Abstract
Various temporal and spatial changes have manifested in Arctic storm activities, including the occurrence of the anomalously intense storms in the summers of 2012 and 2016, along with the amplified warming and rapidly decreased sea ice. To detect the variability of and changes in storm activity and understand its role in sea ice changes, we examined summer storm count and intensity year-by-year from ensemble hindcast simulations with an Arctic regional coupled climate model for the period of 1948–2008. The results indicated that the model realistically simulated the climatological spatial structure of the storm activity, characterized by the storm count and intensity. The simulated storm count captures the variability derived from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP–NCAR) reanalysis, though the simulated one is higher than that in the reanalysis. This could be attributed to the higher resolution of the model that may better represent smaller and shallower cyclones. The composite analysis shows that intense storms tend to form a low-pressure pattern with centers over the Kara Sea and Chukchi Sea, respectively, generating cyclonic circulation over the North Atlantic and North Pacific Arctic Ocean. The former drives intensification of the transpolar drift and Fram Strait sea ice export, and the latter suppresses thick ice transport from the Canada Basin to the Beaufort–Chukchi Seas, in spite of an increase in sea ice transport to the East Siberian Sea. Associated with these changes in sea ice transport, sea ice concentration and thickness show large decreases in the Barents–Kara Seas and the Chukchi–East-Siberian Seas, respectively. Energy budgets analysis suggests that more numerous intense storms substantially decrease the downward net sea ice heat fluxes, including net radiative fluxes, turbulent fluxes, and oceanic heat fluxes, compared with that when a lower number of intense storms occur. The decrease in the heat fluxes could be attributable to an increased cloudiness and the resultant reduction of downward shortwave radiation, as well as a destabilized boundary layer induced increase in upward turbulent fluxes.
Highlights
In conjunction with the amplified surface air temperature increase and accelerated sea ice decreases in the Arctic [1,2,3,4,5,6], the Northern Hemisphere atmospheric circulation has exhibited various pronounced changes
When the high count of intense storms occurs over the Atlantic Arctic Ocean, a slightly negative value of the net sea-ice heat flux occurs in the Northern Barents Sea and the Kara Sea, and a large value of the net sea-ice heat flux occurs in the Northern Barents Sea and the Kara Sea, and a large negative value appears along the sea-ice marginal zone in the East Greenland Sea (Figure 7a)
The recently occurring intense storms show tight linkage with the record lows of summer sea ice extent, it remains unclear how all intense storms have integratively contributed to the observed long-term changes in sea ice and what physical processes are behind these contributions
Summary
In conjunction with the amplified surface air temperature increase and accelerated sea ice decreases in the Arctic [1,2,3,4,5,6], the Northern Hemisphere atmospheric circulation has exhibited various pronounced changes. Storms, serving as the fundamental weather systems on a daily basis, can impact sea ice and ocean in various complex thermodynamic and dynamic ways It is a primary driver for transient heat and moisture transport [29,30], which may alter Arctic energy budgets. A few studies have been conducted on aspects of storm impacts on sea ice in particular for specific cases, it is still unclear how regionally integrated storm activities have impacted sea ice changes during the past decades and what physical processes are underlying these impacts To address this problem, we analyzed the variability of and changes in regional storm activities and associated sea ice and surface energy budgets in ensemble hindcast simulations by a fully coupled Arctic regional climate model. Considering that the number of Arctic storms climatologically reaches its maximum during summer [8,34], and the largest variability and decrease, as well as minimum value, of sea ice extent occur in summer, our analysis focused on the period from 1 July to 15 September of each year during the model simulation 61-year time period 1948–2008
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