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Lecture 15

Earth Science - Lecture 15 Notes.docx

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Earth Sciences
Sergei Basik

October 10, 2013 CLIMATIC CYCLES Days to Seasons  Earth’s atmosphere is subject to cyclic changes (seasonal cycles)  Many cyclic changes have impact on weather-related hazards  Heat building during daytime hours can cause afternoon thunderstorms and tornadoes (daily cycle)  Climate controlled hazards are part of seasonal cycles o Hurricanes occur from summer through fall o Tornados occur from spring through summer  The Earth is NOT closer to the sun in summer  Two hemispheres of Earth experience summer at different times  Earth’s axis of rotation is tilted 23.5 degrees to plane of orbit around sun o Northern hemisphere receives maximum solar radiation when the sun points directly at 23.5 degrees (summer solstice) o Warmest temperatures lag behind by about a month (it takes time to heat up land and water) o If there was no angle, both hemispheres would get the same amount of energy from the sun at different latitudes  Other observed cyclic changes in northern hemisphere climate may be explained by: o Changes in ocean currents o Changes in solar radiation caused by changes in Earth’s orbit o Changes in atmospheric composition El Nino  Oceanic circulation in equatorial Pacific usually is pushed westward by trade winds  This cycle happens approximately every six years  Warm surface water off Peru is blown westward and replaced by upwelling of cold, deep, nutrient-rich water  This type of water is very good for fisheries  Every six years (on average), Pacific Ocean circulation reverses in a pattern called El Nino: o The water near Peru is warm o Subtropical trade winds weaken o Air pressure rises in western Pacific o Incessant rain to west coasts of North and South America o Fisheries suffer (there is no cold, nutrient-rich upwelling water)  Differ
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