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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.

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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 %

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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)

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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)

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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)

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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

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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

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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

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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

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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

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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

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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

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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

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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 %

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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

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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

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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 %

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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

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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)

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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)

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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

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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

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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

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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

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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

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