MHWs enhanced by transport-driven surface thermal/humidity inversion in early summer around the Korean peninsula

Abstract

This study investigated the marine heatwave events (MHWs) that occurred near the Korean Peninsula during the summer of 1994 and 2018, using a regional air-sea coupled model. When the North Pacific High and Tibetan High develop stronger than usual, warm and moist air intrusion from the subtropical region can cause thermal/humidity inversion at the sea surface around the Korean Peninsula in early summer. Air-sea interaction is a vague part of numerical modeling but plays an important role in the development of MHWs. The seasonal lag between the atmosphere and the ocean can lead to a distinctive phenomenon in summer. The combination of intrusion of the air from subtropical regions and insufficiently developed ocean conditions can induce the downward latent heat flux (LHF), resulting in rapidly increased sea surface temperatures (SSTs). To quantify the contribution of downward LHF, we set up two experiments. The first one is CPL_nodown without any modification, and CPL_down is an experiment that allowed downward latent heat flux, that is, negative evaporation value. Results show that the CPL_down experiment capture the strengthened SSTs at the beginning better than CPL_nodown in both events. The thermal/humidity inversion above the ocean surface appeared in both experiments. But CPL_down, which permitted the downward LHF, only reproduced burn-off low-level cloud (cloud under 925 hPa) and improved the MHW reproducibility. Therefore, we suggest that allowing downward LHF is favorable for simulating MHWs in early summer around the Korean Peninsula, and surface physical parameterization must be carefully selected.