Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Atmospheric & Oceanic Sciences

First Advisor

Linnea M. Avallone

Second Advisor

Katja Friedrich

Third Advisor

Baylor Fox-Kemper

Fourth Advisor

Matthew Shupe

Fifth Advisor

Gannet Hallar

Abstract

The phase of cloud water has important impacts on cloud radiative properties, cloud lifetime, and the formation of precipitation. Mixed-phase clouds, or those in which liquid droplets, ice particle and water vapor co-exist, are of particular importance in the Southern Rockies of the United States, where these clouds enhance wintertime mountain precipitation mass and annual water storage in the snowpack. The interaction between multiple water phases within a cloud presents challenges for in situ observation. I describe the existing in situ cloud microphysical instrumentation, and introduce a new instrument for the in situ measurement of total water concentration: the second-generation University of Colorado closed-path tunable-diode laser hygrometer (CLH-2). This compact instrument can be flown within a scientific aircraft under-wing canister and is designed for operation in diverse environmental conditions.

During the winter 2010-2011, the CLH-2 was installed on a wind vane at Storm Peak Laboratory (SPL) in the Park Range of Colorado as a part of the Storm Peak Laboratory Cloud Property Validation Experiment (StormVEx) campaign. I apply a new method for determining the bulk mass-dimensional relationship of ice particles from ground-based observations. Despite important difference between airborne and ground-based particle measurements, my parameterization yields particle masses close to those from recent airborne studies that take into account the effect of ice particle shattering on observed number concentrations. Variations in particle density over the course of a storm are suggested by time variations between the observed and parameterized ice water concentrations.

Using observations from the Wyoming King Air research aircraft collected during the Colorado Airborne Multi-Phase Cloud Study (CAMPS) in winter 2010-2011, cloud water phase is identified using in situ microphysical measurements. While mixed-phase clouds are identified throughout the study area, the fraction of clouds found to be mixed-phase increases amid a region of mean upward vertical air motion that extends 25 km windward of the ridge axis. Near the ridge axis, collocated increases are observed in the CLH observed cloud water concentration and in the number concentration of both cloud-droplet- sized and larger particles. The abundance of mixed-phase clouds decreases sharply in the lee of the ridge, suggesting rapid glaciation or evaporation in the absence of the windward updrafts. These observations largely support existing conceptual models of mixed-phase cloud development over a topographic barrier.

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