INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
Strong Cross-Barrier Flow under StableConditions producing Intense Winter Orographic Precipitation: A Case Study over the Subtropical Central Andes
MAXIMILIANO VIALE; FEDERICO AUGUSTO NORTE
WEATHER AND FORECASTING
AMER METEOROLOGICAL SOC
Lugar: BOSTON MASSACHUSSETS ESTADOS UNIDOS; Año: 2009 vol. 24 p. 1009 - 1009
ABSTRACT The high mountain of Central Subtropical Andes (30º-36º S) and the Central Chile low lands have a winter precipitation regime. The extreme precipitation episodes are not so frequent and when they do occur, there are severe socio-economical impacts specially on transportation and commerce. Snowfall over the high mountain of the Andes is the product of complex interactions between the synoptic scale flow and the mesoscale topography. In 2005 winter season, the most significant event took place on 26-29 August, when the intense snowstorm caused many damage in the mountainous region. The synoptic situation was characterized by a clear baroclinic zone (polar frontal zone) between 30ºS and 40ºS linked with an intense westerly flow at mid-levels. A low surface pressure belt with a typically cyclones family activity (Bjkernes system) was noted southward of this frontal zone. The instability maximum intensity on the windward of the mountain range was observed at same time of maximum rainfall and snowfall over the Central Chile and high mountain, respectively, and with the downslopes wind gusts (Zonda/Foehn) on the leeward. The 15-Km ETA-PRM model is a regional version of the 40-Km ETA-CPTEC(Brazil) South American domain. The ETA-PRM Regional Model is evaluated as a potential forecasting tool.; and numeric simulation experiment with high resolution was used to estimate the spatial structure of the precipitation event. This was because the scarcity of regional meteorological stations that do not allow to establish it with precision. The skill of the ETA-PRM showed that the orographic precipitation over the Andes Cordillera was realistically simulated and was able to forecast downslopes wind (Zonda) on the leeward. But this model had some difficulties over both sides of the mountain range capturing lower magnitude of 10-m wind and 2-m dew point temperature, larger 2-m temperature daily range, and the cold fronts passages nearly six hours later. The spatial model precipitation distribution of the event showed the maximum precipitation (200-300 mm) upstream of the high Andes crest and a very large zonal precipitation gradient downstream showing the great barrier blocking effect.