Precipitation life cycle in trade wind cumuli

信风积云中的降水生命周期

• 批准号: 437320342
• 负责人: Dr. Claudia Acquistapace, Ph.D.
• 金额: --
• 依托单位: Institut für Geophysik und Meteorologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/437320342?language=en
• 关键词: Precipitation; life; cycle; trade; wind

Trade wind cumulus clouds play a vital role in the Earth's radiation budget and produce up to 20% of the total precipitation in the tropics. However, we still don't know how they will respond to global warming. Precipitation from trade wind cumuli can alter cloud macroscopic properties and the boundary layer structure and dynamics. Precipitation development in models is very uncertain, being dependent on simulation setup and microphysics. In particular, the autoconversion scheme dramatically affects precipitation flux, cloud structure, and organization. Currently, no evaluations of the different autoconversion schemes with observations reduced the uncertainties in rain processes. In ground-based observations, radar reflectivity based approaches detect precipitation at an advanced stage, hindering the identification of factors causing rain formation. Precipitation can also impact convection organization and circulation intensity with massive effects on climate sensitivity. Evaporation of precipitation determines the intensity of cold pools and influence the cloud field organization. It is hence key to quantify evaporation rates and their spatiotemporal variability. Parametrizations of evaporation below cloud base are available but strongly depend on the drop size distribution of raindrops. Also, in the observations, evaporation rates are hard to observe directly. The goal of this proposal is to answer the question of what and how triggers precipitation formation in trade wind cumulus clouds in observations and exploit these data to constrain rain formation process in LES models. Moreover, this research aims to quantify the spatiotemporal distribution of evaporation below cloud base in the trades, understanding on which parameters it mainly depends. The project is complementary to the upcoming EUREC4A field campaign and exploits the long-term dataset of the Barbados Cloud Observatory (BCO). Characterization of precipitation onset and development will be achieved through synergetic ground-based observations and novel approaches based on the skewness of the cloud radar Doppler spectrum to detect rain onset. The characterization of precipitation in observations will be used to evaluate the rain formation process in the ICON-LEM and DHARMA-LES models statistically, showing where the model reproduce the observed mean behaviors and where and why biases occur. The analysis will be developed in the observational space by means of the PAMTRA forward simulator.Evaporation rates will be retrieved exploiting the synergy of observations available within EUREC4A and at BCO. The spatiotemporal variability of the observed profiles will be characterized and used as a constraint to verify and improve the description of evaporation rates in LES models.This research will contribute to the Grand Challenge on Clouds, circulation, and climate sensitivity identified by the World Climate Research as high priority research.

信风积云在地球的辐射收支中起着至关重要的作用，并产生了热带地区总降水量的20%。然而，我们仍然不知道它们将如何应对全球变暖。信风积云的降水可以改变云的宏观性质和边界层的结构和动力学。模式中的降水发展非常不确定，取决于模拟设置和微物理。特别是，自转换方案显著地影响降水通量、云结构和组织。目前，对不同的自转换方案与观测资料的评价均未降低降雨过程的不确定性。在地面观测中，基于雷达反射率的方法在较晚阶段才探测到降水，阻碍了对导致降雨的因素的识别。降水还可以影响对流组织和环流强度，对气候敏感性产生巨大影响。降水蒸发决定冷池强度，影响云场组织。因此，量化蒸发速率及其时空变异性是关键。云底以下蒸发的参数化是可用的，但在很大程度上取决于雨滴的大小分布。此外，在观测中，蒸发速率很难直接观测到。本提案的目标是回答观测中是什么以及如何触发信风积云降水形成的问题，并利用这些数据来约束LES模型中的降雨形成过程。此外，本研究旨在量化行业云底下蒸发的时空分布，了解其主要依赖于哪些参数。该项目是对即将到来的EUREC4A野外活动的补充，并利用巴巴多斯云天文台（BCO）的长期数据集。降水发生和发展的特征将通过协同地面观测和基于云雷达多普勒频谱偏度的新方法来实现。观测中降水的特征将用于在统计上评估ICON-LEM和DHARMA-LES模型中的降雨形成过程，显示模型再现观测到的平均行为的位置以及偏差发生的位置和原因。该分析将借助PAMTRA正演模拟器在观测空间中进行。将利用EUREC4A和BCO现有观测资料的协同作用来检索蒸发速率。观测剖面的时空变异性将被表征，并用作验证和改进LES模式中蒸发速率描述的约束条件。这项研究将有助于世界气候研究所确定的“云、环流和气候敏感性大挑战”的优先研究。