‘Observations and Modelling of Cold-air Advection over Arctic Sea Ice’ |
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Authors: | Email author" target="_blank">Timo?VihmaEmail author Christof?Lüpkes J?rg?Hartmann Hannu?Savij?rvi |
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Institution: | (1) Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland;(2) Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany;(3) Division of Atmospheric Sciences, Department of Physical Sciences, University of Helsinki, Finland |
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Abstract: | Aircraft observations of the atmospheric boundary layer (ABL) over Arctic sea ice were made during non-stationary conditions
of cold-air advection with a cloud edge retreating through the study region. The sea-ice concentration, roughness, and ABL
stratification varied in space. In the ABL heat budget, 80% of the Eulerian change in time was explained by cold-air advection
and 20% by diabatic heating. With the cloud cover and inflow potential temperature profile prescribed as a function of time,
the air temperature and near-surface fluxes of heat and momentum were well simulated by the applied two-dimensional mesoscale
model. Model sensitivity tests demonstrated that several factors can be active in generating unstable stratification in the
ABL over the Arctic sea ice in March. In this case, the upward sensible heat flux resulted from the combined effect of clouds,
leads, and cold-air advection. These three factors interacted non-linearly with each other. From the point of view of ABL
temperatures, the lead effect was far less important than the cloud effect, which influenced the temperature profiles via
cloud-top radiative cooling and radiative heating of the snow surface. The steady-state simulations demonstrated that under
overcast skies the evolution towards a deep, well-mixed ABL may take place through the merging of two mixed layers one related
to mostly shear-driven surface mixing and the other to buoyancy-driven top-down mixing due to cloud-top radiative cooling. |
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Keywords: | Arctic Cloud-top radiative cooling Cold-air advection Sea ice Surface fluxes |
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