Preprints
https://doi.org/10.5194/acp-2021-610
https://doi.org/10.5194/acp-2021-610

  17 Aug 2021

17 Aug 2021

Review status: this preprint is currently under review for the journal ACP.

On Warm and Moist Air Intrusions into Winter Arctic

Cheng You1, Michael Tjernström1, and Abhay Devasthale2 Cheng You et al.
  • 1Department of Meteorology & Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 2Remote Sensing Unit, Research and Development Department, Swedish Meteorological and Hydrological Institute, Norrköping, Sweden

Abstract. In this study, warm and moist air intrusions (WaMAI) over the Arctic Ocean sectors of Barents, Kara, Laptev, East Siberian, Chukchi and Beaufort Seas in recent 40 winters (from 1979 to 2018) are identified from ERA5 reanalysis using both Eulerian and Lagrangian views. The analysis shows that WaMAIs, fuelled by Arctic blockings, causes a relative surface warming and hence a sea ice reduction by exerting positive anomalies of net thermal irradiances and turbulent fluxes to the surface. Over Arctic Ocean sectors with land-locked sea ice in winter, such as Laptev, East Siberian, Chukchi and Beaufort Seas, total surface energy budget is dominated by net thermal irradiance. From a Lagrangian perspective, total water path (TWP) increases linearly with the downstream distance from the sea ice edge over the completely ice-covered sectors, inducing almost linearly increasing net thermal irradiance and total surface energy-budget. However, over the Barents Sea, with an open ocean to the south, total net surface energy-budget is dominated by the surface turbulent flux. With the energy in the warm-and-moist air continuously transported to the surface, net surface turbulent flux gradually decreases with distance, especially within the first 2 degrees north of the ice edge, inducing a decreasing but still positive total surface energy budget. The boundary-layer energy-budget patterns over the Barents Sea can be categorized into three classes: radiation-dominated, turbulence-dominated and turbulence-dominated with cold dome, comprising about 52 %, 40 % and 8 % of all WaMAIs, respectively. Statistically, turbulence-dominated cases with or without cold dome occur along with one order of magnitude larger large-scale subsidence than the radiation-dominated cases. For the turbulence-dominated category, larger turbulent fluxes are exerted to the surface, probably because of stronger wind shear. In radiation-dominated WaMAIs, stratocumulus develops more strongly and triggers intensive cloud-top radiative cooling and related buoyant mixing that extends from cloud top to the surface, inducing a thicker well-mixed layer under the cloud. With the existence of cold dome, fewer liquid water clouds were formed and less or even negative turbulent fluxes could reach the surface.

Cheng You et al.

Status: open (until 15 Oct 2021)

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Cheng You et al.

Cheng You et al.

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Short summary
In winter when solar radiation is absent in the Arctic, the poleward transport of heat and moisture into the high Arctic becomes the main contribution of Arctic warming. Over completely frozen ocean sectors, total surface energy budget is dominated by net long-wave heat, while over the Barents Sea, with an open ocean to the south, total net surface energy-budget is dominated by the surface turbulent heat.
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