Two Types of Air-Sea Interaction Mechanisms over the Kuroshio-Oyashio Extension Region

Two types of air-sea interaction mechanisms over the Kuroshio-Oyashio Extension (KOE) region are investigated using the Variable-Resolution Community Atmospheric Model version 6 (VR-CAM6). VR-CAM6 is configured with an enhanced horizontal resolution of 1/8° over the North Pacific, while the rest of the global domain is represented at 1° resolution, with narrow transition regions between the two. The present study focuses on how atmospheric convective heating and large-scale condensational heating are modulated by prescribed sea surface temperature (SST) anomalies during early winter (November-January).

In the control simulation with climatological SSTs as the boundary condition, the meteorological conditions that lead to strong amplitude of large-scale condensational heating over the KOE region are dominated by transient extratropical cyclones, with positive latent heating in their warm sector. On the other hand, strong amplitudes of convective heating are associated with a quasi-stationary cyclonic circulation over the central North Pacific, such that the cyclonic northerly cold flow generates favorable conditions for strong convective activities over the KOE region.

In the presence of a warm SST anomaly forcing in the KOE region, which represents a northward shift of the North Pacific western boundary currents (WBC), large-scale condensational and convective heatings reinforce each other. In cases where large-scale heating is strong in both control and anomaly runs, extratropical cyclone intensity remains similar, but the warm SST anomaly intensifies convective heating over the cold sector of the extratropical cyclones. In cases where convective heatings are strong, large-scale condensational heating is enhanced by warmer SSTs. It is hypothesized that warmer SSTs lead to stronger upward motion which redistributes heat into the free troposphere, ultimately leading to enhanced large-scale condensational heating. Overall results show that there are different flavors of atmospheric response to WBC meridional shifts. A detailed quantification of each mechanism will help improve the prediction of downstream circulation and weather patterns.