Temperature and Its Variation

1. Temperature and Its Variation

2. Earth’s Rotation • Remember we live on a rotating sphere • Direction of rotation: • From above North Pole, counterclockwise • From a distance, with North Pole at top, left to right

3. Effects of Earth’s Rotation • 3 main effects: • Axis and equator basis of geographic grid • A day is a convenient measure of time passing • Diurnal, or daily, rhythm in daylight, air temp, etc. • Surface processes all respond to diurnal rhythm • Coriolis force due to Earth’s rotation • How fast are you moving at the Equator? • At the Poles?

4. Earth’s Revolution around Sun • Elliptical orbit: There is a 6% difference in insolation between Perihelion and Aphelion. • Perihelion • Closest to Sun • Jan. 3rd • Aphelion • Farthest from Sun • July 4th • 365.242 days / orbit → Feb 29th every 4th year • Counterclockwise motion from above

5. World Latitude Zones • Terms used for latitude zones • Generally greater seasonal change with greater distance from Equator

10. Solar Heating of Land & Water • Surface layer of large body of water heats & cools more slowly than land • This difference shows up in temp patterns • e.g. diurnal temp pattern, maritime vs. continental San Francisco (Maritime) Yuma (Continental)

13. Thermal Properties of Water 1. 2. • 4 factors make water heat & cool slower than land Sun penetrates water Heat capacity of water greater 3. 4. Water mixes More evaporation over water

14. 5 Factors Influencing Local Temps • Latitude – less insolation at higher latitudes • Surface type – urban land absorbs more heat • Coastal vs. Interior – less temp range at coast • Elevation – temps decrease with altitude • Greater annual temp range at high latitudes • Atmospheric & oceanic circulation- temp can vary greatly based on where air & sea water are coming from

15. Urban Heat Island • Evapotranspiration helps keep rural areas cool • Urban asphalt & concrete has little evapotranspiration • Building & paving materials absorb more heat than natural surfaces • Automobiles, air conditioning & other machines make city warmer than surroundings

19. Daily Cycle of Radiation & Air Temp • Shortwave radiation from Sun greater than longwave radiation during daylight hours. • Energy surplus in daylight • Deficit in darkness • Temp usually highest in mid- afternoon, lowest just after sunrise

20. Maritime vs. Continental • Daily range of temp less at maritime location • North Head, WA much less range than El Paso, TX throughout the year

21. Annual Cycle of Air Temperature • Annual temperature range = max temp month – min temp month • 2 most important factors: • Annual insolation (latitude) • Maritime or continental effect • Like daily temp cycle, maritime climates have less annual temp range than continental

24. Annual Cycle of Air Temperature • Winnipeg & Scilly Is. have identical insolation curves • Winnipeg much colder fall, winter, spring due to extreme continental location • Scilly Is. Reach max & min temps later Due to influence of water

25. World Temperature Patterns • January • Coldest in Siberia, northern Canada & Greenland • Warmest in southern Africa and interior Australia • Oceans warmer than land in northern hemisphere • Isotherm – line on map connecting all points with same temperature

26. World Temperature Patterns • Maritime influence warms in winter, cools in summer • July • Northern hemisphere continents have warmed dramatically since January • Aside from Antarctica, southern hemisphere not very cold in winter • Maritime influence

27. Annual Temperature Range • = warmest month mean temp – coldest month mean temp • Greatest temp ranges in Siberia & NW Canada • Continental locations • Smallest temp ranges in Equatorial oceans • Maritime influence

28. Wind-Chill Index • “Feel” of temperature – based on: • Actual temperature • Windspeed – higher means colder

29. Heat Index • “Feel” of temperature on hot days, based on: • Actual temperature • Relative Humidity

30. Chapter Summary • Earth’s rotation and orbit • Air Temperature • Daily cycle of air temperature • Annual cycle of air temperature • Measurement of air temperature