Surface Signatures of Stratospheric Variability and Trends

该项目研究了平流层趋势和变化对地表气候的影响。该项目的动机来自观测和数值模拟，这些观测和数值模拟表明，南极臭氧空洞主要通过其对温带外急流的影响，构成了南极气候系统的重要强迫。这种强迫是由于臭氧消耗导致极地平流层冷却，导致急流与风暴路径和地面西风一起向极地移动。这些向极地的变化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(GHGs)的增加，预计也会发生类似的极地迁移，但尽管温室气体浓度预计将无限期增加，但由于对臭氧消耗物质(ODS)的管制，极地平流层臭氧预计将恢复。因此，南极平流层臭氧恢复造成的地面气候强迫与全球温室气体浓度增加之间预计会有一些抵消。这里提出的工作包括两个部分，一个是研究平流层臭氧趋势(特别是臭氧空洞的填补)的气候影响，另一个是研究平流层变化(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)，这是社区地球系统模式(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分量模型(除了完全耦合的陆地、海洋和海冰模型之外)。将进行另外两套综合，一套将温室气体保持在2000年的固定水平，另一套保持在2000年的臭氧消耗物质固定水平。这些综合将能够评估温室气体变暖的影响和臭氧恢复之间的抵消程度。关于平流层可变性的工作将检验WACCM长期模拟中的平流层突然变暖(SSW)。由于观测到的SSW的样本量很小(约30个)，SSW的工作一直受到阻碍，但WACCM能够产生可比较的事件，WACCM模拟的样本量(约500个)足以产生强有力的统计分析。由于更好地了解平流层变异性和变化对地表气候的影响，工作具有更广泛的社会价值。这项工作的一部分旨在确定南极臭氧层空洞中臭氧恢复的影响，以及它可能反对温室气体增加产生的影响，这将使更好地预测未来的气候变化。工作的另一部分是寻求更好地了解SSW的影响，这对长期天气预报将是有价值的。

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.