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.
Highlights
In recent decades, rapidly intensified Arctic warming has been observed (Cohen et al, 2014; Francis and Vavrus, 2012; Graversen et al, 2008), which has become known as Arctic amplification (Serreze and Francis 2006).Accompanying this warming has been a dramatic melting of Arctic sea ice (Simmonds, 2015)
Most of these studies deal with winter and focus either on the dynamical mechanisms resulting in warm and moist air intrusions (WaMAI), or on the effects of WaMAIs on the Arctic climate system conducted from an Eulerian perspective by retrieving composite mean of WaMAIs properties (Liu et al, 2018), or calculating regressions between different metrics (Gong and Luo, 2017)
Unlike over the Barents Sea, where the total water path (TWP) anomaly is dominated by liquid water path (LWP) (Figure 4d and 4e), TWP over the Beaufort Sea is dominated by ice water path (IWP)
Summary
Rapidly intensified Arctic warming has been observed (Cohen et al, 2014; Francis and Vavrus, 2012; Graversen et al, 2008), which has become known as Arctic amplification (Serreze and Francis 2006). The positive trend in number of winter WaMAIs can statistically explain a substantial part of the surface air temperature and sea-ice concentration trends in the Barents Sea (Woods and Caballero, 2016). Most of these studies deal with winter and focus either on the dynamical mechanisms resulting in WaMAIs, or on the effects of WaMAIs on the Arctic climate system conducted from an Eulerian perspective by retrieving composite mean of WaMAIs properties (Liu et al, 2018), or calculating regressions between different metrics (Gong and Luo, 2017). We will attempt understanding the distinctions between the ocean sector with open water and those with land-locked sea ice by comparing surface and boundary-layer energy-budget from both Eulerian and Lagrangian perspectives
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