| 项目编号: | 1433763
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| 项目名称: | Origin, Storm Track Dynamics and Convective Feedback of African Easterly Waves |
| 作者: | Anantha Aiyyer
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| 承担单位: | North Carolina State University
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| 批准年: | 2013
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| 开始日期: | 2014-08-01
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| 结束日期: | 2018-07-31
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| 资助金额: | USD481728
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| 资助来源: | US-NSF
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| 项目类别: | Standard Grant
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| 国家: | US
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| 语种: | 英语
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| 特色学科分类: | Geosciences - Atmospheric and Geospace Sciences
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| 英文关键词: | aew
; stormtrack
; aew stormtrack
; african easterly jet
; origin
; convective instability
; wave packet
; sahel
; african monsoon multidisciplinary analysis
; midlatitude stormtrack
; fundamental dynamics
; model
; aew activity
; african easterly waves
; energy
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| 英文摘要: | African Easterly Waves (AEWs) are north-south undulations of the African Easterly jet with wavelengths of 2,000 to 2,500 kilometers that form as far east as Sudan and propagate westward across the Sahel. They are the principle form of large-scale weather variability over the Sahel in summer and play a key role in bringing monsoon rains to this drought-prone region. When AEWs continue their westward (or easterly) propagation over the Atlantic they can develop into hurricanes, and it is estimated that 85% of major Atlantic hurricanes (including hurricane Sandy) form from AEWs. However, existing theories for the origin and evolution of AEWs do not satisfactorily account for many of their observed characteristics.
This project investigates several aspects of AEWs, including their origin and evolution, the structure of the AEW stormtrack (the typical pathway along which AEWs develop and propagate), intermittency in AEW activity, and interactions between AEWs and moist convection. A key component of the research, developed in previous work by the Principal Investigator (PI), is the idea that AEWs are organized into wave packets in which the dispersion of energy can be tracked according to an empirically determined group velocity. The dynamics are somewhat equivalent to the "downstream development" observed in synoptic weather systems moving along the midlatitude stormtracks, except that in the case of AEWs the energy propagation can be upstream or downstream (as AEWs form along the African Easterly Jet, the upstream direction is eastward). Upstream energy propagation could have a number of significant consequences, including the possibility that energy from mature AEWs on the western end of the stormtrack could propagate to the region of AEW genesis on the eastern end of the stormtrack, thereby promoting the genesis of new AEWs. To some extent, the consequences of upstream and downstream propagation can be interpreted as the difference between convective and absolute instabilities of a unstable jet of limited zonal extent. In convective instability, wave packets growing on the instability of the jet have downstream energy propagation which moves the packet out of the unstable region. In absolute instability, the group velocity at the trailing end of the wave packet is upstream, so that some of the wave packet energy remains in the unstable region and promotes further growth. Thus, intermittency in AEW activity could be caused by a transition from absolute to convective instability, as in the latter case the energy does not propagate upstream into the AEW genesis region.
The primary tool for research in this project is the Weather Research and Forecasting (WRF) model, a regional atmosphere model applied over Africa north of the equator and the adjacent portion of the Atlantic. Model simulations are performed using both the standard full-physics version of the model and an intermediate complexity version in which external thermal forcing terms are used to produce an idealized version of the African Easterly Jet and AEW stormtrack. In addition to simulations designed to examine the role of upstream and downstream energy dispersion, additional numerical experiments are planned to examine the dual structure often observed in the AEW stormtrack, in which southern and northern branches of the stormtrack are found in the free atmosphere (around 650mb) and in the boundary layer (925mb), respectively. Coupling of AEWs to convection is also studied, using the full-physics version of the model. Results of these simulations will be compared to field campaign data collected in the African Monsoon Multidisciplinary Analysis (AMMA) field campaign.
The work has broader impacts due to the links between AEWs and Atlantic hurricanes, including landfalling US hurricanes, and the monsoon rains of the Sahel. A better understanding of the fundamental dynamics of AEWs could be of value for forecasting both individual AEWs and also periods of enhanced or reduced AEW activity. In addition, the work will support and train two graduate students, thereby providing for the future workforce in this research area. |
| 资源类型: | 项目
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| 标识符: | http://119.78.100.158/handle/2HF3EXSE/96263
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| Appears in Collections: | 影响、适应和脆弱性
气候减缓与适应
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| Recommended Citation: | |
Anantha Aiyyer. Origin, Storm Track Dynamics and Convective Feedback of African Easterly Waves. 2013-01-01.
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