Oceanic and atmospheric impact of central American cold surges (Nortes) in the Gulf of Mexico

Abstract

Central American cold surge outbreaks, known as Nortes, are standard features of the Gulf of Mexico (GoM) climate, having significant oceanic and atmospheric impacts over the region that are essential for the marine ecosystem. Fifteen years of analysis of weather reports showed that Nortes occur within a 9 months window (September to May), with a total number of 24 ± 5 episodes per season. On average, there were 2.5 ± 1 events per month, lasting between 1 and 3 days with a maximum duration of 13 consecutive days. A Principal Component Analysis of 15 years of in situ observations identified the air temperature (41.6% of the explained variance) and the wave height (36.3%) as the two main drivers of these events impacts. Cluster Analysis to these same data categorized the Nortes into three types: Moderate, Strong, and Severe, based on the environmental impact caused in the GoM. These events tend to transit between categories as they lose strength while travelling to southern latitudes. Severe events are more frequent in the northwestern coast, occurring from January to March, whereas moderate events are more common in the middle of the GoM during September-December. Our results showed that Nortes increase the wind stress over the sea surface, rising the height and period of the waves over the southwestern and central GoM. Nortes also disturb the sealevel and the surface currents, provoking high amplitude oscillations along the coasts, and accelerating and shifting the currents towards the southwest. Nortes bring cold, dry air that cools the ocean surface and the lower atmosphere and diminishes its relative humidity, which, together with the wind velocity increments, promote a positive sensible and latent heat flux maximized on the northwestern and western coasts. K E Y W O R D S central American cold surges, environmental afections, Gulf of Mexico, ocean-atmosphere interactions 1 | INTRODUCTION Central American cold surge outbreaks, colloquially known in Mexico as Nortes, are common features of the regional Gulf of Mexico (GoM) climate, occurring on short-time scales (in the order of days) during most of the year. These phenomena are a result of the equatorward advection of the lower atmosphere anticyclones, located

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