Tropical gradient influences on Caribbean rainfall

Interbasin and intrabasin gradients play an important role as a part of a regional system of Caribbean climate drivers, which include the Atlantic warm pool (AWP) and the Caribbean low-level jet (CLLJ). When the Caribbean is conditioned to be wet between May and November, near-surface geopotentials in the Caribbean are lower than in the nearby eastern tropical Pacific and east tropical Atlantic. As a result, there is vertical ascent in the Caribbean through to the middle troposphere which connects to zonal circulations with both the eastern tropical Pacific and the eastern tropical Atlantic. The Caribbean Sea is also warm, and there is a moderate easterly flow regime, indicating a weakening of the trade winds. Deviations from this state caused by changes in one or both sides of the Pacific-Caribbean and Caribbean-Atlantic circulations (and diagnosed by changes in their geopotential gradients) reasonably track the transition of the Caribbean from wet to dry and vice versa on intraseasonal and interannual time scales. The study also uses changes to the gradients to offer insight into why the Caribbean region is projected to be drier during its traditional rainy season in the face of warmer surface temperatures under global warming. The Caribbean seemingly enters into a "July" mode, which persists for the duration of the boreal summer. The mode is characterized by higher (lower) geopotentials in the Caribbean (Pacific and Atlantic), a stronger CLLJ, and anomalous descent in the Caribbean in spite of the warmer surface temperatures.