Análisis de la presión de la tropopausa dinámica en bajas segregadas en el sur de Sudamérica

Abstract

Las bajas segregadas son circulaciones ciclónicas cerradas que se desarrollan en niveles altos de la tropósfera, quedando separadas del flujo de los oestes. Estos sistemas se asocian a profundas caídas de la tropopausa, permitiendo intrusiones de aire estratosférico en la tropósfera. Con el objetivo de evaluar la profundidad de estas intrusiones en sistemas de bajas segregadas que afectan la región sur de Sudamérica, en este trabajo se buscó la caída máxima de la tropopausa en 49 eventos de este tipo que se desarrollaron entre los años 1999 y 2008...

Cut-off lows are closed cyclonic circulations that develop in high levels of the troposphere, separated from the westerly flow. These systems associate with deep tropopause folds, allowing stratospheric air intrusions within the troposphere. With the goal of evaluate the deep of this intrusions in cut-off lows that affect the southern South America region, in this work we search the maximum tropopause fold in 49 events of this type that develop between the years 1999 and 2008. For the tropopause identification the dynamic definition was used, based in three potential vorticity thresholds: -1.6, -2 and -3 PVU. Besides, specific humidity fields were useful to rule out tropospheric potential vorticity anomalies, which could be confused with stratospheric air. The analysis of the results show that in the cut-off lows the dynamic tropopause drops to pressure levels in average from 557 to 437 hPa, depending on the threshold used. Winter systems were the deepest, reaching in average pressure values between 592 and 465 hPa. In very intense cases the tropopause reaches levels from 650 to 550 hPa.