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Master's Defense

Department of Atmospheric Science

Tues., Oct. 24, 3:10 pm, EN6085

Characterizing Nocturnal Environmental Boundary Layer Condition Around Convective Storm with Airborne Compact Raman Lidar During PECAN

Guo Lin

University of Wyoming

Abstract

Measurements of environmental conditions around severe local storms are important in advancing our understanding of these severe local storms. These measurements are, however, difficult to collect. During the PECAN (Plains Elevated Convection at Night) field campaign on the Great Plains, a compact Raman Lidar (CRL) system deployed on University of Wyoming King Air (UWKA) Research Aircraft uniquely characterized rapidly changing environments around a nocturnal MCS on July 1st, and an anticipated CI on June 8th, 2015. Compared to conventional observation, CRL was unique to detect multiple structures in boundary layer around storms during PECAN, lending insight into the 2D vertical structure in high spiral and temporal resolutions. CRL firstly detected a small convection initiated and sustained by an elevated convergence in environmental boundary layer that was formed by two reversed flows from the MCS, as well as two distinct layers of water vapor and aerosol triggered by a southern environment flow and a flow from a passed convective cell. Downdraft cold pool and outflow boundary layer was also sampled on July 1st. Flight level vertical wind and temperature transect depicted a cold downdraft structure on the southern edge of a nocturnal MCS. Water vapor and aerosol transects revealed that inflow boundary air was pushed upward by nocturnal MCS outflow. An inversion layer was form by the warmer southwest flow on the top of a cooler southeast flow on the leading edge of density current. A wave-like motion was triggered above an inversion layer, which had strong correlation with in situ flight level vertical velocity on energy distribution of wavelengths from 1.8 to 18 km, that would enable advance data assimilation to improve the prediction of convective system. UWKA also depicted boundary layer structure on an area of anticipated CI on June 8th. Significant water vapor gradients and collision by environmental inflow and outflow of a storm initiated strong uplift of water vapor in a transition zone with high CAPE and low CIN in the environment. The less stabilization and collision boundary layer supported the environmental condition surrounding an MCS to trigger CIs where UWKA had crossed 30 minutes ago. Intense observation networks, such as PISA sites, mobile mesonet and radars, served as additional measurements to prove detail multiple structures that CRL detected around MCSs and anticipated CIs.


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