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Climatology of Iberia Coastal Low-Level Wind Jet: WRF High Resolution Results
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2014 (English)In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 66, 22377- p.Article in journal (Refereed) Published
Abstract [en]

Coastal low level jets are a low-tropospheric wind feature driven by the pressure gradient produced by a sharp contrast between high temperatures over land and lower temperatures over the sea. This contrast between the cold ocean and the warm land in the summer is intensified by the impact of the coast-parallel winds on the ocean generating upwelling currents, sharpening the temperature gradient close to the coast, and giving rise to strong baroclinic structures at the coast.

During summertime the Iberian Peninsula is often under the effect of the Azores High and a thermal low pressure system inland, leading to a seasonal wind, in the west coast, called the Nortada (northerly wind).  This study presents climatology of the costal low level jet off the west coast of the Iberian Peninsula, based on a high resolution (9 km) downscaling data produced using the WRF mesoscale model, forced by 20 years of ERA-Interim reanalysis (1989-2008). The simulation results show that the jet hourly frequency of occurrence in summer is above 30%, and decreases for about 10% in spring and autumn. The monthly frequencies of occurrence can reach higher values, around 40% in summer months, and reveal large inter-annual variability in all the three seasons. In summer, on a daily basis, the low level jet is present in almost 70% of the days. The jet wind direction is mostly from north-northeasterly, and occurs more persistently in three areas, where the interaction of the jet flow with local capes and headlands are more pronounced. The jet occurs at heights between 300 and 400 m, and its speed has a median around 15 m s-1, reaching maximum speeds of 25 m s-1.

Place, publisher, year, edition, pages
2014. Vol. 66, 22377- p.
Keyword [en]
coastal low-level jets, Iberia, WRF, high resolution modeling
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-93149DOI: 10.3402/tellusa.v66.22377ISI: 000329869400001OAI: oai:DiVA.org:su-93149DiVA: diva2:645425
Available from: 2013-09-04 Created: 2013-09-04 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)
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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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