Lake Breezes in SW Ontario and Their Influence During BAQS-Met 2007David Sills1, Jeff Brook2 and Peter Taylor3

1Cloud Physics and Severe Weather Research Section, Environment Canada, Toronto, Canada2Air Quality Research Division, Environment Canada, Toronto, Canada3Department of Earth and Space Science and Engineering, York University, Toronto, Canada2008 AGU Fall Meeting15-19 December, San Francisco, CA

Lake breezes10002000Height (m)0040Distance (km)Lake Breeze InflowLake Breeze InflowReturn FlowReturn FlowAssume midday heating over land between two lakes

Lake breezes10002000Height (m)0040Distance (km)Lake Breeze InflowLake Breeze InflowLake Breeze FrontLake Breeze FrontEight different air regimes crossing from lake to lake

Lake breezes10002000Height (m)0040Distance (km)Lake Breeze InflowLake Breeze InflowLCLLCLLCL

Classic vs. High DeformationClassic lake breeze circulationsWeak synoptic wind regime

Why are lake breezes important?Affect the climate of the region around the lakeAffect air quality:3-D transport of pollutants / precursors in lake breeze circulationsIncreased insolation for photochemistryDecreased mixing heights reduce pollutant dispersionAffect summer severe weather:Lake air suppresses thunderstormsThe lake breeze front provides a lifting mechanism for the initiation of thunderstormsIn SW Ontario, surrounded by large and small lakes

Past Lake Breeze ResearchLots of work done on sea breezes and their effects on air quality in coastal regions: Canada, US, UK, Greece, Japan

A number of studies of Great Lakes lake breezes have been conducted: Biggs and Graves 1962, Moroz 1967, Lyons 1972, Estoque et al. 1976, Comer and McKendry 1993, Sills et al. 2002

Lake breezes and air quality in the Great Lakes region studied by: Lyons and Olsson 1973 (Lake Michigan), Mukammal et al. 1982 (Lake Erie), Sills 1998 (SW Ontario), Hastie et al. 1999 (Lake Ontario)

Outstanding QuestionsAre most ozone exceedances that occur in the absence of long-range transport associated with lake breeze circulations and their effects?

Why do pollutant concentrations often peak with the passage of the lake breeze front then fall off?

How important are vertical motions (upward and downward) associated with lake breeze circulations in transporting pollutants/precursors?

How well do current NWP models handle:changes in boundary-layer depth due to lake breeze circulations?the intensity of upward and downward vertical motions?the initiation of thunderstorms at lake breeze fronts?

BAQS-Met 2007 A multi-agency field program combining both high resolution AQ and met measurementsNLake HuronDetroitWindsorLondonToledoSarniaLake ErieLake HuronDetroitWindsorLondonToledoSarniaLake ErieLake HuronDetroitWindsorLondonToledoLake St. ClairLake St. ClairLake ErieLake ErieHarrowRidgetownBear Creek

BAQS-Met 2007 MesonetIADNPTKVLLDETDTWYIPARBMTCPHNYZRYQGXHAWNBWAJYXUDUHTHLO145005FTGM4THR01TTFXRGXPT45147LSCM4NFNT12016120591300116015KONZ85135SOMALVLARPALCROPAIMERLIGSTAWOOCOTPAQLEAWHEBEALSCLake HuronDetroitWindsorLondonToledoLEGENDExisting operational met stnExisting OME AQ + met stnEC AQ supersite + met stnUniv AQ supersite + met stn + profilesEC ATMOS met stn + AQYorkU ATMOS met stnEC buoy metEC buoy AQ + metEC AMMOS mobile metSarniaLake ErieLake HuronDetroitWindsorLondonToledoSarniaLake ErieLake HuronDetroitWindsorLondonToledo45132AMMMobile: Twin Otter aircraft CRUISER AQ lab AMMOS met vehicle

Lake Breeze DetectionEach of these can also be ambiguous at times...

Positive Factors

Negative Factors

Satellite

line of cumulus clouds,

sharp cloudiness gradient,

gradual inland penetration

of above

cloudy over most or all of lake,

gradual change in cloudiness

from lake to land

Radar

fine line in reflectivity, wind shift line in radial velocity,

gradual inland penetration

of above

large area of precipitation

Surface

rapid changes in observed

parameters via time series,

gradual inland penetration

of onshore winds

no onshore winds

Lake Breeze Detection1 min dataMerlin Station

Lake Breeze Detection

Lake Breeze Stats (Preliminary)

30% were Classic, 70% were HD lake breezes

100% of high ozone* days had active lake breezes

86% of days with thunderstorms had active lake breezes

100% of severe thunderstorm days had active lake breezesFor entire June August 2007 period:* 1-hr avg O3 >= 80 ppb at more than one station

Lake Breeze Stats (Preliminary)

Lake breezes somewhere within study region every day of intensive!

3 Classic lake breeze days (Jun 23rd, 25th, Jul 2nd), the rest HD

9 high ozone days, 3 thunderstorm days, 2 severe thunderstorm days all with lake breezes

Wide variety of synoptic regimes wind speed light to moderate, direction S through NNE

During the 20-day intensive period:

25 Jun 2007

25 Jun 07 Cross-sectionConvectiveMixedLayerResidualLayerResidualLayerF r e e A t m o s p h e r eCAPPING INVERSIONCAPPING INVERSIONCAPPING INVERSIONCAPPING INVERSIONENTRAINMENT ZONESURFACE LAYERTIBLTIBL10002000Height (m)Lake ErieLake St. ClairSouthwestern Ontario0040Distance (km)Lake Breeze InflowLake Breeze InflowConvective Mixed Layer Depth ~ 1500 m Lake St. Clair lake breeze depth ~ 300 m

25 Jun 07 Cross-sectionConvectiveMixedLayerResidualLayerResidualLayerF r e e A t m o s p h e r eCAPPING INVERSIONCAPPING INVERSIONCAPPING INVERSIONCAPPING INVERSIONENTRAINMENT ZONESURFACE LAYERTIBLTIBL10002000Height (m)Lake ErieLake St. ClairSouthwestern Ontario0040Distance (km)Lake Breeze InflowLake Breeze InflowUpdraft at front ~ 2 m s-1Downdraft behind front ~ 3 m s-1

Summary and Future Work Lake breezes very frequently affected SW Ontario in the summer months of 2007

The circulations can strongly influence air quality over all of SW Ontario due to 3-D motions, reduced mixing heights, and increased insolation

They also frequently help to initiate thunderstorms, including severe weather

Mesonet, aircraft and other BAQS-Met data will be used to further address the outstanding questions related to lake breezes

Acknowledgements Norbert Driedger, Emma Bradbury and Lesley Hill for their hard work on the mesoanalysis database and products

Kathy Hayden for discussions (her talk is next!)

ReferencesBiggs, W. G. and M. E. Graves, 1962: A Lake Breeze Index. J. Appl. Meteorol., 1, 474- 480.

Comer, N. T. and I. G. McKendry, 1993: Observations and Numerical Modelling of Lake Ontario Breezes. Atmos-Ocean, 31, 481-499.

Estoque, M. A.; J. Gross and H. W. Lai, 1976: A Lake Breeze over Southern Lake Ontario. Mon. Wea. Rev., 104, 386-396.

Hastie, D. R., J. Narayan, C. Schiller, H. Niki, P. B. Shepson, D. M. L. Sills, P. A. Taylor, Wm. J. Moroz, J. W. Drummond, N. Reid, R. Taylor, P. B. Roussel and O. T. Melo, 1999: Observational evidence for the impact of lake breeze circulation on ozone concentrations in southern Ontario. Atmospheric Environment, 33, 323-335.

Lyons, W. A., 1972: The Climatology and Prediction of the Chicago Lake-breeze. J. Appl. Meteorol., 11, 1259-1270.

Lyons, W. A. and L. E. Olsson, 1973: Detailed Mesometeorological Studies of Air Pollution Dispersion in the Chicago Lake Breeze. Mon. Wea. Rev., 101, 387-403.

Moroz, W. J., 1967: A Lake Breeze on the Eastern Shore of Lake Michigan: Observation and Model. J. Atmos. Sci., 24, 337-355.

Mukammal, E. I., H. H. Neumann, and T. J. Gillespie, 1982: Meteorological conditions associated with ozone in southwestern Ontario, Canada. Atmospheric Environment, 16, 20952106.

Sills, D. M. L., 1998: Lake and land breezes in southwestern Ontario: observations, analyses and numerical modelling. PhD dissertation, CRESS, York University, 338 pp.

Sills, D., P. Taylor, P. King, W. Hocking and I. Nichols, 2002: ELBOW 2001 - studying the relationship between lake breezes and severe weather: project overview and preliminary results. Preprints, 21st Severe Local Storms Conference, San Antonio, TX, Amer. Meteorol. Soc., 611-614.

Lake breezes are thermally direct circulations and result from the temperature difference between warm air over land and cool air over waterUnder ideal conditions, the circulations are quasi-closed and it would take an air parcel a number of hours to complete the circulation - Eight different air regimes crossing from lake to lakeConvective mixed layerLake breeze inflow layers, then TIBLs when lake breezes modified over landResidual layers over the lakes, free atmosphere above- And finally well add some cloud- If the lifting condensation level is below the top of the convective mixed layer, clouds especially at front- No cloud where LCL is above the mixed layer over water and inland from lakesVisible satellite imageryGreen dashed lines are estimated positions of lake breeze fronts HD: lake breeze circulations highly deformed by the gradient windMain difference is that for HD lake breezes the lake breeze fronts do not exist around the perimeter of the lake but mainly along and inland from sections of lakeshore parallel to the synoptic flow

BAQS-Met a multi-agency cooperative field program combining both high resolution AQ and met measurements3 AQ/met supersitesOne novel aspect was co-location of AQ and met sensors at mesonet stationsA 50 station mesonet with ~15 km spacing, 16 stations with 1 min dataAlso several mobile platforms including Twin Otter aircraft, CRUISER AQ lab, and AMMOS met vehicleAmbiguous: no cloud visible or thin cirrostratus or broken mid-level clouds prevents seeing cumulus cloudsno clear air echoes or fine line or gradient in clear air echoes not well definedoften very subtle surface gradients at boundaries in moderate / high low-level wind regimes

Each observational platform has strengths and weaknesses for LB front detectionSynthesis of data from each platform results in a greater number of LB front detections

In this example,Sudden increase in wind speedTemperature stopped rising, dewpoint had sharp increaseWind direction rapidly changed to onshoreIncrease in ozone behind frontMesoscale analyses produced for every hour during intensive daysExample is June 23rd classic lake breezes preceded by a land breeze

A high ozone day has 1 hr avg O3 >= 80 ppb at more than one stationOnly counting shores within study area, not anywhere along entire lakeLight southerly synoptic-scale flowWeak pressure ridge extending from New England back across the Great LakesClassic back of the high synoptic setup for high ozoneLake breeze fronts detected 14Z-02ZClassic then transition to HD as flow increasedNo convective initiation over regionNo convective mixed layer left anywhere in SW Ontario by end of the dayAircraft ran a stepped traverse pattern through the Lake St. Clair lake breezeJust got into lake air at its lowest altitude traverseUpdraft around 2 m/s measured at the Lake St. Clair frontSlightly stronger downdraft just behind the front at around 3 m/s