e-mail: orbit constellations - ssec, uw-madison · 2013-02-15 · orbit constellations. this work...

ResultsStatistics of observation departures from NWP model estimates.• BothNOAA-15andNOAA-19bringsomeimprovementtothe

fittotemperatureobservationscomparedtotheassimilationofdatafromjusttwosatellites,aswellastothefittoAMSU-Adataalreadypresentinthesystem(onboardofNOAA-18andMetOp-A).Thelatterimprovementisslightlygreaterinthe“NOAA-15experiment”thaninthe“NOAA-19experiment”(Figure2).

• WindinformationcanbegainedthroughtheassimilationofATOVSMWsoundersdatain4D-Var(Figure3).

• Whencomparingthe“NOAA-15experiment”andthe“NOAA-19experiment”,therearenorelevantdifferencesinthedeparturestatisticsoftheradiosondetemperaturesinfavourofoneexperimentortheother,andthedifferencesaremarginalalsofortheaircrafttemperaturesandforradiosondehumidityobservations.

Forecast impact• TheassimilationofAMSU-AandAMSU-B/MHSdatafromtwo

satelliteshasaverystrongpositiveimpactontheforecastofthegeopotential.ThefullsystemstilloutperformsthetwoorthreesatellitesystemsintheSouthernHemisphere(Figure4).

• Whenaveragedovertheextra-Tropicstheimpactfortheforecastofthegeopotentialofthe“NOAA-15experiment”versusthe“NOAA-19experiment”isneutraltoslightlypositive.Fortheforecastofthetemperaturetheimpactofthe“NOAA-15experiment”versus“NOAA-19experiment”isalsoquiteneutral,withaslightlypositiveimpactintheSouthernHemispherethatappearsstatisticallysignificantatthe95%levelaboutthe5-dayforecastat1000hPaand850hPa(Figure5).

Observing system experiments on ATOVS

orbit constellationsFor more details on this work please see

http://www.ecmwf.int/publications/library/do/references/show?id=90074

Enza Di Tomaso and Niels BormannEuropeanCentreforMedium-RangeWeatherForecasts,Reading,UKE-mail: Enza.Ditomaso@ecmwf.int and Niels.Bormann@ecmwf.int

TheimpactofATOVSdataontheperformanceofglobalnumericalweatherprediction(NWP)isevaluatedthroughobservingsystemexperimentsondifferentorbitconstellations.ThisworkaimstoprovidesomereferencesforplanningfutureobservingsystemsthatinvolveATOVS-likeinstruments,accordingtotheCGMS’objectivestoharmonisemeteorologicalsatellitemissionparameterssuchasorbits.

80°S

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0°

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160°W 120°W 80°W 40°W 0° 40°E 80°E 120°E 160°E

"two-satellite experiment" METOP-A NOAA-18

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"NOAA-15 experiment" METOP-A NOAA-18 NOAA-15

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"NOAA-19 experiment" METOP-A NOAA-18 NOAA-19

0.75 0.8 0.85 0.9 0.95 1Standard deviation (normalised)

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AMSU

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−0.6 −0.4 −0.2 0 0.2 0.4 0.6Mean (K)

Instrument(s): MetOp-A, AMSU-A. Area(s): N. Hemisphere, S. Hemisphere, TropicsFrom 00Z 20 Apr 2009 to 12Z 4 Aug 2009

“NOAA-15 experiment”“NOAA-19 experiment”

Background departure o−b Analysis departure o−a Bias correction of obs

a b

0.6 0.7 0.8 0.9 1 1.1 1.2Standard deviation (normalised)

1000850700500400300250200150100

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Instrument(s): TEMP-Uwind. Area(s): N. Hemisphere, S. Hemisphere, TropicsFrom 00 UTC 20 Apr 2009 to 12 UTC 4 Aug 2009

“two-satellite experiment”“no-MW sounder experiment”

Background departure o−b Analysis departure o−a

“two-satellite experiment” – “no-MW sounder experiment”“NOAA-15 experiment” – “no-MW sounder experiment”“all-satellite experiment” – “no-MW sounder experiment”

S. Hemisphere, 500 hPa Z

0 1 2 3 4 5 6 7 8−0.12

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0 1 2 3 4 5 6 7 8−0.08

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S. Hemisphere, 1000 hPa temperature

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“NOAA-15 experiment” – “NOAA-19 experiment”

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ExperimentsAtthetimeofwriting,therearesevenpolar-orbitingsatellitespresentintheECMWFsystemcarryingoneormoreATOVSinstruments:theNOAAseries,NASA’sAquasatelliteandtheEuropeanMetOp-Asatellite.AsetofexperimentswererunwhereATOVSMicrowave(MW)sounderdata(AMSU-AandAMSU-B/MHS)fromalready-deployedinstrumentswereaddedordeniedasshowninTable1.TheNOAA-15experimentusesamorehomogeneoussamplingwithequallyspacedorbits,whereasintheNOAA-19experimenttwoorbitsareveryclosetoeachother(Figure1).OnlyAMSU-Ahasbeentestedasanadditionalinstrumentinthe“three-satelliteexperiments”,astherearenotthreesatellitesinthedesiredorbitscarryingallfunctioningATOVSinstruments.Experimentswererunfrom14April2009to4August2009withintheECMWF4D-VarassimilationsystemataT511(40km)resolution.

Experiment name Satellite MW sounders

“no-MW sounder experiment” — —

“two-satellite experiment”NOAA-18 AMSU-AMHS

MetOp-A AMSU-AMHS

“NOAA-15 experiment”

NOAA-15 AMSU-A

NOAA-18 AMSU-AMHS

MetOp-A AMSU-AMHS

“NOAA-19 experiment”

NOAA-18 AMSU-AMHS

NOAA-19 AMSU-A

MetOp-A AMSU-AMHS

Experiment name Satellite MW sounders

“all-satellite experiment”

NOAA-15 AMSU-A

NOAA-16AMSU-A

(until 22 June 2009)

NOAA-17 AMSU-B

NOAA-18 AMSU-AMHS

NOAA-19 AMSU-AMHS

Aqua AMSU-A

MetOp-A AMSU-AMHS

Table 1 ATOVS MW sounders available to the experiments.

Figure 1 Sample coverage for used AMSU-A data in the “two-satellite experiment”, the “NOAA- 15 experiment”, and the “NOAA-19 experiment”.

Conclusions• TheassimilationofAMSU-Aobservationsfromathirdsatellite

hasapositiveforecastimpactintheSouthernHemisphereincomparisontotheuseofjusttwoAMSU-Ainstruments,andthereisaclearadvantageinassimilatingallavailableATOVSdata.ThelattershowsthatthebenefitofATOVSdataisnotsaturatedyetwithathree-satelliteconfiguration.

• ATOVSmicrowavesounderdatafromthreesatellitesprovidingagreatertemporalsampling(i.e.MetOp-A,NOAA-18andNOAA-15)haveaslightlylargerpositiveforecastimpactintheSouthernHemispherethandatafromthreesatelliteshavingalessoptimalcoverage(i.e.MetOp-A,NOAA-18andNOAA-19).

• DeparturesofMetOp-AAMSU-AobservationsfromtheNWPmodelestimatesoftheatmosphericstateshowsomebenefitsfromassimilatingobservationsfromNOAA-15ratherthanNOAA-19inadditiontothea.m.andp.m.satellites(MetOp-AandNOAA-18),providingafurtherindicationofanimprovedshort-termforecastintheconstellationofmoreevenly-spacedorbits.

Figure 2 MetOp-A brightness temperature departure statistics for the “NOAA-15 experiment” (black) and the “NOAA-19 experiment” (red). Standard deviations have been normalised to the “NOAA-19 experiment”.

Figure 3 Radiosonde winds departure statistics for the “two-satellite experiment” (black) and the “no-MW sounder experiment” (red). Standard deviations have been normalised to the “no-MW sounder experiment”.

Figure 4 Normalised differences in the root-mean-square forecast error between the “two-satellite experiment” and the “no-MW sounder experiment” (black), between the “NOAA-15 experiment” and the “no-MW sounder experiment” (red), and between the “all-satellite experiment” and the “no-MW sounder experiment” (green) for the 0Z forecast of the 500 hPa and 1000 hPa geopotential. Verification is against the experiment own-analysis and the sample size is 107. Negative values indicate that the “two-”, “NOAA-15”, and “all-satellite experiment” have smaller RMS errors than the “no-MW sounder experiment”.

Figure 5 Normalised differences in the root-mean-square forecast error between the “NOAA-15 experiment” and the “NOAA-19 experiment” for the 0Z forecast of the 1000 hPa and 850 hPa temperature for the Southern Hemisphere. Verification is against the operational analysis and the sample size is 107. Negative values indicate that the “NOAA-15 experiment” has smaller RMS errors than the “NOAA-19 experiment”.

AcknowledgementsEnzaDiTomasowasfundedbytheEUMETSATfellowshipprogramme.

AlanGeerisgratefullyacknowledgedforprovidingthesoftwaretoproducesomeoftheaboveplotsandRobHinefordesigningtheposter.