Air‐sea interaction over a thermal marine front in the Denmark Strait

Abstract

An investigation was conducted into air‐sea interaction in the Denmark Strait, where a distinct thermal front separates warm North Atlantic water from the cold East Greenland Current. The field data consisted of ship weather station data and rawinsonde soundings from R/V Aranda's expedition in August‐September 1993. The surface energy balance differed drastically between the warm and cold side of the front (net fluxes of 95 W m−2 upward and 82 W m−2 downward, respectively). The difference resulted mostly from the contradictory turbulent fluxes. The air temperature, humidity and wind speed showed more variation on the warm side of the front. Lower wind speeds were observed on the cold side. The cross‐frontal differences in the air temperature and wind speed were largest during front‐parallel flow, but those in the sensible and latent heat flux were largest during cross‐frontal flow. During cases of air advection across the front, the modification in the air temperature was strongest with a low wind speed. Downwind of the front, the sensible heat flux strongly depended on the south‐north wind component. The rawinsonde data revealed temperature inversions and low‐level jets. The wind profile was affected by the combined effects of baroclinity, surface layer stability, and stratification through the atmospheric boundary layer. The surface heterogeneity caused by the sea surface temperature front resulted in the Schmidt paradox: the area‐averaged sensible heat flux was upward, while the area‐averaged air temperature exceeded the area‐averaged surface temperature. A mosaic method, extended by estimates of the local wind speed over the warm and cold water side, was applicable to parameterizing the area‐averaged sensible heat flux.