Polar lows in the Labrador Sea. A case study

Abstract

In this paper, we will describe our analysis of a polar low event that occurred in the Labrador Sea during the winter of 1992. As there are unfortunately no in‐situ observations of this event, we will rely on satellite data as well as the high‐resolution objective analaysis from the ECMWF to document the environment in which the low developed and the structure of the low itself. We will show that the polar low developed during a cold air outbreak that was precipitated by the passage of an intense synoptic‐scale low. The polar low appears to have developed along a linear cloud feature as the result of an interaction between a low‐level diabatically induced potential vorticity anomaly and an upper‐level potential vorticity anomaly that propagated into the area from the Canadian Arctic. We will also show that with the TOMS and TOVS retrievals for total column ozone, we are able to identify a signature of the upper‐level potential vorticity anomaly. In its mature state, we will show that there were very strong winds, and as a result large fluxes of sensible and latent heat, associated with the polar low. In summary, the 1992 Labrador Sea polar low provides one with an excellent opportunity to study air‐sea interactions and the coupling between the troposphere and stratosphere. The realization that the strong heating of the atmosphere and the concomitant cooling of the ocean associated with these storms may be sufficient to initiate downwelling events in the ocean may represent a hitherto undocumented link between the fast and slow climate systems that deserves further attention.

Polar Mesoscale Cyclones in the Northeast Atlantic: Comparing Climatologies from ERA-40 and Satellite Imagery

“…With the advent of satellite imagery it has become apparent that polar mesocyclones are frequent in both hemispheres of the subarctic Atlantic and Pacific Oceans (see, e.g., Businger 1987;Carleton and Carpenter 1990;Harold et al 1999a). In the North Atlantic, vortices are commonly observed over both the Labrador Sea (Moore et al 1996;Rasmussen et al 1996) and the Greenland Sea (Harold et al 1999a;Shapiro et al 1987;Nordeng and Rasmussen 1992) in regions where intense buoyancy loss due to heat exchange with the overlying atmosphere and sea ice formation are important for initiating localized violent open-ocean convection that mixes the surface waters to great depths, given suitable preconditioning (Marshall and Schott 1999;Wadhams et al 2002). The water mass modifications that occur in these regions due to convection appear to be the main Northern Hemisphere control on the strength of the thermohaline circulation, and thus have far-reaching effects on the climate system (Marshall and Schott 1999).…”

A global climatology of favourable conditions for polar lows

“…Many other studies have also found that UPV anomalies are an integral factor in PL developments (e.g. Montgomery and Farrell, 1992;Mailhot et al, 1996;Moore et al, 1996;Bresch et al, 1997;Browning and Dicks, 2001;Moore and Vachon, 2002).…”

Report of a Workshop on Theoretical and Observational Studies of Polar Lows” of the European Geophysical Society Polar Lows Working Group

“…While in its early years polar low research was mainly focused on the areas of European polar seas, polar MCs are now investigated over almost all oceans affected by cold air outbreaks in the Northern Hemisphere (NH) and also in the Southern Hemisphere (SH). For the NH, research has been conducted, for example, for the Japan Sea (Ninomiya 1991;Matsumoto et al 1982); the Bering Sea, the Gulf of Alaska, and the North Pacific (Businger and Baik 1991;Businger 1987;Reed 1979); the Labrador Sea, Hudson Bay, and the Davis Strait (Roch et al 1991;Rasmussen et al 1996;Moore et al 1996); and also for the areas of the Greenland Sea, the Norwegian Sea, and the Barents Sea (e.g., Lystad 1986;Businger 1985;Rasmussen 1985).…”