Low-Level Jets over Utö, Finland, Based on Doppler Lidar Observations

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Tuononen , M , O'Connor , E J , Sinclair , V A & Vakkari , V 2017 , ' Low-Level Jets over Utö, Finland, Based on Doppler Lidar Observations ' , Journal of Applied Meteorology and Climatology , vol. 56 , no. 9 , pp. 2577-2594 . https://doi.org/10.1175/JAMC-D-16-0411.1

Title: Low-Level Jets over Utö, Finland, Based on Doppler Lidar Observations
Author: Tuononen, Minttu; O'Connor, Ewan J.; Sinclair, Victoria A.; Vakkari, Ville
Contributor organization: Department of Physics
Date: 2017-09
Language: eng
Number of pages: 18
Belongs to series: Journal of Applied Meteorology and Climatology
ISSN: 1558-8424
DOI: https://doi.org/10.1175/JAMC-D-16-0411.1
URI: http://hdl.handle.net/10138/308169
Abstract: Over two years of meteorological observations from Utö, a small island in the Finnish outer archipelago in the Baltic Sea, were used to investigate the occurrence and characteristics of low-level jets (LLJs) and the diurnal and seasonal variations in these properties. An objective LLJ identification algorithm that is suitable for high-temporal-and-vertical-resolution Doppler lidar data was created and applied to wind profiles obtained from a combination of Doppler lidar data and two-dimensional sonic anemometer observations. This algorithm was designed to identify coherent LLJ structures and requires that they persist for at least 1 h. The long-term mean LLJ frequency of occurrence at Utö was 12%, the mean LLJ wind speed was 11.6 m s−1, and the vast majority of identified LLJs occurred below 150 m above ground level. The LLJ frequency of occurrence was much higher during summer (21%) and spring (18%) than in autumn (8%) and winter (3%). During winter and spring, the LLJ frequency of occurrence is evenly distributed throughout the day. In contrast, the LLJ frequency of occurrence peaks at night (1900–0100 UTC) during summer and during the evening hours (1700–1900 UTC) in autumn. The highest and strongest LLJs come from the southwest, which is also the predominant LLJ direction in all seasons. LLJs below 100 m are common in spring and summer, are weaker, and do not show a strong directional dependence.
Subject: 114 Physical sciences
Peer reviewed: Yes
Rights: cc_by_nc_sa
Usage restriction: openAccess
Self-archived version: publishedVersion

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