Oreste Reale GEST/UMBC and NASA Goddard Laboratory for Atmospheres

1. Major discrepancies in the analyzed representation of prominent features of the tropical atmosphere Oreste Reale GEST/UMBC and NASA Goddard Laboratory for Atmospheres

2. Outline • AEJ representation in state-of-the-art reanalyses • AEJ representation on weather-time-scales in operational analyses during SOP-3 NAMMA (2006) • Vertical soundings during SOP-3 NAMMA (2006) • Mis-representation of Tropical cyclones’ analyses away from HH flights (Atlantic) in operational analyses (2006) • Absence of TC Nargis (Indian Ocean, 2008) from analyses • Mid-tropospheric flow over the entire tropical Pacific in August 2010 in NCEP operational, ECMWF operational, and MERRA • Conclusions

3. AEJ representation in state-of-the-art reanalyses • Previously published work (Wu et al., 2009) shows substantial differences between reanalyses in the monthly mean representation of the African Easterly Jet (AEJ) • ERA-40, NCEP-R2, JRA-25 provide very different descriptions of the AEJ structure, and of the horizontal shear in the cyclonically-sheared portion of the AEJ M.-L. C. Wu, Reale, O., S. Schubert, M. Suarez, R. Koster, P. Pegion, 2009: African Easterly Jet: Structure and Maintenance. J. Climate, 22, 4459-4480.

4. Large differences in AEJ SHAPE, INTENSITY VERTICAL STRUCTURE and distribution of the horizontal shear in a 22-year average performed on ERA-40, NCEP-R2, and JRA-25. From Wu et al. (2009) Fig 2 July zonal wind (m s−1, contours every 1 m s−1, 0 omitted, solid: positive, dashed: negative) climatology (1980–2001) based on (top to bottom) ERA-40, NCEP R2, and JRA-25 data: (left) meridional horizontal shear of the zonal wind at 600 hPa and (right) meridional cross section at 0° longitude. (Wu et al., 2009, J.Climate)

5. AEJ and its instability properties in state-of-the-art reanalyses • Work submitted in 2010 (Wu et al., 2010) shows differences in the representation of the African Easterly Jet (AEJ)seasonalinstability properties between reanalyses across a 22-year average • Despite revealing some instability property of the AEJ that appear data-independent, ERA-40, NCEP-R2, JRA-25 and MERRA provide very different descriptions of the AEJ horizontal structure, intensity, and of some properties that control wave instability on a seasonal scale (JAS). M.-L. C. Wu, Reale, O., S. Schubert, M. Suarez, C. Thorncroft, 2010: African Easterly Jet: barotropic instability, waves and cyclogenesis. Submitted to: J. Climate.

6. The analyses differ in terms of strength and intensity of the low-level monsoonal flow, slope of the barotropically unstable part of the AEJ, horizontal shear distribution. All Figures show a 22-year JAS average From Wu et al. (2010) Fig 2

7. Unexpected discrepancies between snapshots of analyzed representation of the African Monsoon-Eastern Tropical Atlantic regions • The African Easterly Jet at about 600hPa,the low-level monsoonal flow (predominantly southwesterly between 1000 and 800 hPa)and the Tropical Easterly Jet (between 200 and 100 hPa)are the critical players in Atlantic tropical development. • Comparison between operational NCEP analyses and GEOS-5-produced analyses reveal serious discrepancies • Validation agains the only vertical sounding in the area at Cape Verde (15N, 23.5W) during the 2006 NAMMA campaign, show that both analyses have large errors

8. Huge discrepancies between GEOS-5 and NCEP operational analyses Wind at 5-15N, 500-600 hPa, has opposite direction! Only in the tropics the two analyses differ substantially Section at 23.5W

9. Largest differences between reanalyses are in the tropics, at about 15N (on the order of 12m/s)larger even thandiscrepancies in the southern hemisphere jet stream NCEP GEOS-5

10. Huge differences in the entire tropical zonal flow from 20S to 20N at all levels

11. Largest mid-tropospheric wind difference is in the tropics, at 0-10N GEOS-5 analyses produce a weaker easterly flow than NCEP GEOS-5 NCEP

12. Largest low-tropospheric wind difference is in the tropics, between 10S and Equator Opposite-sign discrepancy with respect to previous slide: GEOS-5 analyses produce stronger easterly flow than NCEP) NCEP GEOS-5

13. Additional vertical soundings at Cape Verde during SOP-3 provided the chance to validate operational analyses in 2006 Both NCEP and GEOS-5 miss the AEJ maximum at 600hPa. Error larger than 10 m/s at AJE level!!! One of the rare cases in which NCEP and GEOS-5 differ less than 5 m/s) obs NCEP vs GEOS-5 obs

14. Catastrophic non-systematic differences NCEP provides a good representation of low-level and upper-level flows but misses the AEJ. GEOS-5 has huge errors at all levels except at 600hPa. NCEP and GEOS-5 both miss the low-level flow, with NCEP having larger errors. obs NCEP vs GEOS-5 obs

15. Catastrophic non-systematic differences NCEP has a stronger AEJ. GEOS-5 has a stronger AEJ. NCEP vs GEOS-5

16. In addition to differences in the general circulation in the Tropics, state-of-the-art operational systems can completely miss existing Tropical Cyclones. • Analyses are particularly deficient in the depiction of developing, deepening and transitioning tropical cyclones • Analyses are deficient in representing cyclogenesis and existing deepening cyclones in the eastern Atlantic • Analyses are particularly deficient in representing even fully-developed TCs over the Indian Ocean

17. TS Debby (2006) at 06z 24 Aug 2006Obs center slp 999 hPa; Max wind 22 m/s NCEP analyses do not produce a closed circulation GEOS-5 An. 200km displacement error for center (obs. center X) Wind speed m/s

18. Published study on the impact of AIRS, focused on tropical cyclone Nargis (2008)emphasizes the difficulty of analysing TCs over the Indian Ocean • Work published in 2009 shows some improvements in analysis over the tropics in in the GEOS-5 DAS and forecasting model consequent to assimilation of AIRS-derived information in CLOUDY areas. Case chosen: catastrophic cyclone Nargis which hit Burma causing devastating loss of life • Tropical Cyclones in the Northern Indian Oceans are extremely difficult to analyze: operational global analyses often do not represent these cyclones’ position (or even the TCs’ very existence) accurately. Forecasts are penalized by these poor analyses Reale, O., W. K. Lau, J. Susskind, R. Rosenberg, E. Brin, E. Liu, L.P. Riishojgaard, M. Fuentes, R. Rosenberg, 2009: AIRS impact on the analysis and forecast track of tropical cyclone Nargis in A global data assimilation and forecasting system. Geophys. Res. Lett., 36, L06812, doi: 10.1029/2008GL037122

19. Complete miss of TC Nargis (2008) in both operational NCEP and MERRA analyses at a time when is declared having hurricane-level winds by the JTPC and IMC COMPLETELYFLAT PRESSUREFIELD 800x600km Contours every 1hPa WINDS DONOT FORMA CLOSEDCIRCULATION 800x600km Contours every 1hPa X observed cyclone’s center WINDS DO NOT REACH 12m/s WINDS DO NOT FORM A CLOSED CIRCULATION

20. Some improvement with AIRS cloudy retrievals Analysis obtained assimilating AIRS cloudy retrievals Well-defined Cyclone Green: Observed Track 108-hour forecast (slp) initialized from improved analyses Green: Observed Track Accurate landfall is produced in the forecasts initialized with AIRS: (Reale et al., 2009, Geophys. Res. Lett.) CNTRL Analysis (above) And forecast (below): No Cyclone

21. Huge differences between operational ECMWF, NCEP and MERRA over the entire tropical Pacific during strong La Nina conditions (Aug 2010) • Weather prediction over the tropical Pacific is controlled by a good representation of the predominantly easterly flow and periodic westerly bursts along the Equator • Large errors in the equatorial flow propagate away from the Equator affecting TC genesis prediction, and TC track forecast as far as 30N/S

22. Huge600hPa zonal wind difference affects the entire tropical Pacific in 2010 Speeds are very comparable away from the tropics. Difference of about 10m/s over Eq.Pacific

23. Huge600hPa zonal wind difference affects the entire tropical Pacific in 2010 50% speed Difference Over Eq. Pacific Opposite sign wind over, and NE of, Hawaii

24. Huge600hPa zonal wind difference affects the entire tropical Pacific in 2010involving all 3 data sets

25. The largest 600hPa wind difference at 165W occurs in the tropics, between 20S and 10N ECMWF NCEP MERRA

26. Conclusions • State of the art reanalyses (ERA-40, JRA-25, NCEP-R2 and MERRA) show susbtantial differences in the seasonally-averaged representation of the African Easterly Jet and more generally of the circulation in the African Monsoon and tropical Atlantic regions • Operational analyses or reanalyses differ also at instantaneous times in the tropical region. On the contrary, away from the tropics, different analyses provide almost identical representations of the wind field • Some limited improvement in the analysis and forecast in the tropics has been locally noted as a consequence of particular methodologies, such as cloudy AIRS retrieval ingestion, or implementation of interactive aerosols. • However, it appears evident that the global tropical wind field is the most deficient aspect of current tropospheric analysis • Despite changes in models and assimilation systems, and increase in resolution, the representation of wind in the tropicsdoes not show much improvement from 2006 to 2010 • Major deficiencies appear on all 3 basins:Atlantic, Indian and Pacific Oceans on scales spanning from storm-scale to planetary, from weatherto seasonal • To reduce the errors in the analyzed wind field on different scales in the tropics is of paramount importance and should be the goal for the next-generation observing systems