1. Global vs mesoscale ATOVS assimilation at the Met Office Global Large obs error (4 K) NESDIS 1B radiances NOAA-15 & 16 HIRS and AMSU thinned to 154 km (2°) ±3hr assim window Mesoscale Smaller obs error (2 K) Direct broadcast radiances NOAA-15 & 16 AMSU only thinned to 0.4° ± 1½ hr assim window

2. AMSU-B Example of full resolution AMSU-B 89 GHz imagery Approximate MetO mesoscale model domain

3. Typical data coverage plots for 15Z and 18Z runs 15Z 18Z

4. Issues and summary Accuracy of the navigation of direct broadcast NOAA-15. Latent heat nudging scheme is applied after the 3D-var analysis. HIRS gridded AMSU-B data used (36 observations averaged). Trials: 20 April - 1 May & 14 May - 1 June 2001 + case studies. 28 days for each main forecast. 4 large impacts (2 improved, 2 degraded) others close to neutral verified subjectively by a trained (and unbiased!) forecaster. (-) ve impact: surface visibility, 6 hourly precipitation, cloud base height, surface temperature (v synop* data). (+) ve impact: total cloud amount, surface wind (v synop data). Using an objective weighted mean of key meteorological fields the skill of the forecast v synop data was reduced by 0.7%. * Synop data: these are routine hourly observations from meteorological stations: cloud observations are made by trained observers and other variables are from standard meteorological station equipment (rain gauge, screen thermometers etc.). No radar or satellite data is used.

5. The mesoscale model analysis pulls strongly to the ATOVS data in the first assimilation cycle RMS Obs - Forward modeled TB / K Fit of radiances to background (six hour forecast) Control = No ATOVS assimilated Trial = ATOVS assimilated

6. AMSU-B positive impact Reduction in rain rate OperationalTrialRadar

7. AMSU-B negative impact Operational No ATOVS assimilation Case study 24 hours of ATOVS assimilation Real time trial 8 days of ATOVS assimilation Stratus probabilities Note that AMSU-B only has a large impact in the real time trial, where AMSU-B has been assimilated for 8 days before this case. The case study had only 24 hours of ATOVS assimilation and impact was minimal. Note satellite data confirmed that the operational stratus analysis was very accurate. Note that AMSU-B only has a large impact in the real time trial, where AMSU-B has been assimilated for 8 days before this case. The case study had only 24 hours of ATOVS assimilation and impact was minimal. Note satellite data confirmed that the operational stratus analysis was very accurate.

8. Conclusions Moisture analysis and background fit to AMSU is improved. AMSU-B had 2 positive and 2 negative impacts - rest neutral. Overall statistical objective verification (v synops) showed slight degradation in forecast skill  not made operational. Previous results are being compared with satellite cloud products. More trials are being run to increase sampling and for which full- resolution (unmapped) AMSU-B can be used. Rain radar and cloud observation processing will be included in 3D- var in the future rather than as a separate nudging scheme. Are 3D-var error correlations, cloud detection, radiative transfer model, quality control, model physics etc. good enough? Next steps