| 项目编号: | 1557353
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| 项目名称: | Understanding Large-scale Zonal Jet Variability and Change |
| 作者: | David Lorenz
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| 承担单位: | University of Wisconsin-Madison
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| 批准年: | 2016
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| 开始日期: | 2016-04-01
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| 结束日期: | 2019-03-31
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| 资助金额: | 490696
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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: | mid-latitude
; mid-latitude jet
; climate model
; natural variability
; position
; reason
; mid-latitudes
; wave
; greenhouse gas
; natural year-to-year variability
; westerly jet
; westerly jet response
; future climate change
; westerly
; pi
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| 英文摘要: | This project will study the dynamics of the westerly wind belt of the mid latitudes of earth's atmosphere. The westerly wind belt is associated with the mid-latitude jet stream in the upper troposphere and it also influences the strength and position of fronts and mid-latitude storm systems. Despite the importance of the westerly jet on mid-latitude weather and climate, complex interactions between motions on a variety of different spatial and temporal scales makes understanding the important dynamical mechanisms controlling the strength and position of the mid-latitude jet very difficult. Progress has been made by separating the total flow into two components: 1) the background westerly flow, which is defined as the winds averaged in the east/west direction around the entire globe, and 2) the waves, which are defined as the difference between the total flow and the background flow. Recently, the PI has developed a methodology to separate the various mechanisms whereby the background westerly flow affects the waves. Because the role of the waves on the background flow is already well understood, this new methodology can be used to understand how the waves and the background flow interact to determine 1) the leading patterns of natural variability and 2) the response to external forcing, such as increasing greenhouse gases.
This study extends previous work by applying the new methodology to state-of-the-art climate models and observations. This will determine the reasons for climate model biases in the mid-latitude circulation that will then help lead to model improvements and therefore more credible predictions of future climate change. For example, the natural variability of the mid-latitude jet is too persistent in time in climate models and moreover this bias has been shown to affect the magnitude of the response to increasing greenhouse gases. The new methodology is ideally suited to separate the proposed reasons for this bias: 1) the mean westerlies are too far equatorward in the climate models or, 2) the planetary wave activity is too weak in the climate models. In addition, the methodology is ideally suited to separate the proposed reasons for latitudinal shifts in the position of the westerlies in response to increased greenhouse gases.
Changes in simulated climate should be considered credible only to the extent that model spread is small. In this research, the reasons for the model spread in the westerly jet response and variability will be diagnosed so that the models can be improved. These improvements are important because increasing greenhouse gases tend to shift the position of the westerlies toward the poles. Furthermore, such latitudinal shifts in the position of the westerlies are a major component of the natural year-to-year variability in the mid-latitudes. For example, an extreme equatorward shift in the mid-latitude jet led to the extremely cold, snowy winter of 2009-2010 in the mid-latitudes of the Northern Hemisphere. A similar situation occurred in March 2013. Besides temperature and precipitation, these shifts in the westerlies also have many other impacts including poleward moisture transport, the earth radiation budget via cloudiness, the ocean circulation and sea ice. This project will have additional broader impacts because the PI is active in the climate impacts community. The PI's familiarity and access to climate model simulations through this and other projects enables him to provide essential information on the robustness of the climate information that these users need. In addition, after publication of the results, the code for the methodology used in this project will be made public on the PI's web site for other groups to diagnose and understand their own simulations and observations. This work will also train a Ph.D. graduate student. |
| 资源类型: | 项目
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| 标识符: | http://119.78.100.158/handle/2HF3EXSE/92658
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| Appears in Collections: | 全球变化的国际研究计划
科学计划与规划
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| Recommended Citation: | |
David Lorenz. Understanding Large-scale Zonal Jet Variability and Change. 2016-01-01.
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