Climatological features of orographic low‐level jets over frobisher bay

Abstract

In this study, based on an analysis of operational hourly surface and 12-hourly upper air data, the seasonal and diurnal climatological features of orographic low-level jets and associated vertical wind shear over Frobisher Bay, southern Baffin Island are discussed. These strong winds are a common phenomenon and fre- quently lead to hazardous flying conditions and hardship on the ground. The influence of the surrounding topog- raphy causes significant channelling of the surface wind at Iqaluit, with prevailing wind directions consequently being from the north-west and south-east. Shifts between the dominant wind directions occur with surface geostrophic winds roughly perpendicular to the valley axis, indicating the controlling influence of large-scale pressure gradients and vertical momentum transfer, in combination with local channelling effects, on the forcing of weak and strong surface winds. Following seasonal shifts in the large-scale surface pressure distribution, there is a shift in prevailing wind direction from north-west in winter to south-east in summer. The importance of the topography for the forcing of boundary-layer flows is also evident in the presence of speed maxima at the typical ridge-top level and below, associated with strong along-valley surface winds. The adjustment of the channelled boundary-layer flow to the large-scale flow conditions above the topography frequently leads to strong vertical wind shear and low-level turbulence. Distinct characteristics of weak and strong surface winds from different directions at Iqaluit are identified, including differences in vertical wind shear and the relationship of these winds to the surface geostrophic wind. RÉSUMÉ (Traduit par la rédaction) Dans cette étude, basée sur une analyse des données opérationnelles de surface horaires et aérologiques aux 12 heures, nous discutons des caractéristiques climatologiques saisonnières et journalières des courants-jets orographiques à basse altitude et du cisaillement vertical du vent qu'ils produisent dans la baie Frobisher, dans le sud de l'île de Baffin. Ces vents forts sont un phénomène courant et occasionnent fréquemment des conditions de vol dangereuses et des difficultés au sol. La topographie environnante est souvent à l'origine d'un important effet de canal sur le vent de surface à Iqaluit et c'est pourquoi les directions dominantes du vent sont le nord-ouest et le sud-est. Les sautes entre les directions