Introduction INSOLATION AND HEAT BALANCE Sun is the
Introduction INSOLATION AND HEAT BALANCE Sun is the main source of energy for Earth. Radiation of solar ray is main source of energy for Atmosphere. Diameter of sun – 1382400 kms (109 times more than earth) Velocity of electro magnetic short waves – 297600 km/ second Time to reach earth – 8 min 20 sec Mass – 332000 times that of earth Average density – 1. 41 earth – 5. 52 Surface temperature – 5500 to 6100 o. C Energy coming to earth – 1/ 2 billionth equal to 23 billion HP Solar constant – 1. 94 gram cal / sq. cm. / minute There Hydrogen is changed in to Helium through nuclear fusion. Electro magnetic waves – 1. longer – Infrared waves 2. shorter - U. V. rays
ELECTROMAGNATIC SPECTRUM The solar energy radiated from the sun in the form of electromagnetic wave is called electro magnetic radiation. The energy from the sun or electromagnetic radiation waves are expressed in terms of wavelength (L). The number of radiation wave passing through a certain point per unit time (one second) is called wave frequency. Wave frequency is generally expressed as wave cycle per second, expressed in hertz, kilohertz(1000 hertz), megahertz(1000, 000 hertz)
• INcoming SOLar radi. ATION • The part of the sun’s radiation that is received by Earth.
1. The first spectrum – include GAMA RAYS, HARD X RAYS, SOFT X RAYS, ULTRAVIOLET RAYS. The wave length unit of measure in terms “ angstrom” 1 angstrom = 0. 00000001 cm 2. The second spectrum – the spectrum of visible light which include violet, blue, green, yellow, orange and red rays. Which carry 41 % of the total energy of the solar spectrum. Micron is the unit measure. 1 micron = 0. 0001 cm 3. The third spectrum – is called as infrared spectrum. Wave length ranging from 0. 7 to 300 microns. 4. The fourth spectrum - consists of long waves including microwaves and radar waves -- radio system & television system.
l Diagram
Factors affecting Insolation 1. Angle of sun’s rays - Angle of incidence – the angle at which the insolation strikes earth’s surface • Altitude of sun determines the angle of incidence. • The higher the sun is in the sky, the higher the angle of incidence and more insolation is absorbed. • A lower angle of incidence more insolation is reflected and less is absorbed. equator pole
Earth's atmosphere reduces the amount of insolation striking earth's surface. Earth's atmosphere and tilt combine to explain variation in received solar radiation.
2. Length of day and night • Duration of insolation: The number of daylight hours at a given location. This varies with latitude and season. • The longer the earth receives light the more insolation it gets. • If I hold a lamp at a great distance from an ice cube, for a long time will the ice cube eventually melt? • The longer the day, the more insolation reaches the earth. • This is a Direct relation ship.
DAY and NIGHT LENGTH Lengths of day and night vary more between the seasons at higher latitudes. This makes climate more seasonal at the poles than the equator Six months daytime (March-Sept), six months night (Sept - March) North Pole 90°N Arctic circle 66. 5°N More seasonal One day with 24 hours daylight (June 21 st); one day with 24 hours darkness (Dec 21 st) Sun is overhead once a year (June 21 st). Day length always at least 10 hours. Tropic of Cancer 23. 5°N Constant day length - 12 hours day and night all year round Equator 0° Tropic of Capricorn 23. 5°N More seasonal Sun is overhead once a year (Dec 21 st). Day length always at least 10 hours. Antarctic circle 66. 5°S South Pole 90°N One day with 24 hours daylight (March 21 st); one day with 24 hours darkness (June 21 st) Six months daytime (Sept - March), six months night (March-Sept)
3. Distance between earth and sun PERIHELION APHELION Earth's surface is 5 million kilometers further from the sun in summer than in winter, indicating that seasonal warmth is controlled by more than solar proximity.
4. Sunspots or Solar constant Created on outer surface of sun due to periodic disturbances and explosions on the solar surface. It is observe that appearing large number of sunspots the intensity of the solar radiation received is larger at earth surface. Haley in 1710 – study 22 years of sunspots- cycle of 11 years the number of sunspots increases or decreases
5. Transparency of the atmosphere – reflection from dust particals, salt particals and smoke particals reflecting short wave solar radiation to space. reflection from the cloud tops also deflects the amount of solar radiation that would be otherwise available to earth. transparency also related to latitude – • Oblique rays • Vertical rays
Latitudinal and Seasonal variation / distribution • Amount of insolation received by earth decreases towards pole. • Temporal variation at different latitudes at diff times of a year. • BAUR & PHILLIPS – solar radiation reaching at outer limit of atmosphere is more than the amount received at earth surface. • But this is the fact that greater portion of insolation is lost while passing through the atmosphere due to the effect of scattering, reflection, absorption, cloudiness. • SUMMER SOLSTICE – (21 June)- maximum insolation reaches at outer limit of atmosphere at North pole. But maximum energy received at the ground surface at 30 to 40 latitude. Because of minimum amount of cloudiness due to presence of subtropical high pressure belt and anticyclone conditions. But at pole the
The summer solstice occurs when the Northern Hemisphere is tipped towards the sun. The winter solstice occurs when the Northern Hemisphere is tipped away from the sun.
The globe is divided in to three zones on the basic of amount of insolation received during the course of year Equatorial: intense insolation, day and night roughly equal Tropical: high annual insolation, marked seasonal cycle Subtropical: large annual insolation; strong seasonal cycle Mid latitude: strong seasonal contrasts in insolation and length of day Arctic/subarctic, Antarctic/ subantarctic: enormous variation in annual insolation, extreme variation in day length Polar: greatest seasonal insolation contrasts, 6 -month day, 6 month night
EFFECT OF ATMOSPHERE ON INSOLATION The electro magnetic solar radiation or incoming short wave solar radiation has to pass through thick layer of atmosphere, hence it is partly absorbed, scattered, and reflected.
ABSORPTION • • • The energy radiated from the sun towards earth. It is 1/ 2 billion part reaches the earth. If it is consider 100% then 14% of energy is absorped by atmospheric gases and water vapor. Ozone is on large extent, O 2, CO 2 are very limited extent, nitrogen on poor absorber of insolation. Process of absorbtion is selective in nature. O 2, O 3 – absorb shortest wave length 0. 02 to 0. 29 micron Ozone – U. V. rays wave length of 1000 to 4000 angstrom Water vapor – wave length of 0. 9 to 2. 1 micron The energy absorb transmitted in to internal molecular motion which causes a rise in temperature.
• • SCATTERING 23 % of insolation scattered in atmosphere by dust particals and Haze. 6 % sent back to atmosphere 17 % reaches to earth. Process of scattering is selective one. When the diameter of dust particals and molecules of atmospheric gases is shorter than the wave length of the solar radiation waves. Blue light is more scattered than red light. Due to scattering effect sky appear blue and at the time of sunrise & sunset sky appears reddish.
DIFFUSION • Diameter of the particals are larger than the wavelength, true scattering dose not possible and the effect of diffusion occur. • it is effective for all wave length. • non selective in nature. • Eg – light reflected from clouds is pure white. • the twilight are longer duration in high latitudes due to diffusion.
REFLECTION • 27 % radiation reflected back is called as reflection of light. • It does not play any roll for heating the atmosphere. • Diameter of dust particals and molecule of water vapor is longer than wave length of incoming solar radiation reflection takes place. • Some energy remains in lower atmosphere.
ALBIDO • The portion of incident radiation energy reflected back from the earth surface is called Albido. • Various data received so far indicate the Earths average albido varying between 29 % to 34 %. Fresh snow – 80 – 85 % Forest 5 – 10 % Old snow 50 – 60 % water (sun near horizon) 50 – 80 % Sand 20 – 30 % Thick cloud 70 – 80 % Grass 20 – 25 % Thin cloud 25 – 50 % Dry earth -15 – 25 % Wet earth 10 %
HEAT BUDJET AND HEAT BALANCE
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