‘Observations and Modelling of Cold-air Advection over Arctic Sea Ice’

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.

Low-Level Jets in the Moscow Region in Summer and Winter Observed with a Sodar Network

“…The experimental studies of LLJs that accompany long-lived wintertime inversions over snow-covered surfaces are few. The LLJs over snow surfaces were studied in the Antarctic (Andreas et al 2000;Anderson 2003;King et al 2008) and in the Arctic (Vihma and Brümmer 2002;Brümmer and Thiemann 2002;Vihma et al 2005). The main parameters of LLJs obtained in the latter studies are similar to those of nocturnal summertime LLJs.…”

Turbulence associated with mountain waves over Northern Scandinavia – a case study using the ESRAD VHF radar and the WRF mesoscale model

“…For example, cloud-top radiative cooling (see e.g. Vihma et al, 2005) is a possible source of turbulence which is likely not captured accurately by our WRF simulations. Records of the cloud cover during our case study exist in the form of allsky photographs during the night hours, from a camera located 20 km east of the radar site which monitors the aurora (http://www.irf.se/allsky/), and in the records of lidar observations from the same site as the radar (K. H. Fricke, personal communication, 2003;Blum et al, 2006).…”

Antarctic local wind dynamics and polynya effects on the Adélie Land coast

“…The model has been applied previously in many studies of katabatic/anabatic, sea/land breeze, and sea ice edge winds (e.g. Savijärvi and Jin, 2011;Savijärvi and Matthews, 2004;Savijärvi et al, 2005;Vihma et al, 2005;Gahmberg et al, 2010); these references and the references therein provide further details of the model.…”