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Finding

Finding Thresholds For Lake Breeze Formation on Lake Mendota. Finding. Stephen Ogden. Methods. Temperature Decrease. CO2 Increase. Water Vapor Increase. Wind Speed Decrease. Wind Shift. TUMBLE site data compared to AOS building and airport data, lake temperatures from MODIS.

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Finding

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  1. Finding Thresholds For Lake Breeze Formation on Lake Mendota Finding Stephen Ogden

  2. Methods Temperature Decrease CO2 Increase Water Vapor Increase Wind Speed Decrease Wind Shift TUMBLE site data compared to AOS building and airport data, lake temperatures from MODIS (images from 15 March at the TUMBLE site)

  3. Out of 18 rain-free days, 11 had lake breezes Two lake breezes appeared to reach the AOS building (13 and 15 March), with the 15 March one most obvious These two days had wind to temperature difference ratios of 0.46 and 0.11, respectively The air-sea temperature differences these days were 17.1 and 22.4C The wind to temperature difference ratio was only useful if wind perpendicular to shore was used, not geostrophic wind or total low-level wind Results Shaded area is 1630 to 1730 LST on 15 March at the AOS building

  4. Wind to temperature difference ratios of less than 5 generally had lake breezes (9 of 12 days) A ratio of greater than 5 generally had no lake breezes (2 of 5 days) One day was ignored because the wind was parallel to the coast (ratio of 0) Temperature differences of less than 8C had no lake breezes (0 of 5 days), while greater than 9.6C difference days tended to have lake breezes (12 of 13 days) A minimum temperature difference of 9C was a good dividing line in these days Results Wind/Temp. Difference Ratio Breeze No Breeze 0 1 2 3 4 5 6 7 8 Lake-Air Temp. Difference Breeze No Breeze 0 3 6 9 12 15 18 21 (11.2)

  5. Negative buoyancy is needed to form the stable layer that is the lake breeze air mass This buoyancy is achieved by having the lake be more than 9C cooler than the air above Stable layers (such as over the lake) tend to trap materials (such as CO2) due to a lack of mixing The lack of mixing also contributes to low wind speeds in the lower levels of the layer, similar to the nocturnal boundary layer Overlap With Class

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