Midlatitude Oceanic Fronts Strengthen the Moisture Transport from Anticyclones to Cyclones

The Kuroshio-Oyashio Extension and Gulf Stream oceanic frontal zones with sharp sea-surface temperature gradients are characterized by enhanced activity of synoptic-scale cyclones and anticyclones and vigorous air-sea exchange of heat and moisture in the cold season. However, the air-sea exchanges attributed separately to cyclones and anticyclones have not been assessed. Here we quantify cyclonic and anticyclonic contributions around the oceanic frontal zones to surface turbulent heat fluxes, precipitation, and the associated hydrological cycle. The evaluation reveals that precipitation exceeds evaporation climatologically within cyclonic domains while evaporation dominates within anticyclonic domains. These features as well as the net moisture transport from anticyclonic to cyclonic domains are all enhanced in the presence of the frontal zones. Oceanic frontal zones thus climatologically act to strengthen the hydrological cycle through increasing low-level storm-track activity and specific humidity. These findings aid our understanding of the relationship between midlatitude air-sea interactions on synoptic- and longer-time scales.