey of ERA-40 users developing applications ofrelevance to GEO (Group on Earth Observations)

� New Strategy.The Council considered the frameworkof the ECMWF strategy for the period 2006-2015 andhad an extended discussion on the main strategic goalsto be set for the future.The Council:

– was impressed by the quality of the preparatory work;– wished ECMWF to remain the world leader in numer-

ical weather prediction;– stressed that the strategy should focus on the prediction

of severe weather events;– supported ECMWF’s contribution to environmental

monitoring (GEMS project);– requested the Director to strengthen collaboration with

the Member States;– encouraged strong interaction with Member States’ devel-

opments in Local Area Modelling (LAM);

– requested the Director to strengthen benefits to theMember States;

– wished ECMWF to further develop relations with theEuropean Union;

– requested the Director to make sure that the new strat-egy becomes affordable.

The Director was asked to prepare, for discussion by theCouncil in autumn this year, a strategy based on the frame-work which takes into account the Council’s suggestions.� Products of the Centre. The Council agreed to add

some items to the catalogue of real-time products, includ-ing all web products. Also it authorised the Director toprovide the Centre’s multi-model seasonal forecast prod-ucts to the EUROBRISA project partners.

ECMWF Newsletter No. 104 – Summer 2005METEOROLOGY

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Figure 1 Illustration of the scope of GEO. On the right hand side the socio-economic benefits of GEO (stratified by time-scale) aredepicted. On the left hand side the in-situ and satellite observational inputs can be found with satellite missions stratified by the frequency

ECMWF Newsletter No. 104 – Summer 2005 METEOROLOGY

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bands used. European Meteorological and Customer Tool Boxes needed to transform measurements to information are shown in the centreof the figure.


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METEOROLOGY

of socio-economic benefit (see box). Globally, these bene-fits will be realized by a broad range of user communities.This will represent a fundamental step towards addressing thechallenges articulated in the declarations of the 2002 WorldSummit on Sustainable Development and fulfilling theMillennium Development Goals agreed at the MillenniumSummit in 2000.

Meeting the GEO deliverables

Figure 1 was prepared to illustrate the ambition, thecomplexity and the feasibility of the GEO objectives, viewedfrom a meteorological perspective.� Left-hand side.This illustrates the diverse in-situ (green)

and satellite data sources (arranged by electromagneticfrequency used) needed to achieve the diverse GEOgoals. The satellite missions listed include current andplanned operational and research missions.

� Right-hand side.This illustrates the diversity of the GEOdeliverables, stratified by the areas of socio-economicbenefit, and by the time-scale for which the deliverablesare relevant.

� Centre.This illustrates the meteorological means used totransform the measurements on the left into the deliver-ables on the right, including current status descriptions andforecasts.Broadly speaking the means used are of two kinds:complex Earth-system models and data assimilation systems(in the left semi-circle), and specialised application modelsand decision aids (such as GIS) in the right semi-circle.

By design, Figure 1 excludes reference to geo-hazardssuch as volcanoes, earthquakes and tsunamis which are keyaspects of GEO and GEOSS activities. It is recognised thatimportant meteorological capabilities are needed and areavailable to address the consequences of such events.

Status of GEO-relevant applications

GEO requires an extremely broad and challenging rangeof applications of Earth Observation data. To provide apreliminary assessment of the current status of developmentof GEO-relevant applications, we made a web survey ofcurrent and future applications of the ERA-40 re-analysisdata.The ERA-40 datasets are gridded global meteorolog-ical and surface fields available four-times daily for theperiod 1957-2003. Further information about ERA-40 canbe found at: www.ecmwf.int/research/era/index.html.

Internet search

As a first step in November 2004,we performed an Internetsearch for projects involving ERA-40 data. Google wasemployed as a search engine using a large number of keywordslike “flood” or “greenhouse gases” in conjunction with the“ERA40” keyword. The web hits were categorised intoresearch areas and timescales of forecasts according to theoverview given on the right-hand side of Figure 1.We foundat least one application for each topic, and identified a largenumber of users in the sections climate (42 independentprojects) and weather (17 independent projects).Altogether,we identified more than 100 projects involving ERA-40data by means of the Internet search.

A clickable image-map of the right half of Figure 1 waslinked to a table containing all the information retrieved inthe course of the Internet survey.This information providesan overview of research areas of ERA-40 applications rele-vant to GEO, and incidentally facilitates communicationbetween ERA-40 users. The data are published on theECMWF website and can be found at:

www.ecmwf.int/research/era/era40survey/

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Figure 2 Number of projects by country (identified from both websurvey and user feedback) using ERA-40 data.

Socio-economic benefits

• Reducing loss of life and property from natural and human-induced disasters.

• Understanding environmental factors affecting human healthand well being.

• Improving management of energy resources.

• Understanding, assessing, predicting, mitigating, and adapt-ing to climate variability and change.

• Improving water resource management through better under-standing of the water cycle.

• Improving weather information, forecasting, and warning.

• Improving the management and protection of terrestrial,coastal, and marine ecosystems.

• Supporting sustainable agriculture and combating desertifi-cation.

• Understanding, monitoring, and conserving biodiversity.

User communities

• National, regional, and local decision-makers.

• Relevant international organizations responsible for the imple-mentation of international conventions.

• Business, industry, and service sectors.

• Scientists and educators.

• General public.

Socio-economic benefits and the user communities that will real-ize these benefits as a result of comprehensive, coordinated andsustained Earth Observations.


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METEOROLOGY

User feedback

As a second step, we asked ERA-40 users to contributeto our database.We sent letters via email to about 3,500 usersregistered at the ECMWF data server. Also the BritishAtmospheric Data Centre (BADC) and National Centers forAtmpspheric Research (NCAR) forwarded our request toERA-40 users registered at their data servers. We askedERA-40 users to send:� A short description of projects for which ERA-40 re-

analysis data was used or is intended to be used;� Names and locations of participating research institutes

if the project was conducted in collaborative work;� A link to a more detailed project description;� Comments on what aspects in the ERA-40 data have

given the most benefit and what improvement in thedata would be the most useful in the future.

We received 127 replies to date and the webpage hasbeen updated to include complementary information aboutprojects involving ERA-40 data.

Figure 2 shows that the largest amount of user feedbackwas received from researchers in the United States (28%),United Kingdom (14%) and Netherlands (8%),with responsesalso coming from 29 other countries. Many researchers notonly reported the requested information, but also addedpersonal comments. A large majority of replies containedpositive feedback about the quality and accessibility of theERA-40 data. Many users compared the quality of ERA-40data with the NCEP data, and an overwhelming majority (9out of 10 researchers) concluded that ERA-40 proved moreuseful. Several users requested a peer-reviewed descriptionof the ERA-40 re-analysis and they were happy to learn thatsuch a paper will be published in the Quarterly Journal of theRoyal Meteorological Society (in press).

A number of suggestions for improvement were made,mainly in terms of increased resolution or a larger time span.Many users would appreciate having the time series regularlyextended to the present. Users also gave an indication aboutthe most beneficial elements of the data and which improve-ments would be most appreciated.Research projects, includinglinks either to a description of the project or to instituteswhere the research was performed, can be found on theERA-40 webpage.

Extension of the survey

The ultimate goal of the presented survey is to cover allareas of GEO-relevant applications of ERA-40 re-analysisdata.The list is by no means considered to be complete atthe current stage and we invite ERA-40 users to contributefurther to our database. Nevertheless, the survey successfullydemonstrates that just two years after release of the ERA-40 re-analysis, the data is already applied in a broad spectrumof areas and by a large number of researchers from all overthe world, including several users from developing countries.

We hope the ERA-40 survey will prove valuable to:� Assess the impact of the ERA-40 re-analysis project;

� Facilitate exchange of information between ERA-40users;

� Compile a review of research work using ERA-40;� Make a case for a more comprehensive and longer re-

analysis later this decade, which will benefit from thelessons learned from ERA-40.

If you are aware of any project using ERA-40 data notbeing included in the current version of the ERA-40 survey,we would be most grateful if you contact us at

[email protected].

Implications for GEO

From a GEO viewpoint, the limitations of the survey aresubstantial, being limited to one community among manyin GEO. Nevertheless the survey results are of interest.Theyhighlight the extensive exploitation of the meteorologicalforecast products (on time-scales from days to inter-annual)and re-analysis products (on time-scales from days to decades)in GEO-relevant areas such as disasters, health, waterresources, weather, climate, and agriculture (see Figure 3).

The survey results also suggest that there is little exploita-tion of the gridded meteorological fields in GEO-relevantareas such as ecosystems and bio-diversity, where one mighthave expected wider application.The perceived under-usemay arise for reasons of unfamiliarity of the two commu-nities or because the meteorological outreach has notextended far enough. Alternatively there may be a varietyof technical reasons which need to be identified andaddressed.

From the viewpoint of geographical spread, users of theERA-40 datasets are found pre-dominantly in Europe andNorth America, with relatively few users in Africa and LatinAmerica. The meteorological community and GEO maywish to consider ways and means to broaden both thegeographic and the cross-disciplinary utilisation of the re-analysis products.

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Figure 3 Number of projects categorised according to subject area(identified from both web survey and user feedback) using ERA-40data.


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METEOROLOGY

Roberto Buizza

The predictability gains of the ECMWF EnsemblePrediction System (EPS) between 1994 and 2005have been assessed. Results show that the accuracyof medium-range EPS probabilistic forecasts over Europe hasimproved by about twice the rate experienced by singleforecasts given by the EPS control.The analysis of the skillof mid-tropospheric forecasts at days 5 and 7 over theNorthern Hemisphere indicates that single forecasts haveimproved by between 1 and 1.7 days/decade and that prob-abilistic forecasts have increased by between 2 and 3.7days/decade. For Europe, corresponding gains amount to~0.8 days/decade for control forecasts and ~1.5 days/decadefor probabilistic forecasts. The extra predictability gains ofprobabilistic predictions are linked to improvements in therepresentation of the probability distribution function offorecast states, achieved through the years by improvementsin all aspects of the ensemble system (resolution, ensemblesize, introduction of evolved singular vectors in the genera-tion of initial perturbations and stochastic physics).

Ensemble Prediction at ECMWF

The skill of single forecasts (i.e. of forecasts given by oneintegration, for example by the EPS control forecast) islimited for two key reasons: the presence of uncertainties inthe initial conditions and the approximate simulation ofatmospheric processes achieved in the state-of-the-art numer-ical models.A further complication is that these two sourcesof uncertainties limit the skill of single forecasts in a ratherunpredictable way. One way to alleviate this problem is tomove from a ‘single’ to a ‘probabilistic’ approach to numer-ical weather prediction. In other words to estimate not onlythe most likely forecast scenario but also the time evolutionof an appropriate probability density function in the atmos-phere’s phase space.An ensemble of forecasts can be used toestimate the probability density function of forecast states.

Since 19 December 1992, ECMWF has been producingoperationally global ensemble forecasts precisely to providean estimate of the probability distribution function of fore-cast states. Initially, the ECMWF EPS included only asimulation of initial uncertainties, but since October 1998the EPS included also a stochastic scheme designed to simu-late the random model errors due to parameterized physicalprocesses.Table 1 lists the key upgrades of the ECMWFfrom the implementation of a 33-member T63L19 system(spectral truncation T63 with 19 vertical levels) in December1992.

EPS configuration operational since November 2000

Each ensemble member is defined by the time integra-tion of a version of the ECMWF model that includesstochastic perturbations to simulate the effect of randommodel errors, starting from perturbed initial conditions.Theuse of stochastic perturbations and of singular vectors to

EPS skill improvements between 1994 and 2005

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Figure 2 (a) Average initial-time total (red dashed line) and kinetic(red dotted line) energy, final-time total (blue solid line) and kinetic(blue chain-dashed line) energy vertical cross section. (b) Averageinitial-time (red dashed line) and final-time (blue solid line) total energyspectra. The averages have been computed considering the lead-ing 25 singular vectors used in the operational EPS started at 12UTC on 1 December 2003.

Figure 1 Amplification rates (i.e. singular values) of the leading 25singular vectors used in the operational EPS started at 12 UTC on 1December 2003, ranked from the fastest growing singular vector(number 1) to the 25th one (number 25). These singular vectors werecomputed at T42L40 resolution, with simplified dry physics, a 48-houroptimisation time interval, and final time total energy norm maximizedover the Northern Hemisphere extra-tropics (latitude 30°N).

generate the initial perturbations are two key features of theECMWF EPS that distinguishes it from the two leadingglobal ensemble systems implemented at the MeteorologicalService of Canada and the National Centers for Environ-mental Prediction of the United States.


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METEOROLOGY

Singular vectors identify perturbations of maximum growthduring a finite time interval, named the optimization timeinterval: small errors in the initial conditions along these direc-tions would amplify most rapidly, and affect the forecastaccuracy. Singular vectors are usually located in regions ofstrong barotropic and baroclinic activity. At initial-time,they have most of their energy confined in the small scaleand are confined vertically in the lower troposphere. Duringthe optimization time interval, they change shape and growin scale, and vertically propagate upward. As an example,Figure 1 shows the amplification rate (i.e. the singular value)of the leading 25 Northern-Hemisphere singular vectors usedin the EPS started at 12 UTC on 1 December 2003.Thecorresponding average vertical distribution of total energyand the total energy spectra for these singular vectors aregiven in Figure 2.These two figures summarize two of thekey characteristics of the singular vectors.� The decreasing spectra of singular values, with all the first

25 singular vectors showing an amplification rate in termsof total energy greater than 10, and the leading singularvectors showing a 15-20 amplification rate.

� The upward energy propagation during the optimizationtime interval coupled with the conversion of initial-timepotential energy into final-time kinetic energy, and theupscale energy propagation from the small- to the large-(synoptic) scales.

The EPS configuration operational in 2005 (Table 1)includes 50 perturbed members and one unperturbedmember (the control forecast) run at TL255L40 resolution.The control starts from the unperturbed analysis, while the50 perturbed members start from perturbed initial condi-tions. These are generated by adding to the unperturbedanalysis a linear combination of the leading singular vectorsgrowing to have maximum energy, at optimization time,inside three sets of area covering the whole globe. Duringthis linear combination, the leading singular vectors are re-scaled to have amplitude comparable to analysis errorestimates.

Figure 3 shows the EPS ensemble-mean forecast and theensemble standard deviation, which is a measure of theensemble spread, at initial and at three forecast times, for theEPS started on 1 December 2004.The ensemble standarddeviation at initial time shows the areas where the EPSinitial perturbations were located, and their average ampli-tude (see Figure 3(a)).Note that the initial perturbations werelocated in regions of strong gradient (e.g. the exit of theNorth Atlantic jet stream) and intense baroclinic activity (e.g.the area of cyclonic depression over Spain). During thesubsequent forecast the perturbations grow following theatmospheric flow (see Figures 3(b), 3(c) and 3(d)). Theseresults illustrate how the ensemble standard deviation variesgeographically with the forecast time. More specifically, its

Date DescriptionSingular Vector Characteristics Forecast Characteristics

HRES VRES OTI Target Area EVOSVsSampleMethod HRES VRES Tend

EnsembleSize

ModelUncert

Dec 1992 OperationalImplementation T21 L19 36 h Globe No Simm T63 L19 10 d 33 No

Feb 1993 SV Local ProjectionOperator “ “ “ NHx “ “ “ “ “ “ “

Aug 1994 SV OptimizationInterval “ “ 48 h “ “ “ “ “ “ “ “

Mar 1995 SV HorizontalResolution T42 “ “ “ “ “ “ “ “ “ “

Mar 1996 Extratropical SVs “ “ “ (NH+SH)x “ “ “ “ “ “ “

Dec 1996 Resolution/Members “ L31 “ “ “ “ TL159 L31 “ 51 “

Mar 1998 Evolved SV “ “ “ “ Yes “ “ L31 “ “ “

Oct 1998 Stochastic Physics “ “ “ “ “ “ “ “ “ “ Yes

Oct 1999 Vertical Resolution “ L40 “ “ “ “ “ L40 “ “ “

Nov 2000 Forecast HorizontalResolution “ “ “ “ “ “TL255 “ “ “ “

Jan 2002 Tropical SVs “ “ “ (NH+SH)x+TC “ “ “ “ “ “ “

Sep 2004 Sampling T42 L40 48 h (NH+SH)x+TC Yes Gauss TL255 L40 10 d 51 Yes

Table 1 List of key changes introduced in the ECMWF EPS configuration. Columns list the horizontal resolution (HRES, expressed in termsof spectral truncation), the vertical resolution (VRES, expressed in terms of number of vertical levels), the optimization time interval used(OTI, in hours) and the target area used to compute the singular vectors (Target Area), the use of evolved singular vectors (EVO SVs), thesampling method used to generate the initial perturbations (Sample), the forecast length (Tend, in days), the number of ensemble members(Ensemble Size) and whether model uncertainty is simulated or not (Model Uncert).


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variation can be used to estimate predictability: regionswith small standard deviation (i.e. with small ensemblespread) should be more predictable than regions with largevalues, since in these regions the verifying analysis shouldbe closer to the forecast states. Considering Europe, forexample, the ensemble standard deviation is small comparedto the other regions during the early forecast range (Figure3(b)), but starts being relatively large on day 4 of the fore-cast (Figure 3(c)).

EPS performance from May 1994 to April 2005

EPS forecasts are used to generate ‘single’ products (e.g.the forecasts given by the EPS control or the ensemble-mean)and probabilistic products, such as the probability of occur-rence of some selected events (e.g. the probability ofoccurrence of positive anomalies, or of positive/negativeanomalies great-than/smaller-than one standard deviation ofmonthly variability).The accuracy of single and probabilis-tic forecasts of the 500 hPa geopotential height fields has beenassessed over the Northern Hemisphere and Europe, from

1 May 1994 to 30 April 2005. Probabilistic forecasts havebeen assessed using 3 skill measures: the area under the rela-tive operating characteristic curve (ROCA), the Brier skillscore (BSS) and the ranked probability skill score (RPSS).

For each skill measure, first a linear regression line has beendetermined, and then the slope of the linear regressioncurve has been translated into predictability gains measuredin terms of days-per-decade (d/de). In other words, thepredictability gain of the time t forecast gives a measure ofthe trend in skill between 2005 and 1994. For example, again of 1 day/decade for a 5-day forecast means that theimprovement in skill between 1 May 1994 and 1 May 2004of the 5-day forecast is equal to the average differencebetween the skill of 4.5-day and a 5.5-day forecast duringthat period.

Considering for example 7-day forecasts over the NorthernHemisphere, Figure 4 shows the time evolution of the skillof the control and the ensemble-mean forecasts in terms ofanomaly correlation coefficient. Results indicate a contin-uous improvement, equivalent to a predictability gain of

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Figure 3 (a) Initial time ensemble mean (which coincide with the unperturbed analysis) and standard deviation. (b) Ensemble mean andstandard deviation at forecast day 2. (c) Ensemble mean and standard deviation at forecast day 4. (d) Ensemble mean and standard devia-tion at forecast day 6. Fields shown refer to the 500 hPa geopotential height field of the EPS started at 12 UTC on 1 December 2003. Contourinterval for ensemble mean is 80 m; contour shading for the ensemble standard deviation are: 5 m at initial time, 15 m at day 2, 30 m at day4 and 45 m at day 6.


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1.06 d/de (days per decade) and 1.68 d/de, respectively, forthe control and ensemble-mean.The corresponding resultsfor the skill of probabilistic forecasts measured in terms ofROCA, BSS and RPSS, are given in Figure 5. In this casethe predictability gains range between 1.98 and 2.90 d/de.

Figure 6 summarizes the predictability gains of the singleand probabilistic forecasts achieved between 1994 and 2005at forecast day 5 and 7 and for the Northern Hemisphereand Europe.Results indicate that for both the Northern Hemisphereand Europe the predictability gains of medium-range EPS proba-bilistic forecasts has improved by about twice the value shown byEPS single control forecast.

The improvement of ensemble forecasts first of all indi-cates that the EPS benefits from ameliorations of theECMWF data assimilation and forecast model. But it alsoindicates that changes introduced in the EPS (Table 1)played an important role in improving the prediction of theprobability distribution function of forecasts states.Althoughit is difficult to clearly identify which of the changes of theEPS configurations had the largest impact on the EPS scores,published works suggest that the improvements shown inFigure 6 are mainly due to three causes.

� Increases of the EPS resolution in 1996 and 2000.� Increase in the ensemble size in 1996.� Introduction of evolved singular vectors and of stochas-

tic physics in 1998.

EPS future upgrades

Work is in progress to improve the current system inthree key areas.� Simulation of initial uncertainties — Work in this area

includes developments in the definition of the normused to compute the singular vectors, in the use of moist,higher-resolution singular vectors, and in the combina-tion of ensemble data assimilation and singular vectors.

� Simulation of model imperfection — Work in this areafocuses in the revision of the scheme designed to simu-late the effect of near-grid scale and sub-grid scale processes.

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Figure 4 Monthly average anomaly correlation coefficient of thecontrol (blue line) and the ensemble-mean (red line) 7-day fore-casts of 500 hPa geopotential height f ields over the NorthernHemisphere. Straight lines show linear regression curves.

Figure 5 Monthly average area under the relative operating char-acteristic curve (red line) and Brier skill score (blue line) of the7-day probabilistic forecasts of positive anomalies, and rankedprobability skill score (black line) of the 7-day probabilistic forecastsof 500 hPa geopotential height fields over the Northern Hemisphere.Straight lines show linear regression curves.

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Figure 6 (a) Gains in predictability of five-day (blue bars) andseven-day (red bars) forecasts of 500 hPa geopotential height fieldsover the Northern Hemisphere, computed from different forecasts.(b) As top panel but for Europe. CON ACC: control anomaly corre-lation coefficient. EM ACC: ensemble-mean anomaly correlationcoefficient. CON TS[f>c]: control threat score of positive anom-alies. CON ROCA[f>c]: area under the relative operating characteristicsof the probabilistic forecast of positive anomalies given by thecontrol. EPS ROCA[f>c]: area under the relative operating char-acteristics of the probabilistic forecast of positive anomalies givenby the EPS. EPS RPSS: ranked probability skill score of the EPS.EPS BSS[f>c]: Brier skill score of the probabilistic prediction ofpositive anomalies. EPS BSS[f>(c+s)]: Brier skill score of theprobabilistic prediction of positive anomalies greater than one stan-dard deviation. EPS BSS[f>(c-s)]: Brier skill score of the probabilisticprediction of positive anomalies less than one standard deviation.


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� System design — Work in this area involves changes inthe ensemble resolution and forecast length, including thepossibility to run the each single forecast with variableresolution (with a TL399 resolution up to forecast day 7,and with a TL255 resolution from the truncation time toforecast day 14).

The ECMWF EPS is based on the Integrated ForecastingSystem/Arpege software, developed in collaboration byECMWF and Météo-France, and is the result of the workof many ECMWF staff members and consultants.Withouttheir contributions the ECMWF EPS would not havereached the mature development stage and accuracy that ithas reached now: their work is fully acknowledged.

FURTHER READING

On singular vectors: Buizza, R. and T.N. Palmer, 1995:The sin-gular-vector structure of the atmospheric general circulation. J.Atmos. Sci., 52, 1434–1456.

On stochastic physics: Buizza, R., M. Miller and T.N. Palmer,1999: Stochastic simulation of model uncertainties. Q. J. R.Meteorol. Soc., 125, 2887–2908.

On the original EPS configuration: Molteni, F., R. Buizza,T.N.Palmer and T. Petroliagis, 1996:The new ECMWF ensemble pre-diction system: methodology and validation. Q. J. R. Meteorol. Soc.,122, 73–119.

On the EPS configuration operational since November 2000:Buizza, R., D.S. Richardson and T.N. Palmer, 2003: Benefits ofincreased resolution in the ECMWF ensemble system and compar-ison with poor-man’s ensembles. Q. J. R. Meteorol. Soc., 129,1269–1288 .

On the latest EPS change: Ehrendorfer, M. and A. Beck, 2003:Singular vector-based multivariate normal sampling in ensembleprediction. ECMWF Technical Report Number 416. Available atECMWF, Shinfield Park, Reading RG2 9AX, UK(www.ecmwf.int/publications/library/).

On the comparison of the performance of the ECMWF, MSCand NCEP ensemble systems: Buizza, R., P.L. Houtekamer, Z.Toth, G. Pellerin, M.Wei and Y. Zhu, 2005:Assessment of the statusof global ensemble prediction. Mon.Wea. Rev., 133, 1076–1097.

Richard Engelen

In 2001 a report by the Intergovernmental Panel onClimate Change (IPCC) noted that “the atmospheric concen-tration of CO2 has increased from 280 ppmv in 1750 to 367 ppmvin 1999 (31%).Today’s CO2 concentration has not been exceededduring the past 420,000 years and likely not during the past 20million years.The rate of increase over the past century is unprece-dented, at least during the past 20,000 years.”

Currently, the global mean atmospheric concentration isabout 380 ppmv. Interestingly enough, this is less than couldbe expected based on anthropogenic emissions. Somehow,the land and ocean take out half the amount of CO2 thatis injected in the atmosphere by the anthropogenic emis-sions.Accurate quantification of the processes responsible forthis so-called ‘missing sink’ is not yet available.

Within the COCO project, funded by the EuropeanCommission, ECMWF has implemented a CO2 estimationwithin the data assimilation system to monitor atmosphericCO2 concentrations. European research groups will usethese estimated concentrations to improve their surface fluxestimates in order to solve the ‘missing sink’ problem.

More than a year of satellite data from the AdvancedInfrared Sounder (AIRS) has now been processed and resultsare very promising. Comparisons with independent obser-vations show that the data assimilation system is able toestimate tropospheric column CO2 with an accuracy ofbetter than 1%. Although these estimates are not sensitiveto the boundary layer concentrations, the wealth of spatial

information will help to improve the flux inversions that arecurrently based on the surface flask network.Recent compar-isons show that for the first time we have a dataset that isable to evaluate differences between CO2 climate modelsimulations on a global scale.Within the EU-funded GEMS(Global and regional Earth-system Monitoring using Satelliteand in-situ data) project the CO2 analysis system will beextended to a full 4D-Var system that will be able to assim-ilate CO2 information from various instruments. Furtherinformation about GEMS can be found in the spring 2005edition of the ECMWF Newsletter.

Carbon cycle

In 1957 Charles Keeling and colleagues started observingatmospheric CO2 concentrations at Mauna Loa,Hawaii, andat the South Pole.Concentrations have risen from 313 ppmv(parts per million by volume) in 1957 to 380 ppmv in 2004,an increase of about 20% in 50 years. It is now clear that thisincrease in atmospheric CO2 is largely due to anthropogenicemissions, such as combustion processes, cement production,and biomass burning.Since these early observations, a networkof accurate flask measurement sites has been set up to obtaina better idea of the variability of atmospheric CO2.From theseobservations and from our knowledge of the amount ofanthropogenic emissions an interesting result arose: only halfthe amount of anthropogenic emissions accumulates in theatmosphere. The other half is somehow absorbed by theocean and/or land biosphere. This phenomenon is nowwidely known as the missing sink (see Figure 1).

CO2 from space: estimating atmospheric CO2 withinthe ECMWF data assimilation system


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Much of the carbon cycle research has been focused onthe possible processes that can account for the missing sink.Bottom-up approaches try to build better flux models forboth the ocean and the natural biosphere.At the same timetop-down methods have used the flask observations togetherwith atmospheric transport models to infer flux estimates.The main problem with the latter approach, the flux inver-sions, is the data sparseness. Only about 100 surface flask sitesexist today and the inversion problem therefore stronglyrelies on the atmospheric transport model being used.Thishas not helped research groups reach consensus as to whichprocesses are responsible for the uptake of anthropogenicemissions. Observing atmospheric CO2 with satellite instru-ments is therefore regarded as a very promising way forwardto improve flux inversions. However, there are currently nosatellite instruments that have been specifically designed toobserve CO2.

Both the National Aeronautics and Space Administration(NASA) and the Japan Aerospace Exploration Agency (JAXA)are building designated CO2 instruments that will use solarreflection in the near infrared to observe atmospheric CO2concentrations (Orbital Carbon Observatory, OCO, andGOSAT, respectively). These instruments will potentiallyprovide accurate observations, but they also suffer from poorreflectivity over ocean, aerosol interference, and the need forsolar radiation. Meanwhile, the AIRS instrument flying onboard of the NASA Aqua satellite observes the infrared partof the spectrum at high spectral resolution.

Important absorption bands in the infrared part of thespectrum consist of CO2 absorption lines.Traditionally, theseCO2 absorption lines have been used to infer atmospherictemperatures from the measurements assuming the CO2concentration to be fixed. It is possible, though, to estimate

both temperature and CO2 from these observations by eitheradding other absorption bands (e.g.water vapour) or makingassumptions about for instance the vertical profile of CO2(e.g. well-mixed profile).Another possibility is to add obser-vations from other instruments that provide informationabout the temperature profile as is routinely done in a numer-ical weather prediction (NWP) data assimilation system.However, the amount of independent CO2 information issmall and can easily be obscured by the other signals and/orthe noise in the observations and the radiative transfer model-ling. Also, measurements in the infrared are generally notsensitive to atmospheric CO2 in the lower part of the tropo-sphere.This is an important restriction, because most of thevariability of CO2 occurs in the boundary layer. However,the infrared option is attractive because it guarantees conti-nuity in time with instruments such as the European InfraredAtmospheric Sounding Interferometer (IASI) and theAmerican Cross-track Infrared Sounder (CrIS) being launchedin the next few years. It also has the advantage over near-infrared observations that there is no restriction to daytimeobservations.

CO2 estimation set-up

ECMWF has been operationally assimilating observationsfrom the AIRS instrument since October 2003.The meas-urements constrain temperature and water vapour by assumingconstant CO2 mixing ratios.Within the COCO project wehave added CO2 to the minimization state vector in anexperimental configuration to prove the feasibility of thisapproach. Instead of including CO2 in the forecast model,which would require extensive coding to transport tracersaround as well as defining proper background statistics, CO2was added to the state vector as a column variable for eachAIRS observation location.Then the output of one analysiscycle consists of all the relevant atmospheric fields (temper-ature,winds, humidity, etc.) together with CO2 troposphericcolumn estimates at all the AIRS observation locations thatgo into the assimilation. Because CO2 is not part of theassimilation transport model, there are no forecasts for CO2.Consequently CO2 information from one analysis cyclecannot be used in the next analysis cycle. Also, to generateglobal fields, individual estimates have to be gridded in forinstance 5° by 5° boxes for a certain time period.

A set of only 18 AIRS spectral channels (out of 324 avail-able channels) sensitive to tropospheric CO2 was used toestimate the tropospheric CO2 columns. These channelswere chosen to minimize the effect of water vapour andozone absorption.Because the signal of CO2 in the observedradiances is so small, it is easily obscured by uncertainties inthe water vapour and ozone distributions.For the backgroundconstraint a global mean value of 376 ppmv was chosen witha background error standard deviation of 30 ppmv. Theanalysis error was estimated based on the background error,the observation error, and the sensitivity of the observationsto atmospheric CO2. This sensitivity largely depends onthe temperature lapse rate and the depth of the tropos-pheric layer (i.e. the height of the tropopause).

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Results of analysing AIRS data

More than one year of AIRS data has been processed andFigure 2 shows monthly mean results for March 2003,September 2003, and March 2004.The fourth panel showsthe monthly mean analysis error for March 2003.White areasrepresent areas with extensive cloud cover throughout themonth.

The largest signal in atmospheric CO2 concentrations comesfrom the terrestrial biosphere.Vegetation absorbs CO2 byphotosynthesis and emits CO2 through respiration.Plant litteron and in the soil releases CO2 as well due to decomposition.A strong seasonal cycle is produced, although the annual netbiosphere flux is very close to zero.The terrestrial biospherealso creates a latitudinal gradient in the atmospheric concen-trations due to the large amount of land in the northernhemisphere compared to the southern hemisphere.This lati-tudinal gradient is amplified by the anthropogenic emissionsthat mainly originate from the northern hemisphere.Both theseasonal cycle and the latitudinal gradient are visible in theresults of Figure 2. It is encouraging to see that the assimila-tion is capable of producing these spatial and temporal variationswithout having that information in the background.

March 2004 shows generally higher CO2 concentrationsthan March 2003, representing the upward trend in global

atmospheric CO2.The difference between March 2003 andMarch 2004 at the location of Hawaii is 1.6 ppmv comparedto the 1.4 ppmv observed at the Mauna Loa flask station.The monthly mean error shows the clear dependence of theanalysis error on the temperature lapse rate as well as thethickness of the tropospheric layer. Errors are smallest in thetropics were the tropopause is high and the temperature lapserate is large, while they increase at higher latitudes wherethe tropopause is lower.The relatively low errors over Europeare caused by a higher tropopause (deeper troposphericlayer) in the sub-tropical air mass.

Validation of the analyses

The presentation of monthly mean results is interestingby itself, but an important check of the validity of our analy-sis results is by comparing these results to independentobservations of atmospheric CO2.There are only very fewdata sources for 2003 and we can generally not use thesurface flask data.This is because our estimates represent alayer between about 700 hPa and the tropopause, while thesurface flasks are sampled in the boundary layer. Only if weare sure that the full tropospheric CO2 profile is well-mixedwould a comparison be useful. However, Dr HidekazuMatsueda and colleagues at the Japanese Meteorological

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Figure 2 Monthly mean CO2 analysis results for March 2003, September 2003, and March 2004 as well as the monthly mean analysiserror for March 2003. Units are ppmv of CO2.


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Agency have been measuring CO2 on board commercialflights of the Japanese Airlines (JAL) flying between Japanand Australia.These observations consist of automatic flasksamples gathered at altitudes between 8 and 13 km on bi-weekly commercial flights. For 2003, there were 21 flightsavailable for our comparisons.

Figure 3 shows the CO2 annual cycle for both the flightobservations and the assimilation estimates. For the fullprocessed period (1 January 2003 to 31 March 2004), CO2analysis estimates were sampled in 6˚ by 6˚ boxes around thelocations of the flight observations and over a period of 5 daysaround the date of those observations.We then generated three

plots that represent the northern hemisphere region, theequatorial region, and the southern hemisphere region, byaveraging the respective box averages for each region together.The figure shows that the analysis estimates follow the JALobserved annual cycle quite well.All differences fall withinthe one standard deviation error bars and are of the order of1 ppmv in most cases.There is a clear improvement comparedto the background, which is 376 ppmv throughout the year.The main anomaly can be seen in both the northern hemi-sphere and the southern hemisphere in January and February,in which period the analysis estimates are consistently higherthan the JAL observations.

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Figure 3 Comparison of ECMWF CO2 esti-mates (blue triangles) with JAL observations(red dots) for three different latitude zonesfrom January 2003 to March 2004. The CO2background value is denoted by the dottedline. Mean analysis errors are denoted by thegreen error bars. Missing ECMWF data arecaused by extensive cloud cover in the area.Units are ppmv of CO2.

Figure 4 Comparison of ECMWF CO2 estimates with Japanese Airlines (JAL) observations (filled circles in same colour scale) for 20January and 20 May 2003. Units are ppmv of CO2.


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METEOROLOGY

Figure 4 shows geographical comparisons with the JALdata for January and May 2003.The figure for 20 January2003 is an example of a bad match between the JAL obser-vations and the analysis results, while the figure for 20 May2003 is an example of a good match.We suspect the mainproblem area in the January plot is affected by undetectedthin cirrus clouds.Although the signal of these undetectedclouds is negligible in terms of the temperature analysis, itcauses the average CO2 field to be high compared to thesurrounding area. This difference in the cloud detectionbetween January 2003 and May 2003 is most likely causedby the effect of the GOES-9 satellite on the moisture fieldsof the ECMWF analysis.The normal geostationary satelliteover the Pacific area was GMS-5, but continuing problemswith the onboard imager required a replacement by theGOES-9 satellite in May 2003.Therefore, during the crit-ical (in terms of amount of convection over the Pacific)months of January, February and March the geostationaryconstraint on the humidity field was lacking. This is acautionary example showing the impact of seemingly unre-lated satellite instrument changes on the CO2 estimates.Continuous validation of the results is therefore of greatimportance.

The next phase

On 1 March 2005 the EU-funded GEMS project startedwith the aim to develop an operational environment moni-

toring system.Within this project the CO2 data assimilationwill be upgraded to a full 4D-Var data assimilation system.Work is now underway to add CO2 as a tracer variable tothe forecast model.We are also defining proper backgroundstatistics that will be very important for the interpretationof the satellite observations. It is envisaged that this systemwill provide even better results than the relatively simpleassimilation system, here described.The main output will bethree-dimensional CO2 fields every 12 hours constrained byobservations from AIRS, IASI, CrIS, and possibly OCO andGOSAT.These fields will then be used by some of the part-ners of the GEMS project to improve their flux estimatesand hopefully get a better idea of the processes behind themissing sink.

FURTHER READING

Engelen, R.J., E. Andersson, F. Chevallier, A. Hollingsworth,M. Matricardi, A.P. McNally, J.-N. Thépaut and P.D. Watts, 2004:Estimating atmospheric CO2 from advanced infrared satellite radi-ances within an operational 4D-Var data assimilation system:Methodology and first results. J. Geophys. Res., 109, D19309,doi:10.1029/2004JD004777.

Engelen, R.J. and A.P. McNally, 2005: Estimating atmosphericCO2 from advanced infrared satellite radiances within an opera-tional 4D-Var data assimilation system: Results and validation.J. Geophys. Res., in press, doi:10.1029/2005JD005982.

Martin Köhler

You are having a sunny summer picnic when suddenlylow cloud moves in. Instantly, your skin feels a cool-ing from the drastic change in radiation. Sunlight isreduced by 50 to 70% or 200 to 300Wm-2.Yet infra-red radia-tive cooling is also reduced by 50 to 100 Wm-2, because thecloud above emits more black body radiation than the colderclear sky.The air temperature sinks by 1°C per hour, the windpicks up and you start to pack up to go home.

It comes as no surprise that low cloud has a command-ing impact on climate as well as climate change. If onecould magically cover an additional 4% of the globe withlow cloud, the global warming resulting from the potentialdoubling of CO2 could possibly be offset.On the other hand,if the amount of low cloud decreased there could be anunpleasant positive feedback which would accelerate globalwarming. Unfortunately, current global climate models aresplit into those that increase low cloud in climate changescenarios and those that produce a decrease.

Turning our attention to weather forecasting, the qualityof cloud forecasts still lags significantly that of temperatureand circulation above the planetary boundary layer (PBL).Figure 1 compares the skill of ECMWF forecasts relative topersistence for a few typical variables. Cloud appears to bethe most difficult to forecast, with the boundary layer vari-ables (i.e. two-metre temperature and ten-metre wind speed)

only a little better. Much better predicted are temperatureand wind at 850 hPa just above the boundary layer and,quite encouragingly, six-hour accumulated precipitation.Apparently, it is easier to forecast the dynamically forcedprecipitation than the small residual — the cloud.The errorsin cloud forecasts produce errors in the radiation calculationsand these in turn affect the PBL temperatures and winds.Thisskill comparison of a diverse set of variables comes withcaveats such as that persistence is a better forecast benchmarkfor cloud than for precipitation.Yet, this figure illustrates thedifficulty of getting good cloud predictions from accuratecirculation forecasts.

At ECMWF considerable work has been invested recentlyin developing an improved representation of low cloud.Asa result the simulation of marine stratocumulus improveddrastically. Continental stratus also benefited as witnessedspecifically in the blocking period of December 2004 overEurope. This article outlines the key aspects of the newplanetary boundary layer parametrization scheme whichhas been incorporated into the ECMWF Integrated ForecastSystem (IFS) in April 2005. Some of the improvements incloud cover are highlighted.

New treatment of stratus and stratocumulus

What are the physical processes needed to adequatelymodel stratus and stratocumulus in particular? And why hasit proved so difficult to develop successful parametrizations?

Improved prediction of boundary layer clouds


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Those low clouds are known to cap well-mixed boundarylayers.The required vigorous mixing is mainly forced by thestrong radiative cooling at the cloud top.This would coolthe entire PBL by 10°C per day if not balanced by surfacefluxes and entrainment of warm air through the cloud top.Assuming that the stratocumulus topped PBL is a turbulentwell-mixed layer there are just three budgets one has tosolve: mass, water and heat.� The mass budget governed by subsidence and cloud-top

entrainment predicts the cloud top height.� The water and heat budgets determine cloud base and

cloud water.The key factors are surface fluxes, cloud top entrainment,

solar warming and infra-red cooling.Writing these three PBL budgets is straightforward, yet

many global models strongly underpredict marine stratocu-mulus clouds. Generally, the problems these models have canbe separated in two categories: inadequate representation ofphysics and inaccurate numerics. Examples of physical prob-lems are a lack of mixing up to cloud top and there beingno scientific consensus about cloud top entrainment.Anotherregion of current inconclusive research is the transitionfrom stratocumulus with unbroken cloud decks to tradecumulus with just a few tens of percent of cloud cover.Numerical difficulties arise from the PBL top movingthrough model levels and the interaction of PBL, convec-tion, cloud and radiation schemes. Maintaining numericalstability whilst using long time-steps is another typical chal-

lenge for transport schemes used to simulate low-level cloud.The main aim in upgrading the PBL parametrization was

to improve low-level cloudiness and pave the way towardsthe unification of the PBL and shallow convection schemes.To achieve that goal the following ingredients were deemednecessary: (a) moist conserved variables, (b) a combinedmass-flux/diffusion solver, (c) a treatment of cloud variabil-ity, and (d) a treatment of the transition between stratocumulusand shallow convection.

Figure 2 illustrates the approach chosen, which is basedon a flux decomposition into diffusion and mass-flux terms.This decomposition goes back to work by Siebesma andCuijpers at KNMI in 1995, who showed that any verticalflux of a scalar quantity can be split into three contributions:the mass-flux, the sub-core flux and the environmental fluxterms.This can be understood by reference to Figure 3.Themass-flux approach (red line) accounts for the strongestupdraughts.Then the small perturbations (blue) along the

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Figure 1 Forecast skill versus persistence against observationsof various atmospheric variables over Europe for the year 2004 at12 UTC. The observations are radiosondes for 500 hPa and 850 hPavariables and SYNOP stations for the rest. Note that SYNOP cloudobservations have significant errors and for cloud and precipitationit is questionable how representative local observations are for themodel scale. With RMSE as the root mean square error of forecastsor persistence, the skill is defined as

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Figure 2 Transition of a dry PBL to stratocumulus. The parametriza-tion of the associated convective transports in the new schemeare illustrated in blue for the diffusion component K and in greenfor the mass-flux component M. Yellow and red arrows denote solarand infra-red radiation respectively. zi is the inversion height andzcb is the cloud base height. See text for explanation.

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red line can be described with a diffusion approach. Thiscombined mass-flux/diffusion methodology allows for amore accurate description of the fluxes than either approachby itself.Additionally, these two traditional transport approx-imations can be combined as desired for specific cloudregimes.Therefore, this combined approach is ideally suitedto unifying PBL parametrization, which often uses purediffusion techniques, with convection parametrization, typi-cally based on mass-flux techniques.

Cloud cover and cloud water are treated in the newparametrization scheme by predicting the variance of totalwater, that is cloud water plus water vapour. If the shape ofthe probability density function of total water is assumed,the conversion between the prognostic variables watervapour and cloud water on the one hand and total water andtotal water variance on the other hand can be represented.

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a�Low Cloud Cover: impact of new PBL scheme

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c�Low Cloud Cover: new PBL scheme

Figure 4 (a) Difference in low-cloud cover between analysis/forecast experiments usingthe new PBL parametrization scheme and the old scheme. The other panels give the low-cloud cover from the analysis/forecast experiments using (b) the old PBL scheme and (c)the new PBL scheme. The results represent 9.5 and 10 day forecasts from six test periodscovering 7–27 July 2001, 9–22 October 2001, 1 February–1 March 2004, 1–31 July 2004,1–31 October 2004 and 3-15 December 2004 amounting to 140 days.

The last key requirement of the new PBL parametriza-tion is to determine the PBL cloud regime. In nature thereare two typical low-cloud regimes: stratocumulus clouds,which occur in well-mixed PBLs with a large cloud frac-tions, and trade cumulus clouds with small cloud fractionsand cloud layers that are weakly stable stratified. Variousalgorithms are available to distinguish between these regimes.In the end we used a criterion based on lower troposphericstability after the work by Klein and Hartmann at theUniversity of Washington in 1993.This criterion reflects theobservation that stratocumulus clouds mostly live in atmos-pheres with strong inversions.

Peruvian stratocumulus

The main impact of the new moist PBL scheme wasexpected to be an increase in low-level cloud cover which

would be more realistic in situations ofcloud-topped mixed layers below inver-sions. Most stratus and stratocumuluslive over relatively cold ocean regionsfavouring condensation.The ocean alsosupplies a near infinite heat sourceoffsetting the cloud top cooling minustop entrainment, which together ther-mally force the well mixed PBLs.Therefore, the subtropical oceans westof continents associated with up-welling and the high latitude oceans aretypical regions of large low-level cloudcover. In addition stratus forms overthe continents during winter in anti-cyclonic regimes.

Testing of the new PBL includedmore than a thousand forecast dayswith the full resolution T511 modelduring six periods in the years 2001 and2004.Figure 4 shows the correspondingrealistic increases in cloud cover of upto 40% locally in all the typical stratocu-mulus and stratus regions and of around2% to 4% globally.This improvementis rather significant for the Earth energybalance.Two of the full-resolution re-analysis periods were specifically chosento coincide with marine stratocumu-lus field experiments: DYCOMS II inJuly 2001 in the California stratusregion and EPIC in October 2001 inthe Peru stratus region.

The field experiment EPIC (EasternPacific Investigation of Climate Process-es) focused on a comprehensive studyof turbulence, drizzle and aerosols instratocumulus in the southeast PacificOcean.The research ship Ron Brownwas located for a full week in the centreof this low-cloud region.Typically thisregion has thick stratocumulus clouds,


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a�Liquid Water Path

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a METEOSAT visible 10 December 2004 b Low Cloud Cover: impact of new PBL scheme 8–16 December 2004

c Low Cloud Cover: old PBL scheme 8–16 December 2004 d Low Cloud Cover: new PBL scheme 8–16 December 2004

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Figure 6 (a) Meteosat 7 visible image for 12 UTC on 10 December 2004 over Europe. This snapshot is characteristic for the 8–16December 2004 period. The red rectangle includes the Hungarian plateau with the thickest stratus occurrence. (b) Low-level cloud coverdifference between the new and old PBL parametrization schemes over Europe for verifying time 12 UTC on 8–16 December 2004. Theday 1, 2 and 3 forecasts were averaged according to verifying time. (c) Low-level cloud cover using the old PBL scheme. (d) As (c) butusing the new PBL scheme.


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which play an integral part in the Equatorial Pacific air-seainteraction. Such interactions include the formation of the“cold tongue” of cool sea surface temperatures (SSTs)extending westward from Peru and the El Niño interannualSST oscillation. Figure 5 shows the vertically integratedliquid water at the EPIC location taken from short-termglobal T511 forecasts with the old and new PBL parame-trizations.The new PBL forecasts significantly improve themagnitude and diurnal cycle of the liquid water path in thisthick stratocumulus regime (Figure 5(a)).The main originsof this improvement can be traced to a more well-mixed PBLand a higher PBL top as seen from the corresponding watervapour profiles (Figure 5(b)).

European winter stratus

In December 2004 the parametrization developmentreached its final stage.At the same time, during a persistentanticyclonic regime the operational forecasts showed acomplete lack of stratus observed over France and Hungary(thanks to Gerald Van der Grijn,ECMWF and Tamás Hirsch,Hungarian Meteorological Service). The Meteosat visibleimage for 10 December 2004 (Figure 6(a)) is typical for theperiod of 8 to 16 December in terms of the persistent thickstratus over the Hungarian plateau and the stratus along thenorthern coast of France. Occasionally marine stratus movedinland into France during this period. An analysis/forecastexperiment for 3 t

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