Cold-air pools

Cold Air Pools - The “Inversion”
C. David Whiteman
Atmos 3200/Geog 3280
Mountain Weather and Climate
Jan 16, 2004
Cold, foul and miserable: Breathing risky in Cache
Utah’s first-ever “very unhealthy” air advisory
Basins and air pollution
Austria’s Klagenfurt basin
©Helmut Ditsch
Vail, Colorado
Salt Lake Basin, Utah
Whiteman photo
Whiteman (2000)
Jan 17, 2004
closure of drive-throughs (MacDonalds)
consolidate car trips; reduce driving times
Stratus or pollution?
Jan 2004
20 Jan 2005
Craig Clements photo
Jim Steenburgh photo
Temperature inversion
•
A layer in the atmosphere in which
temperature increases with height
•
Can occur at any elevation in the
atmosphere
•
Can occur at any location (not just urban
areas)
•
Surface-based inversions are quite
common. They often form when the ground
cools faster than the atmosphere (nights
and winter)
Temperature inversion
Whiteman (2000)
Cold-air pools
Whiteman (2000)
Persistent cold air pool
•
A ground-based layer of air that is confined by
topography, is colder than the air above, and lasts
more than 24 hours
•
Usually forms in winter when solar radiation input
is weak
•
•
Usually forms in anticyclonic weather
The cold pool layer is quiescent (decoupled; low
wind speeds) and moisture and air pollutants tend
to build up in it over time
CAP Effects
Jan 15, 2004
10th consec day of fog, haze and unhealthy air
“Everyone’s sick to death of the fog”
• cold conditions
• suppressed diurnal temperature cycle
• often fog, stratus clouds and air pollutants build up in pool
• if below freezing, rain or drizzle may fall into the pool, producing freezing rain or
freezing drizzle; icing
• affects air and ground transportation, late thawing
• difficult to forecast onset and cessation of pool
Forecasting difficulty with operational (and research) models
Resolution of topography
Resolution of wind and temperature structure
Physics
Typical cold pool weather maps
SLC cold pool
1 Jan 2001-9 Jan 2001
Salt Lake Basin
[prepare for animation]
SLC cold pool from Mt. Ogden, 1 pm on 12/24/01
©Dan Judd
Salt Lake City Cold Pool
26 Dec 2000 - 10 Jan 2001
The Persistent Cold-Air Pool Study
(PCAPS) Field Program
1 December 2010– 7 February 2011
PCAPS Goals
• Identify meteorological processes leading
to development, maintenance, and
breakup of persistent inversions.
• Determine how meteorological models can
be improved to provide more accurate
simulations of persistent inversions.
Climatology of Cold Pools in SLC
Red = Cold Air Pool Period
2005-­‐2006
2006-­‐2007
2007-­‐2008
2008-­‐2009
2009-­‐2010
Climatology of Cold Air Pools In Salt Lake City Ander 2010
PCAPS Instrumenta>on
Processes Influencing CAPs Processes Influencing CAPs Processes Influencing CAPs Processes Influencing CAPs Processes Influencing CAPs Conclusions
• Definitions: Cold-air pool and inversion
• Effects on local populations
• Basin cold pools often form without clouds
• cold pool initiation from drainage or cold frontal passage
• cause: long winter nights, short days, snow & cloud cover
• strength of pool varies with differential advection
• strengthens when warm air comes in aloft
• weakens when cold air comes in aloft
• Some cold pools contain an elevated stratus layer
• this temperature structure allows more vertical diffusion
• mixture of effects from different scales of motion
References
Clements, C. B., C. D. Whiteman, and J. D. Horel, 2003: Cold-air-pool structure and evolution in a
mountain basin: Peter Sinks, Utah. J. Appl. Meteor., 42, 752-768.
Whiteman, C. D., X. Bian, and S. Zhong, 1999: Wintertime evolution of the temperature inversion in
the Colorado Plateau Basin. J. Appl. Meteor., 38, 1103-1117.
Whiteman, C. D., S. Eisenbach, B. Pospichal, and R. Steinacker, 2004: Comparison of vertical
soundings and sidewall air temperature measurements in a small Alpine basin. J. Appl. Meteor., 43,
1635-1647.
Whiteman, C. D., T. Haiden, B. Pospichal, S. Eisenbach, and R. Steinacker, 2004: Minimum
temperatures, diurnal temperature ranges and temperature inversions in limestone sinkholes of
different size and shape. J. Appl. Meteor., 43, 1224-1236.
Whiteman, C. D., S. Zhong, W. J. Shaw, J. M. Hubbe, X. Bian, and J. Mittelstadt, 2001: Cold pools in
the Columbia Basin. Weather and Forecasting, 16, 432-447.
Zhong, S., X. Bian, and C. D. Whiteman, 2003: Time scale for cold-air pool breakup by turbulent
erosion. Meteor. Z., 12, 229-233.
Zhong, S., C. D. Whiteman, X. Bian, W. J. Shaw, and J. M. Hubbe, 2001: Meteorological processes
affecting evolution of a wintertime cold air pool in the Columbia Basin. Mon. Wea. Rev., 129,
2600-2613.