1. SEASONAL sensitivity study on COBEL-ISBA LOCAL FORECAST SYSTEM for fog and low clouds at Paris CDG airport ROQUELAURE Stevie and BERGOT Thierry Météo-France WSN05 september 2005

2. Outlines Météo-France + COBEL-ISBA numerical prediction model + Advection sensitivity on 2002-2003 winter season + Cloud (fluxes) sensitivity on 2002-2003 winter season + 3h data assimilation vs 1h data assimilation (winter 2003-2004) + Conclusions WSN05 september 2005

3. Cobel-Isba numerical prediction Météo-France 3h -Assimilation : - Var + fog and low clouds initialisation 3h -Assimilation : 1D- Var + fog and low clouds initialisation Observat ions ISBA offline COBEL/ISBA – 1D 12h local forecasts: Detection of LVP conditions (fog and low clouds) on 30minutes Visibility < 600m & ceiling < 200ft forecasters guess Aladin forecasts (3D) ? WSN05 september 2005

4. Advection (T,q) sensitivity Météo-France + Simulations set (2002-2003 winter season): - ref : without advections - adv : temperature & humidity advections - AT + std : advections + temperature std - AT – std : advections - temperature std - Aq + std : advections + humidity std - Aq – std : advections - humidity std Aq + std Aq - std ref (no advections) Aq AT WSN05 september 2005

5. Advections (T,q) STD distributions Météo-France + Advection are calculated from NWP model Aladin - spatial and temporal consistency advection std distributions constant linear constant linear WSN05 september 2005

6. Advections (T,q) effects on LVP forecasts Météo-France + All scores are from: - 2002-2003 winter season (5 months dec-April) - 3h assimilation scheme (0Z, 3Z …., 21Z) (~1200 simulations) + Scores are calculated from all initialisations time - Hite Rate = ( forecasted&observed LVP / observed LVP ) - False Alarm Rate = ( forecasted&non-observed LVP / non-observed LVP) WSN05 september 2005

7. Advections (T,q) effects on LVP forecasts Météo-France Advection effect + No improvements with advections (HR & FAR) + Adv is slightly better than persistence (HR) WSN05 september 2005

8. Temperature advection std effects on LVP forecasts Météo-France cold effect + No symetrical effect (cold/warm advection) + AT std impact is important on LVP (colder advection) + No major degradation in FAR WSN05 september 2005

9. Humidity advection std effects on LVP forecasts Météo-France humidification + No symetrical effect (moist/dry advection) + AQ std impact is important on LVP (moist advection) + Degradation in FAR (~10%) with moist advection WSN05 september 2005

10. Clouds initialisation Météo-France + Initialisation of fog and low clouds iterative method for minimizing the divergence between observed & cobel radiation fluxes + Simulations set (2002-2003 winter): - ref : with low clouds & fog initialisation - no : no low clouds & fog initialisation - aladin : low clouds & fog initialisation + cloud cover from aladin (IR and VIS) - obs : low clouds & fog initialisation + persistence of observed clouds (IR) WSN05 september 2005

11. Clouds (oberved IR vs COBEL IR) Météo-France No Bias=-44.2 W/m 2 Ref Bias=-16.6 W/m 2 Aladin Bias=-6.4 W/m 2 Obs Bias=-2.3 W/m 2 WSN05 september 2005

12. Clouds effects on LVP forecasts Météo-France WSN05 september 2005

13. LVP: 3h data assimilation vs 1h data assimilation Météo-France + This result is from the work of MARZOUKI Hicham (master student), for winter season 2003-2004 + The only difference between the 2 simulations is the data assimilation frequency (3h 1h) 8 initialisations/day 24 initialisations/day WSN05 september 2005

14. LVP: 3h data assimilation vs 1h data assimilation Météo-France + Improvements can be observed in HR (5%) & FAR by decreasing the data assimilation frequency to 1 hour. WSN05 september 2005

15. CONCLUSIONS Météo-France + Advections have a important impact on LVP forecasts - moist/cold advections impact is more significant dry/warm advections - advections impact is cumulative more important for long term simulation (4 -12 hours) + Fog and low clouds initialisation is very important - IR radiative impact significant improvement in FAR + Improvements can be observed in HR & FAR by decreasing the data assimilation frequency to 1 hour. WSN05 september 2005

16. Thank you Météo-France WSN05 september 2005

17. Advection STD computation Météo-France Time UTC 00Z06Z18Z12Z24Z30Z + site R=10 km 1- Advection spatial mean & std 2- Advection temporal mean & std On all levels: WSN05 september 2005