DOI: 10.1007/s00382-012-1540-8
Scopus记录号: 2-s2.0-84879550868
论文题名: An index for tropical temperate troughs over southern Africa
作者: Ratna S.B. ; Behera S. ; Ratnam J.V. ; Takahashi K. ; Yamagata T.
刊名: Climate Dynamics
ISSN: 9307575
出版年: 2013
卷: 41, 期: 2 起始页码: 421
结束页码: 441
语种: 英语
英文关键词: El Niño/La Niña
; Floods
; Southern Africa
; Southwest Indian Ocean
; Tropical temperate trough
; TTT Index
英文摘要: Strong cases of the tropical temperate troughs (TTT) that are responsible for the most of the summer rainfall over subtropical southern Africa are analyzed. An index for identifying the TTT is introduced for the first time using anomalies of outgoing longwave radiation (OLR) and the wind. The TTT is associated with a ridge-trough-ridge wave-like structure in the lower troposphere over southern Africa and the adjoining Indian Ocean. Therefore, the index considers physical processes that occur over southern Africa, adjoining the Atlantic and Indian Oceans to depict the variability of the TTT events. Unusually strong TTT events are identified when the standard deviations of the TTT indices defined by the OLR and wind anomalies in the selected regions are above 1.5 and 0.5 respectively. After applying this criterion and filtering out consecutive events, 55 TTT events are identified during the study period of December-January-February seasons from 1980-1981 to 2009-2010. From the composite analyses of those 55 events, it is found that the TTTs evolve with suppressed (enhanced) convection over the southwest Indian Ocean adjacent to Madagascar (southern Africa). The suppressed convection is, in turn, found to be associated with the enhanced convection around Sumatra in the southeast tropical Indian Ocean. This may explain why more TTT events occur in La Niña years as compared to El Niño years. Time evolution of the canonical TTT event shows that it starts 3 days prior to the mature phase of the event, suggesting possible predictability. After reaching a matured state, the system moves east toward the Indian Ocean and decays within the subsequent couple of days. In addition, the intertropical convergence zone (ITCZ) structure changes over Southern Africa/Madagascar during the TTT event and remains similar to climatology over other regions. The results indicate that the continental part of the ITCZ intensifies prior to the TTT event and then spreads southward following the mid-latitude influence during and after the event. © 2012 Springer-Verlag Berlin Heidelberg. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/54873
Appears in Collections: 过去全球变化的重建
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作者单位: Application Laboratory, Yokohama Institute for Earth Sciences, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan; Research Institute for Global Change, JAMSTEC, Yokohama, Japan; Earth Simulator Center, JAMSTEC, Yokohama, Japan
Recommended Citation:
Ratna S.B.,Behera S.,Ratnam J.V.,et al. An index for tropical temperate troughs over southern Africa[J]. Climate Dynamics,2013-01-01,41(2)