Publication Date

Spring 2020

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Meteorology and Climate Science

Advisor

Ryan J. Patnaude

Subject Areas

Meteorology

Abstract

Cirrus clouds are strong controllers of the global radiation budget, but significant uncertainties remain regarding the thermodynamic, dynamic, and aerosol indirect effects on their microphysical properties. The lack of observational analysis on cirrus cloud controlling factors, i.e., temperature, relative humidity, vertical velocity, and aerosol number concentrations (Na), limits our understanding of their impact on cirrus microphysical properties, making quantification and parameterization of cirrus clouds in climate models difficult. Using seven flight campaigns funded by the National Science Foundation (NSF), impacts of cirrus controlling factors and their regional distributions are individually quantified, and used to evaluate the National Center for Atmospheric Research (NCAR) Community Atmosphere Model 6 (CAM6). Na is found to produce positive correlations with respect to cirrus microphysical properties (i.e., ice water content, ice crystal number concentrations, and mean diameter) when Na is 3 – 10 times higher than average values. The magnitudes of the correlations depend on the size of the aerosols (i.e., > 500 nm or > 100 nm) and environmental conditions, indicating different roles of heterogeneous and homogeneous nucleation, respectively. Compared with observations, CAM6 simulations show large biases in terms of aerosol indirect effects and regional variations of cirrus microphysical properties, underscoring the importance of evaluating and improving cirrus cloud parameterizations in climate models.

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