Severe deep convection events in the andes region (men- doza, argentina) and their relation with large amplitude mountain waves

A. DE LA TORRE,; R. HIERRO; P. LLAMEDO; A. ROLLA; P. ALEXANDER

Bremen, Alemanaia

Congreso; 38th COSPAR Scientific Assambly 2010; 2010

COSPAR

In addition to an environmental lapse rate conditionally unstable and suficient available moisture, some process by which a parcel is lifted to its LFC is required for the occurrence of deep convection. Since rising motions associated with synoptic scale processes are too weak to lift a moist parcel to its LFC, some strong sub-synoptic mechanism such us upward motion over a frontal zone, anabatic/katabatic winds or mountain waves are required to supply the necessary energy to trigger deep convection. We analyze here, two selected recent severe storms developed in the absence of fronts and registered at the south of Mendoza, Argentina, a semiarid region situated at midlatitudes (roughly between 32S and 36S) at the east of the highest Andes tops. The storms were initiated at the same local time. In both cases, large amplitude stationary mountain waves with similar wavelengths were generated through the forcing of the NW wind by the Andes Range, just before the rst cell was detected in the S-band radar. Mesoscale model simulatons (WRF3V, three domains, inner at 4 km) were conducted. The wave pattern was analyzed at several constant pressure levels with a Morlet wavelet. This wavelet has proven to be a useful technique for this purpose, as propagating mountain waves are well localized within a horizontal domain of some hundred kilometers. The simulated evolution in space and time of vertical wind oscillations (even better than reectivity) reveal their in uence in the genesis zone of both storms. The synoptic conditions observed (low-pressure system over the NW of Argentina, slow displacement of anticyclones in Pacic and Atlantic oceans, a low level jet carrying warm and moist air from the N and geopotential distribution at 1000, 500 and 300 hPa) are consistent with earlier works. We describe and discuss, in both cases, i) the vertical and horizontal wavelengths, ii) the direction of propagation of the main wave modes, iii) their lineal polarization and phase relation between wind and temperature, iv) the Scorer parameter and v) the validation of WRF results with two measured COSMIC GPS radio occultation temperature proles in the inner domain along their lines-of-sight.