Subtropical Anticyclone Forcing of the Antarctic Stratosphere

关于平流层强迫的一个新假设是，副热带季风反气旋影响冬季长波型，这解释了南半球（SH）的“臭氧羊角面包”以及与厄尔尼诺/南方涛动（ENSO）有关的SH平流层变率。这项研究建立在首席研究员小组早期工作的基础上，该研究表明，东南亚季风外流在SH中纬度臭氧中造成了波1不对称，被称为“臭氧羊角面包”。在南方冬季和春季，东南亚对流在对流层上层/平流层下层维持了两个反气旋：西藏高压和澳大利亚高压。澳大利亚高压周围流入南印度洋的气流形成了澳大利亚副热带西风急流的入口。这个斜压带是臭氧输送的首选经度带，也是臭氧牛角包的根本原因。热带对流的增强加强了澳大利亚高压，它与一个行进的、富含臭氧的温带平流层脊相互作用。随着澳大利亚高压的增强，高压脊减弱并与之合并；这是羊角面包的第二个动力原因。澳大利亚高压的变异性解释了臭氧牛角包强度变异性的大约40%。新的结果还表明，在极地平流层云和臭氧羊角面包中存在明显的ENSO信号。该项目的目标是更好地了解SH平流层的平均动力结构、臭氧输送途径、相关的波平均流动力学及其与ENSO有关的变率。将采用同化臭氧数据集、守恒示踪剂和轨迹进行分层模拟。全球分析将被动态过滤并作为初始条件应用于威斯康星大学麦迪逊分校非流体静力建模系统（UWNMS），该系统覆盖南半球。斜压生命周期实验将在纬向对称初始条件和波1澳大利亚射流下进行。将研究中纬度冲浪带的天气波和行星波的相互作用，并将其与线性理论进行比较。将确定臭氧从副热带平流层输送到臭氧牛角包的途径。研究了副热带反气旋对急流和行波的影响。将进行进一步的统计分析，以确定南向气流的平均结构以及ENSO与平流层之间的关系，从而允许探索南极平流层的年际变化与热带对流有关的假设。这项工作的更广泛影响是加强我们对辐射重要微量成分分布、年际可预测性和全球遥相关的气候动力学的理解。培养一名博士后和一名研究生，一名本科生参与研究。

A new hypothesis regarding the forcing of the stratosphere is that subtropical monsoon anticyclones affect the winter long-wave pattern, and that this explains the Southern Hemisphere (SH) "ozone croissant" as well as SH stratospheric variability related to the El Nino/Southern Oscillation (ENSO). The studies build on earlier work by the Principal Investigator's group, which showed that the Southeast Asian monsoon outflow creates the wave 1 asymmetry in SH midlatitude ozone known as the "ozone croissant." During austral winter and spring, Southeast Asian convection maintains two anticyclones in the upper troposphere/lower stratosphere: the Tibetan High and the Australian High. Outflow around the Australian High into the Southern Indian Ocean forms the entrance to the Australian subtropical westerly jet. This baroclinic zone is a preferred band of longitudes for ozone transport and is a fundamental cause of the ozone croissant. Intensification of tropical convection strengthens the Australian High, which interacts with a traveling extratropical stratospheric ridge that is rich in ozone. As the Australian High amplifies, the ridge stalls and merges with it; this is a second dynamical cause of the croissant. Variability of the Australian High explains approximately 40% of variability of the strength of the ozone croissant. New results also indicate a distinct ENSO signal in polar stratospheric clouds and in the ozone croissant. The goals of this project are to understand better the SH stratosphere, in regard to its mean dynamical structures, the pathways for ozone transport, the relevant wave-mean flow dynamics, and its variability related to ENSO. A hierarchy of simulations with assimilated ozone data sets, conserved tracers, and trajectories will be carried out. Global analyses will be dynamically filtered and applied as initial conditions in the University of Wisconsin -Madison non-hydrostatic modeling system (UWNMS), in a domain covering the Southern Hemisphere. Baroclinic life cycle experiments will be performed with zonally symmetric initial conditions and with a wave 1 Australian jet. The interactions of synoptic and planetary waves in the midlatitude surf zone will be studied and the resulting wave behavior compared to linear theory. Pathways for ozone transport from the subtropical stratosphere into the ozone croissant will be determined. The effects of forcing a subtropical anticyclone on the jet and on traveling planetary waves will be investigated. Further statistical analyses will be performed to establish the mean structure of the austral flow and the relationship between ENSO and the stratosphere, allowing the hypothesis that interannual variability of the Antarctic stratosphere is linked to tropical convection to be explored. Broader impacts of this work are in enhancing our understanding of the climate dynamics underlying the distribution of radiatively important trace constituents, interannual predictability, and global teleconnections. A postdoctoral scholar and a graduate student will be trained, and an undergraduate will participate in the research.