Boundary Layer Meteorology
LES of passive scalar in a convective boundary layer
(grid size = 20 m)
(from Stevens 2005, after Arakawa 1975)
Time-lapse video of fog in Salt Lake Valley
Jan 26 and Feb 2, 2006
Acold-air pool (CAP), defined as a topographic depression filled with cold air,
occurs when atmospheric processes favor cooling of the air near the surface,
warming of the air aloft, or both. The resulting stable stratification prevents the
air within the basin from mixing with the atmosphere aloft while the surrounding
THE PERSISTENT COLD-AIR
BY NEIL P. LAREAU, ERIK CROSMAN, C. DAVID WHITEMAN, JOHN D. HOREL,
SEBASTIAN W. HOCH, WILLIAM O. J. BROWN, AND THOMAS W. HORST
Utah's Salt Lake valley was the setting for a wintertime study of
multiday cold-air pools that affect air quality in urban basins.
FIG. 2. Photos of key PCAPS instrumentation. See Fig. 1 for location of instruments. (a) NCAR ISFS, (b) University
of Utah automatic weather station, (c) University of Utah Hobo temperature dataloggers, (d) University of Utah
scanning Doppler lidar, (e) and (g) NCAR ISS sites, (f) University of Utah minisodar, (h) University of Utah mobile
radiosonde launch, (i) University of Utah mobile weather stations, and (j) instrumented motorized paraglider.
(NWS) soundings deployed at the nearby Salt Lake
International Airport (Fig. 1). The temporal interval
FIG. 2. Photos of key PCAPS instrumentation
FIG. 4. Photos of SLV inversions during PCAPS (photo credits are in parentheses): (a) 14 Jan 2011: combined fog
and pollutants (Sebastian Hoch); (b) 2 Dec 2010: cloud-free deep (~700 m) polluted layer (Chris Santacroce);
(c) 16 Jan 2011: thin surface layer (
king due to sharp vertical gradients in
d aerosols (e.g., Fig. 4c).
table layers were observed on many ocg
PCAPS (Fig. 5f, IOP 5), generally ariso
or more of the processes that control
ty. In this particular case, two elevated
surface local-scale forcing influenced its for
maintenance, and breakup. The thermod
signatures of these processes are summarized
which shows a time–height diagram of poten
perature within and above the SLV as measu
combination of ISS and NWS radiosondes.
(Meteor Crater Experiment)
METCRAX II Field Equipment!
Meteor Crater, 22-23 Oct 2006! • Strong 30-m
on crater floor !
remaining 75% of
jump develops at
• Crater cools
What physical process(es) produce the isothermalcy?!
Conceptual model - DWF!
Would you like to gain some meteorological field experience? The Meteor
Crater II (METCRAX II) experiment will be run this fall looking at nighttime
hydraulic flows and hydraulic jumps at Arizona's Meteor Crater. Helicopter
loading operations will be conducted in early to mid-September, the
equipment setup is scheduled for 25-29 September, the one-month field
experiment will be run from 30 September through 30 October, and
equipment takedown will take place 31 Oct - 2 November. We could use
assistance with all of these operations.
By participating, you could gain experience with hands-on operation of
tethersondes, rawinsondes, scanning Doppler LiDARs, automatic weather
stations, HOBOS, flux towers, tall instrumented towers, SoDARs and other
meteorological instruments. The field study is being supported by NCAR's
Earth Observing Laboratory, and they are providing some of this equipment
and bringing additional instruments and resources to the field. There will be
unique opportunities to enter the Meteor Crater to fly tethersondes at night
from the crater floor during Intensive Operational Periods.
If you would like to know more about the Meteor Crater, we have a webpage
at http://www.inscc.utah.edu/~whiteman/METCRAX/ where you can look at
photographs and other information from our previous experiment there in