Orographic influence of east Greenland on a polar low over the Denmark Strait

Abstract

We present a numerical study of a polar low which hit western Iceland in January 2007, with heavy snowfall and mean wind speeds exceeding 20 m s −1 in several locations. The operational models at the time captured the polar low formation rather well, but there was a large spread in their predictions of the subsequent evolution and track of the polar low. The objective of this study is to investigate possible orographic forcing from Greenland as a trigger for the polar low development. In addition to an analysis of surface observations and satellite imagery, sensitivity studies using HIRLAM were carried out with various degradations of Greenland's orography, as well as with modifications to the sea-surface temperature (SST), surface roughness and the data assimilation scheme. Despite the presence of an upper-level trough and weak static stability in all the simulations, the polar low development was found to be very sensitive to the presence of the high mountains of eastern Greenland. Whereas the control run captured well the main features of the polar low, simulations with parts of east Greenland's orography removed gave a southward-displaced polar low which moved rapidly eastward, resulting in substantially underestimated nearsurface winds and snowfall amounts. Setting the orographic heights over all of Greenland to zero led to the complete disappearance of the polar low. On the other hand, artificially increasing the SST by 4 K in the Denmark Strait, reducing the orographic roughness or replacing the four-dimensional variational assimilation scheme (4D-Var) by 3D-Var had only a small effect on the polar low. We suggest that hitherto unreported interactions between the high mountains of east Greenland and polar low development over the Denmark Strait may be more important for polar low formation than katabatic flow from valleys in east Greenland that was highlighted in earlier studies.

Phase‐locking of a rapidly developing extratropical cyclone by Greenland's orography

“…Ólafsson et al, 2005) propagating downstream towards Scandinavia and the British Isles on the subsequent days. More investigations are needed to reveal the cause of these model errors, but the present study, as well as, for example, the investigation by Kristjánsson et al (2009), indicate that model forecasts of cyclogenesis in the region off east Greenland are extremely sensitive to the orography of Greenland.…”

Structure of a shear‐line polar low

“…In the satellite image at 1220 UTC (Figure ), when the PL was centred at 73°N, 5°E, it can be pinpointed as a beak‐like signature of bright (and hence, deep convective) cloud bands. The large‐scale circulation during the PL event is common in this region: for example, the PL of 3–4 March 2008 developed in a similar background (Kristjánsson et al, ).…”

Recent advances in polar low research: current knowledge, challenges and future perspectives

“…3). In the North Atlantic, PLs form in the Nordic Seas 1 (e.g., Føre et al, 2011;Wu, 2021), the Denmark Strait (e.g., Kristj ansson et al, 2011b), the Labrador Sea (e.g., Moore and Vachon, 2002), the Davis Only the data used to identify PLs is listed, even though some authors also used reanalyses to study the large-scale circulation associated with PL development.…”

“…Surface observations from land meteorological stations have been used to study PLs affecting Norway (e.g., Hallerstig et al, 2021), Iceland (Kristj ansson et al, 2011b and Japan (Fu et al, 2004), as well as more isolated regions such as the Hudson Bay (Albright et al, 1995;Gachon et al, 2003) and Kamchatka (Businger, 1987). Although upper-air stations are particularly sparse in high latitudes and the observation frequency is much lower than that of surface stations, these type of observations have also been used to study PLs (e.g., Kristj ansson et al, 2011b). Observations from maritime stations provide not only atmospheric variables such as MSLP, wind speed and temperature, but also SST and significant wave height associated with PLs (e.g., Rojo et al, 2019).…”

“…In the case of Greenland's coasts, the influence of the Coriolis effect is limited since the flow is canalised by the fjords and valleys (Serreze and Barry, 2014). This double effect of topographythe generation of katabatic winds and the imposition of restrictions to their flowis evident in the study of Kristj ansson et al (2011b), who conducted sensitivity experiments to study the impact of Greenland's topography on the development of a PL observed over the Denmark Strait. The PL did not form in the simulation where the whole Greenland surface was located at sea level, and therefore in absence of katabatic winds.…”