Classification and Synoptic Analysis of Subtropical Cyclones within the Northeastern Atlantic Ocean



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González Alemán, Juan Jesús and Valero Rodríguez, Francisco and Martín León, Francisco and Evans, Jenni L. (2015) Classification and Synoptic Analysis of Subtropical Cyclones within the Northeastern Atlantic Ocean. Journal of climate, 28 (8). pp. 3331-3352. ISSN 0894-8755

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Since more research is needed on subtropical cyclones (STCs) formed within the North Atlantic eastern basin, this survey analyzes them from a synoptic point of view, on a climatological basis, with the main aims of studying their common features, complementing other studies of these storms in the North Atlantic, and aiding the forecasting community. Fifteen cases of STCs were identified during the period 1979-2011 by applying a set of criteria from two databases. Composite analysis reveals that an extratropical depression acts as a precursor when it is isolated from the westerlies and then suffers a deepening when becoming subtropical instead of decaying through occlusion. This process is accompanied by an atmospheric circulation, within the North Atlantic, whose main feature is characterized by notable departures from the climatological pattern with a statistically significant anomalous high pressure to the north of the STCs. Three conceptual models of synoptic pattern of subtropical cyclogenesis are derived and show that these departures appeared because the westerly circulation moves poleward and/ or the flow has a great meridional component, with the possibility of a blocked flow pattern occurring. Moreover, the identified STCs predominantly formed in a highly sheared (>10 m s^-1) environment with low sea surface temperature values (<25 degrees C), which differs from the dominant features of STCs in the North Atlantic, especially within its western region. Finally, a recent (2010) STC, identified by the authors, is synoptically discussed in order to achieve a better interpretation of the general results.

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© 2015 American Meteorological Society. Comments from three anonymous reviewers and the editor, to whom the authors are grateful, greatly improved this manuscript. We highly appreciate the data of subtropical cyclones provided by Dr. Mark P. Guishard from The Pennsylvania State University. We thank Dr. Robert E. Hart from The Florida State University for providing us the cyclone phase diagrams as well. We are also grateful to Dr. Francisco Doblas Reyes from the Catalán Institute of Climate Sciences for his valuable comments and recommendations. This work was supported under a MECD Grant (Spanish government), the MINECO projects CGL2011-25327 and PCIN-2014-013-C07-04 (Spanish government), and by the U.S. National Science Foundation under Grant ATM1322532. Discussions with D. Iñigo Gomara and Dr. David Barriopedro from Complutense University of Madrid about RWB and blockings, respectively, are also appreciated.

Uncontrolled Keywords:Sea interaction theory; QE-II storm; Tropical cyclones; Northern-hemisphere; East-coast; Life-cycle; Climatology; Sensitivity; Evolution; Intensity
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
ID Code:30833
Deposited On:12 Jun 2015 14:05
Last Modified:10 Dec 2018 15:05

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