Understanding the Convection in Water Vapor "Lakes" in the Western Equatorial Indian Ocean

Over the Western Equatorial Indian Ocean (WEIO), isolated high-column Water Vapor "Lakes" stand out in stark contrast to the typically drier zones and often bring rain to the African coast. This study explores the genesis and persistence of these vapor lakes. Central to this research is the hypothesis that vapor lake dynamics are maintained by a combination of horizontal advection, secondary atmospheric circulations, and Precipitation - Evaporation (P-E). We define these lakes by identifying closed contours of 55mm column water vapor in MERRA-2 data and examine the moisture budget as a function of distance from these contours.

Preliminary findings indicate distinct seasonal landfalling patterns of vapor lakes following the warmest SST, but they are stronger in the southern hemisphere. Tracking studies of some vapor lakes show lifespans exceeding a week with behaviors like merging and splitting and an east-to-west drift. The study's composite analysis indicates a distinct peak for clouds and precipitation within the confines of vapor lakes. Inside these lakes, we observed a marked moisture convergence corresponding to the P-E sink. These lakes also have vorticity signatures, raising the question of whether moisture or momentum fields are more important to their dynamics. Also, many other variables exhibit structure across the vapor lake boundary. Future work includes evaluating model forecasts and simulations to gain deeper insights into the longevity and propagation mechanisms of these systems, and the ability of the models to capture these.