ENSO Forced Changes in Precipitation Distributions and Related Global Circulation Patterns : Gulf of Mexico Region

Abstract

The El Nino Southern Oscillation (ENSO) forced precipitation is well documented in several regions around the world. Mid-latitude atmospheric circulations contribution towards extreme precipitation during ENSO is less well understood. One area that has a strong ENSO signal in extratropical and tropical storminess is the Gulf of Mexico. This region is influenced by high SSTs, the subtropical jet, and even polar intrusions. The objective of this research is to improve understanding of the link between ENSO, extreme precipitation, and the role of regional atmospheric circulations. The probability density function, cumulative density function, Kolmogorov-Smirnov (KS) test and a hotspot analysis are employed to explore the independent and spatial statistics of precipitation distributions between phases of ENSO across the Gulf of Mexico region. The months of August through January are examined, but October and December display significant spatial patterns and are selected for a synoptic analysis of six grid boxes to represent five regions of large scale ENSO forcing. Our primary finding indicates subtropical jet stream winds are significantly different and stronger during El Nino, especially for the month of October. This would suggest that El Nino would lead to more extremes throughout the Gulf of Mexico, which is not the case from the spatial autocorrelation analysis. Thus, other synoptic scale forcings must be at work. Differences in the cumulative distribution function (CDF) at lower rain rates seem to be more related to the strength and position of the polar jet and may be influenced by jet-interactions. Extreme precipitation during La Nina was traced to a weaker polar jet and the subtropical jet positioned away from the region of interest.