Evidence for low-level jets caused by coastal baroclinity at the Kurzeme shore of the Baltic Sea

10.3176/earth.2018.11

Tija Sile；Juris Sennikovs；Uldis Bethers

geostrophic wind ； sea breeze ； low-level jet ； coastal low-level jet ； Baltic Sea ； Kurzeme.

Proceedings of the Estonian Academy of Sciences. Geology

67卷2期（2018 / 06 / 20）

149 - 157

英文

Observational wind direction data from meteorological stations along the Kurzeme coast of the Baltic Sea were analysed for the years 1966-2015. The data show that during the daytime in the warm season the winds that aligned with the coastline (northern and southwestern) are more frequent than those from any other direction. A case study was carried out using the Weather Research and Forecast Numerical Weather Prediction model and Advanced Scatterometer wind data to investigate the mechanisms causing the increased frequency of northern winds. The results show a coast-parallel wind flow over the sea that extends for 50 km from the shore and several hundred metres above the sea level. It can be classified as a low-level jet - an air flow where the vertical wind speed distribution has a maximum in the lowest kilometre of the atmosphere. The flow is geostrophic and can be described using the thermal wind expression where wind shear is linked with temperature differences over the coast, therefore allowing classifying the event as a coastal low-level jet.