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Modification of the Baltic Sea wind field by land-sea interaction
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.ORCID iD: 0000-0003-2857-3700
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.ORCID iD: 0000-0001-7656-1881
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2019 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 6, p. 764-779Article in journal (Refereed) Published
Abstract [en]

The wind and turbulence fields over a small, high‐latitude sea are investigated. These fields are highly influenced by the proximity to the coast, which is never more than 200 km away. Simulations with the WRF model over the Baltic Sea are compared with a simplified, stationary wind model driven by the synoptic forcing. The difference between the models is therefore representative of the mesoscale influence. The results show that the largest wind‐field modifications compared with a neutral atmosphere occur during spring and summer, with a mean monthly increase of up to approximately 1 ms−1 at typical hub heights and upper rotor area (120‐170 m height) in the WRF model. The main reason for this is large‐scale low‐level jets caused by the land‐sea temperature differences, likely increasing in strength due to inertial oscillations. These kind of events can be persistent for approximately 12 hours and cover almost the entire basin, causing wind speed and wind shear to increase considerably. The strongest effect is around 2000 to 2300 local time. Sea breezes and coastal low‐level jets are of less importance, but while sea breezes are mostly detected near the coastline, other types of coastal jets can extend large distances off the coast. During autumn and winter, there are fewer low‐level jet occurrences, but the wind profile cannot be explained by the classical theory of the one‐dimensional model. This indicates that the coastal environment is complex and may be affected by advection from land surfaces to a large degree even when unstable conditions dominate.

Place, publisher, year, edition, pages
2019. Vol. 22, no 6, p. 764-779
Keywords [en]
BalticSea, coastalmeteorology, low-leveljet, seabreeze
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
URN: urn:nbn:se:uu:diva-348369DOI: 10.1002/we.2320ISI: 000465869400004OAI: oai:DiVA.org:uu-348369DiVA, id: diva2:1197308
Funder
Swedish Energy Agency, 37279-1Swedish Research Council, 2015-06020Available from: 2018-04-12 Created: 2018-04-12 Last updated: 2019-06-18Bibliographically approved
In thesis
1. Mesoscale Processes over the Baltic Sea
Open this publication in new window or tab >>Mesoscale Processes over the Baltic Sea
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of this thesis is to study mesoscale processes above the Baltic Sea, which is a small, semi-enclosed sea where land-sea interaction may have a large impact on the offshore conditions. It is only the last tens of years that offshore research has become more popular, and one reason for this is the increasing offshore wind energy, which poses the need for accurate estimates of wind speed and turbulence conditions in the marine environment. In this thesis a range of mesoscale processes over the Baltic Sea are studied using the mesoscale model WRF (Weather Research and Forecasting) and different types of measurements.It is found that mesoscale effects are largest during spring and summer, when stable conditions dominate. The whole Baltic sea surface is affected by warm-air advection and low-level jets. There is very little spatial variation in seasonally averaged fields, which shows that the extent of mesoscale effects is several hundred kilometres. Wind speed and temperature profiles can thus not be described solely by the local conditions even far out over sea surface. Sea breezes are relatively unimportant for modyfing the seasonally averaged wind fields, but other types of low-level jets have a large influence. Results show that most of the low-level jets are likely created by inertial oscillations initiated when air flows across a coastline from the convective land surface to stable sea surface.Evaluation of the model shows that the discrepancies are largest during very stable conditions, but are also quite large during very unstable. The reasons for this are discussed.Several cases of boundary layer rolls are investigated using measurements and simulations and it is found that the rolls are likely created over the convective mainland and advected out over the stable sea surface, which may be a new finding that has not been reported before.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 54
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1668
Keywords
Boundary layer, Baltic Sea, stable conditions, low-level jet, sea breeze, boundary layer rolls, mesoscale effects, WRF, LIDAR
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-348417 (URN)978-91-513-0331-4 (ISBN)
Public defence
2018-06-05, Hambergssalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2018-05-14 Created: 2018-04-12 Last updated: 2018-10-08

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