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UID:20250922T150321EDT-3957f4KFsV@132.216.98.100
DTSTAMP:20250922T190321Z
DESCRIPTION:Atmospheric and Oceanic Sciences Departmental Seminar Series\n
 \npresents\n\nNumerically simulated orographic convection across multiple 
 grey zones\n\na talk by\n\nProf. Daniel Kirshbaum\n	Associate Professor & C
 hair\, Department of Atmospheric and Oceanic Sciences\, McGill\n\nAs weath
 er and climate models inexorably move to finer grids\, they traverse so-ca
 lled “grey zones”\, or ranges of horizontal grid spacings where key proces
 ses transition from fully parameterized to fully explicit. Within these gr
 ey zones\, scale-separation between the process of interest and the grid s
 cale\, a fundamental assumption of most subgrid parameterizations\, breaks
  down. For the moist convection problem\, which in the real atmosphere is 
 characterized by horizontal scales from O(10 km) down to O(100 m)\, two im
 portant numerical grey zones exist: (i) the deep convection grey zone [O(1
 0 km) to O(1 km)] and the turbulence grey zone [O(1 km) to O(100 m)]. In t
 his study\, idealized numerical simulations of orographic convection cross
 ing both grey zones are conducted to quantify the errors stemming from ina
 dequate resolution of cloud processes. The experiments consider two differ
 ent mechanisms by which orography commonly initiates moist convection: mec
 hanical and thermal forcing. To aid the diagnosis\, a new method of diagno
 sing entrainment/detrainment in large-eddy simulations is proposed. For bo
 th convection-initiation mechanisms\, cases with parameterized convection 
 exhibit large biases in the timing\, intensity\, and/or horizontal distrib
 ution of clouds and precipitation. Although the results greatly improve fo
 r “convection-permitting” grids of O(1 km) and below\, they do not always 
 converge to a robust solution as the grid spacing is decreased. Robust sol
 utions are found only in flows with well-developed turbulence fields prior
  to convection initiation. By contrast\, in cumulus fields undergoing turb
 ulent transition\, the transition itself is highly sensitive to the grid s
 pacing\, which prevents numerical convergence. For these cases\, O(10 m) o
 r smaller grids may be required to achieve robust solutions.\n\nMonday Jan
  20/ 3:30 PM/ Burnside Hall/ Room 934\n
DTSTART:20200120T203000Z
DTEND:20200120T220000Z
LOCATION:Room 934
SUMMARY:Numerically simulated orographic convection across multiple grey zo
 nes
URL:/meteo/channels/event/numerically-simulated-orogra
 phic-convection-across-multiple-grey-zones-303638
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