Ocean Surface Warming and Cooling Responses and Feedback Processes Associated With Polar Lows Over the Nordic Seas.

Strong surface winds induced by polar lows (PLs) may affect the upper ocean. However, understanding of the oceanic responses and feedback processes associated with PLs remains insufficient, especially for observations. Using a combined analysis of satellite‐based sea surface temperature (SST) and PL tracking data, we investigated the oceanic response to 380 PL passages over the Nordic Sea occurring between 1999 and 2018. Consequently, two types of oceanic responses—warming and cooling—occurred in 32% and 40% of the total occurrences, respectively. The average magnitude of SST response was approximately ±0.2 K. Significant differences in upward surface turbulent heat flux (THF) between warming and cooling response cases were found, causing a significant difference in the decay rate after maximum PL development. By analyzing changes in the state variables of the THF, we identified two different feedback processes depending on the oceanic warming/cooling response. During a warming (cooling) response, the atmosphere near the surface becomes more unstable (stable), and the turbulence of the marine atmospheric boundary layer increases (decreases), which strengthens (weakens) the ocean surface wind and decreases (increases) temperature and specific humidity. These changes contribute to increasing (decreasing) the upward THF that influences PL development. The differences between these two responses may be caused by the state of the upper ocean layer, including temperature inversion. The analysis of the in situ observations of the upper ocean supports the hypothesis that a warming response occurs when inversion is strong. This study emphasizes the importance of feedback through oceanic responses for understanding and predicting PL. Plain Language Summary: Small but strong storms that occur at high latitudes often cause significant damage to society. When such a storm occurs, there is great interest in whether it develops or dissipates. In this study, we investigated the records of past storms in the Nordic Sea, focusing on changes in ocean surface temperatures measured by satellites. In certain cases, the water temperature decreased as the storm passed, whereas in others, the water temperature increased. We found that when the water temperature increased, more thermal energy was supplied to the storm from the ocean, and storm attenuation was smaller than when the water temperature decreased. Although the change in water temperature caused by the passage of a storm is small, at approximately 0.2°C, it has been revealed that, simultaneously, changes in near‐surface wind and air temperature occur, which cause thermal energy to be transferred to the storm. These results show that storms and the ocean are not unrelated and that ocean structure is crucial for predicting storms. Key Points: Satellite‐based data revealed two types of oceanic responses—surface warming and cooling—to the passage of polar lows (PLs) over the Nordic SeasOcean observation data suggest that the difference between the two responses is related to the vertical structure in the upper oceanResponses and feedback result in differences in the upward surface turbulent heat flux, which changes the characteristics of PLs [ABSTRACT FROM AUTHOR]