1 ATOVS and SSM/I assimilation at the Met Office Stephen English, Dave Jones, Andrew Smith, Fiona Hilton and Keith Whyte

2 NESDI S NWP system for ATOVS+SSM/I AAP P 1D-var 3D-var 1D-var 1B1D 1D+QC T* etc. 1C HRP T ATOVS SSM/I NWP system Global (4 x 6 hrs) 3D-var/FGAT 325x217 30L Mesoscale (8 x 3 hrs) 43-63N, 15E-15W 12km 38L AMVs, sondes, synop, AIREP, AMDAR, buoy and ship data Winds TCWV LWP T+6 or T+3 Analysis

3 Status NOAA-15 AMSU 4-12 NOAA-14 MSU 2-4 HIRS 1-8, DMSP-F13 Windspeed NOAA-15 AMSU 4-12, 18, 20 NOAA-16 AMSU 4-12, HIRS 5-8, 10-12, 15 DMSP-F13 Windspeed DMSP-F15 Windspeed Sept 2000Feb 2002 ATOVS SSM/I

4 Impact of satellite and relevant assimilation change since introduction of 3D-var March       Introduction of 3DVAR and NOAA-15 ATOVS July  Use of ATOVS over Siberia, covariance retuning, increased thinning of scatterometer winds October    Direct assimilation of (A)TOVS Radiances, Use of Surface Wind from SSM/I, Remove scatterometer winds over ice, improved use of Synop pressures May   Time interpolation of background, covariance retuning February  Second SSM/I satellite, humidity covariance retuning, improved use of AMSU channel 5 in cloudy conditions April   Use of AMSU-B and NOAA-16 ATOVS replaces NOAA-14 TOVS October    Improved use of SSM/I, AMVs, ATOVS thinning, ATOVS over sea ice

5 ATOVS & 3D-var +4 ATOVS sea ice & AMVs +2 NOAA-16 & AMSU- B +1.5 ATOVS over Siberia Direct radiance assimilation +2 Tuning of 3D-var nd SSM/I etc

6 Examples: Upper level wind and SH pmsl SS = 1 - RMS f 2 /RMS p 2 20N - 90N 250 hPa windspeed 20S - 90S mean sea level pressure 20S - 90S 250 hPa windspeed 20N - 20S 250 hPa windspeed MetO 2002 ECMWF 2002 MetO 2001 MetO 1999

7 ATOVS changes 1. AMSU channel 5: increased use in cloudy areas Date: Feb Trials: Dec 99 + Jul 00 Method Stop using HIRS cloud flag status when cloud checking for AMSU ch.5 Impact Large at short range –improved fit to radiances and radiosondes at T+6 –RMSE slightly lower (  1-2%) for height at T+24-T+72, especially in SH and tropics (RMSE  3% at 700 hPa in tropics), but < 1% improvement for winds and RH. Neutral in medium range (T+96-T+144)

8 2. Replacement of NOAA-14 TOVS with NOAA-16 ATOVS Date: April Trials: Mar-Apr 01 Method As NOAA-15 ATOVS. Impact Replacing NOAA-14 with NOAA-16 had a very large impact 500 hPa height RMSE  10% in SH and  3-5% in NH at short and medium range Also losing NOAA-14 without replacing with NOAA-16 would have had a significant negative impact The largest impact of any ATOVS change since the original introduction of NOAA-15

9 3. Use of AMSU-B from NOAA-15 and NOAA-16 Date: April Trials: Dec 99 + Jul-Aug 00 + Mar-Apr 01 Method AMSU-B channels 18, 20 from NOAA-15, from NOAA-16. Sea points only. Cirrus check for channel 20. Precipitation checks for channels 18, 19. Impact AMSU-B had a small positive impact on mass and wind field –tropical low level wind (T+24 RMSE  2% at 850 hPa). –20S -70S low level height (T+24 RMSE  5% at 850 hPa). AMSU-B had a large positive impact on tropical relative humidity –tropical low level RH hPa (RMSE  5% at 850 hPa T+24). –improved to RMSE  10% when bias corrections were recalculated. Subjective verification of cloud and rain fields –improvements versus SSM/I global rain retrievals from NESDIS and versus geostationary VIS/IR imagery.

10 Fit to radiances Fit much improved in tropics Ch. 18 ( hPa) 90S 45S Equator 45 N 90N Std. Dev. Obs-FG K Observation error = 4 K assumed Fit marginally improved in SH Almost neutral in NH

11 Tropical humidity verification T+24 RH at 500 hPa Red line: No ATOVS humidity Blue line: NOAA-14 HIRS humidity Yellow line: NOAA- 16 HIRS humidity Green line: AMSU- B humidity Note that the blue line represents Met Office operations at the time and that after 18 April AMSU-B became operational and so the blue line and green line converge. MarchApril Forecast - Obs RMS error %

12 RH verification for the UK April 2000-Jan 2002 Performance for Mesoscale model area is consistently higher in Apr 2001-> than April 2000-Mar 2001 (so far…) Global model (red = longer data cut-off) Mesoscale model 500 hPa RH v radiosondes at T+12

13 4: New sea ice analysis allowing use of more ATOVS over sea ice Date: Oct Trials: Mar-Apr 01 + Jun-Aug 01 Method Emissivity = E w F w + E ice F ice + (E myi - E ice )F myi F w + F ice = 1.0, E ice =0.92, E myi =0.85, E w =Fastem or 0.71) Ice type is determined by AAPP and at present sea ice is all multi-year ice or all young ice i.e. F myi = 0 or F myi = F ice. If F myi = F ice, E w = 0.71 to allow for likely formation of grease ice in leads. Impact Improved fit to radiances at T+6 over ocean near sea ice and over sea ice Neutral in NH (Height RMSE  0.5% at and below 500 hPa, up to T+72, 1-2% in Med. range) Slightly positive in SH (Height RMSE  1-2% at and below 500 hPa at all forecast ranges)

14 5: Modify ATOVS thinning to increase number of cloudy obs assimilated Date: 17 October 2001Trials: Mar-Apr 01 + Jun-Aug 01 Method Favour observations where microwave cloud check detects no cloud, but infra-red cloud check detects cloud. Why? Model background errors are found to be systematically higher in cloudy areas. Impact Very positive at short range (T+6) in fit to radiances and also radiosondes. Height RMSE  2-3% T+24 to T+48 in SH, 1-2% in NH Neutral at T+72 to T+144 and in tropics * * ** *** ** * ** * * * ? ** *** * * * ** * **

15 SSM/I changes 1: Assimilate surface windspeeds from a second SSM/I satellite Date: Feb & Oct Trials: Dec 99 + Jul 00 Method Initially F15 was added to F13, but the number of observations was limited to per cycle. In October 2001 this was increased to Impact RMS difference between analysis and altimeter windspeeds (which are not assimilated)  9% RMS difference between T+6 forecast and altimeter windspeeds only  1% compared to  16% for “first satellite” SSM/I set of windspeeds 850 hPa wind RMSE  > 1% only at T+24. Largest impact in tropics.

16 Work in progress AMSU-B in the Met Office Mesoscale Model –see poster Jones et al. presented by me. Move ATOVS b ias correction into 3D-var with new predictors Preparation for SSMIS Cloud analysis in 1D-var and 3D-var –see poster by English and Weng presented by me. Improved use of ATOVS over sea ice –still reject too much ATOVS over sea ice. ATOVS over land –no significant progress since last ITSC. Total column water vapour from SSM/I

17 Conclusions NOAA-16 and AMSU-B gave a major improvement in NWP skill and the second ATOVS satellite now gives a large and measurable impact, even in the NH. Tuning of 3D-var and regular improvements to ATOVS and SSM/I processing mean that Met Office global forecasts are improving very rapidly (last 3 years improvement = previous 9 years at Met Office, sum of small changes since ATOVS+3Dvar introduced now twice the impact of the original change). Final thought…data denial experiments at the Met Office confirm ECMWF result that satellite data impact is comparable with conventional data impact even in the NH.