Intensification of extreme wind events over the Chukchi Sea during autumn-winter freeze-up

Abstract:

In recent decades, the Pacific Arctic region has shown significant sea ice decline and notable delays in the freeze-up season. An increase in open water areas intensifies heat and moisture transfers from the sea surface to the atmosphere and increases in near surface air temperature.

Could these environmental changes affect the extreme wind conditions over the marginal seas of the Pacific Arctic?

In this work, we consider the activity of high wind events over the Chukchi Sea during autumn-winter freeze-up season, using both the cross-calibrated multi-platform ocean wind vector analysis version 2.0 (CCMPv2) data set and state-of-the-art ERA5 reanalysis from 1979 to 2018.

For 40 autumn-winter periods we revealed 325 extreme wind events (EWEs) associated with passing of synoptic-scale cyclones, the intrusion of cold air masses from the polar cap and the formation of mesocyclones and polar lows. Distribution of EWEs duration indicated a separate class of prolonged (more than 5 days) events associated with marine cold air outbreaks with a strong winds (more than 20 m/s), extreme ocean heat loss and rapid sea ice formation and drift. On average, these prolonged EWEs accounted for about 8-9% of all cases. However, the interannual variability of their repeatability showed a statistically significant increase (p < 0.05) from the beginning of the 21st century.

In addition, we examine most intense extreme wind event on October, 2017, when fall freeze-up was anomalously late. We found that the frequency of extreme wind events was the highest this year. The wind regime of the Chukchi and Beaufort seas on October 19-20, 2017 was affected by an intense polar low (PL). PL evolved under impact the favorable synoptic conditions and moved southward along the Alaska coast. Wind speed estimates at the PL obtained from ERA5 showed 20% underestimation (for values more than 20 m/s) compared with CCMP2.

It is established that reanalysis ERA5 compared to satellite-based CCMPv2 systematically underestimates wind speed in both synoptic and mesoscale weather systems over open water areas.