DOI: 10.1002/joc.5214
论文题名: Simulations of the observed ‘jump’ in the West African monsoon and its underlying dynamics using the MIT regional climate model
作者: Im E.-S. ; Eltahir E.A.B.
刊名: International Journal of Climatology
ISSN: 8998418
出版年: 2018
卷: 38, 期: 2 起始页码: 841
结束页码: 852
语种: 英语
英文关键词: absolute vorticity
; boundary-layer entropy
; regional climate model
; West African monsoon jump
Scopus关键词: Air
; Atmospheric radiation
; Atmospheric thermodynamics
; Boundary layers
; Entropy
; Rain
; Vorticity
; Absolute vorticity
; Momentum conserving
; Radiative forcings
; Radiative-convective equilibrium
; Rainfall distribution
; Regional climate modeling
; Underlying dynamics
; West African Monsoon
; Climate models
; boundary layer
; climate modeling
; computer simulation
; entropy
; monsoon
; regional climate
; vorticity
; West Africa
英文摘要: The observed seasonal migration of rainfall associated with the West African monsoon (WAM) is characterized by two regimes of relatively intense rainfall: an early, intense peak over the Guinean Coast during late May to early July; and a late, less-intense peak over the Sahel during mid-July to mid-September. The transition between these two rainfall regimes occurs relatively quickly around the beginning of July. This quick transition can be described as a ‘jump’ of the WAM into the continent. Eltahir and Gong (1996) proposed a theory for the WAM whereby the solar radiation forcing during the summer shapes a distribution of boundary-layer entropy that peaks over the continent. By assuming a quasi-equilibrium balance between moist convection and the large-scale radiative forcing, the distribution of boundary-layer entropy can be linked to the absolute vorticity at the tropopause. According to this analytical theory, the onset of the monsoon, characterized by the ‘jump’, reflects of a nonlinear shift from a radiative-convective equilibrium regime to an angular momentum conserving regime that would only occur when the value of absolute vorticity in the upper troposphere approaches a threshold of zero. It is because, when the absolute vorticity is significantly different from zero, then the air as a rotating fluid is too rigid to exhibit a meridional overturning. Here, we use the MIT regional climate model (MRCM) to test this theory further and reach a couple of conclusions. First, MRCM succeeds in reproducing the main features of the observed rainfall distribution, including the ‘jump’. Second, analysis of the rainfall, vorticity, entropy, and wind fields simulated by the model reveals a dynamical picture consistent with the proposed theory. © 2017 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/117082
Appears in Collections: 气候减缓与适应
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作者单位: Center for Environmental Sensing and Modeling, Singapore-MIT Alliance for Research and Technology, Singapore; Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, China; Division of Environment and Sustainability, The Hong Kong University of Science and Technology, China; Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, United States
Recommended Citation:
Im E.-S.,Eltahir E.A.B.. Simulations of the observed ‘jump’ in the West African monsoon and its underlying dynamics using the MIT regional climate model[J]. International Journal of Climatology,2018-01-01,38(2)