1. 1 Les règles générales WWOSC 2014 16-21 August, Montréal, Canada Didier Ricard 1, Sylvie Malardel 2, Yann Seity 1 Julien Léger 1, Mirela Pietrisi 1. CNRM-GAME, METEO-France, Toulouse 2. ECMWF, Reading Sensitivity of short-range forecasting with the AROME model to a modified semi-Lagrangian scheme and high resolution.

2. 2 AROME (Seity et al., 2011): operational fine-scale NWP model used at METEO-France since 2008  In 2008: 2.5-km horizontal resolution, 41 vertical levels Domain 1500 km * 1300 km (600*512 points)  Current version: 2.5-km horizontal resolution, 60 vertical levels Domain 1875 km * 1800 km (750*720 pts)  In 2015: 1.3-km horizontal resolution, 90 vertical levels Domain 1996 km * 1872 km (1536*1440 pts) 1 – Introduction Next version: 1.3 km 90

3. 3 Dynamics package : Nonhydrostatic model based on a fully compressible system Spectral model, A grid Semi-Lagrangian scheme  Tri-linear interpolation for computation of trajectories (origin point)  quasi-cubic interpolations for calculating advected variables at origin point Time scheme  2 Time Levels semi-implicit scheme with SETTLS option (operational version)  ICI (iterative centred implicit) scheme (Predictor-corrector scheme) 4th order spectral diffusion and gridpoint SLHD on hydrometeors Characteristics of the AROME model Physics package : one moment mixed-phase microphysical scheme: 5 hydrometeor classes 1D Turbulence scheme: pronostic TKE equation with a diagnostic mixing length (Bougeault Lacarrere, 1989) Surface scheme: SURFEX (ISBA parametrisation, TEB scheme for urban tiles, ECUME for sea tiles) Radiation scheme: ECMWF parameterization EDMF Shallow convection scheme 1 – Introduction

4. 4  Evaluation of the AROME model at convective scale for preparing the next operational version  Test of a modified SL scheme at 2.5-km horizontal grid spacing during several periods (in particular between 15 July - 15 September 2013)  Comparison between AROME forecasts at 1.3-km and 2.5-km horizontal resolutions during June-November 2012 for days with thunderstorms 1 – Introduction

5. 5 Motivation  Evaluation on a 2-month period (15 July 2013 - 15 September 2013) including deep convection with important effects of divergence Bias for precipitation:  too much precipitation  sometimes too strong outflows under convective cells (with a strong diffusion ) Convection:  small-scale processes dominated by divergent modes  strong interaction between physics and dynamics  excessive behaviour: lack of conservation of SL scheme is suspected Solution: more conservative SL schemes (CISL, finite volume …)  complex to implement  expensive for operational use Simpler alternative approach (proposed by S. Malardel):  taking into account expansion/contraction of atmospheric parcels associated to each gridpoint  small modifications of the SL interpolation weights as a function of deformation 2 – Test of a modified Semi-Lagrangian scheme

6. 6 COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme t+1 Departure or origin point t * Computation of the trajectories: no modification O

7. 7 COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme t+1 t dx L * Computation of the trajectories: no modification * Computation of the value of variables at the origin point  modification of the SL interpolation weights For example, with linear interpolations (2D and regular grid): Original SL scheme: 2 linear zonal interpolations V B = w x1 V B1 + w x2 V B2 with w x2 = /dx, w x1 = 1 - /dx V C = w x1 V C1 + w x2 V C2 = 1 - w x2 dy B1 B2 C2 C1 O

8. 8 COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme t+1 t dx L * Computation of the trajectories: no modification * Computation of the value of variables at the origin point  modification of the SL interpolation weights For example, with linear interpolations (2D and regular grid): Original SL scheme: 2 linear zonal interpolations V B = w x1 V B1 + w x2 V B2 with w x2 = /dx, w x1 = 1 - /dx V C = w x1 V C1 + w x2 V C2 = 1 - w x2 dy B1 B2 C2 C1 O B C

9. 9 COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme t+1 t dx L * Computation of the trajectories: no modification * Computation of the value of variables at the origin point  modification of the SL interpolation weights For example, with linear interpolations (2D and regular grid): Original SL scheme: 2 linear zonal interpolations V B = w x1 V B1 + w x2 V B2 with w x2 = /dx, w x1 = 1 - /dx V C = w x1 V C1 + w x2 V C2 = 1 - w x2 1 meridian linear interpolation V O = w y1 V B + w y2 V C with w y1 = L / dy, w y2 = 1 - L /dy dy B1 B2 C2 C1 O B C

10. 10 COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme t+1 t dx * Computation of the trajectories: no modification * Computation of the value of variables at the origin point  modification of the SL interpolation weights For example, with linear interpolations (2D and regular grid): COMAD scheme: 2 linear zonal interpolations V B = w’ x1 V B1 + w’ x2 V B2 with w x2 = /dx, w x1 = 1 - /dx V C = w’ x1 V C1 + w’ x2 V C2 = 1 - w x2 1 meridian linear interpolation V O = w’ y1 V B + w’ y2 V C with w y1 = L / dy, w y2 = 1 - L /dy dy B1 B2 C2 C1 O B C w’ x1 =  x w x1 + 0.5 * (1-  x ) with  x = (1 +  U/  x * dt) deformation factor along x axis w’ x2 =  x w x2 + 0.5 * (1-  x ) w’ y1 =  y w y1 + 0.5 * (1-  y ) with  y = (1 +  U/  y * dt) deformation factor along y axis w’ y2 =  y w y2 + 0.5 * (1-  y ) L

11. 11 COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme t+1 t B1 B2 C2 C1 O w’ x1 =  x w x1 + 0.5 * (1-  x ) with  x = (1 +  U/  x * dt) deformation factor along x axis w’ x2 =  x w x2 + 0.5 * (1-  x ) w’ y1 =  y w y1 + 0.5 * (1-  y ) with  y = (1 +  U/  y * dt) deformation factor along y axis w’ y2 =  y w y2 + 0.5 * (1-  y )  modified linear weights can also be used after for computing cubic weights B0 B3 C3 C0 A1A2 D1 D2 * Computation of the trajectories: no modification * Computation of the value of variables at the origin point  modification of the SL interpolation weights For example, with linear interpolations (2D and regular grid): COMAD scheme: 2 linear zonal interpolations V B = w’ x1 V B1 + w’ x2 V B2 with w x2 = /dx, w x1 = 1 - /dx V C = w’ x1 V C1 + w’ x2 V C2 = 1 - w x2 1 meridian linear interpolation V O = w’ y1 V B + w’ y2 V C with w y1 = L / dy, w y2 = 1 - L /dy

12. 12 COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme t+1 t B1 B2 C2 C1 O w’ x1 =  x w x1 + 0.5 * (1-  x ) with  x = (1 +  U/  x * dt) deformation factor along x axis w’ x2 =  x w x2 + 0.5 * (1-  x ) w’ y1 =  y w y1 + 0.5 * (1-  y ) with  y = (1 +  U/  y * dt) deformation factor along y axis w’ y2 =  y w y2 + 0.5 * (1-  y )  modified linear weights can also be used after for computing cubic weights AROME uses quasi-cubic interpolations (2 linear, 3 cubic ones) B0 B3 C3 C0 A1A2 D1 D2 * Computation of the trajectories: no modification * Computation of the value of variables at the origin point  modification of the SL interpolation weights For example, with linear interpolations (2D and regular grid): COMAD scheme: 2 linear zonal interpolations V B = w’ x1 V B1 + w’ x2 V B2 with w x2 = /dx, w x1 = 1 - /dx V C = w’ x1 V C1 + w’ x2 V C2 = 1 - w x2 1 meridian linear interpolation V O = w’ y1 V B + w’ y2 V C with w y1 = L / dy, w y2 = 1 - L /dy

13. 13 2 – Test of a modified Semi-Lagrangian scheme Example: 30 June 2012 24-h precipitation (mm) from 00 UTC - Wind vectors at 10 m (m/s), 00 UTC 1 July Less precipitation Less intense wind ahead of precipitation area COMADOPER SL

14. 14 2 – Test of a modified Semi-Lagrangian scheme Example: 30 June 2012 3-h precipitation (mm) 15-18 UTC, Wind vectors at 10 m (m/s) 18 UTC 30 June Less intense convective cells Less intense outflows COMADOPER SL

15. 15 2 – Test of a modified Semi-Lagrangian scheme Example: 30 June 2012 Less intense convective cells Less intense outflows 3-h precipitation (mm) 15-18 UTC, Wind vectors at 10 m (m/s) 18 UTC 30 June COMADOPER SL

16. 16 2 – Test of a modified Semi-Lagrangian scheme Example: 30 June 2012 Virtual potential temperature (K) - Wind vectors at 10 m (m/s), 18 UTC 30 June Less intense convective cells Less intense cold pools COMADOPER SL

17. 17 2 – Test of a modified Semi-Lagrangian scheme 15 July - 15 September 2013 Mean 24-h precipitation over the forecast domain Less precipitation amount COMAD OPER SL

18. 18 2 – Test of a modified Semi-Lagrangian scheme 15 July - 15 September 2013 Mean 24-h precipitation over the forecast domain Less precipitation amount Variation between 1 and –26 %

19. 19 2 – Test of a modified Semi-Lagrangian scheme 15 July - 15 September 2013 24-h precipitation distribution for all gridpoints of the forecast domain Smaller frequencies of moderate and heavy precipitation COMAD OPER SL

20. 20 2 – Test of a modified Semi-Lagrangian scheme Scores:15 July - 15 September 2013 6-h precipitation: better scores Surface pressure: slight improvement for bias 6-h precipitation (mm) Surface pressure (hPa) Forecast range (hour) bias mse bias mse COMAD OPER SL

21. 21 2 – Test of a modified Semi-Lagrangian scheme Scores:15 July - 15 September 2013 Near-surface wind and temperature: slight degradation after 18h forecast Forecast range (hour) 2m temperature (K) 10m Wind intensity (m/s) bias mse bias mse COMAD OPER SL

22. 22 2 – Test of a modified Semi-Lagrangian scheme Fuzzy scores: 15 July - 15 September 2013 Brier Skill Scores for 24-h precipitation (06UTC-06UTC) Better scores for all thresholds and all neighbourhoods RR24 > 0.2mm RR24 > 5 mm RR24 > 10 mm RR24 > 20mm Neighbourhood (km) COMAD OPER SL

23. 23 2 – Test of a modified Semi-Lagrangian scheme Fuzzy scores: 15 July - 15 September 2013 Brier Skill Scores for 6-h precipitation (12UTC-18UTC) Better scores for all thresholds and all neighbourhoods RR6 > 0.5 mm RR6 > 2 mm RR6 > 5 mm RR6 > 10mm Neighbourhood (km) COMAD OPER SL

24. 24 2 – Test of a modified Semi-Lagrangian scheme Example: 30 June 2012 Running variance (100 km * 100 km) of wind at 10 m (m/s)², 18 UTC 30 June Less intense convective cells Less intense downdrafts COMAD OPER SL

25. 25 2 – Test of a modified Semi-Lagrangian scheme 15 July -15 September 2013 Running variance (100 km * 100 km) (hourly averaged over the forecast domain and the period 15 July - 15 September 2013) Less variance during the afternoon and evening Less intense density currents under convective cells 10-m Wind (m²/s²) 10-m downdrafts (m²/s²) 925 hPa Virtual potential temperature (K²) COMAD OPER SL

26. 26 2 – Test of a modified Semi-Lagrangian scheme 15 July -15 September 2013 Diurnal cycle of surface covered by convective cells (simulated reflectivities above 30 dBZ) Less intense convective cells COMAD OPER SL

27. 27 3 – Evaluation of AROME at kilometric resolution Methodology Smaller forecast domain (720 points *720 points - 1.3km) (360 points *360 points - 2.5km) Configuration: for stability: ICI scheme (instead of 2TL SI scheme) time step: 45s (instead of 60s) initial conditions: dynamical adaptation from 2.5km 3DVAR Analysis LBC: from operational AROME better representation of the orography at 1.3km Experiments Horizontal grid spacing Vertical levels 2.5km602.5 km60 (21 levels < 2000m) 2.5km902.5 km90 (33 levels < 2000m) 1.3km901.3 km90 (33 levels < 2000m) 1.3km90BC1.3 km90 (41 levels < 2000m) Layer thickness (m) L 60 L 90 L 90BC

28. 28 3 – Evaluation of AROME at kilometric resolution Methodology Period: 1 June-30 November 2012 Selection of days with moderate and intense convective activity over the forecast domain  lightning data (more than 5000 strikes per day)  48 days 12345678910111213141516171819202122232425262728293031 June July August September October November 24-h lightning data (21 June) : 88897 lightning strikes

29. 29 3 – Evaluation of AROME at kilometric resolution Scores Increase of vertical resolution:  better classic scores (temp and humidity) but no better fuzzy scores 2m Temperature 2m Humidity 10m Wind 24-h precipitation 6-h precipitation 1-h Downdraft Brightness temperature 2.5km90 vs 2.5km60 ++-=--+ 1.3km90 vs 2.5km90 --+++++ 1.3km90 vs 2.5km60 =-+++++ 1.3km90BC vs 2.5km60 =-+++++ Classic scores (bias, MSE) Fuzzy scores (Brier Skill scores)

30. 30 3 – Evaluation of AROME at kilometric resolution Scores Increase of vertical resolution:  better classic scores (temp and humidity) but no better fuzzy scores Increase of horizontal resolution:  better fuzzy scores  degradation for temperature and humidity scores but improvement for wind score 2m Temperature 2m Humidity 10m Wind 24-h precipitation 6-h precipitation 1-h Downdraft Brightness temperature 2.5km90 vs 2.5km60 ++-=--+ 1.3km90 vs 2.5km90 --+++++ 1.3km90 vs 2.5km60 =-+++++ 1.3km90BC vs 2.5km60 =-+++++ Classic scores (bias, MSE) Fuzzy scores (Brier Skill scores)

31. 31 3 – Evaluation of AROME at kilometric resolution Scores Increase of vertical resolution:  better classic scores (temp and humidity) but no better fuzzy scores Increase of horizontal resolution:  better fuzzy scores  degradation for temperature and humidity scores but improvement for wind score No further improvement with more levels below 2000m 2m Temperature 2m Humidity 10m Wind 24-h precipitation 6-h precipitation 1-h Downdraft Brightness temperature 2.5km90 vs 2.5km60 ++-=--+ 1.3km90 vs 2.5km90 --+++++ 1.3km90 vs 2.5km60 =-+++++ 1.3km90BC vs 2.5km60 =-+++++ Classic scores (bias, MSE) Fuzzy scores (Brier Skill scores)

32. 32 3 – Evaluation of AROME at kilometric resolution Characteristics of convective cells Comparison to observations using a tracking algorithm (Morel et al., 2002) to detect convective cells (2 thresholds > 30 dBZ and > 40 dBZ)  size, number, intensity maximum of convective cells Simulated reflectivities at 1500 m 21 June 12UTC 2.5km: 76 cells > 40 dBZ 5 dbZ 10 15 20 30 50 40

33. 33 5 dbZ 10 15 20 30 50 40 3 – Evaluation of AROME at kilometric resolution Characteristics of convective cells Simulated reflectivities at 1500 m 21 June 12UTC 2.5km: 76 cells > 40 dBZ Comparison to observations using a tracking algorithm (Morel et al., 2002) to detect convective cells (2 thresholds > 30 dBZ and > 40 dBZ)  size, number, intensity maximum of convective cells

34. 34 3 – Evaluation of AROME at kilometric resolution Characteristics of convective cells Simulated reflectivities at 1500 m 21 June 12UTC 2.5km: 76 cells > 40 dBZ 1.3km: 122 cells > 40 dBZ 5 dbZ 10 15 20 30 50 40 Comparison to observations using a tracking algorithm (Morel et al., 2002) to detect convective cells (2 thresholds > 30 dBZ and > 40 dBZ)  size, number, intensity maximum of convective cells

35. 35 3 – Evaluation of AROME at kilometric resolution Characteristics of convective cells > 40 dBZ - 21 June  1.3 km vs 2.5km: omore cells omore numerous small cells ofewer large cells omore realistic Time evolution of cell number Surface distribution radar 1.3km radar 1.3km 2.5km

36. 36 3 – Evaluation of AROME at kilometric resolution Characteristics of convective cells > 30dBZ and > 40 dBZ - 48 days  Over the 48 days at the peak of convection, 1.3 km vs 2.5km: omore realistic omore numerous small and medium cells ofewer large cells Surface distribution > 30dBZ Surface distribution > 40dBZ radar 1.3km 2.5km radar 1.3km 2.5km

37. 37 Conclusion Increase of horizontal grid spacing (1.3km versus 2.5km):  more realistic number of cells  more numerous small cells, fewer large cells  reduction of precipitation amount  better fuzzy scores (for precipitation, brightness temperature, downdrafts …) Use of the modified SL scheme (COMAD versus original SL scheme)  less intense convective cells  improvement of QPF, less amount  better fuzzy scores for precipitation  test on other periods: June 2012, January 2013 (frontal precipitation)  Test of the modified SL scheme at 1.3km

38. 38

39. 39 2 – Test of a modified Semi-Lagrangian scheme Fuzzy scores: 15 July - 15 September 2013 Brier Skill Scores for brightness temperature 10.8  m (forecast range 18 UTC) For peak of convection: better scores in particular for lower temperature thresholds  better representation of the high clouds Neighbourhood 20 km Temperature thresholds (K) Neighbourhood 52 km Temperature thresholds (K) COMAD OPER SL

40. 40 2 – Test of a modified Semi-Lagrangian scheme 1-31 January 2013 Mean 24-h precipitation over the forecast domain Less impact on frontal precipitation COMAD OPER SL

41. 41 2 – Test of a modified Semi-Lagrangian scheme 1-31 January 2013 Mean 24-h precipitation over the forecast domain Less impact on frontal precipitation Variation between 1 and –5 %

42. 42 2 – Test of a modified Semi-Lagrangian scheme Fuzzy scores: 1-31 January 2013 Brier Skill Scores for 24-h precipitation (06UTC-06UTC) RR24 > 0.2mm RR24 > 5 mm RR24 > 10 mm RR24 > 20mm Neighbourhood (km) COMAD OPER SL

43. 43 2 – Test of a modified Semi-Lagrangian scheme 1-30 June 2012 Mean 24-h precipitation over the forecast domain Less precipitation amount OPER MODIFSL

44. 44 2 – Test of a modified Semi-Lagrangian scheme 1-30 June 2012 Mean 24-h precipitation over the forecast domain Less precipitation amount Reduction between –1 and –25 %

45. 45 2 – Test of a modified Semi-Lagrangian scheme 1-30 June 2012 24-h precipitation distribution for all gridpoints of the forecast domain Smaller frequencies of moderate and heavy precipitation COMAD OPER SL

46. 46 2 – Test of a modified Semi-Lagrangian scheme Fuzzy scores: 1-30 June 2012 Brier Skill Scores for 24-h precipitation (forecast range 30h) Better scores for all thresholds and all neighbourhoods OPER MODIFSL RR24 > 0.2mm RR24 > 1 mm RR24 > 10 mm RR24 > 20mm Neighbourhood (km)

47. 47 2 – Test of a modified Semi-Lagrangian scheme Fuzzy scores: 1-30 June 2012 Brier Skill Scores for brightness temperature 10.8  m (forecast range 18 UTC) For peak of convection: better scores in particular for lower temperature thresholds  better representation of the high clouds OPER MODIFSL Neighbourhood 20 km Temperature thresholds (K) Neighbourhood 120 km Temperature thresholds (K)

48. 48 2 – Test of a modified Semi-Lagrangian scheme Example: 30 June 2012 Running variance (100 km * 100 km) of wind at 10 m (m/s)², 18 UTC 30 June Less intense convective cells Less intense downdrafts COMAD OPER SL

49. 49 2 – Test of a modified Semi-Lagrangian scheme Example: 30 June 2012 Running variance (100 km * 100 km) of downdrafts at 10 m (m/s)², 18 UTC 30 June Less intense convective cells Less intense downdrafts COMAD OPER SL

50. 50 2 – Test of a modified Semi-Lagrangian scheme Example: 30 June 2012 Running variance (100 km * 100 km) of 925 hPa v at 10 m (K)², 18 UTC 30 June Less intense convective cells Less intense downdrafts COMAD OPER SL

51. 51 3 – Evaluation of AROME at kilometric resolution Characteristics of convective cells > 40 dbZ - 21 June  Time step impact: o30s: slightly more cells, in particular small cells o60s: slightly less cells in particular small cells Time evolution of cell number Surface distribution

52. 52 3 – Evaluation of AROME at kilometric resolution Characteristics of convective cells > 40 dbZ - 21 June  Diffusion impact: oWithout spectral diffusion: sightly more cells oSpectral diffusion constant on vertical: weak impact oWithout SLHD: more cells Time evolution of cell number Surface distribution