NWP in the Met Office

1. NWP in the Met Office

2. Topics to be covered... 1. Describing the atmosphere 2. Using observations 3. Model mathematics 4. Operational models purposes 5. Model outputs

3. The Weather Prediction Process OBSERVATIONS NUMERICAL FORECASTS R&D VERIFICATION CUSTOMERS ARCHIVES HUMAN FORECASTER

4. Unified Model • Met. Office has several requirements: • local forecasting • global forecasting • climate modelling • ocean and wave modelling • a common model: • shares code and operating structure • is modular where differences are necessary • gives considerable savings in maintenance cost

5. Unified Model configurations

6. Met Office models Based on Unified Model • Global • North Atlantic and European model • 4km and 12km Mesoscales • Crisis Area Mesoscale Models • Stratospheric • FOAM ocean forecasting models

7. Met Office models Other models including • Wave (Global, European, UK Waters) • Surge • NAME • SSFM

8. Fundamentals of NWP 1. Specify atmospheric initial conditions in a numerical form 2. Use equations describing atmospheric physical processes to predict how the initial state will evolve 3. Output the forecast in a useful form for the user

9. 1. Describing the atmosphere

10. Unified Model is a gridpoint model Grid length Grid point Specify the properties in the grid box from observational data (temp, pressure humidity, wind etc.)

11. GM Vertical resolution – 50 levels 65 km In free atmosphere levels are height coordinates In between levels are a combination of the 2 Lowest model levelspresent/new 70L at10m/2.5m for wind at20m/5m for temp 17.5 km In boundary layer levels are terrain-following

12. Global Model (GM) Horizontal Resolution: Mid-latitude 40km Timestep: 20mins Vertical levels: 50, then 70 Grid: Standard lat/long type, with filtering near the poles Mesoscale Model (MES) Horizontal Resolution: 12km/4km Timestep: 5/ 1.7 mins Vertical levels: 38, eventually 70 Grid: Rotated lat/long (‘Equatorial Lat-long Fine-mesh’ - ELF) Global, North Atlantic & European, mesoscale models North Atlantic & European Model (NAE) Horizontal Resolution: 12km Timestep: ~5 mins Vertical levels: 38, eventually 70 Grid: Rotated lat/long (‘Equatorial Lat-long Fine-mesh’ - ELF)

13. 2. Using observations

14. Data assimilation • GM uses 4-D VAR; 12km MES and NAE 3-D VAR • 4km MES has no data assimilation yet • Model is run for an assimilation period prior to the forecast • 6 hrs for GM model • 3 hrs for the MES and NAE

15. Data assimilation • Observations firstly qualitycontrolledagainst • climate data • model background field • nearby obs. • Theninserted into the run at or near their validity time to nudge the model towards reality

16. GP GP GP GP GP GP Using observations Models try to make the best possible use of observations Observations are checked for quality and interpolated onto the model grid points Different types of data have differentareas of influence airep GP sonde sonde ship synop synop synop LAND synop GP synop ship SEA GP

17. Moisture Observation Pre-processing System (MOPS) • Used only in 12km MES/NAE • Latent heating and cooling important in driving mesoscale systems • MOPS is an analysis of humidity, cloud and precipitation for 12km MES and NAE

18. Soil moisture in the GM • No longer reset weekly to climatology • New soil moisture nudging scheme • Not as complex as MOPS • Produced verifiable improvement, especially surface temperatures

19. 3. Model Mathematics

20. Model variables • PRIMARY PROGNOSTIC variables are explicitly calculated using the primitive equations • ANCILLARY FIELDS are fixed lower boundary conditions • SECONDARY PROGNOSTIC variables are calculated at each timestep from the prognostic variables.

21. Horizontal and vertical wind components potential temperature specific humidity cloud water and ice surface pressure surface temperature soil temperature canopy water content snow depth Primary prognostic variables

22. land/sea mask soil type vegetation type grid-box mean and variance of orography sea surface temperature proportion of sea-ice cover sea-ice thickness sea surface currents Ancillary fields Prognostic variables in coupled atmosphere/ocean models

23. Global model orography

24. NAE Model orography

25. 12km / 4km MES Model orography

26. Model variables • PRIMARY PROGNOSTIC variables are explicitly calculated using the primitive equations • SECONDARY PROGNOSTICvariables are calculated by the parameterisation schemes

27. primary prognostic variables horizontal and vertical wind components potential temperature specific humidity cloud water and ice surface pressure surface temperature soil temperature canopy water content snow depth secondary prognostic variables boundary layer depth sea surface roughness convective cloud amount convective cloud base convective cloud top layer cloud amount ozone mixing ratio Model variables

28. Parametrised processes 1. Layer cloud and precipitation 2. Convective cloud and precipitation 3. Radiative processes 4. Surface and sub-surface processes 5. Gravity wave drag

29. 1. Layer cloud and precipitation * * * * * * * * * * * * *

30. 2. Convective cloud and precipitation Convective cloud model

31. 3. Radiative processes

32. 4. Surface and sub-surface processes

33. 5. Gravity wave drag

34. Boundary conditions • Land & sea: ancillary fields • Stratosphere: ‘lid’ to model • required in MES and NAE models • primary prognostic variables required at each grid point • NAE and 12km MES supplied from global model • 4km MES supplied from NAE • possible source of error • Lower and upper boundaries • Lateral boundaries

35. 4. Purposes of Operational Models

36. Global model • 4 times daily • Run times … 00Z, 06Z,12Z, 18Z • Data accepted up to T+1 hour 45 min • Out to T+144 (6 days) at 00Z and 12Z, T+48 at 06Z and 18Z • Takes 2hr 15 mins to run out to T+144, 1hr 15min for T+48

37. Global model • Used for:- • regional synoptic guidance • medium range guidance • civil aviation products • mesoscale model boundary conditions

38. North Atlantic & European model • Run times … 00, 06, 12 and 18Z • Takes boundary conditions from Global Model (previous GM run) • Run partly overlaps with the GM • Out to T+48

39. North Atlantic & European model • Used for:- • wider range of products to international customers • Improved Synoptic development guidance • Better for rapid developments and extremes • Boundary conditions for 4km MES

40. Advantages of NAE Model • Large domain • Captures developing systems over North Atlantic • Covers all of Europe and European Nimrod area • includes some other model areas • Higher resolution than GM (12km-v-40km) • Better for rapid developments and extremes

41. 12km Mesoscale model • Run times … 00Z, 06Z, 12Z and 18Z • Takes boundary conditions from Global Model • Runs in parallel with the GM (starts 10 mins later) • Out to T+48 (2 days)

42. 12km Mesoscale model • Used for:- • UK local detail (ppn, cloud,temp,wind) • Input to other systems (SSFM, and Nowcasting systems etc.)

43. 4km MES model • Run times … 03Z, 09Z, 15Z, 21Z • Takes boundary conditions from NAE Model • Out to T+36 • No data assimilation

44. Model Dependencies (simplified!) NAME GLOBAL WAVE GLOBAL FOAM NAE MODEL EUROPEAN WAVE SHELF SEAS 12KM MES 4KM MES SSFM UK WATERS WAVE SURGE Scheduling must account for all dependencies and timeliness requirements of each model run

45. GM, NAE and MES output. • http://www-nwp/~meso/current_mesglob_charts.html • NWP Gazette • http://www.metoffice.gov.uk/research/nwp/publications/nwp_gazette/index.html • NWP technical reports • http://www.metoffice.gov.uk/research/nwp/publications/papers/technical_reports/index.html • 4km mesoscale runs: • http://www-nwp/~meso/current_uk4mesglob_charts.html Any questions?