Stratosphere-troposphere Exchange of Ozone and its Changes in the Future

臭氧会导致呼吸问题并破坏植被，因此人们对了解对流层中臭氧的来源及其随时间的变化有很大的兴趣。由于平流层中的臭氧浓度高于对流层，两者之间的空气混合，称为平流层-对流层交换（STE），是对流层臭氧的重要来源。 但是，平流层的贡献很难量化，而且根据再分析产品对臭氧STE的直接估计与根据对流层臭氧收支残差进行的估计不同。另一个令人担忧的问题是，两个著名的再分析产品（ERA 5和MERRA 2）对40年STE趋势的估计显示出很大的差异。 最近，首席研究员（PI）发现了臭氧STE计算的一个潜在的重要缺陷，即它们只考虑了中高纬度的STE，臭氧传输的方向是向下进入对流层，臭氧STE的大部分发生在那里。 与预期相反，他发现热带臭氧STE是向上的，因此是对流层的损失，不能忽视，因为它使全球臭氧STE减少了约35%。这一发现，沿着相关的高质量卫星观测的可用性，需要重新审查臭氧的STE，以解决三个问题：1）什么是臭氧的STE和基于观测数据的相关不确定性？2)造成不同再分析产品的臭氧STE存在巨大差异的主要因素是什么？3)臭氧STE在气候变化中将如何变化？STE计算使用的方法是假设热带对流层顶位于等熵面（现代气候中的380 K等熵面）上，而热带对流层顶位于380 K等熵面以下的位涡面（3.5PVU）上。 该项目使用来自CloudSat，CALYPSO，MODIS和COSMIC等卫星任务的数据，结合辐射传输代码，计算创建观测STE估计所需的加热速率和大气密度。 关于未来科技和经济变化的工作审查了化学-气候模式倡议的气候模拟。 一个令人关切的问题是，由于温室气体的增加，平流层翻转环流（布鲁尔-多布森环流）预计将加强，这可能导致中高纬度地区向下的臭氧STE增加。 另一个问题是，热带对流层顶预计将上升，这可能会减少通过热带STE进入平流层的臭氧损失，鉴于地面臭氧的有害影响以及更好地估计其来源和可能的未来演变的实际价值，这项工作具有社会意义。 此外，PI进行公共宣传，包括多个活动，重点是K-12参与科学。 PI还积极开发数据可视化软件和技术，其中一些在美国地球物理联盟数据可视化竞赛中脱颖而出。此外，该项目还为两名研究生提供支持和培训。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Ozone causes breathing problems and damages vegetation, thus there is considerable interest in understanding the sources of ozone in the troposphere and how they change over time. Because ozone concentration is higher in the stratosphere than the troposophere the mixing of air between the two, referred to as stratosphere-troposphere exchange (STE), is an important source of tropospheric ozone. But the stratospheric contribution is hard to quantify and direct estimates of ozone STE from reanalysis products differ from estimates based on tropospheric ozone budget residuals. A further concern is that estimates of the 40-year STE trend from two prominent reanalysis products (ERA5 and MERRA2) show substantial differences. Recently the Principal Investigator (PI) found a potentially important shortcoming of ozone STE calculations, which is that they only consider STE in the middle and high latitudes, where the direction of ozone transport is downward into the troposphere and where the bulk of the ozone STE occurs. Contrary to expectations he found that the tropical ozone STE, which is upward and thus a loss for the troposphere, cannot be neglected as it reduces the global ozone STE by about 35%. This finding, along with the availability of relevant high-quality satellite observations, warrants a reexamination of ozone STE addressing three questions: 1) what is the ozone STE and associated uncertainty based on observational data? 2) what are the main factors responsible for the large discrepancies in ozone STE from different reanalysis products? 3) How will ozone STE change in a changing climate?The STE calculations use a methodology in which the tropical tropopause is assumed to lie on an isentropic surface (the 380K isentrope in present-day climate) while the extratropical tropopause lies on a potential vorticity surface (3.5PVU) below the 380K isentrope. The project uses data from satellite missions including CloudSat, CALYPSO, MODIS, and COSMIC, in combination with radiative transfer codes, to calculate the heating rates and atmospheric density needed to create observational STE estimates. The work on future STE change examines climate simulations from the Chemistry-Climate Model Initiative. One concern is that the stratospheric overturning circulation (the Brewer-Dobson circulation) is expected to strengthen due to greenhouse gas increases, which could lead to an increase in downward ozone STE in the middle and high latitudes. Another is that the tropical tropopause is expected to rise, which could reduce the loss of ozone to the stratosphere through tropical STE.The work is of societal interest given the harmful effects of ground-level ozone and the practical value of better estimates of its sources and likely future evolution. In addition, the PI conducts public outreach including multiple events focusing on K-12 engagement in science. The PI has also been active in developing data visualization software and techniques, some of which were featured in the American Geophysical Union Data Visualization Competition. In addition, the project provides support and training to two graduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.