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Observations of Great Salt Lake
Breezes During Salt Lake Valley
Persistent Cold Air Pools
Erik Crosman, John Horel, Neil Lareau, and Xia Dong
`
University of Utah
Department of Atmospheric Sciences
15th AMS Conference on Mountain Meteorology
Steamboat Springs, CO
Paper 8.3 Tuesday, 21 August 2012
Part of Larger Effort to Improve Understanding of
Summertime and Wintertime Sea and Lake Breezes
Summer 2009 Great Salt Lake Breeze
Undergraduate Field Study
Winter 2010-2011 Persistent Cold Air Pool Study
•Great Salt Lake relatively ideal environment for observing lake breezes
•Large variability in atmospheric, land and lake surface state
•Lake breezes for small and medium sized lakes less well-understood
than sea breezes
•Very few observations of mid-latitude wintertime lake breezes
•No previous studies on lake breezes occurring during wintertime cold
air pools
The Persistent Cold Air Pool Study (PCAPS)
Lareau,N., E.Crosman, C.D.Whiteman, J.D.Horel,
S.W.Hoch, W.O.J.Brown, and T.W.Horst,2012:The
Persistent Cold Air Pool Study Bulletin of the
American Meteorological Society In press
Unprecedented wintertime
observations!
Great Salt
Lake
4,400 km2
Salt
Lake
Valley
~1,000 km2
1 December 2010-5 February 2011
Research Questions
1. What are the characteristics of and processes controlling
winter lake breezes during persistent cold air pools?
Great Salt Lake
Lake Breeze Front
PCAPS IOP1
5 December 2010
Research Questions
Salt Lake Valley
Lake
2. How do the lake breezes impact
persistent cold air pools?
Photo Dave Bowling
PCAPS IOP5
7 January 2011
MODIS July 17 2009
Great Salt Lake
Sensitivity of Summer Lake Breezes to
Land Surface Sensible Heat Flux
May 17
Salt Lake
City
July 17
High heat
flux
MODIS May 17 2009
Great Salt Lake
Medium heat flux
Salt Lake
City
Land Surface Skin Temperature (°C)
Low Flux LES Simulation ‘Winter’
100 W m-2
z (m)
0
20 Lake
40
60
km
80
Land
High Flux LES Simulation ‘Summer’
100
120
400 W m-2
z (m)
0
20 Lake
40
60 km
u ms-1
80
Land
100
120
Crosman and Horel 2010 Sea and Lake Breezes: A Review of Numerical Studies BLM 137:1-29
Crosman and Horel 2012 Idealized Large-Eddy Simulations of Sea and Lake Breezes: Sensitivity
to Lake Diameter, Heat Flux and Stability BLM 144(3):309-328
Observations of Typical Summer vs. Winter
Great Salt Lake Breezes
3 Feb 2011 ‘PCAPS Winter’
17 July 2009 ‘Summer’
10
5
0
Summer
Winter
Cross-Coast Breeze Wind Speed (m s-1)
5-8
2-3
Depth (m)
600 m
200 m
Duration (hr)
10 hr
6 hr
Not Expecting ‘Enhanced’ Lake Breezes During PCAPS!
•Wind speed, duration, and depth comparable to summer in several cases
•Lake breeze surface frontal contrast and inland movement higher than summer
IOP3 13 December 2010
⁰C
⁰C
•Lake/land ΔT of 7 ⁰C
•Lake breeze wind
speeds ~4-5 m s-1
•Lake breeze depth near
shoreline >500 m
Inland movement ~10
km h-1
⁰C
⁰C
IOP3 13 December 2010
Processes Contributing to Great Salt Lake
Summertime Breezes
• Heat Flux (insolation, soil moisture)
• Background wind (occurrence or not and inland
movement)
Great Salt Lake
Salt Lake Valley
Processes Contributing to Great Salt Lake
Wintertime Breezes During CAPs
Winter lake breezes during PCAPS complex due to:
1. Weak solar forcing allows other processes (e.g., lake heat flux, cold air drainage)
to become significant
2. Interactions between solar heating, boundary-layer stable layers and background
winds result in mixing and horizontal temperature gradients
3. When these processes favorably combine the lake breeze is enhanced
mixing
Insolation
Ɵ + ΔƟ
Valley wind channeling
stability
Ɵ
Snow cover
Clouds and fog
Great Salt Lake
Lake heat flux
Cold air drainage pooling
Salt Lake Valley
(⁰C)
12 Dec
13 Dec
IOP3 12-13 December 2010
Temperature
Air over
Valley
Lake breeze
front
Air
over
Lake
5
11
17
23
5
5 m s-1
mixing
Insolation
Ɵ + ΔƟ
COLD
17 Time (MST)
11
Valley wind channeling
stability
Ɵ
COLD
Snow cover
Clouds WARM
and fog
Great Salt Lake
Lake heat flux
Cold air drainage pooling
Salt Lake Valley
Low-Budget Research Aircraft: Motorized Paraglider
Valley
Glider shoreline
5 m s-1
IOP3 13 December 2010
Research Questions
Salt Lake Valley
Lake
2. How do the lake breezes impact
persistent cold air pools?
Photo Dave Bowling
Difference in BL temperature (⁰C)
between Valley and Near Lake
Large Horizontal Variations in Salt Lake Valley
Persistent Cold Air Pools Occur During Lake Breezes
Lake Breezes
Day of January 2011
Lake Breeze ‘Recharge’
•8 documented cases
•Lake a ‘reservoir’ of cold air
26 Jan
1100
Height (m)
IOP9 26-27 Jan 2011
•Influences CAP intensity and
Ɵ (K)
duration
27 Jan
292
287
500
0
17
26 Jan
1100
Height (m)
23
05
11
Time (MST)
17
27 Jan
282
23
Ɵ (K)
292
287
500
0
05
11
Time (MST)
Estimating mixed-layer heights (Horel et al. previous talk 8.2)
17
23
17
23
282
Lake Breezes ‘Recharge’ Persistent Cold Air Pool
Boundary Layer
U (ms
26 Jan
Height (m)
1100
27 Jan
6
Lake breeze winds
3
500
less daytime heating near lake
0
0
17
1100
Height (m)
IOP9 26-27 Jan 2011
-1)
23
26 Jan
05
11
Time (MST)
17
27 Jan
23
U (ms-1)
6
‘Pulsing’ nocturnal drainage flows
3
500
More nocturnal cooling over valley
0
17
23
05
11
Time (MST)
17
23
0
Great Salt Lake Lake Breezes Modulate Clouds, Fog
MODIS Terra ~IOP9
18 UTC 28 Jan 2011
Great
Salt
Lake
PCAPS
IOP5 Jan 6
2011
fog
Salt Lake
Valley
Lake Breezes Modulate Valley Pollutants
IOP9 27 Jan 2011
Noon
2 pm
Wind Speed (m s-1)
Convergence and
Advection
Noon 2 pm
Summary
• Winter lake breezes typically ~1/3 speed, depth of summer
case
• Winter lake breeze forcing mechanisms complex and
variable
• Several ‘enhanced’ wintertime lake breezes unexpectedly
observed during PCAPS
• Afternoon lake breezes were found to ‘recharge’ cold air in
the lowest 200-800 m of Salt Lake Valley boundary layer
• Lake breezes play role in cold air pool fog and low cloud
occurence
• Lake breeze passage lowered pollutant concentrations
within SLV
Questions?
Photo Sebastian Hoch
Observed Spectrum of Winter GSL Breezes
Less complex
Weakest
surface heat fluxes
(land surface)
More complex
Strongest
surface heat fluxes
background winds
Generally discussed spectrum
surface heat fluxes
-land surface
-lake surface
background winds
-terrain channeling and
blocking
-differential mixing
stability
cold air pooling
clouds
10 Factors That Impact Sea and Lake Breezes
mixing
Lake surface sensible heat flux
Nocturnal drainage cold pool
Crosman and Horel 2010 Sea and Lake Breezes: A Review of Numerical Studies BLM
137:1-29
Summer Great Salt Lake Breeze
Great
Salt
Lake
Salt Lake Valley
Tooele
Valley
~2 pm 17 July 2009
snow
Salt
Lake
Valley
Land Surface Skin Temperature (°C)
High land surface
sensible heat flux
drives lake breeze
circulations
Background
synoptic wind
modulates
occurrence,
intensity and inland
extent
Lake Breezes Modulate SLV Cloud Cover
Photo: Sebastian Hoch
18 UTC IOP9 28 Jan 2011
High RH
Great
Salt
Lake
MODIS Terra ~18 UTC 28 Jan 2011
Salt
Lake
Valley
Low RH
Utah Valley
Understanding The Effects of The Great Salt Lake
Lake breeze fronts strengthen the lowlevel stability during CAPs
Cold lake air
Warm
Salt Lake
Valley
air
Lake modulates clouds
and fog during CAPs
Large-eddy sensitivity simulations currently
being run to assess the role of GSL in
•Strengthening and prolonging cold air pools
•Impacting fog occurrence and formation
•Serving as a reservoir for cold air drainage