Interannual variability of Northern activity over the Americas

The winter atmospheric circulation over Mexico and the Caribbean is characterized by the continuous passage of midlatitude systems. When these systems penetrate into low-latitude, they are called northerns, tehuantepecers or cold surges. The intense northerly low-level winds that occur during a northern, interact with the regional topography imprinting unique characteristics to the regional climate. The changes in the circulations, associated with the El Niño phenomenon, modifiy the mean flow over which the northern propagate. By defining a northern in terms of the observed changes in surface temperature, and changes in wind speed and direction, the characteristics pattern of a northern is identified. Trhough a composite analysis with 40 years of reanalysis data, it is found that more northerns occur over Mexico and the Caribbean during El Niño years than during La Niña years. However, there appears to be less precipitation with more northerns than with less northerns. The mechanisms that control such relationships between northerns and El Niño are explored.