The severe zonda wind event of 11 July 2006 east of the Andes Cordillera (Argentine): a case study using the BRAMS model

The zonda is a wind that exhibits the so-called foehn effect: a warm, dry, strong wind related to adiabatic compression upon descending in the lee of the Andes. This phenomenon occurs mostly in winter and spring over the entire length of the extratropical Andes. It is frequently detected near the cities of Mendoza and San Juan, the most important urban regions of western Argentina. The aim of this work is to understand why a zonda wind event, occurring on 11 July 2006, reached and maintained the higher category Z4 during several hours. A secondary aim is to evaluate the ability of a Brazilian regional atmospheric modeling system (BRAMS) model to represent the features of this extreme episode and to explore if it can be used to predict a zonda event. The difference found with respect to other severe zonda wind episodes analyzed was that the wind registered the highest category (Z4) with extreme gusts during a long period. This condition was registered in particular on southern plain areas of San Juan province. The phenomenon had a great impact on the community, with residences and buildings being affected or destroyed, trees being felled, power supply and communications being shutdown, and several rural and urban fires being reported. The event was characterized through surface and upper-level information and model results. The synoptic surface and upper-air conditions were those typically associated with a severe zonda wind occurrence: a surface cold front approaching the region, driven by a 500 hPa trough, a strong upper-air jet stream, and a deep low-pressure surface system at higher latitudes over the Atlantic Ocean. The North West Argentine Low in central west Argentina during the following hours could be observed centered approximately at 31S 66W. in a few lower latitude than the location observed by National Center of Environmental Prediction (NCEP) reanalysis. On the other hand, it is the authors' impression that the BRAMS model achieved an acceptable representation of some aspects of this zonda wind event. This is the first study on BRAMS model performance in predicting a zonda event. Further and thorough research is required to study the application of BRAMS to contribute to the analysis of the three-dimensional structure and the related physical mechanisms, and to enable skillful comparison with others models. To apply this sophisticated high-resolution model in a region with complex topography and without a dense surface and upper-air observational network is a challenge.