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EESA09H3 (185)
Lecture

THERMAL WINDS.docx

6 Pages
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Department
Environmental Science
Course Code
EESA09H3
Professor
Tanzina Mohsin

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Description
THERMAL WINDS - LAND/ SEA BREEZES Land/sea breezes arise from differential heating of the earth‟s surface on a daily (diurnal) basis. HOW DO LAND/ SEA BREEZES OCCUR? Differential heating of the earths surface, so its THERMALLY INDUCED CIRCULATION - Which results in ? DAY AND NIGHT CONTRASTS , and that is called (DINURIAL VARIATION) SEA BREEZE FRONT Land surfaces heats more rapidly and cools more rapidly than water surfaces. DURING THE DAY what is more warmer , LAND OR WATER? LAND tends to more warmer during the day. Because warm air rises, air rises over the land and SINKS at the water surface. 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 sumAtr. the upper level there is a reverse flow with air moving out over the water. WHAT HAPPENS AT NIGHT ? at night the opposite tends to occur, and as a result the water surface is WARMER than the land at night. THIS means that air rises at the water and sinks at the land LAND BREEZE: when the induced surface flow is from WATER TO LAND (opposite from sea breeze) Sea breezes are strongest in the summer when the temperature contrast is the greatest. Even on seasonal scales, bodies of water warm up and cool down slower than land masses. In 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 contrast. Land breezes, for similar reasons, are stronger in the winter. SEA BREEZE FRONT • As the sea breeze develops the advancing on-shore breeze forms a front This is called the.. sea breeze front. – Sea breeze front • Land air is forced up and can generate sea breeze frontal clouds • Shallower than fronts produced by midlatitude cyclones MONSOON What is a monsoon and how is it different from a land/sea breeze? A monsoon is similar to a land/sea b reeze , except it occurs over a large spatial area (continental) and also over a long time span (seasonal rather than daily) - Referred to as seasonal trade winds that occur where ? ARABIAN SEA - It’s a seasonal scale thermal wind South Asia (Sri Lanka, India, Bengladesh, Pakistan) and Africa experience a monsoon each year usually beginning in late May. - Where do monsoons tend to occur? Monsoons tend to occur in South Asia, (india, sri lanka, etc) and it tends to begin in MAY How does it occur? During the winter months the Indian Ocean is warmer than the surrounding land mass, and air tends to rise over the ocean and sink over the land. But the opposite will happen in the summer. During the summer, the land is warmer than the Indian Ocean, and air will rise over the land and sink over the water, which induces 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. MONSOONS create… copoulous amounts of rain. WHAT ARE the negative impacts of a monsoon ? rain that forms as a result of the monsoon can last for weeks at a time. This is bad, because it can affect, crops and drinking water. - monsoons can also be formed in Africa, Australia, South America, North America but its not as pronounced. VALLEY BREEZE - Valley breeze is a smaller scale wind - What are valley breezes driven by ? dinurial thermal heating (variations in heating in the day and in the night) - What happens in the day ? In the day land heats up faster than the air above it, and upslope airs are induced. This means that air will start flowing up the sides of the valley causing an uphill wind. WHAT HAPPENS AT NIGHT? At night, the land cools faster than the air above it , and downslope winds are induced instead. This air at the surface becomes denser and tends to flow down the valley sides, a downhill wind or breeze. - DAY= UPSLOPE WINDS, NIGHT=DOWNSLOPE WINDS - This is especially important to hikers KATABATIC WIND - Where do katabatic winds form? They form over mountains, in glacial regions of the world. - What happens when air passes over the glacier/ ice sheet? It becomes very col d and dense (moving from high to low pressure) - What happens when air moves away from the cold glacier? It can move rapidly downhill (mountain) and the very dense wind tends to form 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 CHINOOOK -This is a pre-eminently Canadian wind. -Where do Chinooks occur? Chinooks tend to occur on the lee-side of mountains. IN which part of Canada? CALGARY OR ALBERTA 1. What happens to air travelling above the windward side of a mountain? Air traveling up the windward side of the mountain typically reaches a point where the water vapour condenses and a cloud is formed. 2. What is released during the formation of a cloud? The formation of clouds releases energy (latent heat) due to the phase change from vapour to liquid. 3. What conditions exist on the leeward side of the mountain? On the leeward side of the mountain the air warms rapidly and is quite dry. Why do these dry , conditions exist on the lee-ward side of the mountain? 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. Chinook winds have been linked to human health (Cooke et al., 2000). There is more on the effect of the chinooks in the research section. Chinooks and Human Health • Cooke et al. (2000) • Linked chinook episodes in Calgary, Alberta to migraine headache occurrence • Epidemiological study – statistical linkage between two factors – not necessarily causal Explanations , why does Chinook cause medical problem s (migranes)? Psychological triggers, because many think that migraines are triggered by poor weather conditions and weather changes. • Psychological trigger – many believe that migraines are triggered by weather and weather change • C
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