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Near‐surface strong winds in a marine extratropical cyclone: acceleration of the winds and the importance of surface fluxes
Author(s) -
Slater Tim P.,
Schultz David M.,
Vaughan Geraint
Publication year - 2016
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.2924
Subject(s) - mesoscale meteorology , extratropical cyclone , cold front , warm front , atmospheric sciences , front (military) , geology , boundary layer , cyclone (programming language) , wind speed , climatology , surface pressure , thermal wind , meteorology , pressure gradient , wind gradient , planetary boundary layer , cyclogenesis , temperature gradient , wind shear , mechanics , physics , field programmable gate array , computer science , computer hardware
A rapidly developing extratropical cyclone named Tini brought strong winds to Ireland and the United Kingdom on 12 February 2014. A mesoscale‐model simulation is used to analyze the development of the strong winds through the terms in the horizontal momentum equation. The maximum of near‐surface wind speed equatorward of the cyclone was composed of two different airstreams that underwent different paths to acceleration. First, horizontally moving air in the cold conveyor belt was accelerated by the along‐flow pressure gradient force but was decelerated by friction. Second, descending air accelerated into the eastern end of the maximum of near‐surface wind speed and was associated, in part, with a sting jet, caused by the increasing along‐flow horizontal pressure gradient force at lower levels. When this descending air entered the boundary layer, it too was decelerated by surface friction. Surface fluxes of heat and moisture were necessary to destabilize and deepen the boundary layer, allowing mixing of the strongest winds from the free troposphere down to the surface. A simulation with the surface fluxes turned off during cyclogenesis showed a more stable boundary layer around the bent‐back front, which inhibited the strongest winds from reaching the surface. The descent of the sting‐jet air was associated with a maximum in quasigeostrophic omega, which consisted of both synoptic‐scale and mesoscale descent, the latter associated with frontolysis occurring at the end of the bent‐back front. Thus, the near‐surface wind maximum was created by the synoptic‐scale and mesoscale dynamics, whereas localized moist processes were negligible.