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Unformatted text preview: Chapter 5: Global Temperatures Temperature Concepts and Measurement • Heat- form of energy tht flows fr one sys/object another b/c the two are at diff temps; temperature- measure of avg kinetic energy of indv molcs in matter; effect of temp felt as sensible heat transfer fr warmer cooler objects; temp/heat related b/c temp changes due to absorption/emission of heat energy- energy that’s added to/removed fr a sys/substance Temperature Scales • Temp at which all atomic, molc motion in matter stops- 0° absolute temp/ absolute zero = -273°C, -459.4°F, 0 Kelvins; F ice melting pt- 32°, boiling pt water- 212°; C- 0° melting pt, 100° boiling pt water; K- starts temp at abs zero, so readings proportional to actual kinetic energy in a material: • Water melting pt- 273 K, boiling pt 373 K; most countries use C scale for temp (as well as other SI units)- US only major one that uses F Measuring Temperature • Mercury thermometer / alcohol therm- sealed glass tube tht measures outdoor temps; cold climates need alcohol therms b/c Hg freezes at -39°C; how therm works: expansion/contraction of fluid w/changing heat reflects temp of therm’s envt; Hg min-max therm preserves readings of: • Day’s highest, lowest temps til reset; recording therm creates inked record on turning drum; therms for standardized, official readings put outdoors in sml shelters- white for high albedo, louvered for ventilation to avoid overheating; placed 1.2-1.8 m above surface; measurements in shade to prevent: • Efect of direct insolation; thermistor- measures temp by sensing electrical resistance of semi-conducting material; resistance changes at 4% per °C; temp readings taken daily worldwide, eg by Global Climate Observing Sys (GCOS); daily mean temperature- avg of daily min-max readings • Monthly mean temp- total of daily mean temps for the mth divided by # of days in tht mth; annual temp range expresses difference btwn lowest/ highest mthly mean temps for given year Principal Temperature Controls Latitude • Insolation- most impt influence on temp variations; insolation intensity decr w/incr’g distance fr subsolar pt (which moves annually btwn Tropics of Cancer, Capricorn); daylength, Sun angle also change thruout yr, incr’g seasonal effect w/incr’g lat Altitude • W/in troposphere, temps/atmos density decr w/incr’g alt above Earth’s surface; normal lapse rate of temp change w/alt- 6.4°C/1000 m; thinner atmos= less ability to absorb, radiate sensible heat; high elevations- avg air temps lower, nighttime cooling greater, temp range btwn day/night greater: • Surface gain/lose energy much quicker to thinner atmos; higher elevations- insolation received= more...
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This note was uploaded on 06/24/2008 for the course GEOG 1 taught by Professor Okin during the Fall '06 term at UCLA.
- Fall '06