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Observations of Great Salt Lake Breezes During Salt Lake Valley

Persistent Cold Air PoolsErik Crosman, John Horel, Neil Lareau, and Xia Dong

University of UtahDepartment of Atmospheric Sciences

15th AMS Conference on Mountain MeteorologySteamboat Springs, CO

Paper 8.3 Tuesday, 21 August 2012

Part of Larger Effort to Improve Understanding of Summertime and Wintertime Sea and Lake Breezes

Winter 2010-2011 Persistent Cold Air Pool Study

Summer 2009 Great Salt Lake Breeze Undergraduate Field 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)

Great SaltLake4,400 km2

SaltLake Valley~1,000 km2

1 December 2010-5 February 2011

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!

Oquirrh

Mtns

Wasatch M

ountains

Research Questions1. 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

Lake

Salt Lake Valley

2. How do the lake breezes impact persistent cold air pools?

Research Questions

PCAPS IOP57 January 2011Photo Dave Bowling

MODIS May 17 2009

MODIS July 17 2009 Sensitivity of Summer Lake Breezes to Land Surface Sensible Heat Flux

Great Salt Lake

Great Salt Lake

Salt LakeCity

Salt LakeCity

Land Surface Skin Temperature (°C)

May 17 July 17

High heat flux

Medium heat flux

Mtns

Mtns

z (m)

z (m)

u ms-1

0 20 40 60 80 100 120 LandLake km

0 20 40 60 80 100 120 LandLake km

400 W m-2

100 W m-2Low Flux LES Simulation ‘Winter’

High Flux LES Simulation ‘Summer’

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

Crosman and Horel 2010 Sea and Lake Breezes: A Review of Numerical Studies BLM 137:1-29

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

Observations of Typical Summer vs. Winter Great Salt Lake Breezes

3 Feb 2011 ‘PCAPS Winter’17 July 2009 ‘Summer’

0

5

10

Not Expecting ‘Enhanced’ Lake Breezes During PCAPS!

•Lake/land ΔT of 7 ⁰C•Lake breeze wind speeds ~4-5 m s-1

•Lake breeze depth near shoreline >500 mInland movement ~10 km h-1

IOP3 13 December 2010

⁰C ⁰C

⁰C⁰C

•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

Processes Contributing to Great Salt Lake Summertime Breezes

Great Salt Lake Salt Lake Valley

• Heat Flux (insolation, soil moisture)• Background wind (occurrence or not and inland

movement)

Processes Contributing to Great Salt Lake Wintertime Breezes During CAPs

Great Salt Lake Salt Lake Valley

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 significant2. Interactions between solar heating, boundary-layer stable layers and background

winds result in mixing and horizontal temperature gradients3. When these processes favorably combine the lake breeze is enhanced

Ɵ

Ɵ + ΔƟ

Insolation mixing

Valley wind channeling

Lake heat flux

Clouds and fog

Cold air drainage pooling

stability

Snow cover

Great Salt Lake Salt Lake Valley

Ɵ

Ɵ + ΔƟ

Insolation mixing

Valley wind channeling

Lake heat flux

Clouds and fog

Cold air drainage pooling

stability

Snow cover

IOP3 12-13 December 2010T

emp

erat

ure

(C

)⁰ Lake breeze

front

5 51711 23 1711 Time (MST)

12 Dec 13 Dec

5 m s-1

COLD

WARM

5 m s-1

COLD

Air over Lake

Air over Valley

Low-Budget Research Aircraft: Motorized Paraglider

Valley

Glider shoreline

5 m s-1

IOP3 13 December 2010

Lake

Salt Lake Valley

2. How do the lake breezes impact persistent cold air pools?

Research Questions

Photo Dave Bowling

Lake Breezes

Day of January 2011

Diff

eren

ce in

BL

tem

pera

ture

(⁰C)

b

etw

een

Valle

y an

d N

ear L

ake

Large Horizontal Variations in Salt Lake Valley Persistent Cold Air Pools Occur During Lake Breezes

Hei

ght (

m)

1100

500

0

Ɵ (K)

292

287

282H

eigh

t (m

)

1100

500

0

IOP9 26-27 Jan 2011

Lake Breeze ‘Recharge’

17 23 05 11 17 23

Estimating mixed-layer heights (Horel et al. previous talk 8.2)

Ɵ (K)

292

287

28217 23 05 11 17 23

Time (MST)

Time (MST)

26 Jan 27 Jan

27 Jan26 Jan

•8 documented cases •Influences CAP intensity andduration

•Lake a ‘reservoir’ of cold air

More nocturnal cooling over valley

less daytime heating near lake

Hei

ght (

m)

1100

500

0

U (ms-1)

6

3

0

U (ms-1)

6

3

0

Hei

ght (

m)

1100

500

0

‘Pulsing’ nocturnal drainage flows

Lake breeze winds

Lake Breezes ‘Recharge’ Persistent Cold Air Pool Boundary Layer

17 23 05 11 17 23

17 23 05 11 17 23

Time (MST)

Time (MST)

IOP9 26-27 Jan 2011 26 Jan 27 Jan

27 Jan26 Jan

fog

Great Salt Lake Lake Breezes Modulate Clouds, Fog

PCAPS IOP5 Jan 6 2011

MODIS Terra ~IOP9 18 UTC 28 Jan 2011

Great Salt Lake

Salt LakeValley

Convergence and Advection

Noon2 pm

Noon 2 pm

Wind Speed (m s-1)

Lake Breezes Modulate Valley PollutantsIOP9 27 Jan 2011

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 More complex

surface heat fluxes(land surface)

surface heat fluxesbackground winds

surface heat fluxes-land surface -lake surface background winds-terrain channeling and blocking-differential mixingstabilitycold air poolingclouds

Weakest Strongest

Generally discussed spectrum

Crosman and Horel 2010 Sea and Lake Breezes: A Review of Numerical Studies BLM 137:1-29

Nocturnal drainage cold pool

Lake surface sensible heat flux

mixing

snow

Salt Lake Valley

~2 pm 17 July 2009

Summer Great Salt Lake BreezeHigh land surface sensible heat flux drives lake breeze circulations

Great Salt Lake

SaltLake Valley

Background synoptic wind modulates occurrence, intensity and inland extent

Land Surface Skin Temperature (°C)

TooeleValley

Wasatch

Mtns

Mtns

StansburyM

tns

Low RH

High RH

Lake Breezes Modulate SLV Cloud Cover

Utah Valley

Salt Lake Valley

Photo: Sebastian Hoch

GreatSalt Lake

18 UTC IOP9 28 Jan 2011 MODIS Terra ~18 UTC 28 Jan 2011

Understanding The Effects of The Great Salt LakeLake modulates clouds and fog during CAPs

Lake breeze fronts strengthen the low-level stability during CAPs

Cold lake airWarm Salt Lake Valleyair

Large-eddy sensitivity simulations currentlybeing 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