Enhanced Air-Sea Heat Flux during Cold Air Events: Observations and Mechanism Analysis

Air-sea heat flux intensifies during cold airs and other strong weather events. However, due to the lack of long-term observations during such cold air processes, the quantitative enhancement of air-sea heat flux and its underlying mechanisms remain poorly understood. To address this issue, based on a tower-based platform in the southern Bohai Sea, a high-frequency turbulence measurement system was implemented to conduct a two-year air-sea flux measurement, collecting air-sea heat flux data covering 20 cold air outbreak events. This study quantitatively analyzes and reveals the pronounced variations in air-sea sensible heat flux of SHF and latent heat flux of LHF during cold air events, as well as the distinct roles of wind speed, air-sea temperature difference and specific humidity difference. The enhancement of SHFand LHF is further quantified. Our results show that the significant increases in wind speed and air-sea temperature difference are the primary drivers of the enhanced heat flux. Although LHF exhibits higher magnitude than SHF during cold air processes, LHF is predominantly controlled by increased wind speed, whereas SHF is mainly influenced by both wind speed and the air-sea temperature difference, with its enhancement being substantially greater than that of LHF. Compared to calm weather conditions, SHF and LHF under cold air conditions increased by an average of 12.8 and 1.6 times, respectively, while the total heat flux increased by 2.6 times on average. The increasement of heat flux can exceed 10 times during cold waves, even can reach the magnitude comparable to that observed during tropical cyclones.