Status of GCOS Upper-Air Reference Network Planning

Achieving Satellite Instrument Calibration for Climate Change Workshop16-18 May 2006, Landsdowne, VA

Dian SeidelNOAA Air Resources Laboratory

Silver Spring, Maryland

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Radiosondes

• Workhorse of the global observing system since 1950’s

• “Gold standard” for validation of GPS data (as quoted in Science, April 2006)

• A blessing and a curse for climate studies

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Value of In Situ Sounding Data

• High vertical resolution• Possibility of co-located measurements of

a suite of variables• Continuity with historical radiosonde

archive• Independent alternative to remotely

sensed observations• Potential for calibration of satellite

observations

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Inadequacy of Exisiting Radiosonde Network for Climate Monitoring

• Observations from many networks - by many types of instruments - are not referenced to standards, or to each other.

• Instrument and observing method changes are not well documented, and there is no overlap to guide data adjustments.

• Humidity observations are not accurate enough, particularly in cold, dry regions.

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Need for a Reference Upper-Air Network

• To ensure that climate monitoring findings, climate projections and predictions, and climate policy decisions are based on reliable observations

• Reliability requires:– Redundant measurements and analyses– Small uncertainty in observations– Long-term continuity of observing system– Stability of observations and their accuracy– Complete metadata– Ongoing data quality control and analysis– Dedicated data center

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Key Climate Science Drivers for a Reference Upper-Air Network

• Monitoring and detecting climate variability and change• Understanding the vertical profile of temperature trends• Understanding the climatology and variability of water

vapor, particularly in the upper-troposphere and lower stratosphere

• Understanding and monitoring tropopause characteristics• Understanding and monitoring the vertical profile of ozone,

aerosols and other constituents• Reliable reanalyses of climate change• Prediction of climate variations• Understanding climate mechanisms and improving climate

models

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Temperature Trends from Different Observing Systems and Datasets

Source: Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences. Thomas R. Karl, Susan J. Hassol, Christopher D. Miller, and William L. Murray, editors, 2006. A Report by the Climate Change Science Program and the Subcommittee on Global Change Research,ashington, DC. (Figure from Executive Summary, page 9)

1979-20041958-2004

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Effect of Unadjusted "Interventions" on Temperature Trend Estimates

Maximum Intervention (deg K)

0.0 0.5 1.0 1.5 2.0 2.550-y

ear

Tem

pera

ture

Tre

nd E

rror

Rat

e (%

)

0

10

20

30

40

Source: Seidel, D.J., and M. Free, Measurement requirements for climate monitoring of upper-air temperature derived from reanalysis data, J. Climate, 19, 854–871.

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Importance of Upper-Tropospheric Water Vapor Observations

Source: Soden, B.J, and I.M. Held: An assessment of climate feedbacks in coupled ocean-atmosphere models, J. Climate, submitted.

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Defining Observational Requirements

• “NOAA/GCOS Workshop to Define Climate Requirements for Upper-Air Observations” - Boulder, CO, February 2005.

• ~ 70 scientists and data users from a wide cross-section of the climate community.

• Workshop report reviewed by a larger group.

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Cascade of Upper-Air Observations

Benchmark Network~10 stations

Upper Air Reference Network30-40 stations

GCOS Upper Air Network (GUAN)

161 stations

Comprehensive observing networkAll stations, observing systems,

satellites, reanalyses etc.

Spatial density

Climate driven

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Benchmark Network

• Problem: Current observations have both known and unknown biases that are very difficult to correct.

• Solution: Continuous, stable observations whose accuracy is traceable to international standards.

• How to get there: A research question.

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Comprehensive Network

• Provides the detailed spatial resolution necessary to relate climate change and variability to human activities and the environment.

• Includes multiple data types, including satellite data.

• Relies not only on network measurements but also on assimilation and analysis of the observations.

• Meets other (non-climate) requirements.

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Reference Network

• Establishing a reference upper-air network is articulated in the GCOS Implementation Plan (2004).

• Goals:– Provide long-term, high-quality climate records– Serve to constrain and calibrate data from more spatially-

comprehensive global observing systems (inc. satellites)– Measure a larger suite of co-related climate variables than can

be provided at benchmark observations• Boulder workshop (Feb 2005) focused on

requirements for the reference network.• Seattle workshop (May 2006) will focus on

instrumentation and deployments for the reference network.

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Terms Used in Requirements Tables

• Priority - Ranking from 1 to 4, with 1 as highest priority for GCOS. Based on GCOS “Essential Climate Variables” concept.

• Precision – repeatability; standard deviation of random errors

• Accuracy – systematic error; measured minus actual value

• Long-Term Stability – Maximum tolerable change in systematic error over time (multiple decades)

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Related Issues

• Measurement frequency is not specified, but for radiosonde-type measurements, a program of two observations per day, every 2 or 3 days would provide a reasonable climate record.

• Sonde launch schedule would likely combine fixed synoptic times and times of satellite overpass

• Spatial location of network stations is TBD. Candidates include existing upper-air stations and stations already operating as part of other climate observing networks.

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Variable

Temperature Water Vapor Pressure

Priority (1-4) 1 1 1

Measurement Range

100-350 K 0.1 ppm to 55 g/kg 1 to 1100 hPa

Vertical Range

0 km to stratopause 0 to ~30 km 0 km to stratopause

Vertical Resolution

0.1 km (surface to ~30 km)0.5 km (above ~30 km)

0.05 km (surface to 5 km)0.1 km (5 to ~30 km)

0.1 hPa

Precision 0.2 K 0.1 g/kg in lower troposphere0.001 g/kg in upper troposphere0.1 ppm stratosphere

0.1 hPa

Accuracy 0.1 K in troposphere0.2 K in stratosphere

0.5 g/kg in lower troposphere0.005 g/kg in upper troposphere0.1 ppm stratosphere

0.1 hPa

Long-Term Stability

0.05 K1 11% 0.1 hPa

Comments 1The signal over the satellite era is order 0.1-0.2K/decade (Section 2.1.1) so long-term stability needs to be order of magnitude smaller to avoid ambiguity.

1Stability is given in percent, but note that accuracy and precision vary by orders of magnitude with height.

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Satellite Calibration/Validation

• Proposals have been made to launch soundings coincident with satellite overpasses.

• Reference network concept presupposes a comprehensive network, anchored by reference and benchmark.

• Reference observations can provide transfer functions from one satellite to the next

• Coordination between satellite community and reference network should be established before implementation.

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Websites for More Information

• On requirements (Boulder workshop, Feb. 2005) www.oco.noaa.gov/docs/ua_workshopreport_v7.pdf

• On Seattle workshop www.oco.noaa.gov/workshop2

• On GCOS Implementation Plan www.wmo.ch/web/gcos/Implementation_Plan_(GCOS).pdf

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Summary• Reference upper-air network for climate

research and monitoring would complement satellite observations.

• In situ observations could be optimized for satellite calibration.

• Requirements have been developed for several “essential climate variables”.

• Technologies and deployments to meet the requirements are TBD. Workshop 24-26 May 2006 will address this.

• Implementation will require long term US and international support, under GCOS auspices.

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Requirements Tables

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Variable

Temperature Water Vapor Pressure

Priority (1-4) 1 1 1

Measurement Range

100-350 K 0.1 ppm to 55 g/kg 1 to 1100 hPa

Vertical Range

0 km to stratopause 0 to ~30 km 0 km to stratopause

Vertical Resolution

0.1 km (surface to ~30 km)0.5 km (above ~30 km)

0.05 km (surface to 5 km)0.1 km (5 to ~30 km)

0.1 hPa

Precision 0.2 K 0.1 g/kg in lower troposphere0.001 g/kg in upper troposphere0.1 ppm stratosphere

0.1 hPa

Accuracy 0.1 K in troposphere0.2 K in stratosphere

0.5 g/kg in lower troposphere0.005 g/kg in upper troposphere0.1 ppm stratosphere

0.1 hPa

Long-Term Stability

0.05 K1 11% 0.1 hPa

Comments 1The signal over the satellite era is order 0.1-0.2K/decade (Section 2.1.1) so long-term stability needs to be order of magnitude smaller to avoid ambiguity.

1Stability is given in percent, but note that accuracy and precision vary by orders of magnitude with height.

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Variable

Vector Wind

Priority (1-4) 2

Measurement Range

0 – 300 m/s

Vertical Range

0 km to stratopause

Vertical Resolution

0.05 km in troposphere0.25 km in stratosphere

Precision 0.5 m/s in troposphere1.0 m/s in stratosphere

Accuracy 1.0 m/s1

Long-Term Stability

0.5 m/s in troposphere1.0 m/s in stratosphere

Comments 1to delineate calm conditions from light winds. Direction may be problematic under these circumstances.

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Variable

Ozone Carbon Dioxide Methane

Priority (1-4) 2 3 2

Measurement Range

0.005-20 ppmV

Vertical Range

Surface to 100 km

Vertical Resolution

0.5 km in stratosphere1 km in troposphere

Precision

Accuracy 3% total column5% stratosphere5% troposphere

Long-Term Stability

0.2% total column0.6% stratosphere1% troposphere

Comments

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Variable

Net Radiation Incoming Shortwave Radiation

Outgoing Shortwave Radiation

Priority (1-4) 1 2 2

Measurement Range

0-1500 W/m2 0-2000 W/m21 0-1365 W/m2

Vertical Range

Surface Surface Surface

Precision 5 W/m21 3 W/m22 2 W/m21

Accuracy 5 W/m21 5 W/m22 3%1

Long-Term Stability

0.1 W/m2 0.1 W/m2 0.1 W/m2

Comments 1Accuracy and precision units from BSRN.

1Incorporates cloud reflection effects.2Accuracy and precision units from BSRN.

1Accuracy and precision units from BSRN.

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Variable

Incoming Longwave Radiation

Outgoing Longwave Radiation

Radiances

Priority (1-4) 2 2 1

Measurement Range

0-900 W/m2 0-900 W/m2 Full spectral range300-1700 cm-1

190 K<Tb<330 K

Vertical Range

Surface Surface Surface to top of atmosphere.Need TOA upwelling and surface downwelling but not levels in between.

Vertical Resolution

N/A N/A N/A

Precision 1 W/m21 1 W/m21 0.01%

Accuracy 3 W/m21 3 W/m21 0.15%

Long-Term Stability

0.1 W/m2 0.1 W/m2 0.03% per decade

Comments 1Accuracy and precision units from BSRN.

1Accuracy and precision units from BSRN.

Stability requirement achievable through SI traceability; precision/accuracy requirement for mean seasonal radiances at ~1000 km spatial scale.

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Variable

Aerosol Optical Depth

Total Mass Conc. Chemical Mass Conc.

Priority (1-4) 2 2 2

Measurement Range

0.005 - 5 0.1-100 g m‑3 0.1-30 g m‑3

Vertical Range

Total column 0-6 km 0-6 km

Vertical Resolution

N/A 500 m 500 m

Precision 0.005 10% 10%

Accuracy 0.005 10% 10%

Long-Term Stability

0.005 10% 10%

Comments Spectral measurements

Size-fractionated Size-fractionated

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Variable

Light Scattering Light Absorption

Priority (1-4) 2 2

Measurement Range

0.1-1000 Mm‑1 0.1-1000 Mm‑1

Vertical Range

0-6 km 0-6 km

Vertical Resolution

500 m 500 m

Precision 10% 10%

Accuracy 10% 10%

Long-Term Stability

10% 10%

Comments Size-fractionated, spectral

Size-fractionated, spectral

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Variable

Cloud Amount/Frequency

Cloud Base Height Cloud Layer Heights and Thicknesses

Priority (1-4) 2 2 2

Measurement Range

0-100% 0-20 km1 (1000-50 mb)

0-20 km

Vertical Range

0 to 20Km surface to 50 mb Surface to 50mb

Vertical Resolution

50 m 5 mb 50 m1

Precision 0.1-0.3%1 100 m (10-40 mb2) 50 m2

Accuracy 0.1-0.3%1 100 m (10-40 mb2) 50 m2

Long-Term Stability

0.1-0.2%2 20 m/decade3 50 m/decade

Comments 11-3% variations from ISCCP21-2%/decade trend (Norris 2005)

1 1000-50mb (Rossow and Schiffer 1999)2 10-40 mb variations from ISCCP3 44/154 m/decade for base/top from Chernykh et al. (2001), which was questioned by Seidel and Durre (2002)

1the minimum layer thickness of ~30 m (cirrus) (Del Genio et al. 2002; Winker and Vaughan 1994)2the standard deviation of >= 100 m (Wang et al. 2000)

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Variable

Cloud Top Height Cloud Top Pressure Cloud Top Temperature

Priority (1-4) 3 3 3

Measurement Range

0-20 km 1013-15 hPa 190-310 K

Vertical Range

0-20 km 0-20 km 0-20 km

Vertical Resolution

150 m 150m 1 km

Precision 50m 1 hPa

Accuracy 150 m 15 hPa 1 K/(cloud emissivity)

Long-Term Stability

30 m 3 hPa 0.2 K/(cloud emissivity)

Comments

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Variable

Cloud Particle Size Cloud Optical Depth Cloud Liquid Water/Ice

Priority (1-4) 4 4 4

Measurement Range

Vertical Range

0-20 km 0-20 km 0-20 km

Vertical Resolution

1 km 1 km 1 km

Precision

Accuracy 10% water20% ice

10% 25% water0.025 mm ice

Long-Term Stability

2% water4% ice

2% 5% water0.005 mm ice

Comments

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Source: Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences. Thomas R. Karl, Susan J. Hassol, Christopher D. Miller, and William L. Murray, editors, 2006. A Report by the Climate Change Science Program and the Subcommittee on Global Change Research,ashington, DC. (Figure from Executive Summary, page 9)

1979-20041958-2004

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Notes on Water Vapor Feedback Figure from Soden and Held

• The magnitude water vapor feedback as a function of height and latitude under the assumption of a uniform warming and constant relative humidity moistening in units of W/m2/K/100 mb. Results shown are zonal and annual means. The main contribution to the positive feedback is the increase in water vapor content with increased temperature, leading to increased greenhouse effect and thus further temperature increases.  Note that the maximum feedback occurs in the tropical upper troposphere.