Nuages stratocumulus et cumulus dans GEM. Stéphane Bélair

Transcription

1 Nuages stratocumulus et cumulus dans GEM Stéphane Bélair Séminaire RPN 19 septembre 3

2 Représentation des nuages dans GEM UNRESOLVED PBL cumulus (small cumulus) Deep convection Towering Cumulus (shallow convection) Organized deep convection RESOLVED Meso-β-scale cloud systems Large-scale Weather systems Horizontal scales (km) SUBGRID-SCALE REG15 and GLOBAL-MESO (35 km) GRID-SCALE Ri modification in turbulence scheme (CONRES) Fritsch-Chappell (REG) Kuo (GLOBAL) Sundqvist

3 Représentation des nuages dans GEM UNRESOLVED PBL cumulus (small cumulus) Deep convection Towering Cumulus (shallow convection) Organized deep convection RESOLVED Meso-β-scale cloud systems Large-scale Weather systems Horizontal scales (km) SUBGRID-SCALE REG15 and GLOBAL-MESO (35 km) GRID-SCALE MoisTKE Kuo Transient Kain-Fritsch Sundqvist (or MixPhas)

4 Objectifs Montrer que les schémas de la nouvelle suite de nuages proposée pour REG15 et GLOBAL-MESO est en mesure de représenter la grande variété de nuages qui existent dans les systèmes grandeéchelle et méso-échelle (hivernal et estival) Examiner l impact que les nuages stratocumulus et cumulus ont sur la précipitation

5 Résultats extraits de deux études Bélair, S., J. Mailhot, C. Girard, and P. Vaillancourt, 4: Boundary-layer and shallow cumulus clouds in a medium-range forecast of a large-scale weather system. To be submitted. Bélair, S., and J. Mailhot, 4: Influence of implicit, explicit, and boundary-layer cloud processes on the statistical properties of precipitation produced by a mesobeta-scale model. To be submitted. Plus tard cette annee: Séminaire sur Global-Méso par Paul Vaillancourt et Michel Roch Infos sur Global-Meso: (cliquer sur modèle global-méso)

6 Le schéma Kuo Transient pour la convection restreinte Transient shallow cloud model driven at its base by turbulent boundary layer fluxes developed at RPN by Claude Girard. This scheme is essentially the same as the Kuo Symmetric scheme (also by C. Girard) in which the humidity "accession" is given by the tendencies from the vertical diffusion scheme: Shallow transient cloud (T c,q c ) θ q Shallow transient cloud (T c,q c ) q t T t shallow shallow = K = K ( qc q) Dq ( T T ) c D q > Daytime well-mixed layer in which the K coefficients are calculated using the energy conservation principle.

7 Le schéma MoisTKE pour les nuages de couche limite From Jocelyn Mailhot Unified approach for turbulence-cloud interactions Implicit cloudiness scheme with treatment of mixed-phase clouds Appropriate for TKE model Based on Bechtold et al. Unified description of stratiform clouds and shallow non-precipitating convection Mixing and dissipation lengths from Bougeault-Lacarrère Flux enhancement factor (f N ) and implicit cloud fraction (N) as a function of Q 1, a normalized measure of supersaturation for a series of observational experiments (taken from Bechtold and Siebesma 1998)

8 La configuration de la physique pour REG15 et GLOBAL-MESO Constant thermodynamic roughness over water surfaces Bougeault-Lacarrere mixing length for the vertical diffusion MoisTKE for boundary-layer clouds Shallow convection with Kuo Transient Deep convection with Kain-Fritsch Grid-scale condensation with a modified Sundqvist scheme (consun) Modifications to the radiative fix at the model top (only for GLOBAL-MESO)

9 La configuration de la physique pour REG15 et GLOBAL-MESO Constant thermodynamic roughness over water surfaces Bougeault-Lacarrere mixing length for the vertical diffusion MoisTKE for boundary-layer clouds Shallow convection with Kuo Transient Deep convection with Kain-Fritsch Grid-scale condensation with a modified Sundqvist scheme (consun) Modifications to the radiative fix at the model top (only for GLOBAL-MESO) Cloud and precipitation package

10 La configuration de la physique pour REG15 et GLOBAL-MESO Constant thermodynamic roughness over water surfaces Bougeault-Lacarrere mixing length for the vertical diffusion MoisTKE for boundary-layer clouds Shallow convection with Kuo Transient Deep convection with Kain-Fritsch Grid-scale condensation with a modified Sundqvist scheme (consun) Modifications to the radiative fix at the model top (only for GLOBAL-MESO) Cloud and precipitation package Total cloud fraction and cloud water content

11 Un système grand échelle au-dessus du Pacifique /9 UTC B GOES (visible + IR) A C UTC 9 Feb 3

12 Les cumulus à l arrière du système Merci à René Servranckx A GOES visible Valide à UTC le 8//3

13 Les cumulus à l arrière du système Merci à René Servranckx B GOES visible Valide à UTC le 9//3

14 Les nuages stratocumulus à l avant du système C /9 UTC (merci a Serge T.) AVHRR (~ 1 km) Valide a 7 UTC 9 Feb 3

15 La prévision 7-h du GLOBAL MESO /9 UTC PNM + 6h precip 999 7h W 976 H H E /9 UTC Dominant cloud types Explicit 7h 17 Integrated cloud water content /9 UTC 7h KT MTKE KF

16 Coupes Ouest-Est Height (km) h forecast Circulation Pa s -1 5 m s -1 - Explicit Cloud water (g kg -1 ) Cloud fraction (%) Cloud type 4 W KT A MTKE E

17 Coupes Sud-Nord Height (km) h forecast Circulation Pa s -1 4 m s -1 1 (g kg -1 ) Cloud water (%) Cloud fraction Cloud type 6 4 Explicit KT S MTKE N

18 Impact de MoisTKE + Kuo Transient sur les nuages Height (m) Cloud water Cloud fraction Potential temperature Specific humidity CTRL NOKT NOSHAL q c (g kg -1 ) f n (%) θ (K) q v (g kg -1 )

19 Impact de MoisTKE + Kuo Transient sur les nuages MoisTKE Height (m) Cloud water Cloud fraction Potential temperature Specific humidity CTRL NOKT NOSHAL q c (g kg -1 ) f n (%) θ (K) q v (g kg -1 )

20 Impact de MoisTKE + Kuo Transient sur les nuages MoisTKE Kuo Transient Height (m) Cloud water Cloud fraction Potential temperature Specific humidity CTRL NOKT NOSHAL q c (g kg -1 ) f n (%) θ (K) q v (g kg -1 )

21 Impact de MoisTKE + Kuo Transient sur la précipitation (mm/6h) 7-h Forecast TOTAL PRECIPITATION Height (m) Equivalent potential temperature (mm/5 days) CTRL NOKT NOSHAL TOTAL PRECIPITATION CTRL NOKT NOSHAL CTRL NOKT NOSHAL IMPLICIT PRECIPITATION CTRL NOKT NOSHAL θ e (K) W E

22 Un cas d été GOES (visible + IR) 18 UTC 6 July 1

23 Impact de MoisTKE et de Kuo Transient sur la partition implicite / explicite de la précipitation (36-h) Normalized Freq. Dist. 6 4 TOTAL -17% KTRS CTRL MTKE -5% Precipitation distribution skewed towards small accumulations BUT the tail is important MoisTKE: Decrease implicit precip Increase explicit precip Reduce number of events with very large precip accumulations Kuo Transient Significant decrease of implicit precip Not much change for explicit precip, except for the increase in large precipitation events Together: precipitation is MORE EXPLICIT (!) but better control of excessive precipitation accumulations ( grid point storms ) Normalized Freq. Dist. Normalized Freq. Dist KTRS MTKE CTRL IMPLICIT EXPLICIT -34% -% KTRS CTRL MTKE KTRS CTRL MTKE -16% +7% (mm)

24 Impact de MoisTKE et de Kuo Transient sur les spectres de variance de la precipitation (36-h) Normalized Variance Difference Horizontal Scale (km) RADAR MTKE KTRS 4 x Implicit Wavenumber 3 Normalized Variance Difference Normalized Variance Difference Horizontal Scale (km) RADAR MTKE KTRS RADAR MTKE KTRS 4 x TOTAL Explicit Wavenumber 3

25 Résultats pour REG15 - BIAIS HIVER ETE SHEF SYNOP (Résultats de l expérience bfc tels que donnés sur la page web de Donald Talbot)

26 Bénéfices Meilleure représentation des nuages dans REG15 et GLOBAL- MESO (impact sur la construction du nuage total et de son interaction avec le rayonnement) Réduit de manière significative la présence de minces couches nuageuses explicite au sommet de la couche limite dans les régions océaniques (stratus partout!) Réduit de manière significative la présence de grid-point storms Devrait permettre une meilleure balance entre la précipitation implicite (convection profonde) et la précipitation explicite (condensation à l échelle du modèle); Peut-etre pas encore le cas dans REG15 à cause de problèmes de spin-up (?) Réduit de manière significative les biais de précipitation

27 Modèles haute-résolution (e.g., 1 km) UNRESOLVED PBL cumulus (small cumulus) Deep convection Towering Cumulus (shallow convection) Organized deep convection RESOLVED Meso-β-scale cloud systems Large-scale Weather systems Horizontal scales Modele 1 km (km) SUBGRID-SCALE REG15 and GLOBAL-MESO GRID-SCALE MoisTKE Kuo Transient Kain-Fritsch Sundqvist

28 Modèles haute-résolution (e.g., 1 km) UNRESOLVED PBL cumulus (small cumulus) Deep convection Towering Cumulus (shallow convection) Organized deep convection RESOLVED Meso-β-scale cloud systems Large-scale Weather systems Horizontal scales Modele 1 km (km) SUBGRID-SCALE REG15 and GLOBAL-MESO GRID-SCALE MoisTKE Kuo Transient Kain-Fritsch Sundqvist