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 pr...
| Published in: | Quarterly Journal of the Royal Meteorological Society |
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| Main Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Wiley
2011
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1002/qj.831 https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fqj.831 https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.831 |
| Summary: | 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 near‐surface 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. Copyright © 2011 Royal Meteorological Society |
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