Impact of Laptev Sea flaw polynyas on the atmospheric boundary layer and ice production using idealized mesoscale simulations

Abstract

The interaction between polynyas and the atmospheric boundary layer is examined in the Laptev Sea using the regional, non-hydrostatic Consortium for Small-scale Modelling (COSMO) atmosphere model. A thermodynamic sea-ice model is used to consider the response of sea-ice surface temperature to idealized atmospheric forcing. The idealized regimes represent atmospheric conditions that are typical for the Laptev Sea region. Cold wintertime conditions are investigated with sea-ice–ocean temperature differences of up to 40 K. The Laptev Sea flaw polynyas strongly modify the atmospheric boundary layer. Convectively mixed layers reach heights of up to 1200 m above the polynyas with temperature anomalies of more than 5 K. Horizontal transport of heat expands to areas more than 500 km downstream of the polynyas. Strong wind regimes lead to a more shallow mixed layer with strong near-surface modifications, while weaker wind regimes show a deeper, well-mixed convective boundary layer. Shallow mesoscale circulations occur in the vicinity of ice-free and thin-ice covered polynyas. They are forced by large turbulent and radiative heat fluxes from the surface of up to 789 W m−2, strong low-level thermally induced convergence and cold air flow from the orographic structure of the Taimyr Peninsula in the western Laptev Sea region. Based on the surface energy balance we derive potential sea-ice production rates between 8 and 25 cm d−1. These production rates are mainly determined by whether the polynyas are ice-free or covered by thin ice and by the wind strength

Effects of Arctic Sea Ice Decline on Weather and Climate: A Review

“…Effects of Arctic leads and polynyas on the atmospheric boundary layer (ABL) have been addressed in numerous experiments applying numerical weather prediction (NWP) models, large-eddy simulation models, and process models for ABL dynamics (e.g., Ledley 1988;Vihma 1995;Esau 2007;Lüpkes et al 2008aLüpkes et al , b, 2012Ebner et al 2011). These studies have yielded a better understanding of various processes: the magnitude of turbulent fluxes of sensible and latent heat, the effects on air temperature and humidity, formation of sea smoke, the rise of a heat plume under variable background stratification, and the recapture of part of the heat by sea ice downwind of the lead/polynya, as well as on the effect of thin ice on the lead/polynya surface.…”

Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review

“…On the basis of airborne observations and high-resolution modelling, Lüpkes et al (2008bLüpkes et al ( , 2012b concluded that convection over 1-2 km wide leads reached altitudes of 50-300 m depending on the boundary layer structure on the upstream side of leads. On the basis of aircraft in situ, drop sonde, and lidar observations, Lampert et al (2012) observed that over areas with many leads, the potential temperature decreased with height in the lowermost 50 m and then was nearly constant due to convective mixing up to the height of 100-200 m. When the leads were frozen and their fraction was small, however, an SBL extended up to a height of 200-300 m. Ebner et al (2011) showed in a modelling study that convective plumes generated over the Laptev Sea polynya influence atmospheric turbulence even 500 km downstream of the polynya, and Hebbinghaus et al (2006) found that cyclonic vortices can be generated or intensified over polynyas due to convective processes. Such processes over large polynyas may be important with respect to the drastic changes in sea ice cover observed in recent years.…”

“…Marcq and Weiss, 2012) and on coupled atmosphere-sea-ice-ocean modelling (e.g. Ebner et al, 2011). Challenges remain in the high sensitivity of winter air temperatures to sea ice concentration (Lüpkes et al, 2008a;Tetzlaff et al, 2013) in the representation of new, thin ice in atmospheric models (Tisler et al, 2008) and in the interaction of convective plumes with capping stable or near-neutral environments (Lüpkes et al, 2008b).…”

Brief Communication: Trends in sea ice extent north of Svalbard and its impact on cold air outbreaks as observed in spring 2013

“…It is also interesting to consider the impact of polynyas on local atmospheric temperatures (e.g., Raddatz et al, 2013;Ebner et al, 2011;Fiedler et al, 2010). Using ERA-Interim data, Onarheim et al (2014) found an air temperature increase of 7 K in the Whaler's Bay polynya between 1979 and 2012 associated with the observed decrease in sea ice cover.…”