MODIS Polar Winds in ECMWF’s Data Assimilation System: Long-term Performance and Recent Case Studies Lueder von Bremen, Niels Bormann and Jean-Noël Thépaut European Centre for Medium-Range Weather Forecasts (ECMWF) Reading, United Kingdom High Latitude NWP Workshop at IARC, Fairbanks, 8-10 October 2003

 History and use of MODIS Polar Winds at ECMWF  Long-term performance a) one satellite (Terra) b) two satellites (Terra and Aqua)  Case study  Conclusions and prospects OUTLINE

History of MODIS AMVs at ECMWF  trial 3DVAR experiments with MODIS Terra AMVs very successful (spring 2001)  operational archiving of MODIS Terra AMVs since July 2002  4DVAR experiments with MODIS Terra AMVs i) 2 study periods (spring 2001 and summer 2002, 58 cases) ii) operational configuration (T159 60L analysis and T511 forecast) iii) usage like geostationary AMVs iv) modification of mean polar wind analyses v) reduction of key analysis errors in case study experiment vi) good impact on forecast over NH (especially over Europe and N. Atlantic)  operational use of MODIS AMVs (Terra) since 14 Jan 2003  operational archiving of MODIS Aqua AMVs since Feb 2003 monitoring since May 2003  4DVAR experiments with MODIS Aqua AMVs are described here (operational analysis and model configuration)

Received/Used MODIS Terra AMVs (N. Hemisphere) IR WV Cloud WV ClEAR Height<400hPa400hPa<Height<550hPa  Need for reduction and quality/bias check

Pre-Processing and usage of MODIS AMVs Usage: Land: above 400 hPa Ocean/Ice: IR above 700hPa WV above 550hPa FG check: asymmetric to remove negative OBS-FG bias ( FG-Dep. is scaled with background error) Thinning: 2 cycles with different box/volume sizes (96x96km then 140x140km) WV clear 400hPa<h<550hPa all FG [m/s] OBS [m/s] used FG [m/s] OBS [m/s] OBS errors: AMV AIREP PILOT,SONDE

Observation Monitoring (WV clear, hPa) all OBS-FG OBS-AN stdv(OBS-FG) stdv(OBS-AN) stdv(OBS) used

500 hPa Z anomaly correlation (58 days) Bormann and Thépaut,2003 (spring 2001 and summer 2002) LONG-TERM PERFORMANCE

absolute valuesDifference Modis-Control Sensitivity perturbations for streamfunction around 500 hPa Positive impact of MODIS (negative differences) occurs where Sensitivity patterns are large Sensitivity results: 4 August 2002, 12 Z

Modis Terra and Aqua data coverage at May 27, Z Light: 06Z Dark: 12Z

Experiments with MODIS (Terra and Aqua)  2 study periods Feb. and May 2003, 51 cases  revision of MODIS impact in general and clean control to monitor both i) noMODIS (gives chance for clean OBS-FG statistic for Terra and Aqua) ii) Terra (operational usage (140km thinning)) iii) Terra+Aqua (140km thinning) iv) BOTH200km (Terra and Aqua with 200km thinning and QI usage)  stronger OBS-FG bias for Aqua over Antarctic than for Terra WV cloud IR Aqua Terra

Mean Polar Wind Analysis/Difference to noMODIS at 400 hPa noMODIS Terra Terra+Aqua [m/s]

RMS of Analysis Increments 400 hPa geopotential height noMODIS Terra Terra+Aqua [gpdm]

Used MODIS AMVs (above 400 hPa) S.Hem. N.Hem. Terra Terra+Aqua BOTH200km Total: Terra:  huge amount of Aqua over Antarctica  Terra and Aqua AMVs not competitive  moderate increase with BOTH200km only

N.Hem S.Hem EuropeN.Atlantic (winter and spring 2003) noModis Terra Terra+Aqua BOTH200km Forecast scores: 500 hPa Z anomaly correlation (51 days)

Operations noMODIS eSuite eSuite(noMODIS) Terra+Aqua half err.cov QI Day5, 500Z, Europe 12UTC  Trials with cycles at 30 June 00 and 12 UTC using noMODIS background CASE STUDY Experiment: BIASED has MODIS from 30 June UTC on

500Z Forecast 30 June UTC vs Analysis Analyses noMODIS BIASED +12h +36h+48h+60h+24h

OBS-Time: 0415Z 0555Z 0735Z 0915Z 1050Z 1230Z 1410Z Study Area 1 – Analysis at 30 June 2003, 12UTC used AMVs hPa in Exp. BIASED OBS-FG Departure: [m/s] blacklisted AMVs are coloured Exp.BIASBLACK

Analysis at 30 June 2003, 12UTC background BIASBLACKBIASED [Pa/s] [gpdm] vertical velocity at 500 hPa BIASBLACK-BIASED 500Z difference

Short-term forecast at 30 June 2003, 12UTC vertical velocity at 500 hPa +3h +6h BIASBLACKBIASED [Pa/s] Straight model forecast +18h Operations +3h +6h

BIASBLACK 24h forecast error (400Z) at 30 June 2003, 12UTC BIASED Operations noMODIS [gpdm]

CONCLUSIONS - PROSPECTS MODIS Polar winds  have impact on ECMWFs polar wind analysis (stronger over Antarctic)  introduce analysis increments over very bad observed areas  are consistent with the other sparse wind observations  improve forecast over Europe  impact is decreased since much more other satellite data is in the system 2 satellite systems  increase the spatial coverage  may lead to overfitting (SH) (thinning is an appropriate way to handle this)  give potential also for better temporal coverage, ECMWF is encouraging the combination of Terra and Aqua very much (tracking of fast moving systems might be improved substantially (special benefit to 4DVAR)) … challenging is  difference between Terra and Aqua (bias, number of AMVs)  usage of ECMWF forecast data for the height assignment  usage of clear sky WV radiances from MODIS