The Air–Sea Response during Hurricane Irma’s (2017) Rapid Intensification over the Amazon–Orinoco River Plume as Measured by Atmospheric and Oceanic Observations

Considerable progress has been attained in the recent decade of understanding how upper ocean structure, especially subsurface thermal structure, influences the transfer of heat and moisture into tropical cyclones (TC) through sea surface temperature (SST) modulation. However, subsurface salinity influenced by river discharge is starting to be considered with respect to SST cooling during TC passage such that upper ocean salinity stratification plays a role in modulating upper ocean mixing and air-sea fluxes. Previous literature has investigated the influence of the salinity stratification on air-sea interaction during TCs undergoing rapid intensification (RI) over this plume but there has continuously been a lack in coupled air-sea observations. Recently, several in situ oceanic and atmospheric boundary layer observations were attained via Aircraft eXpendable BathyThermographs (AXBT), Air-launched Autonomous Micro Observer (ALAMO) floats, and atmospheric dropwindsondes during Hurricane Irma’s (2017) passage over the Amazon-Orinoco River plume. During this time, the storm underwent RI as it passed over the core of the river plume. Dropwindsonde observations are referenced into a wind-shear coordinate system to identify links between the ocean response before and during Irma’s RI and the modulation of atmospheric boundary layer temperature and moisture in the inner core of the TC. Analyses of these coupled measurements highlight the involvement of subsurface salinity stratification, imparted by the river plume, on reduced SST cooling and its influence on favorable atmospheric boundary layer conditions through surface fluxes during Irma's RI.