Possible triggering effect of large amplitude mountain waves in storms initiation in the Andes region (Mendoza, Argentina)

R. HIERRO1, A. DE LA TORRE, H. PESSANO, P. LLAMEDO, P. ALEXANDER AND A. ROLLA

Mysore

Congreso; COSPAR CONF; 2012

COSPAR

Under certain conditions, the rising motions associated with synoptic-scale processes are too slow to lift a potentially buoyant parcel to its level of free convection in the required time, to develop deep convection. In this work, we analyze a selected subset of 39 storms, in the absence of cold fronts, that produced a considerable damage to vineyards in a protected region at the South of Mendoza, Argentina, between 2006 and 2011. This is a semiarid region situated at midlatitudes (roughly between 32S and 36S) at the East of the highest Andes tops and constitutes a natural laboratory where usually diverse sources of gravity waves take place. We consider a particular subregion near to San Rafael city, where every summer a systematic generation of storms is observed. The lift mechanism required to raise a parcel to its level of free convection, partially supplied by mountain waves (MWs), is analyzed. Nevertheless, additional triggering factors such as diurnal warming may be active too. From Weather Research and Forecasting (WRF) mesoscale model simulations of vertical velocity (w) as an appropriate dynamical variable to evidence the presence of MWs, temperature and radar network data, we calculate the evolution of convective available potential energy (CAPE) and convective inhibition (CIN) indexes during each storm development. Global Final Analyses (FNL) are used to construct initial and boundary conditions. CIN is compared with the kinetic energy able to be supplied by the mountain wave alone, in order to provide a rough estimation of this triggering possibility. w is used to analyze the presence of MW in the vicinity of detected first radar echoes. After establishing a criteria based on a previous work for the significant presence of MWs, the 39 storms originally selected are splitted into two subsets: with and without the presence of MWs. As a result, 12 cases with considerable MWs are retained and considered. A Morlet Continuous Wavelet Transform along zonal and meridional direction is applied to w to isolate parameters belonging to main stationary MW modes. Clear differences between the average i) maximum reflectivity of first echoes, ii) height of maximum reflectivity, iii) angle of cell displacement, iv) precipitation flux and v) CAPE and CIN values are found and discussed.