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Global distribution and seasonal variability of coastal low-level jets derived from ERA-Interim reanalysis
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
2013 (English)In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 65, 20412- p.Article in journal (Refereed) Published
Abstract [en]

A low-level wind maximum is often found over the oceans near many coasts around the world. These Coastal Low-Level Jets (CLLJs) play an important role in the coastal weather and have significant impacts on regional climate and ecology as well as on a number of human activities. The presence of CLLJs is related to various local circumstances such as land-sea temperature contrasts, upwelling, coastal terrain, orientation of the coast, etc., but also to the large-scale atmospheric dynamics. This makes studies of CLLJs not only interesting but also challenging.

In the present study, based on ERA-Interim reanalysis data, the global distribution, spatio-temporal structure, and the seasonal variability of CLLJs are documented. Seasonal data from 1980 to 2011 are used to identify areas where CLLJs are frequently found in the lowest 2 km, following criteria based on the vertical profiles of wind speed and temperature. The results are analyzed to highlight the fundamental aspects and distinctive features of the CLLJs across the globe, including their occurrence rate, jet height, wind-speed maximum and horizontal extent.

Global maps of CLLJs are constructed for the summer and winter seasons. The west coasts of North America, the Iberian Peninsula, north-western Africa and the south-eastern coast of the Arabian Peninsula make up the northern-hemispheric CLLJ regions, while the west coasts of South America, Australia and southern Africa comprise the south-hemispheric equivalents. The existence and characteristics of CLLJs along the southern coast of Oman and the western coast of the Iberian Peninsula regions are also discussed, not fully envisaged before in the context of CLLJs. The highest occurrence of CLLJs is found during the summer in both hemispheres, and the coast of Oman has the globally highest CLLJ frequency, with also the highest maximum wind speeds. The most commonly found CLLJ has a maximum wind speed between 9 and 15 m s-1, and occurs at heights between 500 and 700 m a.s.l.

Place, publisher, year, edition, pages
2013. Vol. 65, 20412- p.
Keyword [en]
coastal low-level jets, global climatology, ERA-Interim, ECMWF, low-level jets
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-93000DOI: 10.3402/tellusa.v65i0.20412ISI: 000322764200001OAI: oai:DiVA.org:su-93000DiVA: diva2:643694
Note

AuthorCount: 4;

Funding Agencies:

Higher Education Commission of Pakistan

Available from: 2013-08-28 Created: 2013-08-28 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Global Climatology and Regional Modeling of Coastal Low-Level Jets
Open this publication in new window or tab >>Global Climatology and Regional Modeling of Coastal Low-Level Jets
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Localized coast-parallel wind-speed maxima at low altitude, known as coastal low-level jets (CLLJs) have important ramifications to the coastal climate and a number of human activities. This thesis documents the existence of the CLLJs around the globe including their mesoscale structure, dynamics and spatio-temporal variability.

A CLLJ-detection algorithm is presented, which identifies their occurrence and can distinguish between CLLJs and other types of low-level wind maxima. The method is based on vertical profiles of wind speed and temperature, and is applied to the ERA-Interim reanalysis dataset to obtain a 31-year-CLLJ climatology. Coastal jets are found to exist on many continents, including the previously undocumented CLLJs along the coasts of Oman and Iberian Peninsula. The study highlights a pronounced seasonality among the CLLJ regions and links to large-scale flow. The Oman coastal jet exhibits the globally highest CLLJ frequency (~70%).

The thesis also includes detailed analysis of the Oman and Iberian CLLJs using high-resolution regional modeling by dynamical downscaling. The Oman CLLJ is located close to the coast, at low altitude and is forced primarily by the coastal baroclinicity, unlike the previously known Somali-Jet, driven by the Asian summer-monsoon circulation. Although on a large-scale, the Oman CLLJ and the Somali jet appear to merge, the high-resolution simulations clearly illustrate that these are two distinctive phenomena with different forcing. The 20-year-climatology of the Iberian CLLJ reveals a strong seasonality with large inter-annual variations within spring, summer and autumn seasons while the maximum CLLJ frequency is found during the summer. Regional modeling studies were able to resolve detailed mesoscale structure of CLLJs, not visible from the coarse resolution reanalysis climatology. It is concluded that 6-km horizontal resolution can reproduce most of the small-scale features in a reasonable manner.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2013. 39 p.
Keyword
coastal low-level jets, climatology, regional modeling, boundary layer
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-93002 (URN)978-91-7447-743-6 (ISBN)
Public defence
2013-10-07, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper 4: Manuscript.

Available from: 2013-09-16 Created: 2013-08-28 Last updated: 2013-09-04Bibliographically approved

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