Extended Abstract

A southward shift of the frontal evident at the maritime portion of the front precipitation(the broken line in left panel of the Figure 1 denote the frontal position), is observed in the E1and this is associated with the stronger northerlies denoted in Figure 2 and the enhancedconvergence at the exit region of the LLJ –which is displaced towards the south. The windresponse in E3 (not shown) is weaker, compatible with reduced northerlies over centralArgentina (i.e associated with weaker NAL) and at the frontal area that can be related withthe northward location of the precipitation maximum associated with the front.Figure 2: Mean 850 hPa wind anomalies in m s-1 at 0600UTC for E1-CTRL.To identify the pathways forland-atmosphere interactions it isuseful to analyze the day-by-dayevolution of soil moisture,precipitation and ConvectiveAvailable Potential Energy (CAPE).We compute the areal average overa selected box located in the southportion of SESA indicated in Figure1a. The results are depicted inFigure 3 and 4.Changes in soil moisture(Figure 3a) affect the precipitation,where the stronger impacts areassociated with the convectiveportion of precipitation.If we compare E3 with E1, it is clear that convective precipitation starts earlier when soilmoisture is higher over the area.Besides the marginal precipitation in the first few days, the most important differencesappear by February 2. This helps to explain soil moisture behavior from the beginning of themodel run: before rainfall occurrence (i.e before February 2) soil moisture evaporates,especially in experiments with increased soil moisture (E3 and E4 values decreasesubstantially). Just after this time, all the experiments except E1 show the start of heavierprecipitation, and soil moisture recovers rapidly, with larger increases in closecorrespondence to larger rainfall rates. There is a sustained recuperation of soil moistureamounts from February 3 rd which is more evident in the drier runs.0,060,050,040,030,020,010-0,01-0,02-0,03Ctrl( M=0.25)E1(M=0.14)E2(M=0.23)E3 (M=0.32)E4 (M=0.28)(a)30Jan20031Jan 01Feb 02Feb 03Feb 04Feb 05Feb 06Feb 07Feb 08Feb12108642030Jan2003 31Jan 01Feb 02Feb 03Feb 04Feb 05Feb 06Feb 07FebFigure 3: a) soil moisture anomalies (m 3 m -3 ), b) Daily accumulated convective precipitation (mm),area averaged over the box indicated in Figure 1.(b)-22-