Surface Signatures of Stratospheric Variability and Trends

该项目研究平流层趋势和变化对地面气候的影响。 该项目的动机来自于观测和数值模拟，这些观测和数值模拟表明，南极臭氧洞主要通过其对赤道外急流的影响，构成了对南极气候系统的一个重要作用力。 这种强迫是指由于臭氧消耗导致极地平流层的冷却，使急流沿着风暴路径和地面西风带向极地移动。 这些向极地的移动对地表气候产生了各种后果，包括对南大洋和南极海冰的影响。 由于温室气体的增加，预计也会出现类似的向极移动，但尽管温室气体浓度预计会无限期增加，但由于针对消耗臭氧层物质的法规，极地平流层臭氧预计会恢复。 因此，由于南极平流层臭氧的恢复和全球温室气体浓度的增加，地面气候强迫之间预计会有一些抵消，这里提议的工作有两个组成部分，一个是审查平流层臭氧趋势的气候影响（特别是臭氧空洞的填补），另一个是审查平流层变化（在两个半球）对地面条件的影响。 大多数拟议的工作涉及全大气社区气候模式（WACCM），社区地球系统模式（CESM）的一个版本，其中包括一个具有良好分辨率的平流层的大气成分模式（除了完全耦合的陆地，海洋和海冰模式）。 另外还将进行两套综合计算，一套是将温室气体固定在2000年的水平，另一套是将消耗臭氧层物质固定在2000年的水平。 这些综合将有助于评估温室气体升温效应与臭氧恢复效应之间的抵消程度。 关于平流层变率的工作将在长期WACCM模拟中研究平流层突然变暖。 由于观测到的SSW样本量较小（约30个），SSW的研究受到了阻碍，但WACCM能够产生可比的事件，并且WACCM模拟的样本量（约500个）足够大，可以产生可靠的统计分析。由于提高对平流层变率和变化对地表气候影响的理解的社会价值，这项工作具有更广泛的影响。这项工作的一部分是设法确定南极臭氧空洞中臭氧恢复的影响，及其可能对温室气体增加所产生的影响的对抗作用，这将有助于更好地预测未来的气候变化。 另一部分的工作旨在更好地了解SSW的影响，这将是长期天气预报的价值。

This project examines the surface climate impacts of trends and variability in the stratosphere. Motivation for the project comes from observations and numerical simulations which suggest that the South Polar ozone hole constitutes an important forcing for the Antarctic climate system, primarily through its impact on the extratropical jet stream. The forcing is in the sense that the cooling of the polar stratosphere due to ozone depletion causes the jet stream to shift poleward, along with the storm tracks and surface westerlies. These poleward shifts have a variety of consequences for surface climate, including impacts on the Southern Ocean and Antarctic sea ice. Similar poleward shifts are expected due to increases in greenhouse gases (GHGs), but while GHG concentrations are expected to increase indefinitely, polar stratospheric ozone is expected to recover as a consequence of regulations against ozone-depleting substances (ODSs). Thus, some cancellation is expected between the surface climate forcing due to the recovery of ozone in the South Polar stratosphere and the global increase of GHG concentrations.The work proposed here has two components, one examining the climatic impacts of trends in stratospheric ozone (specifically the filling in of the ozone hole), and the other looking at the effects of stratospheric variability (in both hemispheres) on surface conditions. Most of the proposed work involves the Whole Atmosphere Community Climate Model (WACCM), a version of the Community Earth System Model (CESM) which includes an atmospheric component model with a well-resolved stratosphere (in addition to fully coupled land, ocean, and sea ice models). Two additional sets of integrations will be performed, one with GHGs held fixed at year 2000 levels, and the other with fixed year 2000 levels for ozone depleting substances (ODSs). These integrations will allow an assessment of the level of cancellation between the effects of GHG warming and ozone recovery. The work on stratospheric variability will examine sudden stratospheric warmings (SSWs) in long WACCM simulations. Work on SSWs has been hampered by the small sample size of observed SSWs (about 30), but WACCM is able to produce comparable events, and the sample size in the WACCM simulations (about 500) is large enough to produce robust statistical analyses.The work has broader impacts due to the societal value of improved understanding of the effects of stratosphere variability and change on surface climate. One portion of the work seeks to determine the effects of ozone recovery in the Antarctic ozone hole, and its possible opposition to the effects produced by GHG increases, which would allow better projections of future climate change. Another portion of the work seeks a better understanding of the effects of SSWs, which would be of value for long-term weather forecasts.