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1. Solar Radiation

2. SUN The sun is located at the center of our solar system Sun is the prime source of energy Sun is the nearest star to the planet earth Diameter of the sun is 1.39 X 10 6 km It rotates on its axis about once every four weeks (27 days near equator & 30 days – polar ) Sun is on an average 1.5 X 10 8 km (150 X 10 6 km) away from the earth Surface temperature of the SUN is 5780 K (degrees kelvin = degrees C + 273.15 )

3. Energy is due to the fusion, Hydrogen is transformed to helium . Every minute, the sun radiates approximately 56 X 10 26 calories of energy 99 % of the energy to biosphere is only from the sun and the rest one percent is from stars , lightning discharge, sun’s radiation reflected from the moon, re-radiation from the earth etc .

4. Solar Radiation : Solar radiation is radiant energy emitted by the sun; this energy is the source of all the physical, biological processes in the atmosphere. Heavenly bodies emit – short wave radiation Near surfaces including earth emit - long wave radiation Solar Radiation contains a variety of Electromagnetic radiations , all this possible variety of radiations together called Electromagnetic spectrum. Electromagnetic spectrum - It is a range of all possible frequencies of electromagnetic radiation, which are classified as Gamma radiation X – ray radiation Ultraviolet radiation Visible radiation Infrared radiation Microwave radiation Radio wave

5. Effect of solar radiation in atmosphere Absorption Reflection Scattering INSOLATION : IN coming SOLA r radia TION Electromagnetic energy radiated in to the space by the sun . Or Energy received on the surface of the earth.

6. Solar constant Solar constant is the energy received on a unit area at the outer most boundary of the earth ( atmosphere) surface held perpendicular to the sun’s direction, at the mean distance between the sun and the earth . Value of 1.94 cal /cm 2 /min . It is not constant it varies between (1.92 and 2.02 cal /cm 2 /min )

7. Factors affecting INSOLATION : IN coming SOLA r radia TION The solar constant which depends on a. Energy output of the sun b. Distance from the earth to sun. 2. Transparency of the atmosphere 3. Duration of daily sunlight period 4. Angle at which sun’s noon rays strike the earth.

8. Albedo It is the percentage of reflected radiation to the incident radiation. (Varies with colour and composition of the earth’s surface, season, angle of the sun rays ). Value is Highest in winter and at sunrise and sunset. Pure water – 5-20%, Vegetation 10-40%, Soils 15-50%, Earth 34-43% Clouds 55 %. High albedo indicates that much of the incident solar radiation is reflected rather than absorbed.

9. Albedo Depends up on Angle of incidence of radiation. Albedo increase with decreasing elevation of sun with minimum during noon. Physical characteristics of surface Season 4. Time of the day For plant community albedo depends upon 1. Age of the crop 2. Percentage of ground cover 3. Colour and reflectivity of the foliage

10. Outgoing long wave radiation After being heated by solar radiation, the earth becomes source of radiation. Average temperature of the earth’s surface (14º C) 99 % of radiation is emitted in the farm of IR range (4 to 120 µ) About 90% of the outgoing radiation is absorbed by the atmosphere. Water vapour absorb in wavelengths of 5.3 to 7.7 µ Ozone 9.4 to 9.8 µ. CO2 – 13.1 to 16.9 µ Clouds – in all wavelengths

11. Long wave radiation escapes to the space between 8.5 and 11 µ and this is known as the atmospheric window . Atmosphere for this spectrum acts as transparent medium instead of absorbing . This spectral region is used in microwave remote sensing to monitor the features of the sky in case of overcast sky. A large part of the radiation absorbed by the atmosphere is sent back to the earth’s surface as counter – radiation . This counter radiation prevents the earth’s surface from excessive cooling at night .

12. Radiation flux: The amount of radiant energy emitted, received, transmitted across a particular area is known as radiant flux. Radiation flux density: The radiant flux divided by the area , across which the radiation is transmitted is called radiant flux density. Emissive power : The radiant flux density emitted by a source. Energy measurement : Solar radiation expressed in Watts cm -2 or cal /cm 2 /min

13. Spectrum of radiation:

14. Band Spectrum Wavelength ( μ ) Importance Ultraviolet Cosmic rays Gamma rays, X rays UV rays < 0.005 0.005 – 0.20 0.20 – 0.39 Shorter wave length of spectrum & chemically active. U nless filtrated there is danger of life on earth Visible Violet Blue Green Yellow Orange Red 0.39 – 0.42 0.42 – 0.49 0.49 – 0.54 0.54 – 0.59 0.59 – 0.65 0.65 – 0.76 Visible spectrum known as light essential for all plant processes. Infra red Infrared rays > 0.76 Essential for thermal energy of the plant ( source of heat ) Spectrum of radiation:

15. Solar radiation and crop plants …… Crop production is exploitation of solar radiation. Three broad spectra : Shorter than visible range Chemically very active. Effects are detrimental Atmosphere acts as regulator for this radiation & none of cosmic, gamma and x-rays reaches the earth. UV reaches earth – very low 2. Higher than visible range IR radiation. Thermal effect on plants. In the presence of water vapour , not harm plants. 3. Visible spectrum Between UV and IR and also referred as light Intensity, quality and duration are important for normal plant growth. Poor light leads to abnormalities.

16. Wave length (nm) Specific effect on plant 1000 and more radiation No specific effect on plant activity. Radiation absorbed by plants are transformed into heat. 1000-720 Radiation in this band helps in plant elongation , can be accepted as an adequate measure of plant elongation activity. The FR region has imp role in photo- periodism , germination of seeds, flowering and colouration of fruits. 720-610 Light is strongly absorbed by chlorophylls. Generates strong photosynthetic and photoperiodic activity. 610-510 This is green-yellow region. Absorption in this spectral region has low photosynthetic effectiveness & weak formative activity. 510-400 Strongest chlorophyll and yellow pigment absorption region. Photosenthetic activity becomes very strong . 400-315 Radiation in this band produces formative effects. It has dwarfing effect on plants and thickening effect on plant leaf . 315-280 Detrimental effect on most plants. < 280 Lethal effect most of the plants get killed due to UV – germicidal action.

17. Radiation balance (Energy balance)

18. There is also variation in the daily intensity . The intensity is greatest in the noon (1pm) and low in the morning and evening time . Variability of insolation is varies with latitude. Radiation is responsible for temperature. It depends on angle also i.e. morning and evening it varies. Always for heating earth surface it takes time. The earth’s inclination is 23 ½ that produces seasonal difference in insolation at any given latitude. There are 3 latitudinal zones namely : 1. Tropical (torrid) zone 2. Temperate zone 3. Polar (Frigid) zone.

19. The sun’s path which determines the flow of energy provides a basis for dividing the globe into three latitudinal zones . 1. Tropical (torrid) zone 2. Temperate zone 3. Polar (Frigid) zone.

20. Tropical (torrid) zone : It is zone between tropic of cancer (23 ½ N ) and the tropic of Capricon (23 ½ S ). The sun rays are falling vertically over all during the part of year. The seasonal contrast is minimum in the year within this zone. The seasonal contrast will increase in the latitude up to 23 ½ and least around the equator or 0 latitude .

21. 2. Temperate zone : This lies between the tropic of cancer (23 ½ N ) and the arctic circle (63 ½ N ) in northern hemisphere and tropic of capricon (23 ½ S ) and the antarctic circle (63 ½ S ) in southern hemisphere . Here sun rays are never vertical during any part of the year. The angle of incidence and the deviation of sunshine are greater in summer than winter. The seasonal contrast are much greater in the temperate zone than in the tropical zones .

22. 2. Polar / Frigid zone : The regions on each pole extends from arctic circle (63 ½ N ) in northern hemisphere and antarctic circle (63 ½ S ) in sothern hemisphere . The sun rays are not received during the long winter in these regions and sun may shine for >20 hrs during summer. Even in summer the temperature is quite low due to low angle of incidence of sun’s rays and greater spreading.

23. Climatic controls: Weather – varies from day to day Climate – differ from place to place . Weather elements : Air, temp. wind velocity, RH. Etc. The values of weather elements are modified from place to place by some factors accounting for different climates (temp. rainfall etc.) The Physical, geographical, edaphic , physiographic, biotic or even social factors which interact with climate elements and determine the climate of a place are called as ‘ climatic controls ’.

24. Climatic factors: Latitude Altitude Wind direction Distance from sea Topography Soil type Vegetation Ocean currents Storms …… etc. Thus these climatic controls act upon the weather elements and produce various types of weather and climate.

25. Seasons and climate: Changes in seasons on earth surface due to the movement of earth around the sun. Earths completes one rotation around the sun in one year . Therefore northern hemisphere receives more sunlight and heat when its axis is tipped towards the sun and less sunlight and heat when axis is tipped away from the sun . Important happenings between sun and earth December 21 – 22 is largest night and shortest day June 20-21 / 21-22 largest day and shortest night March 20-21 / 21-22 and Sept. 22-23 , both day and night are equal .

26. Important happenings between sun and earth:

27. Equinox: It is the movement of earth at which the length of day and night are equal in a year. Two equinoxes: Vernal (Spring) – equinox falls on March 21-22 Autumn (Winter) - equinox falls on Sept. 22 -23 Solstice: The time during the revolution of earth at which earth reaches its maximum declination (bending) when the day and nights are shortest and longest or the vice-versa is called solstice. Two types: Winter solstice : - falls on 22 nd December when night longest and day is shortest. Summer solstice : - falls on 21 st June when the day longest and night is shortest.

28. Common seasons: Seasons : The changes in temperature and length of day and night divide the year in different periods which are called seasons. Temperate zone seasons: Spring – March , April and May - 3 Months Summer – June, July and Aug. - 3 months Autumn – Sept., Oct., Nov. - 3 months Winter – Dec., Jan., and Feb. – 3 months

29. Summer – March , April and May - 3 Months Monsoon – June, July, Aug., and Sept. - 4 months Post monsoon – Oct., Nov. - 2 months Winter – Dec., Jan., and Feb. – 3 months IMD – has divided the climate of the year of India into 4 seasons :

30. Kharif (rainy season) – 15 th June - 15 th Oct. Rabi – 15 th Oct. – 15 th Feb. Summer – 15 th Feb – 15 th June Three crop seasons – for agriculture purpose