Analysis of Cirrus Clouds and Atmospheric Humidity with Cloud Resolving Numerical Model Calculations

Princeton University, Princeton NJ

Investigators

Abstract

Clouds pose a major challenge for global climate models, and uncertainties remain from process level understanding of cloud formation to processes that control the global cloud distribution. This project provides high-resolution numerical model simulations that will advance our theoretical understanding of the dominant factors controlling the genesis and global distribution of cirrus clouds, their impact on atmospheric water vapor, and the radiative impact of the combined cloud/vapor system. The role of cirrus clouds in dehydration of the upper troposphere remains not well quantified. The project's focus is on the importance of the interaction between cirrus clouds and the environment, and aims to bridge the gap in numerical modeling between the detailed study of individual cirrus clouds and the full domain-wide properties of the cloud field. The objectives of this project are (i) to determine the relative importance of nucleation processes (traditionally a focus of cirrus research) to post-nucleation processes (such as gravitational redistribution of condensate) on the cloud's microphysical properties; (ii) to quantify the impact of the cloud microphysical properties on the domain-wide moisture field (which in turn may feed back onto cloud formation) and domain-wide cloud field properties (such as occurrence frequency and ice water path); and (iii) to put the results from (i) and (ii) in context with the dynamical constraints on conditions favorable for cloud formation. The project focuses specifically on the role of cirrus in the tropical tropopause layer (TTL). Results from the project will contribute to improved understanding of the role of cirrus clouds for the regulation of water vapor in the TTL and stratosphere (with important consequences for the radiative forcing of climate, and stratospheric chemistry). The TTL is also in several ways ideal to study cirrus clouds and their interaction with the environment as both the dynamical conditions favoring in-situ cirrus cloud formation, as well as the large-scale structure of the TTL, can be reasonably well idealized. The objectives of the project are addressed with a wide range of numerical experiments with a cloud-resolving model that is scalable from very high resolution simulations at cloud scale to simulations of the entire tropics. Intellectual Merit : Insights from this project will help to improve parameterizations for general circulation models, leading to improved climate predictions. Broader Impacts : This project will help to reduce uncertainties in climate predictions, providing policy makers with more accurate information on future climate. The project will support a designated post-doctoral researcher with excellent reputation and a graduate student, thus training the next generation of cloud modeling specialists. Further, the PI will actively promote involvement of undergraduate students (in the form of Junior and Senior Theses) at Princeton University, thereby providing a first-hand experience and better understanding of climate science to a body of students that frequently follows careers in industry, finance and government.