Effects of Midwinter Arctic Leads on Clouds and the Surface Energy Budget

Leads (open water within the polar ice pack) have significant effects on the winter-time Arctic surface energy budget due to the extreme air-water temperature contrast (20 to 40 °C). For example, the sensible heat flux (SHF) and latent heat flux (LHF) above open leads are about two orders of magnitude larger than those over the snow-covered pack ice. However, due to the paucity of observations in the Arctic, the quantitative effects of leads on the surface energy budget remains a fundamental uncertainty. Our goal is to quantitatively understand the impact of leads on Arctic surface energy budget. We are using a 3-D cloud-resolving model, the System for Atmospheric Modeling (SAM) to simulate the Arctic boundary-layer atmosphere in conditions of “no lead”, “open lead”, and “refrozen lead”. Results for a large, 4.2-km-wide, lead demonstrate that compared with the negligible turbulent heat fluxes in the “no lead” case, over open lead the SHF (LHF) is 344 W m^-2 (102 W m^-2), which is in agreement with earlier studies. The Lead-generated plume and associated condensate increase the downward infrared (IR) flux by roughly 67 W m^-2 at the surface. When the open lead is refrozen (with a 2.65-cm thin ice layer), the LHF decreases to zero while the SHF remains relatively large (273 W m^-2). Consequently, the associated cloud dissipates due to the absence of water vapor injection and the entrainment of drier air. This is consistent with our preliminary observational analyses of cloud-lead associations that show less boundary layer clouds under high lead flux conditions than under low lead flux conditions. Meanwhile, the net upward IR flux is enhanced due to the slow decay of the plume and cloud. Further simulations will involve realistic lead-width distributions and examine the influences of leads and lead-generated clouds on the Arctic surface energy budget under different atmospheric conditions.