Tropical High Altitude Clouds and their Impact on Stratospheric Humidity

热带高空云及其对平流层湿度的影响

• 批准号: 233493169
• 负责人: Dr. Wiebke Frey
• 金额: --
• 依托单位: Abteilung Atmosphärische Mikrophysik
• 依托单位国家: 德国
• 项目类别: Research Fellowships
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2014-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/233493169?language=en
• 关键词: Tropical; Altitude; Clouds; their; Impact

Clouds play a key role in the Earth's climate system by regulation of the incoming and outgoing radiation, chemical and dynamical processes. Ice clouds at high altitudes in the tropics, the so called tropical tropopause layer, are particularly important since this is the main region where air ascends slowly from the troposphere into the dry stratosphere. Thus, these ice clouds affect the stratospheric water vapour content which in itself is a main driver of radiative and chemical processes, e.g. ozone depletion, there. These clouds can either be of convective nature, and occur in convective overshooting cloud turrets, or they form in situ by large scale upwelling and cooling as subvisible cirrus. Although the latter occur frequently, little is known about the exact microphysical formation mechanisms and how they can be maintained. Previous modelling efforts using various different mechanisms, however, have failed to agree with the observed properties. This project aims to improve our knowledge of the impact clouds in the tropical tropopause layer have on stratospheric humidity, by studying their formation, maintenance, and occurrence frequencies.A set of state-of-the-art numerical models will be used to simulate the clouds in the tropical tropopause layer, taking advantage of their particular strengths. These models are the Weather Research and Forecasting (WRF) Model, the GLObal Model of Aerosol Processes (GLOMAP), and the Australian Community Climate and Earth-System Simulator (ACCESS). First, the questions related to the formation and maintenance of subvisible cirrus will be addressed. In a second step the impact of subvisible cirrus and overshooting convection on the stratospheric humidity will be assessed. Both the direct effects (e.g. injection of ice particles into the stratosphere) and indirect effects (e.g. change in dynamical processes) will be studied. In order to estimate the net effect, occurrence frequencies of both cloud types will be derived from a complementary set of ground based remote sensing observations from the Darwin site and satellite observation from the International Satellite Cloud Climatology Project. The data of airborne in situ measurements which I analysed during my PhD will help to constrain and test the model simulations.A better understanding of the complex processes related to the clouds in the tropical tropopause layer will improve their representation in numerical models and thus, enhance the quality of model predictions. This will improve our ability to constrain climate predictions due to highly uncertain ice cloud processes. Additionally, knowing the impact of these clouds on stratospheric humidity will enable an improved quantification of their climate impact.

云通过调节传入和传出的辐射、化学和动力学过程在地球气候系统中发挥关键作用。热带高海拔地区的冰云，即所谓的热带对流层顶层，特别重要，因为这是空气从对流层缓慢上升到干燥平流层的主要区域。因此，这些冰云会影响平流层的水蒸气含量，而水蒸气含量本身就是辐射和化学过程的主要驱动因素，例如臭氧消耗。这些云可以是对流性质的，并发生在对流过冲云塔，或他们形成的大规模上升流和冷却的地方，作为肉眼可见的卷云。虽然后者经常发生，但对确切的微物理形成机制以及如何保持它们知之甚少。 然而，以前使用各种不同机制的建模工作未能与观察到的特性一致。本项目旨在通过研究热带对流层顶云的形成、维持和出现频率，提高对热带对流层顶云对平流层湿度影响的认识，并利用热带对流层顶云的独特优势，采用一套先进的数值模式对热带对流层顶云进行模拟。这些模型是天气研究和预报模型、全球气溶胶过程模型和澳大利亚共同体气候和地球系统模拟器。首先，将讨论与次可见卷云的形成和维持有关的问题。第二步将评估次可见卷云和过冲对流对平流层湿度的影响。将研究直接影响（如冰粒注入平流层）和间接影响（如动力过程的变化）。为了估计净效应，将从达尔文站点的地面遥感观测和国际卫星云气候学项目的卫星观测的一组互补数据中得出两种云类型的出现频率。 通过对博士期间的机载实测资料的分析，可以更好地约束和检验模式的模拟结果，更好地理解热带对流层顶云的复杂过程，将有助于改善其在数值模式中的表现，从而提高模式的预报质量。这将提高我们限制气候预测的能力，因为高度不确定的冰云过程。此外，了解这些云对平流层湿度的影响将有助于更好地量化其气候影响。

项目成果

Tropical deep convective life cycle: Cb-anvil cloud microphysics from high-altitude aircraft observations

• DOI: 10.5194/acp-14-13223-2014
• 发表时间: 2014-12
• 期刊: Atmospheric Chemistry and Physics
• 影响因子: 6.3
• 作者: W. Frey;S. Borrmann;F. Fierli;R. Weigel;V. Mitev;R. Matthey;F. Ravegnani;N. Sitnikov;A. Ulanovsky;F. Cairo