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Sensitivity of AROME Model to Modified Semi-Lagrangian Scheme

Evaluation of the AROME model's performance at convective scale with a modified semi-Lagrangian scheme. Includes tests of precipitation bias and convection behavior.

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Sensitivity of AROME Model to Modified Semi-Lagrangian Scheme

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  1. WWOSC 2014 • 16-21 August, Montréal, Canada • Les règles générales • Didier Ricard1, Sylvie Malardel2, Yann Seity1 • Julien Léger1, 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. 1 – Introduction • 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) • Next version: 1.3 km 90

  3. Characteristics of the AROME model 1 – Introduction • 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 • 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

  4. 1 – Introduction  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

  5. Motivation 2 – Test of a modified Semi-Lagrangian scheme • 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 •  Evaluation on a 2-month period (15 July 2013 - 15 September 2013) including deep convection with important effects of divergence

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

  7. COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme • * 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 • VB = wx1 VB1 + wx2 VB2 with wx2 =  /dx, wx1 = 1 -  /dx • VC = wx1 VC1 + wx2 VC2 = 1 - wx2 • t+1 • dx • B1 • B2 •  • t • dy • O • L • C2 • C1

  8. COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme • * 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 • VB = wx1 VB1 + wx2 VB2 with wx2 =  /dx, wx1 = 1 -  /dx • VC = wx1 VC1 + wx2 VC2 = 1 - wx2 • t+1 • dx • B1 • B2 • B •  • t • dy • O • L • C • C2 • C1

  9. COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme • * 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 • VB = wx1 VB1 + wx2 VB2 with wx2 =  /dx, wx1 = 1 -  /dx • VC = wx1 VC1 + wx2 VC2 = 1 - wx2 • 1 meridian linear interpolation • VO = wy1 VB + wy2 VC with wy1 = L / dy, wy2 = 1 - L /dy • t+1 • dx • B1 • B2 • B •  • t • dy • O • L • C • C2 • C1

  10. COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme • * 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 • VB = w’x1 VB1 + w’x2 VB2 with wx2 =  /dx, wx1 = 1 -  /dx • VC = w’x1 VC1 + w’x2 VC2 = 1 - wx2 • 1 meridian linear interpolation • VO =w’y1VB + w’y2 VC with wy1 = L / dy, wy2 = 1 - L /dy • t+1 • dx • B1 • B2 • B •  • t • dy • O • L • C • C2 • C1 • w’x1= xwx1 + 0.5 * (1- x) with x = (1 + U/ x * dt) deformation factor along x axis • w’x2 = xwx2 + 0.5 * (1- x) • w’y1 = ywy1 + 0.5 * (1- y) with y = (1 + U/ y * dt) deformation factor along y axis • w’y2= ywy2 + 0.5 * (1- y)

  11. COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme • * 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 • VB = w’x1 VB1 + w’x2 VB2 with wx2 =  /dx, wx1 = 1 -  /dx • VC = w’x1 VC1 + w’x2 VC2 = 1 - wx2 • 1 meridian linear interpolation • VO =w’y1VB + w’y2 VC with wy1 = L / dy, wy2 = 1 - L /dy • t+1 • A1 • A2 • B1 • B3 • B0 • B2 • t • O • C2 • C3 • C1 • C0 • D2 • D1 • w’x1= xwx1 + 0.5 * (1- x) with x = (1 + U/ x * dt) deformation factor along x axis • w’x2 = xwx2 + 0.5 * (1- x) • w’y1 = ywy1 + 0.5 * (1- y) with y = (1 + U/ y * dt) deformation factor along y axis • w’y2= ywy2 + 0.5 * (1- y) •  modified linear weights can also be used after for computing cubic weights

  12. COMAD scheme (Malardel and Ricard, in review, QJ) 2 – Test of a modified Semi-Lagrangian scheme • * 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 • VB = w’x1 VB1 + w’x2 VB2 with wx2 =  /dx, wx1 = 1 -  /dx • VC = w’x1 VC1 + w’x2 VC2 = 1 - wx2 • 1 meridian linear interpolation • VO =w’y1VB + w’y2 VC with wy1 = L / dy, wy2 = 1 - L /dy • t+1 • A1 • A2 • B1 • B3 • B0 • B2 • t • O • C2 • C3 • C1 • C0 • D2 • D1 w’x1= xwx1 + 0.5 * (1- x) withx = (1 + U/ x * dt) deformation factor along x axis w’x2 = xwx2 + 0.5 * (1- x) w’y1 = ywy1 + 0.5 * (1- y) withy = (1 + U/ y * dt) deformation factor along y axis w’y2= ywy2 + 0.5 * (1- y) • modifiedlinearweightscanalsobeusedafter for computingcubicweights AROME uses quasi-cubic interpolations (2 linear, 3 cubicones)

  13. Example: 30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • OPER SL • COMAD • 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

  14. Example: 30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • OPER SL • COMAD • 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

  15. Example: 30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • OPER SL • COMAD • 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

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

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

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

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

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

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

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

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

  24. Example: 30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • OPER SL • COMAD • 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

  25. 15 July -15 September 2013 2 – Test of a modified Semi-Lagrangian scheme • 10-m downdrafts (m²/s²) • 10-m Wind (m²/s²) • OPER SL • COMAD • 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 • 925 hPa Virtual potential temperature (K²)

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

  27. Methodology 3 – Evaluation of AROME at kilometric resolution • L 90BC • L 90 • L 60 • Smaller forecast domain • (720 points *720 points - 1.3km) • (360 points *360 points - 2.5km) • Layer thickness (m) 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

  28. Methodology 3 – Evaluation of AROME at kilometric resolution 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 • 24-h lightning data (21 June) : 88897 lightning strikes

  29. Scores 3 – Evaluation of AROME at kilometric resolution • Classic scores (bias, MSE) • Fuzzy scores (Brier Skill scores) • Increase of vertical resolution: • better classic scores (temp and humidity) but no better fuzzy scores

  30. Scores 3 – Evaluation of AROME at kilometric resolution • Classic scores (bias, MSE) • Fuzzy scores (Brier Skill 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

  31. Scores 3 – Evaluation of AROME at kilometric resolution • Classic scores (bias, MSE) • Fuzzy scores (Brier Skill 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

  32. Characteristics of convective cells • dbZ • 5 • 10 • 15 • 20 • 30 • 40 • 50 3 – Evaluation of AROME at kilometric resolution 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 • 2.5km: 76 cells > 40 dBZ • Simulated reflectivities at 1500 m 21 June 12UTC

  33. Characteristics of convective cells • dbZ • 5 • 10 • 15 • 20 • 30 • 40 • 50 3 – Evaluation of AROME at kilometric resolution 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 • 2.5km: 76 cells > 40 dBZ • Simulated reflectivities at 1500 m 21 June 12UTC

  34. Characteristics of convective cells • dbZ • 5 • 10 • 15 • 20 • 30 • 40 • 50 3 – Evaluation of AROME at kilometric resolution 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 • 2.5km: 76 cells > 40 dBZ • 1.3km: 122 cells > 40 dBZ • Simulated reflectivities at 1500 m 21 June 12UTC

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

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

  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. Fuzzy scores: 15 July - 15 September 2013 2 – Test of a modified Semi-Lagrangian scheme • OPER SL • Neighbourhood 52 km • Neighbourhood 20 km • COMAD • Temperature thresholds (K) • Temperature thresholds (K) • 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

  39. 1-31 January 2013 2 – Test of a modified Semi-Lagrangian scheme • OPER SL • COMAD • Mean 24-h precipitation over the forecast domain • Less impact on frontal precipitation

  40. 1-31 January 2013 2 – Test of a modified Semi-Lagrangian scheme • Mean 24-h precipitation over the forecast domain • Less impact on frontal precipitation • Variation between 1 and –5 %

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

  42. 1-30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • OPER • MODIFSL • Mean 24-h precipitation over the forecast domain • Less precipitation amount

  43. 1-30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • Mean 24-h precipitation over the forecast domain • Less precipitation amount • Reduction between –1 and –25 %

  44. 1-30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • COMAD • OPER SL • 24-h precipitation distribution for all gridpoints of the forecast domain • Smaller frequencies of moderate and heavy precipitation

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

  46. Fuzzy scores: 1-30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • MODIFSL • Neighbourhood 120 km • Neighbourhood 20 km • OPER • Temperature thresholds (K) • Temperature thresholds (K) • 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

  47. Example: 30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • OPER SL • COMAD • 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

  48. Example: 30 June 2012 2 – Test of a modified Semi-Lagrangian scheme • OPER SL • COMAD • 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

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

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