Within the Footprint of Atmospheric Rivers, Surface Heat Fluxes from the Ocean into the Atmosphere are Anomalously Weak, even During Formation

Atmospheric Rivers (ARs) are large conduits of poleward movement of heat and water. This study assesses surface heat fluxes and moisture sources fueling ARs a NASA CYGNSS flux product. Extratropical surface energy fluxes are reduced in AR events, particularly when ARs are fully developed. This observed damping of surface fluxes during ARs is also found in the NASA Goddard Institute for Space Studies ModelE, 2.1 (GISS-E2.1) configured with nudging to reanalysis winds. These results imply that ARs are not fueled from the surface immediately below – and therefore, must be fueled from fluxes further afield. To confirm this, we analyze tracers in GISS-E2.1that identify the moisture source for AR events as evaporating further away and equatorward compared to climatological moisture sources. Thus, the ‘fueling’ of atmospheric river events from non-local sources indicated by CYGNSS is bolstered by our moisture provenance results.