Wintertime Marine Cold Air Outbreaks over the Northwest Pacific: Lagrangian Climatology and Downstream Impacts

Abstract

Marine cold air outbreaks (CAOs), cold continental air masses outflow over extratropical oceans, are key drivers of wintertime air-sea interactions. This study presents a Lagrangian climatology of marine CAOs over the North Western Pacific and marginal seas during the past 39 Januaries (1982–2020), focusing on their pathways, thermodynamic evolution, and downstream hydrological impacts. By tracking cold air masses that undergo ocean-induced modifications, we identify distinct regions of initial air-sea interaction and their associated transformation characteristics. On average, 46.1% of CAO trajectories first interact with the Sea of Japan, followed by the Sea of Okhotsk (18.5%) and the Yellow and East China Seas (YS/ECS; 12.0%). They play a significant role in climatological surface turbulent heat fluxes, accounting for more than 80% of the total flux over the midlatitude basins. The most pronounced air-mass transformation occurs within 2–3 days of the first interaction with the ocean with rapid heat and moisture uptake, as the air masses traverse increasingly warmer ocean surfaces. The characteristics of air-mass transformations and downstream impacts vary by regions: CAOs over the Sea of Japan, Sea of Okhotsk, and Bering Sea tend to exhibit rapid moisture turnover. In contrast, CAOs over the YS/ECS more frequently exhibit prolonged moisture retention during subsequent air-sea interactions, contributing to a remote water cycle. Our findings thus underscore the importance of treating northwestern Pacific CAOs as a collection of distinct regional processes, each shaped by basin-specific air-sea interactions.