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The Role of the Meridional Sea Surface Temperature Gradient in Controlling the Caribbean Low-Level Jet.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Costa Rica, Ctr Geophys Res CIGEFI, San Pedro, Costa Rica. (AWEP)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (AWEP)ORCID iD: 0000-0001-7656-1881
Stockholm Univ, Dept Meteorol, Stockholm, Sweden.; Stockholm Univ, Bolin Ctr Climate Res, Stockholm, Sweden .
Stockholm Univ, Dept Meteorol, Stockholm, Sweden.; Stockholm Univ, Bolin Ctr Climate Res, Stockholm, Sweden.; Univ Quebec Montreal, Dept Earth & Atmospher Sci, Montreal, PQ, Canada .
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2017 (English)In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, no 11, 5903-5916 p.Article in journal (Refereed) Published
Abstract [en]

The Caribbean low-level jet (CLLJ) is an important modulator of regional climate, especially precipitation, in the Caribbean and Central America. Previous work has inferred, due to their semiannual cycle, an association between CLLJ strength and meridional sea surface temperature (SST) gradients in the Caribbean Sea, suggesting that the SST gradients may control the intensity and vertical shear of the CLLJ. In addition, both the horizontal and vertical structure of the jet have been related to topographic effects via interaction with the mountains in Northern South America (NSA), including funneling effects and changes in the meridional geopotential gradient. Here we test these hypotheses, using an atmospheric general circulation model to perform a set of sensitivity experiments to examine the impact of both SST gradients and topography on the CLLJ. In one sensitivity experiment, we remove the meridional SST gradient over the Caribbean Sea and in the other, we flatten the mountains over NSA. Our results show that the SST gradient and topography have little or no impact on the jet intensity, vertical, and horizontal wind shears, contrary to previous works. However, our findings do not discount a possible one-way coupling between the SST and the wind over the Caribbean Sea through friction force. We also examined an alternative approach based on barotropic instability to understand the CLLJ intensity, vertical, and horizontal wind shears. Our results show that the current hypothesis about the CLLJ must be reviewed in order to fully understand the atmospheric dynamics governing the Caribbean region.

Place, publisher, year, edition, pages
2017. Vol. 122, no 11, 5903-5916 p.
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:uu:diva-304653DOI: 10.1002/2016JD026025ISI: 000404131800022OAI: oai:DiVA.org:uu-304653DiVA: diva2:1033370
Funder
Sida - Swedish International Development Cooperation Agency
Available from: 2016-10-06 Created: 2016-10-06 Last updated: 2017-09-20Bibliographically approved
In thesis
1. Inter-annual variability of rainfall in Central America: Connection with global and regional climate modulators
Open this publication in new window or tab >>Inter-annual variability of rainfall in Central America: Connection with global and regional climate modulators
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Central America is a region regularly affected by natural disasters, with most of them having a hydro-meteorological origin. Therefore, the understanding of annual changes of precipitation upon the region is relevant for planning and mitigation of natural disasters. This thesis focuses on studying the precipitation variability at annual scales in Central America within the framework of the Swedish Centre for Natural Disaster Science. The aims of this thesis are: i) to establish the main climate variability sources during the boreal winter, spring and summer by using different statistical techniques, and ii) to study the connection of sea surface temperature anomalies of the neighbouring oceans with extreme precipitation events in the region.

Composites analysis is used to establish the variability sources during winter. Canonical correlation analysis is employed to explore the connection between the SST anomalies and extreme rainfall events during May-June and August-October. In addition, a global circulation model is used to replicate the results found with canonical correlation analysis, but also to study the relationship between the Caribbean Sea surface temperature and the Caribbean low-level jet.

The results show that during winter both El Niño Southern Oscillation and the Pacific Decadal Oscillation, are associated with changes of the sea level pressure near the North Atlantic Subtropical High and the Aleutian low. In addition, the El Niño Southern Oscillation signal is intensified (destroyed) when El Niño and the Pacific Decadal Oscillation have the same (opposite) sign.

Sea surface temperature anomalies have been related to changes in both the amount and temporal distribution of rainfall. Precipitation anomalies during May-June are associated with sea surface temperature anomalies over the Tropical North Atlantic region. Whereas, precipitation anomalies during August-September-October are associated with the sea surface temperature anomalies contrast between the Pacific Ocean and the Tropical North Atlantic region. Model outputs show no association between sea surface temperature gradients and the Caribbean low-level jet intensification. Canonical correlation analysis shows potential for prediction of extreme precipitation events, however, forecast validation shows that socio-economic variables must be included for more comprehensive natural disaster assessments.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1438
Keyword
Precipitation, climate variability, El Niño Southern Oscillation, Tropical North Atlantic, Canonical Correlation Analysis, EC-EARTH, Caribbean Low-Level Jet
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-304656 (URN)978-91-554-9716-3 (ISBN)
Public defence
2016-11-25, Axel Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency, 54100006
Available from: 2016-10-31 Created: 2016-10-06 Last updated: 2016-11-02

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