Insolation and Temperature variation. The Sun & Insolation. The Sun (cont.) The Sun

Transcription

1 Insolation and Temperature variation Atmosphere: blanket of air surrounding earth Without our atmosphere: cold, quiet, cratered place Dynamic: currents and circulation cells June 23, 2008 Atmosphere important in equalizing temperature and pressure by transfer of,, and Meteorology...the study of weather condition of atmosphere at a given time for a given area temperature, pressure, wind, moisture Climatology...the study of long term average weather usually over past 30 years The Sun & Insolation The Sun The Sun (cont.) Provides an immense and continuous flow of radiant energy Electromagnetic waves Uv, visible, infrared Almost all is shortwave (uv & visible) Dispersed in all directions Less than one billionth of total solar output reaches Earth s atmosphere 1

2 Driving force behind weather and climate How bright the sun shines Total insolation is a function of Factors affecting intensity Controlled primarily by affects intensity of insolation Latitudinal comparison Angle of incidence Surface area covered (Latitude and season affect angle of sun s rays) affects intensity of insolation How bright the sun shines Factors affecting intensity 2

3 100% at top of atmosphere 5% scattered or reflected 15% absorbed by molecules and dust 80% can reach ground on clear day 5-20% absorbed by clouds 30-60% reflected by clouds 0-45% reaches ground on cloudy day How bright the sun shines Factors affecting intensity affects intensity of insolation Mt. Everest, 5.5 mi high How long the sun shines during the day Depends on and N.Pole N.Mid-Lat Equator S.Mid-lat S. Pole Spring Equinox Duration of Insolation June Solstice 24 hrs. ~15 hrs ~9 hrs. 0 hrs. Fall Equinox December Solstice 0 hrs. ~9 hrs. ~15 hrs 24 hrs. -latitudes Mid-latitudes: sun never directly overhead Tropics: sun is directly overhead twice a year Low latitudes Mid-latitudes: sun never directly overhead -latitudes June Equinoxes December 3

4 TROPICS: insolation high year round due to high sun angle and constant duration Seasonal variation in insolation at top of atmosphere Equator Poles Duration Angle Total Duration Angle Total Mid-latitudes: insolation highest at summer solstice due to higher sun angle and longer day, lowest at winter solstice due to low angle and short day Spring Equinox Sum. Solstice hrs Horizon Low Low latitudes: insolation highest at summer solstice due to 24 hour duration low angle sun, extremely low to none at winter solstice Fall Equinox Winter Solstice hrs. Horizon Below horizon Low Zero Total annual insolation decreases as latitude increases Insolation that reaches the Earth can be Seasonality increases as latitude increases albedo Low albedo Absorbed radiation heats the earth. The earth then radiates energy back out. Earth radiates in longer wavelengths 90% of this radiation absorbed by atmosphere Earth s energy balance There is a balance between the total amount of insolation received by Earth & atmosphere & total amount radiation returned to space Clouds also absorb outgoing longwave energy Atmosphere is warm, therefore it also radiates energy Counter radiation directed back to Earth 4

5 Net Radiation Global average energy balance Incoming Outgoing radiation energy Surplus est at low latitudes = surplus energy Lowest at high latitudes = deficit of energy Tropics Deficit Mid- latitudes San Francisco St. Louis Washington DC How does heat move from one place to another? How can earth move energy from surplus to deficit areas? (Methods of heat transfer) All bodies above -460 F (-273 C) (0 Kelvin) radiate energy. Lower body temperature, longer wavelength. Thermal infrared wavelength energy radiated by Earth heats troposphere. Heat that is transferred from one part of a stationary body to another when the two are in contact Earth-air interface Land heats up transferred to lower atmosphere Heat transferred from one point to another by a moving substance For this only important at earth-air interface Convection- Vertical currents Advection- Horizontal currents 5

6 Temperature Measurement of sensible heat/energy Temperature is an expression of the degree of hotness or coldness of a substance There is a link between troposphere temperature and Earth surface conditions The air temperature represents the balance between insolation and terrestrial radiation Temperature Depends On Temperature depends on Intensity x Duration angle of sun s rays atmospheric transparency altitude latitude season Temperature depends on Relative rates of heat flow into soil and water Most land has low albedo. It absorbs radiation and heats up 6

7 Relative rates of heat flow into soil and water Why does water heat and cool slower than land? Soil 5 C 10 C 20 C 40 C Water heats up (and cools down) slower than land CONTINENTALITY Temperature Varies Temporal variation in temperature 1990 Daily temperature ranges Minneapolis-St.Paul Freezing Summer Solstice Winter Solstice Lapse Rate Temperature varies vertically. In the troposphere, it usually gets colder as you go up. This normal change in temprature is called the normal or environmental lapse (change) rate. Rate at which temperature decreases with height 7

8 Temperature varies horizontally Based on insolation and continentality Horizontal variation in temperature Winter 40º 0º Summer Horizontal variation in temperature Average sea level temperature F in July Summer Winter 8