The subgrid‐scale orographic blocking parametrization of the GEM Model

Abstract

The impact of the physical parametrization called subgrid-scale orographic blocking, recently introduced in the physics of the Canadian Global Environmental Mutiscale (GEM) model is described. It is based on a formulation by Lott and Miller (1997) and represents the unresolved component of the drag on low-level winds that are blocked at the flanks of mountains. The blocking term plus the gravity-wave drag are now part of a unified parametrization of the subgrid orographic drag that became operational in the global GEM model on 11 December 2001. Results from tests made with various configurations of the model are shown, Lott et Miller (1997), permet de représenter la composante non-résolue de l'effet de résistance sur les vents de surface due aux montagnes. Le terme de blocage ainsi que le paramétrage de la résistance sur l'écoulement due aux ondes de gravité déferlantes forment maintenant un paramétrage unifié des effets orographiques sous-maille devenu opérationnel dans le modèle GEM global le 11 décembre 2001. illustrating how the blocking term impacts the large-scale flow and improves both the short-and the medium-range forecasts, especially in winter. It is shown that at day 5 of the model integrations, the influence of the blocking force applied near the surface is felt by the entire tropospheric and the lower-stratospheric circulation. A mechanism based on perturbations of the Eliassen-Palm flux caused by the low-level forcing is proposed to explain the vertical propagation of the signal generated by the blocking term. RÉSUMÉ L'impact d'un blocage orographique sous-maille sur le modèle canadien GEM (Global Environnemental Multi-échelle) est étudié. Le paramétrage, basé sur une formulation deDes résultats provenant de tests faits avec différentes configurations du modèle sont présentés, démontrant l'impact du terme de blocage sur l'écoulement à grande échelle ainsi que l'amélioration des prévisions à courtes et moyennes échéances, particulièrement en hiver. Il est démontré qu'au jour cinq de l'intégration du modèle, l'influence de la force de blocage appliquée près de la surface est en fait ressentie sur toute la profondeur de la troposphère ainsi que sur la basse stratosphère. Un mécanisme basé sur les perturbations du flux d'Eliassen-Palm induites par le forçage près de la surface est proposé afin d'expliquer la propagation verticale du signal induit par la force de blocage. ATMOSPHERE-OCEAN 41 (2) 2003, 155-170

Dynamical downscaling with the fifth-generation Canadian regional climate model (CRCM5) over the CORDEX Arctic domain: effect of large-scale spectral nudging and of empirical correction of sea-surface temperature

“…These include the Kain-Fritsch deep convection (Kain and Fritsch 1990), Kuo-transient shallow convection (Kuo 1965;Bélair et al 2005), Sundqvist resolved-scale condensation (Sundqvist et al 1989), correlated-K solar and terrestrial radiations (Li and Barker 2005), subgrid-scale orographic gravity-wave drag (McFarlane 1987), low-level orographic blocking (Zadra et al 2003), and planetary boundary layer parameterization (Benoit et al 1989;Delage and Girard 1992;Delage 1997) modified by Zadra et al (2012) to introduce hysteresis effects.…”

3-Step dynamical downscaling with empirical correction of sea-surface conditions: application to a CORDEX Africa simulation

“…CRCM5 is based on a limited-area configuration of the Global Environment Multiscale (GEM) model (Bélair et al 2005(Bélair et al , 2009) employed for numerical weather prediction by the Canadian Meteorological Centre (CMC). The subgrid-scale physical parameterisations include the Kain and Fritsch (1990) deep-convection and Kuo-transient (Kuo 1965) shallow-convection schemes, as well as the Sundqvist et al (1989) large-scale condensation scheme, the correlated-K scheme for solar and terrestrial radiations (Li and Barker 2005), a subgrid-scale mountain gravitywave drag (McFarlane 1987) and low-level orographic blocking (Zadra et al 2003), a turbulent kinetic energy closure in the planetary boundary layer and vertical diffusion (Benoît et al 1989;Delage and Girard 1992;Delage 1997), and a weak ∇ 6 lateral diffusion. The land-surface scheme however is changed from ISBA used in GEM for the Canadian LAnd Surface Scheme (CLASS; Verseghy 2000Verseghy , 2008 in its most recent version, CLASS 3.5.…”

Reanalysis-driven climate simulation over CORDEX North America domain using the Canadian Regional Climate Model, version 5: model performance evaluation

“…The following physical parameterizations, inherited from GEM, are used in CRCM5: deep convection following Kain and Fritsch (1990), shallow convection based on a transient version of Kuo (1965) scheme (Bélair et al 2005), large-scale condensation (Sundqvist et al 1989), correlated-K solar and terrestrial radiations (Li and Barker 2005), and subgridscale orographic gravity-wave drag (McFarlane 1987). The low-level orographic blocking parameterization of Zadra et al (2003), with recent modifications described in Zadra et al (2012) is also used. The planetary boundary layer parameterization (Benoît et al 1989;Delage and Girard 1992;Delage 1997) has also been modified as described in Zadra et al (2012), introducing turbulent hysteresis, i.e.…”