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DTSTAMP:20250509T092039Z
DESCRIPTION: \n\nStudent Seminar Series\n\nDepartment of Atmospheric & Ocea
 nic Sciences\n\npresents\n\na talk by\n\nSonja Drueke\n	PhD student\n\nSens
 itivity of Shallow-Cumulus Dilution to Vertical Wind Shear\n\nShallow cumu
 lus clouds are prevalent over land and ocean and play an essential part in
  weather and climate by regulating the thermodynamic structure of the atmo
 sphere. The vertical growth of shallow cumuli is inhibited by entrainment\
 , the process by which environmental air is ingested into the clouds. It c
 auses cloud dilution and the evaporation of cloud droplets\, which reduces
  the liquid water content (LWC)\, buoyancy\, and vigor of convection. Cumu
 lus dilution is potentially sensitive to numerous environmental conditions
 \, including humidity\, static stability\, aerosol loading\, surface condi
 tions\, and vertical wind shear. Of particular interest to this study is t
 he role of vertical shear\, which has been assumed to enhance cumulus entr
 ainment for decades. However\, the large-eddy simulations (LES) of Brown (
 1999) have shown that this is not always the case.\n\nAs part of an ongoin
 g study on the environmental sensitivities of dilution\, we have conducted
  LES of observationally constrained shallow-cumulus cloud fields over the 
 ocean and over land\, based on two LES intercomparison projects (BOMEX ove
 r the ocean and ARM-SGP over land). By modifying the wind profiles in thes
 e test cases\, we systematically investigate the sensitivity of cloud dilu
 tion to vertical wind shear. The maritime BOMEX case is found to exhibit a
  strong sensitivity to cloud-layer shear with up to 60% larger dilution ra
 tes in the strongly sheared experiments. In these flows\, a pressure dipol
 e develops across the cloud with high pressure on the upshear side and low
  pressure on the downshear flank. Upshear\, it tends to divert the flow ar
 ound the cloud\, whereas it enhances the inflow into the downshear cloud f
 lank. As a result of the dynamic entrainment downshear\, the cumuli are mo
 re strongly diluted on the downshear flank. While a stronger pressure dipo
 le as a consequence of the higher vertical velocities in the cloud core is
  observed in the continental case\, the dilution rate exhibits a weaker se
 nsitivity. This weaker sensitivity is explained by the larger surface heat
  fluxes and higher levels of turbulence in the continental case.\n\nWednes
 day Feb 19/ 2.30 PM/ Room 934 Burnside Hall\n\n \n
DTSTART:20200219T193000Z
DTEND:20200219T203000Z
LOCATION:Room 934\, Burnside Hall\, CA\, QC\, Montreal\, H3A 0B9\, 805 rue 
 Sherbrooke Ouest
SUMMARY:Sensitivity of Shallow-Cumulus Dilution to Vertical Wind Shear
URL:/meteo/channels/event/sensitivity-shallow-cumulus-
 dilution-vertical-wind-shear-320310
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