Dynamical processes related to cyclone development near Greenland

Abstract

An unusual cyclone that moved over Greenland and caused blizzard conditions over eastern Greenland and northern Iceland on 20-21 September 2003 is investigated. Numerical simulations are conducted to assess the role of Greenland's orography for the development, as well as to evaluate the significance of other factors such as latent heating and sea surface temperature (SST). The simulations reveal that the cyclone evolution was crucially dependent on an interaction between the background flow and the orography of Greenland. When the orography is removed, a deep, well organized baroclinic low develops rapidly and moves eastward at 75°N. Conversely, in the control run, which is similar to the analyses, the evolution of the (primary) baroclinic low is greatly suppressed by the orographic retardation of the warm air ahead of and the cold air behind the low. Instead, a secondary low developing off Greenland's east coast at 68°N intensifies due to a coupling between an approaching upper level PV-anomaly and a lower level PV-anomaly generated from lee effects. This secondary low, absent in the run without orography, then moves eastward and causes the extreme weather conditions that were observed. Inversion of selected potential vorticity anomalies lends support to the above explanation. Further sensitivity experiments show that latent heating contributes about half of the deepening of the low, while SST amounts contribute much less.