Mountain gravity waves in Mendoza and their possible relation with the triggering of convective storms

A. DE LA TORRE; P. ALEXANDER; P. LLAMEDO; D. LUNA; G. FERNÁNDEZ; A. ROLLA; J. DESSENS

Mendoza

Congreso; Meeting of the Weather Modification Association; 2008

The conditions for the development of deep convection processes depend on the vertical distribution of convective available potential energy. If the level of free convection is situated high enough respect to the humid parcels, the convection cannot begin spontaneously and an accumulation of this energy takes place. A dynamic external phenomenon might work as a triggering mechanism and raise the humid parcels up to the level of free convection, initiating a deep convection. From the different external phenomena capable of initiating a deep convection, some of them might be directly associated with the mountains: i) By the direct forcing of the mean wind, generating mountain waves, or ii) by the development of anabatic and katabatic winds inside the valleys, originated in turn by the differential warming of the sun in the slopes. Both mechanisms might be capable, under appropriate local conditions, to contribute with the moment required to raise a mass of humid air up to the level of free convection. On a global scale, the importance of mountain waves has proven to be decisive in the acceleration and slowdown of the general circulation of the atmosphere. It is well known that an inadequate parameterization of the effect of these waves in the global models causes over or underestimations in the predicted zonal and meridional winds, with respect to measured values. In recent years, remote systems of observation on board of satellites coincide in revealing a significant activity of these waves in the proximity of the Andes Mountains. In the present work, we will overview these tools of observation, complemented with simulations performed from numerical studies with mesoscale models, such as WRF.          The proposal of an experimental campaign in the region of the Andes Mountains during the winter of 2009 will be presented. The main aim of it will consist to obtain in situ measurements of basic atmospheric parameters (temperature, speed of the air, etc), making use of the same aircrafts and infrastructure provided by the Province of Mendoza during the operations for hail prevention. These aircrafts are not operated during the winter months, when the mountain waves coincidently exhibit maximum amplitude, due to the atmospheric stability and the enhanced intensity of the subtropical jet. The measurements to be tracked by 4 aircrafts, flying to different pressure levels simultaneously and along paths designed to optimize the wave detection, might be ideally complemented by radiosonde launchings from land. The experimental results to be obtained will provide valuable information to adjust the WRF operational model currently used in Mendoza, since March 2008. For the planning and accomplishment of this campaign, a reasonable collaboration from foreign institutions may be expected, bearing in mind the increasing interest observed in the proposed topic. The feasibility to install on board the aircrafts an instrument to detect the particles of silver iodide released by the generators distributed along the Uco Valley, will be proposed. This will allow to measure in situ, during the deep convection period, the penetration of this substance at the base of the clouds.