Electromagnetic Spectrum Relationship between wavelength distribution and temperature

Electromagnetic Spectrum

Relationship between wavelength distribution and temperature of radiation emitting surface

Wavelength Distribution of Solar Radiation (Light Quality) Total Solar Radiation (300 – 10000 nm) – Ultra-Violet (UV) Radiation (~ 300 – 400 nm) – Photosynthetically Active Radiation (PAR) (~ 400 – 700 nm) – Infra-Red (IR) Radiation (~ 700 nm – 10000 nm)

300 – 2500 nm

Distribution of solar radiation energy in different wavelength classes For the range 100 – 10, 000 nm: – UV : 8 – 9% – PAR : 46 – 47% – IR : 45%

Relationship between Energy Content and Wavelength Distribution • Wavelength and energy content is inversely-related E = (h c)/λ E = Energy of a photon in given wave length (J) h = Planck’s Constant (6. 63 x 10 -34 Js) c = Velocity of light (3 x 108 ms-1) λ = Wave length (m) A photon in the Blue (λ = 450 nm) region => 4. 42 x 10 -19 J A photon in the Red (λ = 650 nm) region => 3. 06 x 10 -19 J

Measures of Radiation Intensity • Energy units • • • J m-2 s-1 (W m-2) MJ m-2 d-1 k. Wh m-2 yr-1 – MJ m-2 d-1 = k. Wh m-2 yr-1 x (3. 6 / 365) • Molar units – μmol (PAR) m-2 s-1 – mol (PAR) m-2 d-1 1 J (PAR) ≈ 4. 6 μmol (PAR)

Daily Total Solar Radiation (MJ m-2 d-1) = Day length (h d-1) x Mean Daily Irradiance (W m-2)

Variation of Day length

Earth’s rotation around the sun determines the variation of day length

Variation of day length on June 21

Variation of irradiance with latitude

Variation of the Intensity of incident solar radiation (Irradiance) with latitude

Global patterns of solar irradiance Source: http: //www. physicalgeography. net/fundamentals/7 g. html

Measures of Radiation Intensity • Energy units • • • J m-2 s-1 (W m-2) MJ m-2 d-1 k. Wh m-2 yr-1 – MJ m-2 d-1 = k. Wh m-2 yr-1 x (3. 6 / 365) • Molar units – μmol (PAR) m-2 s-1 – mol (PAR) m-2 d-1 1 J (PAR) ≈ 4. 6 μmol (PAR)

Variation of Solar Radiation Intensity in Sri Lanka 13. 81 MJ m-2 d-1 20. 71 MJ m-2 d-1

Clear negative relationship between annual precipitation and annual solar radiation intensity