Abstract
The sensitivity of numerical simulations of the low level jet stream (LLJS) in South America to the choice of parameterization schemes for the planetary boundary layer (PBL) and for cumulus convection using the Advanced Research core of the Weather Research and Forecast (WRF) model was assessed for two cases in which the development of Mesoscale Convective Systems (MCSs) was observed in the La Plata Basin at the exit of the LLJS. The MCSs developed under distinct synoptic forcing. Overall, the general area over the La Plata Basin where the wind profiles met LLJS criteria was larger in the situation with stronger frontal forcing. Regarding the impact of the choice of the PBL parameterization scheme upon the simulated LLJS, the nonlocal Yonsei University (YSU) scheme displayed slightly better results for most simulations regardless of the cumulus parameterization scheme utilized. In fact, the characterization of the LLJS in the simulations exhibited no significant sensitivity to the choice of the cumulus parameterization. In situations under stronger [weaker] frontal forcing, less [more] dispersion among the simulations was found regarding the identification of the LLJS.
Highlights
The South American low level jet stream (SALLJS), observed east of the Andes Mountain Range, is the main atmospheric mechanism responsible for the meridional moisture transport from the Amazon Basin to the subtropics of South America south of 20∘S [1]
Salio et al [3] discussed the strong relation between the development of Mesoscale Convective Systems (MCSs) in the La Plata Basin and the occurrence of SALLJS, especially during the warm season
The 21 October 2008 MCS event developed over north-central Argentina in association with a migratory baroclinic system (Figure 4(a)), with the combined manifestation of cyclogenesis off the Patagonian coast and the intensification of the Northwestern Argentinean Low (NAL; [21]) over the Andes foothills (Figure 4(b))
Summary
The South American low level jet stream (SALLJS), observed east of the Andes Mountain Range, is the main atmospheric mechanism responsible for the meridional moisture transport from the Amazon Basin to the subtropics of South America south of 20∘S [1]. Saulo et al [2] addressed the connection between the exit region of the SALLJS and the triggering of deep moist convection. They showed that the development of deep convection is favored by the low level warm and most advection induced by the SALLJS. The strong latent heating accompanying the convective activity leads to geopotential height falls in the lower troposphere over the La Plata Basin which enhances northerly winds and low level convergence at the SALLJS exit region, leading to further convective development and increased longevity of the MCSs
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