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UID:20261031T010410EDT-2829ur90Kd@132.216.98.100
DTSTAMP:20261031T050410Z
DESCRIPTION:Dr. Thibault Dauhut joins us from Laboratoire d'Aérologie with 
 CNRS and the University of Toulous to discuss the Giga-LES of Hector the C
 onvector Keeping the Tallest Updrafts Undiluted\n\nAbstract\nThe failure o
 f global models to explain the decadal trend of stratospheric water vapor 
 may stem from a lack of representation of rapid water transfers from tropo
 sphere to stratosphere. This motivates our modeling study of Hector the Co
 nvector on 30 November 2005. This was a particular case of very deep conve
 ction over the Tiwi Islands\, Australia\, for which plumes of ice particle
 s reaching 19 km altitude were observed. We performed a Giga Large-Eddy Si
 mulation (100 m horizontal resolution\, more than 1 billion grid points) u
 sing cutting-edge computing resources\, together with a series of simulati
 ons with coarser resolutions\, from 200 m to 1600 m. Whatever the resoluti
 on\, two updrafts overshot the tropopause\, carrying ice crystals into the
  stratosphere and leading to moistening. Grid spacing of the order of 100 
 m may be necessary for a reliable estimation of hydration (Dauhut et al. A
 SL 2015\, doi: 10.1002/asl2.534). The mechanisms leading to very deep conv
 ection were investigated.\nThe low-level convergence lines determined the 
 locations of the tallest updrafts. Created by the sea breeze in the mornin
 g\, they appeared along the coasts over which mid-level convection popped 
 up at noon. The associated congestus then produced cold pools that supplie
 d the convergence lines with surface buoyant air. Deep convection became v
 isible shortly after\, due to the enhanced buoyancy both at the base of th
 e updrafts and above the freezing level with the generation of icy hydrome
 teors.\nBy continuing to move inland\, the convergence lines drew together
  and reinforced each other. Above them\, very deep convection developed as
  two updrafts expanding over an 8-km width and keeping their core undilute
 d up to the tropopause. Large cold pools were then generated and drove con
 vective cells at their edges. The convective cells merged into each other 
 above the island center\, leading to several mesoscale convective complexe
 s. Although they did not reach the stratosphere\, the convective complexes
  still transported a large amount of water into the upper troposphere. Fin
 ally\, the resulting heavy precipitations fed a massive cold pool that cut
  Hector the Convector off from the ground and expelled its remnants outsid
 e the Tiwi Islands. A comprehensive analysis of individual updrafts and th
 eir properties shows that the overshooting updrafts present higher buoyanc
 y\, stronger vertical velocities and larger hydrometeor contents than ordi
 nary deep convective updrafts and mesoscale convective complexes. In the t
 allest updrafts\, the equivalent potential temperature exceeds the maximum
  value at the surface by 10 K\, the upward wind speed reaches 50 m/s\, and
  the loading of condensed water exceeds 10 g/kg. Both the low-level conver
 gence lines intensified by cold pools and the reduced mixing in the tropos
 phere are found to be determinant for the transition from deep to very dee
 p convection. The isentropic analysis of Hector the Convector will also be
  presented.\nRefreshments will be served.\n
DTSTART:20150814T190000Z
DTEND:20150814T200000Z
LOCATION:Room 934\, Burnside Hall\, CA\, QC\, Montreal\, H3A 0B9\, 805 rue 
 Sherbrooke Ouest
SUMMARY:Seminar: Thibault Dauhut
URL:https://www.mcgill.ca/meteo/channels/event/seminar-thibault-dauhut-2544
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