Extended Abstract (308K)5.3
Flow in the Lee of Greenland-size mountains
G. N. Petersen, Univ. of Oslo, Oslo, Norway and Univ. of Iceland, Iceland; and H. Ólafsson and J. E. Kristjánsson
In order to get a better understanding of Greenland's impact on airflow over the North Atlantic a series of idealized simulations was conducted. Three-dimensional flow over an elliptical mountain of aspect ratio 5 was explored keeping the upstream profile of wind and stability constant and neglecting surface friction. The Rossby number was 0.4 and the nondimensional mountain height varied from 1.0 to 6.0. Three nondimensional parameters were calculated, the absolute maximum pressure perturbation at sea level, the absolute maximum perturbation of the geopotential at the 500 hPa level and the potential vorticity integrated over a finite volume. All the parameters increased with increasing nondimensional mountain height, with no signs of abrupt changes at the shift from non-blocked to blocked flow. The potential vorticity produced by the mountain is accumulated in vortices in the wake, decreasing the height of the 500 hPa level as well as the sea level pressure. The geopotential height deficit downstream of the mountain results in a larger gradient to the south of the wake.
This process can explain how Greenland may affect cyclones moving far outside the mountain wake. An example from FASTEX shows that a cyclone moving from the southwest towards Scotland becomes shallower and slower if the Greenland topography is removed.
Consequently, coarse resolution models with poor representation of Greenland's orography can be expected to have systematic errors in predicting cyclones moving far to the southeast of Greenland towards central or Northern Europe.
Session 5, Orographically Modified Cyclone Evolution
Tuesday, 18 June 2002, 8:00 AM-9:00 AM
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