Simulating Wind Channelling over Frobisher Bay and its Interaction with Downslope Winds during the 7-8 November 2006 Wind Event

摘要

Previous observational studies have identified wind channelling over Frobisher Bay induced by pressure fields associated with cyclones as the main cause for the occurrence of strong and sustained surface winds at Iqaluit. The wind event of 7-8 November 2006, when a surface cyclone moved over the Labrador Sea, is representative of many such occurrences. Our simulations of the event with the Global Environmental Multiscale -Limited Area Model (GEM-LAM 2.5 km) show an almost simultaneous development of wind channelling over Frobisher Bay and of downslope winds over the lee slopes of Hall Peninsula, as well as their interaction. The winds are caused by the passage of the same cyclone, but they advect different air masses. The channelled wind is initiated by a barrier jet generated as a result of the low-level blocking of northeasterly winds by steep orography near the head of the bay. Later, it intensifies, while being driven primarily by large-scale pressure gradients. The cross-bay development of the channelled wind against the downslope wind over the lee slopes of Hall Peninsula explains the shift in surface wind direction and the high surface wind speeds recorded at Iqaluit. Some of the findings are also supported by data from radiosondes launched at Iqaluit. A short sensitivity study shows the beneficial effect of a distributed orographic drag parametrization on the near-surface winds. The impact of using a modified Lenderink-Holtslag mixing length and of increasing the vertical resolution near the surface are also addressed.