Stratospheric Water Vapor Simulations: From Polar Regions to the Tropical Tropopause

水蒸气是造成自然温室效应的最重要因素。平流层水汽浓度及其分布的变化可以影响地球的辐射收支和地表温度以及平流层化学。水也是极地平流层云（PSCs）的重要组成部分，在极地臭氧破坏中起着关键作用。此外，平流层最下层的卷云可能具有重要的化学和辐射效应，但对其形成机制知之甚少。同时，靠近对流层顶的区域对水汽的微小变化也特别敏感，深入了解该区域的云微物理过程是进行可靠气候预测的重要前提。在该提案的框架内，“平流层水汽模拟：从极地到热带对流层顶”(i)热带对流层顶层（TTL）的冻干过程，（ii） LMS中的中纬度卷云，以及（iii） psc及其对臭氧破坏的影响将在全球模拟中改进表示的背景下进行研究。对psc的各种新测量和研究挑战了对地层路径的传统理解。应根据不同的成核途径对氯活化的潜力加以量化，以便对臭氧层的恢复作出更精确的预测。此外，该项目的一个主要目标是研究在中纬度和TTL形成的平流层卷云。卷云对全球辐射收支的贡献高度依赖于其大小分布，因此也依赖于冰粒的成核率，它仍然是全球气候预测中一个重要的不确定性来源。此外，有必要了解通过TTL上升气团的脱水情况。研究中心开发的平流层化学拉格朗日模型（CLaMS）可以精确模拟脱水和反硝化过程，这两个过程都影响臭氧消耗和平流层成分的变化。结合高分辨率的原位测量和全球卫星数据，平流层冰云的微物理将以独特的方式进行研究。将CLaMS的拉格朗日概念与气候模式EMAC相结合，可以研究平流层水汽浓度变化对地表温度的影响。因此，该项目有助于提高对关键过程的理解，这些过程决定平流层水汽的年际变率和趋势，并驱动年代际气候变率。

Water vapor is the most important contributor to the natural greenhouse effect. Changes in stratospheric water vapor concentrations and its distribution can affect the Earth's radiative budget and surface temperatures as well as stratospheric chemistry. Water is also an essential constituent of polar stratospheric clouds (PSCs), which play a key role in polar ozone destruction. In addition, cirrus clouds in the lowermost stratosphere (LMS) may have important chemical and radiative effects, but little is known about their formation mechanisms. At the same time, the region close to the tropopause is particularly sensitive to even small changes in water vapor and an in-depth understanding of cloud microphysical processes in this region is an important prerequisite for reliable climate predictions.Within the framework of the proposal, "Stratospheric Water Vapor Simulations: From Polar Regions to the Tropical Tropopause" (i) freeze-drying processes in the tropical tropopause layer (TTL), (ii) mid-latitude cirrus clouds in the LMS, and (iii) PSCs and their impact on ozone destruction will be examined in the context of an improved representation in global simulations. A variety of new measurements and studies on PSCs has challenged the conventional understanding of formation pathways. Different nucleation pathways shall be quantified in terms of their potential for chlorine activation to achieve more refined forecasts for the recovery of the ozone layer. Moreover, a main goal of this project is research on stratospheric cirrus clouds that form both in the mid-latitudes and in the TTL. The contribution of cirrus clouds to the global radiation budget is highly dependent on the size distribution and therefore on the nucleation rate of ice particles and remains an important source of uncertainty in global climate predictions. Furthermore, it is essential to understand dehydration of ascending air masses through the TTL. The Chemical Lagrangian Model of the Stratosphere (CLaMS), developed at the Forschungszentrum Jülich, allows a precise simulation of dehydration and denitrification, both processes influencing ozone depletion and changes in the stratospheric composition. In combination with high-resolution in-situ measurements and global satellite data, the microphysics of stratospheric ice clouds will be investigated in a unique way. Coupling the Lagrangian concept of CLaMS with the climate model EMAC enables one to investigate the effect of changes in stratospheric water vapor concentrations on surface temperatures. Therefore, the project contributes to an improved understanding of key processes, which determine inter-annual variability and trends in stratospheric water vapor and drive decadal climate variability.