• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文学位 >Effects of Saharan Mineral Dust Aerosols on the Dynamics of an Idealized African Easterly Jet-African Easterly Wave System over North Africa.
【24h】

Effects of Saharan Mineral Dust Aerosols on the Dynamics of an Idealized African Easterly Jet-African Easterly Wave System over North Africa.

机译：撒哈拉矿物粉尘气溶胶对北非理想非洲东风急流非洲东风波浪系统动力学的影响。

获取原文
获取原文并翻译 | 示例
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The central objective of this work is to examine the direct radiative effects of Saharan mineral dust aerosols on the dynamics of African easterly waves (AEWs) and the African easterly jet (AEJ). Achieving this objective is built around two tasks that use the Weather Research and Forecasting (WRF) model coupled to an online dust model (WRF-dust model). The first task (Chapter 2) examines the linear dynamics of AEWs; the second task (Chapter 3) examines the nonlinear evolution of AEWs and their interactions with the AEJ.;In Chapter 2, the direct radiative effects of dust on the linear dynamics of AEWs are examined analytically and numerically. The analytical analysis combines the thermodynamic equation with a dust continuity equation to form an expression for the generation of eddy available potential energy (APE) by the dust field. The generation of eddy APE is a function of the transmissivity and spatial gradients of the dust, which are modulated by the Doppler-shifted frequency. The expression predicts that for a fixed dust distribution, the wave response will be largest in regions where the dust gradients are maximized and the Doppler-shifted frequency vanishes.;The numerical analysis calculates the linear dynamics of AEWs using zonally averaged basic states for wind, temperature and dust consistent with summertime conditions over North Africa. For the fastest growing AEW, the dust increases the growth rate from ~15% to 90% for aerosol optical depths ranging from tau=1.0 to tau=2.5. A local energetics analysis shows that for tau=1.0, the dust increases the maximum barotropic and baroclinic energy conversions by ~50% and ~100%, respectively. The maxima in the generation of APE and conversions of energy are co-located and occur where the meridional dust gradient is maximized near the critical layer, i.e., where the Doppler-shifted frequency is small, in agreement with the prediction from the analytical analysis.;In Chapter 3, the direct radiative effects of dust on the evolution of AEJ-AEW system are examined using the WRF-dust model. The model is initialized with zonal-mean distributions of wind, temperature and dust used in linear study (Chapter 2). The dust modifies the lifecycle of the AEWs in the following way: the domain-averaged eddy kinetic energy (EKE) is enhanced during the linear and nonlinear growth phases, reaching a larger peak amplitude that subsequently decays more rapidly, eventually equilibrating at lower amplitude. The increase in EKE during the growth phases is due to local increases in barotropic energy conversions in the dust plume north of the AEJ. The dust-modified, rapidly decaying phase is primarily associated with enhanced barotropic decay that occurs near the top of the plume north of the AEJ. The timing of peak EKE depends on the initial dust concentration.;Throughout the evolution of the AEJ-AEW system, the dust increases the maximum zonal-mean wind speeds. The increase is due to the dust-modified mean meridional circulation during the AEW growth phase and the dust-modified wave fluxes during the AEW decay phase. During AEW growth, the dust-modified maximum wind speeds are also displaced farther southward and upward, which is due to the enhanced wave fluxes decelerating the flow more efficiently north of the AEJ. These changes to the AEJ structure affect the critical surface, which expands vertically and meridionally as the AEW grows to finite amplitude. The dust-modified effects on the evolution of the AEJ-AEW system are discussed in light of tropical cyclogenesis.;By better understanding the direct radiative effects of dust on the AEJ-AEW system, we can expect improvements in the modeling, forecasting and understanding of the connection between AEWs and the meteorology over North Africa and the Eastern Atlantic Ocean.
机译：这项工作的主要目标是研究撒哈拉矿物粉尘气溶胶对非洲东风（AEW）和非洲东风（AEJ）动力学的直接辐射影响。实现此目标的基础是两个任务，这些任务使用天气研究和预报（WRF）模型以及在线尘埃模型（WRF-尘埃模型）。第一项任务（第2章）研究了AEW的线性动力学。第二个任务（第3章）检查了AEW的非线性演化及其与AEJ的相互作用。在第二章中，通过分析和数值研究了灰尘对AEW线性动力学的直接辐射影响。分析分析将热力学方程式与粉尘连续性方程式结合起来，形成一个表达式，用于通过粉尘场生成涡流可用势能（APE）。涡流APE的产生是灰尘的透射率和空间梯度的函数，灰尘的空间梯度由多普勒频移调制。该表达式预测，对于固定的尘埃分布，在尘埃梯度最大且多普勒频移消失的区域中，波响应将最大;数值分析使用区域平均风态来计算AEW的线性动力学，温度和灰尘与北非夏季条件一致。对于增长最快的AEW，对于从tau = 1.0到tau = 2.5的气溶胶光学深度，粉尘的增长率从〜15％增至90％。局部能量学分析表明，在tau = 1.0时，灰尘将最大正压和斜压能量转换分别提高了〜50％和〜100％。与分析分析的预测相一致，APE的产生和能量转换的最大值位于同一位置，并且在临界层附近子午尘埃梯度最大的位置（即多普勒频移的频率较小）发生。 ；在第三章中，使用WRF-灰尘模型研究了灰尘对AEJ-AEW系统演化的直接辐射作用。该模型使用线性研究中使用的风，温度和尘埃的区域平均分布进行初始化（第2章）。灰尘通过以下方式改变了AEW的生命周期：在线性和非线性生长阶段，域平均涡动能（EKE）增强，达到更大的峰值振幅，随后其衰减更快，最终达到更低的振幅。生长阶段EKE的增加是由于AEJ以北的尘埃羽流中正压能量转换的局部增加。尘埃改性的快速衰变相主要与增强的正压衰变有关，这种正压衰变发生在AEJ以北羽状流顶部附近。 EKE峰值的时间取决于初始尘埃浓度。在AEJ-AEW系统的整个演化过程中，尘埃会增加最大纬向平均风速。该增加归因于AEW生长阶段的粉尘修正平均子午环流和AEW衰减阶段的粉尘修正的波通量。在AEW生长期间，粉尘修正后的最大风速也向南和向上移动，这是由于增强的波通量使AEJ北部的气流更有效地减速。 AEJ结构的这些变化会影响临界表面，该临界表面会随着AEW增长到有限幅度而在垂直方向和子午方向扩展。结合热带气旋作用讨论了粉尘对AEJ-AEW系统演化的影响。通过更好地了解粉尘对AEJ-AEW系统的直接辐射影响，我们可以期望在建模，预测和理解上有所改进预警机与北非和东大西洋气象学之间的联系。

著录项

  • 作者

    Grogan, Dustin Francis Phillip.;

  • 作者单位

    University of California, Davis.;

  • 授予单位 University of California, Davis.;
  • 学科 Atmospheric sciences.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 106 p.
  • 总页数 106
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号