A Climatology of Extreme South American Andean Cold Surges

Abstract

Interactions between the tropics and midlatitudes have been an ongoing area of research since the inception of meteorology. Cold surges represent one of several phenomena by which midlatitude features can modulate the atmosphere, both dynamically and thermodynamically, deep into the tropics. This study performs a climatology of particularly strong South American cold surges that follow along the Andes mountains to quantify the maximum extent to which these surges can modulate the atmosphere from the midlatitudes to the tropics. Data was collected for Austral winter (JJAS) from 1980-2010 (31 years). To identify events, standardized anomalies for 925 hPa meridional wind and temperature are calculated. To ensure the cold surges are on the stronger end of the spectrum, steep conditions of anomalies exceeding three above (below) zero for meridional wind (temperature) were set as the criteria which must occur in conjunction on the meso-alpha scale or larger. Using these criteria, 57 events are identified, and composites and area-averages are created, focused on the same fields used to identify the events. The duration of these events was approximately four days on average, with the strongest event lasting eight days. It is shown that some extreme cold surge events can have lasting impacts on the lower parts of atmosphere over much of northern South America, with anomalies up to three above (below) zero for meridional wind (temperature) reaching the southern Caribbean.