Physical Geography Week 5 Notes
Physical Geography Week 5 Notes GEOG 101 001
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GEOG 101 001
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This 4 page Class Notes was uploaded by Julia Parenti on Wednesday March 2, 2016. The Class Notes belongs to GEOG 101 001 at Towson University taught by Dr. Ken Barnes in Spring 2016. Since its upload, it has received 26 views. For similar materials see Physical Geography in Geography at Towson University.
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Date Created: 03/02/16
Physical Geography Week 5 Notes Large Scale Global Circulations Drivers of Atmospheric Circulation Uneven distribution of sun’s radiation on the Earth’s surface air flows from high to low pressure (wind) pressure gradient force air flow is also affected by: coriolis effect friction at the surface (slows down winds) Earth’s rotation coriolis effect apparent deflection of winds: to the right in the norther hemisphere to the left in the southern hemisphere Geographical Air Pressure Variations Air pressure: force exerted on the surface by the weight of the atmosphere the unit most often used to express air pressure is the millibar (mb) average atmospheric pressure at sea level is 1013.2 mb isobar: a line connecting points of equal atmospheric pressure on a map Air pressure varies not only vertically but horizontally Horizontal variations in the pressures stem from: temperature and water vapor differences behaviour of air aloft and at the surface Geographic Differences in Air Pressure: Rules of Thumb Cold air is more dense than warm air Dry air is more dense than moist air when water vapor is added to the air, the weight of a unit volume of air decreases avogadro’s law: a unite volume of gas always contains the same number of molecules. lighter molecules of H20 displace heavier molecules such as N2 and 02 When air is ascending (rising) from the surface, pressure at the surface is low cyclone: low pressure cell Where air is descending (sinking) to the surface, air pressure at the surface is high anticyclone: high pressure cell Seasonal Variations in Air Pressure Land heats rapidly and cools rapidly limited capacity to store heat Water heats and cools slowly high capacity to store heat Summer Land masses heat rapidly pump heat into atmosphere creates low pressure Water bodies heat slowly overlying air is cooler creates high pressure Winter Land masses lose heat rapidly cold dense air builds up creates high pressure Water bodies retain heat and cool slowly heat is released and temperatures are more moderate creates low pressure January Pressure higher over land July Pressure higher over water Air flow and Pressure Gradient Force Air drifts down pressure gradient tendency is called pressure gradient force Steeper the gradient, higher the wind velocity Earth’s Rotation / Coriolis Effect Air does not flow straight down the pressure gradient because of the Coriolis Effect This is the apparent deflection of objects including winds moving freely over earth’s surface deflections to the right in the Northern Hemisphere deflections to the left in the Southern Hemisphere Caused by rotation of the earth and differences in rotational velocities over the Earth’s surfaces faster air flow = greater Coriolis Effect Strength of Coriolis Effect changes by latitude does NOT exist on the equator stronger in poler regions Idealized Distribution of Global Pressure Systems These pressure systems are dynamic produced by the convergence and divergence of air at surface and aloft Shift positions seasonally in response to changing locations of subsolar point Polar highs and subpolar lows weaken in the summer and strengthen in the winter Convergence and Divergence: The general circulation of the atmosphere can be explained by convergence and divergence Convergence: a location where airflows or ocean currents meet, characteristically marked by upwelling (of air) or downwelling (of water). Divergence: occurs when there is an outflow of air and air streams are separating. Rossby Waves and Jet Streams Rossby Waves: greatly undulating westerly air flow patterns helps to redress global energy imbalances in the fall, winter and spring, these deliver tropical air into higher latitudes and enable polar air to flow towards equator (polar outbreaks) positions effected by mountains Jet Streams: irregular concentrated factors controlling large scale ocean circulation. Water Salinity: source is chemical weathering of rocks on land carried by runoff into oceans concentrations carried by locations diluted by glacial meltwater and precipitation concentrated by evaporation Water Temperature Absorbs solar energy; gains and stores heat Surface Winds Drive surface currents Coriolis Effect Deflects surface currents Surface Ocean Currents Driven by planetary winds Deflected approximately 45 º from wind direction due to Coriolis Effect Broad circulatory systems called gyres driven by wind and deflected by land masses Five Subtropical Gyres: results in: warm currents off east coast of continents cold currents off west coast of continents climate differences between coasts Center of gyres are calm plastics and other rubbish accumulate one circumpolar current around Antarctica Deep Ocean Currents Circulate slowly moves only a few centimeters per second transfers water between the oceans estimated that one complete cycle takes 1000 years moves vast amounts of water (100x the flow of the Amazon) Driven by differences in water density Thermohaline circulation increase in salinity increases water density decrease in temperature increases water density Example: gulf stream flowing into the North Atlantic Water is saltier due to evaporation Cools as it flows poleward Salty cooler water sinks Upwelling currents occur where wind drives surface water away from coasts (ex: west coast of South America) currents are nutrient rich Downwelling currents occur where there is an accumulation of water and the excess water gravitates downward