Land-atmosphere interactions during a Northwestern Argentinean Low event: impacts on precipitation fields

FERREIRA, L.; SAULO, C.; RUIZ, J.

Nanjing

Congreso; 3rd International Conference on QPE, QPF and Hydrology; 2010

Organización Meteorológica Mundial

The impact of changes in soil moisture in subtropical Argentina in rainfall amounts and distribution, and low level circulation is studied with a state-of-the art regional model in a downscaling mode, with different scenarios of soil moisture for a 10 day period. Four tests were conducted at 40 km horizontal resolution with 31 sigma levels, decreasing and increasing the soil moisture initial condition by 50% over the entire domain, and imposing a 50 % reduction over northwest Argentina and 50% increase over South East South America. In all cases, the WRF-NOAH model is used to represent the meteorological variables and the surface processes.It was  found that land-surface interactions are  stronger when soil moisture is decreased, with a coherent reduction of precipitation over southern South America. Enhanced northerly winds result form an increase in the zonal gradient of pressure at low levels. In contrast, when soil moisture is increased, smaller circulation changes are found, though there appears to be a local feedback effect between the land and precipitation The combined effects of changes in the circulation and in local stratification induced by soil moisture modifications, through variations in evaporation and CAPE, are in agreement with what has been found by other studies. Finally, this sensitivity study shows the need to gain insight into the uncertainties in the initial condition, and in the interaction between the precipitation, one of the main forcing of the soil model, and the soil moisture in this region.