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K elvin– H elmholtz waves in extratropical cyclones passing over mountain ranges
Author(s) -
Medina Socorro,
Houze Robert A.
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.2734
Subject(s) - extratropical cyclone , middle latitudes , geology , shear (geology) , mesoscale meteorology , mesocyclone , atmospheric sciences , meteorology , climatology , radar , physics , petrology , telecommunications , doppler radar , computer science
K elvin– H elmholtz billows with horizontal scales of 3–4 km have been observed in midlatitude cyclones moving over the I talian A lps and the O regon C ascades when the atmosphere was mostly statically stable with high amounts of shear and Ri < 0.25. In one case, data from a mobile radar located within a windward facing valley documented a layer in which the shear between down‐valley flow below 1.2 km and strong upslope cross‐barrier flow above was large. Several episodes of K elvin– H elmholtz waves were observed within the shear layer. The occurrence of the waves appears to be related to the strength of the shear: when the shear attained large values, an episode of billows occurred, followed by a sharp decrease in the shear. The occurrence of large values of shear and K elvin– H elmholtz billows over two different mountain ranges suggests that they may be important features occurring when extratropical cyclones with statically stable flow pass over mountain ranges.