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Environmental Science
Tanzina Mohsin

EESA09H WINDLecture 7 NotesOutline of this lecturePart 1 Thermal WindsPart 2 Urban Heat IslandPart 3 Research a Trends in Temperature Time Series in the GTA b Day to day temperature variability and ChinooksPart 1 Thermal Winds 11 Landsea breezes Landsea breezes arise from differential heating of the earths surface on a daily diurnal basis Land surfaces heats more rapidly and cools more rapidly than water surfaces During the day the land surface is typically warmer than the water surface Warmer air rises and so air is rising over the land and sinking over the water To complete the circulation air moves from the water area to the land area at the surface This forms a cool breeze at the surface and is called a sea or lake breeze It is particularly noticeable during the day in the summer At the upper level there is a reverse flow with air moving out over the waterAt night the opposite occurs the water surface is warmer than the land Air rises over the water and sinks over the land The induced surface flow is from land to water or a land breeze Sea breezes are strongest in the summer when the temperature contrast is the greatestEven on seasonal scales bodies of water warm up and cool down slower than land massesIn the summer therefore the average temperature of the land over the entire 24 hour period is warmer than the average sea temperature the diurnal heating of the land mass adds to this seasonal difference to create a larger temperature contrastLand breezes for similar reasons are stronger in the winter 12 Monsoons A monsoon is similar to a landsea breeze except it occurs over a large spatial area continental and a longer time span seasonal rather than daily South Asia Sri Lanka India Bengladesh Pakistan and Africa experience a monsoon each year usually beginning in late May During the winter months the Indian Ocean is warmer than the surrounding land mass and air rises over the ocean and sinks over the land inducing a land breeze and dry conditions During the summer the land is warmer than the Indian Ocean Air rises over land and sinks over the water This induces a sea breeze This breeze has high moisture content As the air moves over the land it rises cools and water vapour condenses into water droplets clouds generating copious amounts of rain The monsoon persists into the fall 13 Valley BreezeBreezes develop in a valley on a diurnal basis During the day the land heats faster than the air above it Air starts flowing up the sides of the valley causing an uphill wind At night the land cools faster than the air above it This air at the surface becomes denser and tends to flow down the valley sides a downhill wind or breeze This is especially important to hikers 14 Katabatic wind In glaciated regions of the world katabatic winds can form Air pools over the glacier and becomes denser When the air moves away from the glacier it can move rapidly down hill very dense air and forms intense cold winds Hikers need to be aware of these winds as well Often the local topography the valley will act to tunnel the wind making it more intense 15 Chinook This is a preeminently Canadian wind It occurs on the lee side of mountains eg Calgary Alberta Air traveling up the windward side of the mountain typically reaches a point where the water vapour condenses and a cloud is formed The formation of clouds releases energy latent heat due to the phase change from vapour to liquid On the leeward side of the mountain the air warms rapidly and is quite dry This is a result of the latent heat release and cloud formation on the windward side This warm drier air can occur in winter and cause a dramatic change in temperature in a few hours The wind is often referred to as a snow eater In Germany the wind is referred to as a Foehn and comes off of the Alps These winds have been linked to human health Cooke et al 2000 There is more on the effect of the chinooks in the research section Part 2 Urban Heat Island The urbanization of the earths surface has lead to a substantial change in the surface microclimate Below is a list of observable differences between the meteorological data collected in urban areas compared to surrounding rural areas Urban vs RuralPollution level Higher Sunshine hours Lower Temperature Higher Relative humidity Lower VisibilityLower Wind speed Lower Precipitation Higher
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