![]() The Maud Rise Polynya has been interpreted as the result of an interaction between the background flow and the Maud Rise, a seamount that rises to a depth of 2000 m (e.g., Gordon and Haxby 1990). 2004), and Ekman-induced upwelling of warm waters ( Prasad et al. More recent studies suggest that the polynya may have been forced by synoptic atmospheric variability instead, with transient low pressure systems causing both a divergence of sea ice transport ( Arbetter et al. Comiso and Gordon (1996) argue that the Cosmonaut Polynya results from the upwelling of warm water induced by vortex stretching, which is required to balance the enhanced shear that develops when Cape Ann forces the westward Antarctic Coastal Current northward onto the eastward Antarctic Circumpolar Current. Smaller open-ocean polynyas like the Maud Rise and Cosmonaut Polynya are in general more transient (e.g., Comiso and Gordon 1987). If so, the absence of the Weddell Polynya since that time would have to be understood as representing a significant regime shift that would be convolved with other changes involving deep waters today (e.g., Gordon 2014). (2014) argue that the Weddell Polynya may have previously occurred before its mid-1970s observation and subsequent disappearance, in particular around 1960, implying that deep convection may have been a natural mode of ventilation before the mid-1970s. 2007), and triggered by ocean–topography interaction at Maud Rise ( Holland 2001). 1981 Gordon 1982) it may have been preconditioned by anomalous atmospheric conditions associated with a prolonged negative phase of the southern annular mode ( Gordon et al. This polynya was associated with deep convection that tapped into the heat of the relatively warm Weddell Sea Deep Water, which is modified Circumpolar Deep Water supplied by the Weddell Gyre ( Martinson et al. The most spectacular example is the Weddell Polynya, a large persistent polynya that was observed in the mid-1970s, but has not appeared since ( Zwally and Gloersen 1977 Carsey 1980). Open-ocean polynyas are more enigmatic, as they require an ocean heat source to keep the polynya ice free. Polynyas also often sustain high levels of biological productivity (e.g., Smith and Gordon 1997 Arrigo and Van Dijken 2003).Ĭoastal polynyas are a ubiquitous feature of the Antarctic coastal environment, as in many places cold katabatic winds push newly formed sea ice away from the land, keeping the coastal waters virtually ice free (e.g., Adolphs and Wendler 1995). 1985), the most voluminous water mass in the World Ocean ( Johnson 2008). Antarctic polynyas are thought to play a key role in the formation of Antarctic Bottom Water (AABW Zwally et al. They facilitate a strong heat exchange between the atmosphere and ocean, and often feature intense sea ice production. ![]() Polynyas are areas of open water enclosed by the seasonal ice pack (and oftentimes the coast). Surface air pressure anomalies over the polynya are only found to be significant when cold, dry air masses strike over the polynya (i.e., in the case of southerly winds). The strongest regional impacts are found when northeasterly winds cross the polynya and interact with katabatic winds. Impacts are found to be sensitive to the synoptic wind direction. Also, in this model, enhanced longwave radiation emitted from the warmer surface of polynyas is balanced by stronger downwelling fluxes from the thicker cloud deck. Although the lower albedo of polynyas significantly increases the net shortwave absorption, the enhanced cloud brightness tempers this increase by almost 50%. In particular, it is found that clouds over polynyas are optically thicker and higher than clouds over sea ice during nonpolynya years. The results indicate significant local impacts on turbulent heat fluxes, precipitation, cloud characteristics, and radiative fluxes. This has been pursued here by investigating the seasonal cycle of differences of surface and air-column variables between polynya and nonpolynya years. This provides an ideal opportunity to study the polynya’s impact on the overlying and surrounding atmosphere. While coarser-resolution versions of CESM generally do not produce open-ocean polynyas in the Southern Ocean, they do emerge and disappear on interannual time scales in the synoptic-scale simulation. In this paper the atmospheric response to an open-ocean polynya in the Southern Ocean is studied by analyzing the results from an atmospheric and oceanic synoptic-scale resolving Community Earth System Model (CESM) simulation.
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