Insolation and heat budget

GEOGRAPHY

1. CLIMATIC AND HYDROLOGICAL STUDIES INSOLATION AND HEAT BUDGET

2. Energy System Atmosphere is open energy system . It receives energy from both directions ( earth and sun ). Compared with sun (solar energy), earth’s energy can be negligible . All life processes and all exchanges of matter and energy between the earth’s atmosphere and the surfaces of the oceans and lands are driven by solar energy . The planetary circulation systems of atmosphere and oceans are also driven by solar energy . Water changes in various forms (liquid, solid and gas) over the globe also driven by solar energy . Sun is the energy source of the earth.

3. Solar Radiation Emitted from sun (surface temperature 6000 o C) It is a spectrum (combination energy of different wavelengths) Most of it is visible light rays (short-wave) Energy emitted by earth (surface temperature 15 o C) is terrestrial radiation (long-wave) Higher temperature of an object emits shorter-wave of radiation . The radiant energy received from the sun, transmitted in a form analogous to shortwave, and travelling at the rate of 1,86,000 miles per second . That it reaches earth in 8 minutes 20 seconds .

4. Insolation The prime source of the energy injected into our atmosphere is the sun. The sun is constantly releasing energy in all direction. This energy is known as solar radiation . It is a electro-magnetic wave energy radiating from sun, which is also called Insolation . All weather phenomena are affected by various meteorology parameters which all affected by Insolation

5. in coming Sol ar Radi ation Insolation is a measure of Solar Radiation incident of a surface. It is the amount of solar energy received over a given area in a given time. It is commonly expressed in: kilowatt-hours per square meter per day ( kw.h/m 2 /day ) (or) watts per square meter( w/m 2 ).

6. Electromagnetic Radiation The Electromagnetic Spectrum

7. Spectrum of Solar rays Short-wave radiation (wavelength < 0.8 micron) Ultra-violet, x-rays, gamma rays , Invisible and harmful for living organisms. Most of them absorbed by thermosphere and ozone layer . Visible lights (violet, indigo, blue, green, yellow, orange and red). 90% of solar rays . It provides most of the heat energy to the atmosphere. Long-wave radiation (wavelength > 0.8 micron) Infrared, micro waves and radio waves They are also absorbed by ozone, CO 2 and clouds .

8. Our atmosphere is transparent to radio waves, visible light, and some infrared and UV radiation.  Atmospheric Window

9. Shortwave and Longwave Most of the radiation emitted from the sun is in the visible part of the spectrum.

10. What happens to Incoming Solar Radiation?

11. Reflection The earth and its atmosphere reflect part of the solar radiation back to space. Reflectivity, or albedo , is expressed as a percentage of the incident radiation reaching the surface. Reflection of sunlight depends on the type and size of the particles as well as the wavelength

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13. Scattering Scattering is the process by which small particles and molecules of gases diffuse part of the radiation in different directions. The amount and direction of scattering depends on the ratio of the radius of the scattering particle to the wavelength of the energy. The most obvious effect of scattering in the atmosphere is sky color . The only reason our sky appears blue is because of scattering of radiation in the shorter wave-lengths of visible light.

14. Rayleigh Scattering Rayleigh scattering is primarily caused by oxygen and nitrogen molecules. The effective diameters are at least 0.1 times smaller than the affected wavelengths. Rayleigh scattering is most influential at altitude above 4.5 km (pure atmosphere). The amount of Rayleigh scattering is 1/ λ 4 As the result, invisible ultraviolet radiation is greatly affected by Rayleigh scattering. Rayleigh scattering can be called small particle scattering. In visible light, blue wavelength at 0.4 μ m is scattered 5 times as the red wavelength at 0.6 μ m. This explains why the clear sky appears blue. The scattering made blue light reach our eyes from all parts of the sky.

15. Mie Scattering Occurs when there are sufficient particles in the atmosphere that have mean diameters from 0.1 to 10 times larger than the wavelength under consideration. Mie scattering can be called large particle scattering . The important Mie scattering agents include water vapor and tiny particles of smoke, dust , etc. The influence of the Mie scattering is most affected in the lower 4.5 km of the atmosphere. Mie scattering influences longer radiation wavelengths than Rayleigh scattering. The wavelength of Mie scattering is between to λ 4 to λ .

16. Absorption Absorption retains incident radiation and converts it to some other form of energy. Most often it changes to sensible heat , which raises the temperature of the absorbing object. Gas molecules, could particles, haze, smoke, and dust absorb part of the incoming solar radiation. The two most common gases in the atmosphere, nitrogen and oxygen absorb ultraviolet radiation.

17. Factors Affecting Insolation The amount of Insolation received on the earth’s surface is not uniform everywhere. It varies according to the place and time. When the tropical regions received maximum annual Insolation, it gradually decreases towards the poles. Insolation is more is summers and less in winters.

18. The major factors affecting Insolation Solar output Distance from the sun Angle of solar incidence Length of day

19. Solar output Solar radiation is light energy from the Sun. Millions of Nuclear reaction happens across the sun every second. Hydrogen atoms get compressed and fuse together, creating helium. This process is called  nuclear fusion . It's constantly giving off a huge amount of energy and radiation.  The core of  the sun temperature , which can reach more than 15 million degrees Celsius. The  temperature in the photosphere  is about 6000 C. Solar output of the total solar energy sent out into space the earth intercepts only some two thousand millionth , equivalent too a power of 1.8x10 14 kw . The energy received on a surface normal to the solar beam is about 2 cal/cm 2 /min (1.396kw/m 2 ) 3 ;this is termed the solar constant. There are 11 years cyclic variations of 1% in the output of solar energy. More energy can be received when sunspot activity is less active .

20. Distance from the sun The ever-changing distance of the earth from the sun produces more frequent variation in our receipt of solar energy. Since the earth revolves around the sun in an elliptical orbit . The mean distance between the earth and sun is about 149.6million km. Each year, on about January 3, the earth comes closer to the sun (distance 147.3 million kilometers ). This position is known as perihelion.   On about July 4, the earth is a little farther from the sun when the distance becomes about 152.1 million kilometers . This position is called aphelion. the receipt of solar energy on a surface normal to the beam is 7% in January than in July. January world surface temperature of about 4 c(7 F) , over those of July.

21. Angle of solar incidence Angle of incidence: It is the angle between the sun’s rays and the horizon. Greater the angle of incidence, the more concentrated energy , hence higher is the temperature . Intensity of Insolation is greatest where the sun’s rays strike vertically . Polar regions receive the least heat per unit area. Temperatures are maximum at low latitudes and minimum near the poles . Angle of incidence is affected by latitude , the time of day , seasons and length of daytime .

22. Angle of insolation varies with:

23. Length of day The length of daylight also affects the amount of Insolation which received. At the equator the length of days and nights is 12 hours . On the autumnal and vernal equinoxes that occur on September 23 and March 21 respectively, the mid-day sun is overhead at the equator. The winter solstice (December 22) onward the length of day increases in the northern hemisphere till the summer solstice (June 21).    June 21 to December 22 the length of day in the northern hemisphere decreases, and in the southern hemisphere it increases. the summer solstice the northern hemisphere has the longest day and the shortest night . the winter solstice the southern hemisphere has the longest day , and the northern hemisphere has the longest night .

24. Latitude Longest day Latitude Longest day or night or night 12 hours 63.4 20 hours 17 13 hours 66.5 24 hours 31 14 hours 67.4 1 month 41 15 hours 69.8 2 months 49 16 hours 78.2 4 months 58.5 18 hours 90.0 6 months Maximum length of day in different latitudes.

25. Heat budget Incoming heat being absorbed by the Earth, and outgoing heat escaping the Earth in the form of radiation are both perfectly balanced.   If they were not balanced, then Earth would be getting either progressively warmer or progressively cooler with each passing year.  This balance between incoming and outgoing heat is known as Earth’s heat budget .

26. First let us understand the amount of solar Insolation received by earth and atmosphere separately. Suppose incoming solar insolation is = 100 units . Amount lost through scattering and reflection: a) Through Clouds - 27 units b) By dust particles - 6  units c) By Ice Caps and Glaciers - 2  units Total 35 units are reflected back into space . (known as albedo of earth) Now, the units received by earth and its atmosphere = 100- 35 = 65 units

27. Heat Budget of the Earth Surface 51 units of solar insolation is received by earth as direct radiation which can be segregated as follows: Received through direct Radiation = 34 units Received as diffused day light = 17 units Which comes out to be 51 units .

28. Heat Budget of Atmosphere Absorption by atmospheric gases in different vertical zones of atmosphere - 14 units Now 51 units + 14 units= 65 units (total solar insolation received by earth and atmosphere) Out of the solar radiation received directly by Earth i.e. 51 units, 17 units are re-radiated back into outer space, and rest 34 units (51-17 units) is absorbed by atmosphere in the form of outgoing terrestrial radiation . Which comes out to be 48 units (14+ 34 = 48) .

29. Albedo Albedo= Reflected radiation Incoming radiation A measure of the amount of radiation reflected. Some things reflected radiation better than others “ dry ” or “ cold ” snow & ice = high albedo Water =moderate for visible , low for infrared Plants =moderate for visible Land absorbs and releases radiative energy quicker than water

30. Typical albedos of various surfaces to incoming solar radiation Type of surface Percent reflected energy (Albedo) Fresh Snow 75 - 95% Old Snow 30 - 40% Water 0° 99% 10° 35% 30° 6% 90° 2% Clouds Cumulus 70 - 90% Stratus 60 - 84% Cirrus 44 - 50% Forest 5 - 20% Grass 10 - 20% Sand 35 - 45% Plowed soil 5 - 25% Crops 3 - 15% Concrete 17 - 27% Earth as a Planet 30%

31. Atmosphere, Weather and Climate – Barry and R.J. Chorley Page No: 10,11,12,13,14,15,16,17,18,19,21,27,28 Climatology an Atmospheric Science – John E. Oliver and John J. Hidore. Page No: 21,26,27,28,29 https://Zolushka 4 earth.Wordpress.com/2010/08/27/understanding-heat-budget/ https://www.clearias.com/insolation-heat-balance/ References:

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