Assessing Vertical Moisture Variability in the Caribbean

It is widely acknowledged that El Niño Southern Oscillation [ENSO] is a primary modulator of inter-annual, global climate variability. This is especially true in the tropics, including the Caribbean Basin. Many parts of this region experience extreme precipitation deficits and drought during positive ENSO events resulting from enhanced subsidence over the Atlantic Ocean as the Walker Circulation migrates eastward. Drought conditions prevail when the occurrence of El Niño maturation, i.e., when forcing is strongest, coincides with the beginning of the region’s naturally occurring dry season during the Northern Hemisphere winter. Since no two ENSO events, positive or negative, are alike, the corresponding impacts can vary both horizontally and potentially vertically, and therefore it is also critical to understand to what extent the surface variations in humidity extend through the lower troposphere. Recent research has shown that variability exists in the vertical structure of the atmosphere among ENSO events through analysis of variables such as temperature, circulation, and moisture divergence. In this study, we employ the National Centers for Environmental Prediction North American Regional Reanalysis specific humidity data for six pressure levels up to, and including, 500hPa to investigate how vertical moisture differs among ENSO events during boreal winter over the Caribbean Basin. Furthermore, we assess the differences between El Niño events of varying spatial characteristics (cold tongue vs. warm pool) and intensity of ENSO events (moderate vs. extreme). The results point toward a need to consider more than surface conditions observed during ENSO events. We should also consider the three-dimensional impact, i.e., both horizontal and vertical variability, on critical atmospheric constituents that modulate the state of the atmosphere during teleconnection-influenced climatic events. Knowledge of three-dimensionality of atmospheric variables in the Caribbean may improve long term understanding and eventually improved forecasting of ENSO-driven drought.