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Seminar coordinator: Prof. Greg McFarquhar (mcfarq at illinois.edu)

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Event Detail Information

Event Detail Information

Observations of the 6 June 2010 Nontornadic Supercell and 14 April 2012 Tornadic Supercell

Speaker Jeff Frame, Clinical Assistant Professor, Department of Atmospheric Sciences, University of Illinois
Date Sep 25, 2013
Time 3:00 pm  
Location Room 114 of the Transportation Building
Sponsor Department of Atmospheric Sciences, University of Illinois
Contact Shirley Palmisano
Phone 217-244-5737
Event type Graduate colloquium
Views 750

In the first portion of this talk, radar observations of a nontornadic supercell obtained by two Doppler on Wheels (DOW) radars on 6 June 2010 near Ogallala, NE, during the Verification of the Origins of Rotation in Tornadoes Experiment 2 (VORTEX2) are presented. A dual-Doppler wind synthesis from near the beginning of the radar observation period depicts the three-dimensional wind field near the storm, including a region of inflow southeast of the cell, the rear-flank downdraft, and a weak low-level mesoscyclone. Later in the observation period, radar observations reveal that a surge of outflow displaced the rear-flank gust front southeast of the low-level mesocyclone and updraft; a preliminary analysis of in-situ thermodynamic data collected within this outflow surge reveals it to be potentially cold, with virtual potential temperature deficits in excess of 6 K. This, when combined with the lack of inflow parallel to the forward-flank gust front likely resulted in the eventual demise of the low-level circulation and the midlevel updraft associated with this supercell.

 

In the second portion of this talk, thermodynamic observations of a tornadic supercell that passed over three surface observing sites near Wichita, Kansas, on 14 April 2012 are documented. Numerous special observations were recorded, with temporal resolution as fine as one minute, providing a rare opportunity to assess the thermodynamic properties and fine-scale variability within the outflow of a tornadic supercell with conventional surface weather observations. An analysis of these data reveals virtual potential temperature deficits of only about 2 K near the hook echo of the supercell, although deficits exceeding 5 K were present farther into the core of the storm. This analysis also detected a slight equivalent potential temperature surplus near the hook echo, and deficits in excess of 8 K in the core of the storm. It will be demonstrated that the lack of appreciable equivalent or virtual potential temperature deficits near the low-level mesocyclone in the tornadic case but not in the nontornadic case is consistent with current conceptual and dynamical models of supercell tornadogenesis.

 

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