eesti teaduste
akadeemia kirjastus
SINCE 1952
Earth Science cover
Estonian Journal of Earth Sciences
ISSN 1736-7557 (Electronic)
ISSN 1736-4728 (Print)
Impact Factor (2021): 0.811
Evidence for low-level jets caused by coastal baroclinity at the Kurzeme shore of the Baltic Sea; pp. 149–157

Tija Sīle, Juris Seņņikovs, Uldis Bethers

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.


Bergström, H. A. 1992. Climatological Study of Wind Power Potential in the Blekinge Area Using a Meso-γ-scale Higher Order Closure Model. Wind Energy Report WE 92:01. Department of Meteorology, Uppsala University.

Burk, S. D. & Thompson, W. T. 1996. The summertime low-level jet and marine boundary layer structure along the California coast. Monthly Weather Review, 124, 668–686.<0668:TSLLJA>2.0.CO;2

Cui, Z., Tjernström, M. & Grisogono, B. 1998. Idealized simulations of atmospheric coastal flow along the central coast of California. Journal of Applied Meteorology, 37, 1332–1363.<1332:ISOACF>2.0.CO;2

Dee, D. P., Uppala, S. M., Simmons, A. J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M. A., Balsamo, G., Bauer, P. & Bechtold, P. 2011. The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Quarterly Journal of the Royal Meteorological Society, 137, 553–597.

Dudhia, J. 1989. Numerical study of convection observed during the winter monsoon experiment using a mesoscale two-dimensional model. Journal of the Atmospheric Sciences, 46, 3077–3107.<3077:NSOCOD>2.0.CO;2

Gahmberg, M., Savijärvi, H. & Leskinen, M. 2010. The influence of synoptic scale flow on sea breeze induced surface winds and calm zones. Tellus A, 62, 209–217.

Gemmill, W., Katz, B. & Li, X. 2007. Daily Real-time Global Sea Surface Temperature – High Resolution Analysis at NOAA/NCEP. NCEP Off. Note, 260, 39 pp.

Gill, A. E. 1982. AtmosphereOcean Dynamics. Academic Press, New York, 217 pp.

Floors, R., Peña, A. & Gryning, S. E. 2015. The effect of baroclinicity on the wind in the planetary boundary layer. Quarterly Journal of the Royal Meteorological Society, 141, 619–630.

Holton, J. 2004. Dynamic Meteorology. Elsevier Academic Press, 40 pp.

Hong, S. Y., Dudhia, J. & Chen, S. H. 2004. A revised approach to ice microphysical processes for the bulk parameterization of clouds and precipitation. Monthly Weather Review, 132, 103–120.<0103:ARATIM>2.0.CO;2

Hong, S. Y., Noh, Y. & Dudhia, J. 2006. A new vertical diffusion package with an explicit treatment of entrain­ment processes. Monthly Weather Review, 134, 2318–2341.

Hunt, J. C. R., Orr, A., Rottman, J. W. & Capon, R. 2004. Coriolis effects in mesoscale flows with sharp changes in surface conditions. Quarterly Journal of the Royal Meteorological Society, 130, 2703–2731.

Kain, J. S. 2004. The Kain–Fritsch convective parameteri­zation: an update. Journal of Applied Meteorology, 43, 170–181.<0170:TKCPAU>2.0.CO;2

Lebassi, B., Gonzalez, J., Fabris, D., Maurer, E., Miller, N., Milesi, C., Switzer, P. & Bornstein, R. 2009. Observed 1970–2005 cooling of summer daytime temperatures in coastal California. Journal of Climate, 22, 3558–3573.

Lin, Y. L. 2007. Mesoscale Dynamics. Cambridge University Press, Cambridge, 433 pp.

Miller, S. T. K., Keim, B. D., Talbot, R. W. & Mao, H. 2003. Sea breeze: structure, forecasting, and impacts. Reviews of Geophysics, 41, 1-1-1-30.

Mlawer, E. J., Taubman, S. J., Brown, P. D., Iacono, M. J. & Clough, S. A. 1997. Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave. Journal of Geophysical Research: Atmospheres, 102, 16663–16682.

Mu-oz, R. C. & Garreaud, R. 2005. Dynamics of the low-level jet off the west coast of subtropical South America. Monthly Weather Review, 133, 3661–3677.

Nunalee, C. G. & Basu, S. 2014. Mesoscale modeling of coastal low-level jets: implications for offshore wind resource estimation. Wind Energy, 17, 1199–1216.

Persson, C. & Kindell, S. 1981. Nederbördens beroende av den geostrofiska markvinders och den verkliga vindens riktning. Meddelande No. 8, SMHI, Norrköping.

Ranjha, R., Svensson, G., Tjernström, M. & Semedo, A. 2013. Global distribution and seasonal variability of coastal low-level jets derived from ERA-Interim reanalysis. Tellus A, 65, 20412.

Smedman, A. S., Tjernström, M. & Högström, U. 1993. Analysis of the turbulence structure of a marine low-level jet. Boundary-Layer Meteorology, 66, 105–126.

Soomere, T. & Keevallik, S. 2001. Anisotropy of moderate and strong winds in the Baltic Proper. Proceedings of the Estonian Academy of Sciences, Engineering, 7, 35–49.

Steele, C. J., Dorling, S. R., von Glasow, R. & Bacon, J. 2015. Modelling sea-breeze climatologies and interactions on coasts in the southern North Sea: implications for offshore wind energy. Quarterly Journal of the Royal Meteorological Society, 141, 1821–1835.

Stensrud, D. J. 1996. Importance of low-level jets to climate: a review. Journal of Climate, 9, 1698–1711.<1698:IOLLJT>2.0.CO;2

Svensson, N., Bergström, H., Sahlée, E. & Rutgersson, A. 2016. Stable atmospheric conditions over the Baltic Sea: model evaluation and climatology. Boreal Environment Research, 21, 387–404.

Tjernstrom, M. & Grisogono, B. 1996. Thermal mesoscale circulations on the Baltic coast. 1. Numerical case study. Journal of Geophysical Research Atmospheres, 101, 18979–18997.

Tuononen, M., Sinclair, V. A. & Vihma, T. 2015. A climatology of low-level jets in the mid-latitudes and polar regions of the Northern Hemisphere. Atmospheric Science Letters, 16, 492–499.

Verhoef, A. & Stoffelen, A. 2013. Validation of ASCAT Coastal Winds. Technical Report, version 1.5, SAF/OSI/ CDOP/KNMI/TEC/RP/176, Sponsored by EUMETSAT.

Back to Issue