Atmospheric circulation associated with the arrival of sargassum in the Caribbean Sea.

<p>The arrival of sargassum in a massive way generates adverse environmental, social and economic impacts. Little is known about its origin and trajectory, as well as the atmospheric and oceanic conditions under which it arrives at the Mexican coasts of the Caribbean. This poster presents a diagnosis of the seasonal, annual and interannual variability of atmospheric circulations in the Atlantic and Caribbean Sea, identifying the atmospheric conditions under which sargassum arrived on the Mexican coasts. 30 years of surface wind data from CFSR (Climate Forecast System Reanalysis) of NCAR on the Atlantic and Caribbean were analyzed, dividing the area into six areas, for each one its seasonal, annual and interannual variability was estimated, as well as its extreme values from 1989 to 2018, focusing the study on both the Caribbean Sea and the Atlantic coast of Brazil.</p><p>Once the mean, extreme winds (10th and 90th percentiles) and their correlation with the NAO (North Atlantic Oscillation) were diagnosed interannually, particular years of the recent period were analyzed: from 2010 to 2019 incorporating the wind convergence as a physical process associated with the accumulation of sargassum, surface pressure and sea surface temperature (SST) and also correlating it with the NAO index.</p><p>The results show that the atmospheric conditions for transporting sargassum along the Mexican coasts of the Caribbean are more favorable in summer than in winter, besides it, the higher extremes (90th percentile) in the Caribbean favor the transport of sargassum both in winter and in summer. However, "connectivity" with other regions (Central Atlantic) makes summer more favorable, but winter is potentially viable. The atmospheric conditions of recent extreme years are discussed: 2013 (without the arrival of sargassum), medium: 2015 and extreme 2018 (with abundant sargassum) for both summer and winter.</p>

Annual and Interannual Variability of the Tropical Instability Vortices in the Equatorial Eastern Pacific Observed from Lagrangian Surface Drifters

This study documents the spatial distributions and temporal variations of anticyclonic eddies with identified radii ≥100 km in the equatorial eastern tropical Pacific Ocean [viz., tropical instability vortices (TIVs)] using Lagrangian surface drifters. The TIVs identified from Lagrangian surface drifters are distributed in a band along 5°N and are closely associated with latitudinal barotropically unstable shear between the westward South Equatorial Current (SEC) and the eastward North Equatorial Countercurrent (NECC). Fewer TIVs are identified from February to June when the shear between the SEC and NECC is weak, whereas more TIVs are found from July to January when the shear is enhanced. The number of identified TIVs also exhibits substantial interannual variability, with fewer TIVs identified during El Niño events and more TIVs found during La Niña events. This relationship is likely associated with the interannual variations of the zonal circulation in the equatorial Pacific modulated by El Niño–Southern Oscillation (ENSO).

Interrelated variations of O₃, CO and deep convection in the tropical/subtropical upper troposphere observed by the Aura Microwave Limb Sounder (MLS) during 2004–2011

The interrelated geographic and temporal variability seen in more than seven years of tropical and subtropical upper tropospheric (215 hPa) ozone, carbon monoxide and cloud ice water content (IWC) observations by the Aura Microwave Limb Sounder (MLS) are presented. Observed ozone abundances and their variability (geographic and temporal) agree to within 10–15 ppbv with records from sonde observations. MLS complements these (and other) observations with global coverage and simultaneous measurements of related parameters. Previously-reported phenomena such as the ozone "wave one" feature are clearly seen in the MLS observations, as is a double peak in ozone abundance over tropical East Africa, with enhanced abundances in both May to June and September to November. While repeatable seasonal cycles are seen in many regions, they are often accompanied by significant interannual variability. Ozone seasonal cycles in the southern tropics and subtropics tend to be more distinct (i.e., annually repeatable) than in the northern. By contrast, carbon monoxide shows distinct seasonal cycles in many northern subtropical regions, notably from India to the Eastern Pacific. Deep convection (as indicated by large values of IWC) is typically associated with reductions in upper tropospheric ozone. Convection over polluted regions is seen to significantly enhance upper tropospheric carbon monoxide. While some regions show statistically significant correlations among ozone, carbon monoxide and IWC, simple correlations fall well short of accounting for the observed variability. The observed interrelated variations and metrics of annual and interannual variability described here represent a new resource for validation of atmospheric chemistry models.

Interrelated variations of O₃, CO and deep convection in the tropical/subtropical upper troposphere observed by the Aura Microwave Limb Sounder (MLS) during 2004–2011

The interrelated geographical and temporal variability seen in more than seven years of tropical and subtropical upper tropospheric (215 hPa) ozone, carbon monoxide and cloud ice water content (IWC) observations by the Aura Microwave Limb Sounder (MLS) are presented. Observed ozone abundances and their variability (geographical and temporal) agree to within 10–15 ppbv with records from sonde observations. MLS complements these (and other) observations with global coverage and simultaneous measurements of related parameters. Previously-reported phenomena such as the ozone "wave one" feature are clearly seen in the MLS observations, as is a double peak in ozone abundance over tropical East Africa, with enhanced abundances in both May to June and September to November. While repeatable seasonal cycles are seen in many regions, they are often accompanied by significant interannual variability. Ozone seasonal cycles in the southern tropics and subtropics tend to be more distinct (i.e., annually repeatable) than in the northern. By contrast, carbon monoxide shows distinct seasonal cycles in many northern subtropical regions, notably from India to the Eastern Pacific. Deep convection (as indicated by large values of IWC) is typically associated with reductions in upper tropospheric ozone. Convection over polluted regions is seen to significantly enhance upper tropospheric carbon monoxide. While some regions show statistically significant correlations among ozone, carbon monoxide and IWC, simple correlations fall well short of accounting for the observed variability. The observed interrelated variations and metrics of annual and interannual variability described here represent a new resource for validation of atmospheric chemistry models.