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contributor authorStrong, Courtenay
contributor authorMagnusdottir, Gudrun
date accessioned2017-06-09T16:22:47Z
date available2017-06-09T16:22:47Z
date copyright2008/09/01
date issued2008
identifier issn0022-4928
identifier otherams-66791.pdf
identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4208165
description abstractObjective analysis of several hundred thousand anticyclonic and cyclonic breaking Rossby waves is performed for the Northern Hemisphere (NH) winters of 1958?2006. A winter climatology of both anticyclonic and cyclonic Rossby wave breaking (RWB) frequency and size (zonal extent) is presented for the 350-K isentropic surface over the NH, and the spatial distribution of RWB is shown to agree with theoretical ideas of RWB in shear flow. Composites of the two types of RWB reveal their characteristic sea level pressure anomalies, upper- and lower-tropospheric velocity fields, and forcing of the upper-tropospheric zonal flow. It is shown how these signatures project onto the centers of action and force the velocity patterns associated with the North Atlantic Oscillation (NAO) and Northern Hemisphere annular mode (NAM). Previous studies have presented evidence that anticyclonic (cyclonic) breaking leads to the positive (negative) polarity of the NAO, and this relationship is confirmed for RWB over the midlatitudes centered near 50°N. However, an opposite and statistically significant relationship, in which cyclonic RWB forces the positive NAO and anticyclonic RWB forces the negative NAO, is shown over regions 20° to the north and south, centered at 70° and 30°N, respectively. On a winter mean basis, the frequency of RWB over objectively defined regions covering 12% of the area of the NH accounts for 95% of the NAO index and 92% of the NAM index. A 6-hourly analysis of all the winters indicates that RWB over the objectively defined regions affects the NAO/NAM without a time lag. Details of the objective wave-breaking analysis method are provided in the appendix.
publisherAmerican Meteorological Society
titleTropospheric Rossby Wave Breaking and the NAO/NAM
typeJournal Paper
journal volume65
journal issue9
journal titleJournal of the Atmospheric Sciences
identifier doi10.1175/2008JAS2632.1
journal fristpage2861
journal lastpage2876
treeJournal of the Atmospheric Sciences:;2008:;Volume( 065 ):;issue: 009
contenttypeFulltext


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