` 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 15 th 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 Winter 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 Salt Lake 4,400 km 2 Salt Lake Valley ~1,000 km 2 1 December 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 Mountains

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

Lake Salt Lake Valley 2. How do the lake breezes impact persistent cold air pools? Research Questions PCAPS IOP5 7 January 2011 Photo Dave Bowling

MODIS May MODIS July Sensitivity of Summer Lake Breezes to Land Surface Sensible Heat Flux Great Salt Lake Salt Lake City Salt Lake City Land Surface Skin Temperature (°C) May 17July 17 High heat flux Medium heat flux Mtns

z (m) u ms Land Lakekm Land Lakekm 400 W m W m -2 Low 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): 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 ) 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’

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 m Inland movement ~10 km h -1 IOP3 13 December 2010 ⁰C 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 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 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 IOP December 2010 Temperature ( ⁰ C) Lake breeze front Time (MST) 12 Dec13 Dec 5 m s -1 COLD WARM 5 m s -1 COLDAir 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 2011Difference in BL temperature (⁰C) between Valley and Near Lake Large Horizontal Variations in Salt Lake Valley Persistent Cold Air Pools Occur During Lake Breezes

Height (m) Ɵ (K) Height (m) IOP Jan 2011 Lake Breeze ‘Recharge’ Estimating mixed-layer heights (Horel et al. previous talk 8.2) Ɵ (K) Time (MST) 26 Jan27 Jan 26 Jan 8 documented cases Influences CAP intensity and duration Lake a ‘reservoir’ of cold air

More nocturnal cooling over valley less daytime heating near lake Height (m) U (ms -1 ) Height (m) ‘Pulsing’ nocturnal drainage flows Lake breeze winds Lake Breezes ‘Recharge’ Persistent Cold Air Pool Boundary Layer Time (MST) IOP Jan Jan27 Jan 26 Jan

fog Great Salt Lake Lake Breezes Modulate Clouds, Fog PCAPS IOP5 Jan MODIS Terra ~IOP9 18 UTC 28 Jan 2011 Great Salt Lake Salt Lake Valley

Convergence and Advection Noon 2 pm Noon2 pm Wind Speed (m s -1 ) Lake Breezes Modulate Valley Pollutants IOP9 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 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 complexMore complex surface heat fluxes (land surface) surface heat fluxes background winds surface heat fluxes -land surface -lake surface background winds -terrain channeling and blocking -differential mixing stability cold air pooling clouds WeakestStrongest 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 Breeze High land surface sensible heat flux drives lake breeze circulations Great Salt Lake Salt Lake Valley Background synoptic wind modulates occurrence, intensity and inland extent Land Surface Skin Temperature (°C) Tooele Valley Wasatch Mtns Stansbury Mtns

Low RH High RH Lake Breezes Modulate SLV Cloud Cover Utah Valley Salt Lake Valley Photo: Sebastian Hoch Great Salt Lake 18 UTC IOP9 28 Jan 2011MODIS Terra ~18 UTC 28 Jan 2011

Understanding The Effects of The Great Salt Lake Lake modulates clouds and fog during CAPs Lake breeze fronts strengthen the low- level stability during CAPs Cold lake air Warm Salt Lake Valley air 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