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Welcome. Ultraviolet (UV) Radiation and its Physical Modulating Factors in Africa Based on TOMS and NOAA Polar Orbiting Satellites Data. Introduction. What is solar ultraviolet radiation?

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  1. Welcome Ultraviolet (UV) Radiation and its Physical Modulating Factors in Africa Based on TOMS and NOAA Polar Orbiting Satellites Data

  2. Introduction What is solar ultraviolet radiation? • Ultraviolet radiation is part of the solar electromagnetic radiation spectrum from about 400 nm to 100 nm (where the visible ray range ends) • It is a little over 8% of the total solar spectrum Classification: • UV-A • UV-B • UV-C

  3. Effects of UV radiation • Different types of Skin cancer (DNA damage) • Early ageing of skin • Eye disease called cataract • Human immune system • Decreasing plant yield • Decrease in service time of infrastructure • Fading up of closes

  4. Gaps in understanding UV and the Determining Factors • Very few scientific studies in Africa on isolated cases. • Reports say the total column ozone is intact (no depletion) in Africa. But few show the trend of ozone in Africa. • UV interaction with clouds is complex and no attempt has been made in Africa.

  5. Problem Statement and Contribution Having the gaps the problems are: • Estimation of the dose of UV index (UVI) in Africa • Quantification of the relationship of UV with ozone, aerosols and clouds in Africa • Investigation of the vertical distribution of ozone in Africa and comparison with the higher latitudes.

  6. Objectives • The research’s central objective is towards development and understanding modes of variability for UV radiation in Africa and establishment of its interplay with ozone, aerosols, and cloud parameters in eigenvector domain. Specific Objectives a) To quantify the UV dose in Africa b) To identify and explain the modes of variability of UV radiation, ozone, aerosols, and cloud physical parameters in Africa in space and time, c) To illustrate the seasonal variability of UV, Ozone, and aerosols in Africa, understand how UV are modulated by various physical processes and factors, d) To establish the physical mechanisms of the variation of UV in space and time

  7. Absorption in the UV • Absorption by ozone, oxygen and nitrogen are wavelength dependent UV irradiance at surface are : - UV-A94% -- very small absorbed - UV-B 6% -- almost all absorbed - UV-C 0% -- all are absorbed

  8. The UV absorption cross-sections :

  9. UV Absorption Spectrum of Ozone: - The strongest absorption bands of O3 is called Hartley bands (200 to 300 nm) • Weak absorption of UV by O3 in Huggins bands (300 – 360 nm) • Very weak absorption of UV by O3 in the visible and infrared region (440 – 1180 nm)

  10. Biologically active UV radiation The dose rate is an instantaneous measure of the biologically-weighted UV irradiance Irradiance Biological action spectrum The dose rate is an instantaneous measure of the biologically-weighted UV irradiance

  11. BAS Cont… Integration of the dose rate over a period of the year in units of Jm-2, dose rate = Diurnal dependence of DNA damaging UV: Equator 400 600 Diurnal dependence of DNA-damaging dose rate on 21 June at three different latitudes (Madronich 1993a).

  12. UV Dependence on Geophysical variables • Surface UV (UV irradiance) affected • Scattering • Absorption in the atmosphere • The stability of extraterrestrial solar radiation: extraterrestrial solar spectrum results in Ozone which further results in UV • How is long term solar UV behaving? An increase of solar spectral irradiance at the 11-year solar activity cycle minimum since the Maunder minimum (year 1700) of 3.0% for wavelengths less than 300 nm and 1.3% for the band 300-400 nm

  13. UVD Cont… Dependence of UV on ozone and other trace gases As ozone decreases UV rises. The ozone in any given location is a balance between three processes: in situ creation, in situ destruction, and transport in to or out of the location. How do we measure ozone? • Mixing ratio (ppmv) • Number density P ozone= n KT (26) • Partial pressure • Dobson unit (1 DU = 10-5m )

  14. Ozone Circulation (Brewer Dobson Circulation) Average number density of ozone (DU per km) as measured by the Nimbus-7 Solar Backscatter ultraviolet Instrument (SBUV) plotted versus latitude and altitude, dataset from 1980-1989. The black arrows show the stratospheric Brewer – Dobson circulation.

  15. UVD Cont… Dependence on Clouds! • Under overcast conditions, clouds decrease the irradiance measured at the surface • However, enhancements of up to 25% can occur under broken cloud conditions They attenuate UV flux through the atmosphere aerosol optical depth (AOD) and the average column value of the single scattering albedo Dependence on Aerosols!

  16. Data Types and Methods UV, aerosols and ozone data • TOMS/ Nimbus 7 data (1979 to 1992) • EPTOMS data (1997 to 2003) Vertical distribution of ozone data • SBUV (TOMS/Nimbus 7) (1981 to 1985) • NOAA-11 (1999 to 2000) • NOAA-16 ( 2001 to 2003) Clouds data Obtained fromISCCP (1984-2001)

  17. DTM cont… Methods • Singular value decomposition (svd) /empirical orthogonal function (EOF)/ Principal Component analyses (PCA) • variance analyses • Correlation and regression analyses • Establishing physical relationship

  18. Res. Cont… The Spatial and Temporal Results of UV, AI and Ozone over Africa UV space-time mode The first few modes explain the total variability of the data. -The first spatial mode of UV ~19% of the total variability, -the second Spatial mode ~9% and so on: • The first four modes alone explained 39% Of the total variability of the 84 modes

  19. Seasonal variability of UV in Africa • In the JJAS 66% trend decrease (1979 to 1992) • In the same season 37 % trend increase (1997 to 2002)

  20. Res. Cont… Aerosols space-time mode • The first mode explains 28% • The second mode ~10% • The third mode ~7% and • The fourth mode ~5%

  21. The aerosols temporal modes

  22. Res. Cont… The ozone spatial and temporal modes • The first spatial mode ~30% • The second spatial mode ~17% • 11% the third mode • 5% by the fourth mode The first four values alone represent ~50% of the total variance in the data

  23. The Temproal modes of ozone

  24. Res. Cont… Vertical ozone mixing-ratio 10 years average ozone amount tropical Africa (ONDJ)

  25. Res. Cont… • If ozone concentration is highest in the stratosphere in the period, it is also the least in the troposphere in the same period. • In general, the vertical ozone concentration shows opposite quantitative variability in the two spheres of the atmosphere.

  26. Res. Cont… • For the other cross sections ~30S and ~30N is taken and compared with the other latitudes, ~0, ~60S, ~60N, ~90S and ~90N. • The vertical ozone concentration is relatively highest in October for 60N (9.544 ppmv), and least for 60S (8.48 ppmv). The difference is 11% lower than the peak.

  27. Res. Cont… • In November, the ozone-mixing ratio is least in values at and around 90N and 90S in the stratosphere. • the greatest ozone-mixing ratio is observed for 30S and its nearest locations (because of the ozone transport from the equator to higher latitudes throughBrewer-Dobson Circulation).

  28. Res. Cont…

  29. Results and Discussion Ultraviolet Radiation in Africa • Around 18N, UVery dose = 5500 J/m2 • At tropics high, At high latitudes less UVI = dose rate/unit time (mW/m2) x 20 m2/mW

  30. Res. Cont… • Latitudinal Comparison of UV and ozone Why higher latitudes ?

  31. Ozone Circulation (Brewer Dobson Circulation) Average number density of ozone (DU per km) as measured by the Nimbus-7 Solar Backscatter ultraviolet Instrument (SBUV) plotted versus latitude and altitude, dataset from 1980-1989. The black arrows show the stratospheric Brewer – Dobson circulation.

  32. Due to the Saharan and Arabian Deserts Latitudinal Comparison of UV, ozone and Aerosol Index UV Ozone

  33. UV and ozone UV (O3) = -18.595 -12.233x O3 (41%)

  34. Res. Cont… b) Aerosols and UV Association • only 7% of the total variability of UV over the African continent can be expressed by aerosols. UV (AI) = -4.085 – 210.140 x AI (Ts_1) – 187.982 x AI (Ts_2) – 717.297 x AI (Ts_4) where Ts (1-4) means respective time series of eigenvectors.

  35. Res. Cont… The clouds, which have shown significant relationship, are as follows: • All clouds- Top Temperature • Altocumulus Liquid clouds – Optical Thickness and top temperature • Cirrostratus cloud – Top Pressure • Cirrus cloud – Water Path Of 100 cloud parameters attempted to associate.

  36. Res. Cont… The general model which accounts for the clouds in this UV investigation is UV = -30.293 – 11.492 x (all-cloud-temp.) – 56.791 x (altocumulus Liquid-top-opt.) – 49.453 x (altocumulus liquid – temp.) – 3.488 x (cirrostratus cloud – top - press) – 7.029 x (cirrus cloud water path) The overall contribution of clouds to the UV analysis is around 39%.

  37. conclusion • The possible range of values of UV index (UVI) obtained in Africa is between 4 and 9. • The overall trend of the UVery is decreasing in all of the seasons. • Ozone trend is on the increase in Africa. • The tropical Africa vertical ozone profile show stable variability. • The 30N and 30S show relatively higher stratospheric ozone.

  38. UV interplayed with all cloud type and properties ( top pressure, top temperature, water path, and optical thickness) except cloud amount. • UV interplayed with all cloud type and properties ( top pressure, top temperature, water path, and optical thickness) except cloud amount. • Deep convective clouds does not show significant relationship with UV but are the main cloud types in tropical Africa.

  39. Sum. Cont…. • Interesting results come out from the UV and cloud relationships: • UV interplayed with all cloud type and properties ( top pressure, top temperature, water path, and optical thickness) except cloud amount • All clouds account for 39 % of the total variability of UV irradiance. • Deep convective clouds does not show significant relationship with UV but are the main cloud types in tropical Africa.

  40. Clouds (39%) Ultraviolet Radiation in Africa Ozone concentration (40%) Aerosol Index (7%)

  41. Thank y u!

  42. Ultraviolet radiation spectrum

  43. UV Absorption Spectrum of Molecular oxygen: • Schumann - Runge band: 200 – 125 nm • Several bands: 125 – 100 nm (e.g. Lyman- 121 nm) • Hopfield bands: <100 nm • Hertzberg Bands: 260 – 200 nm

  44. BAS Cont… • Seasonal and latitudinal dependence of daily dose rate (Jm-2 day-1) for DNA damage calculated for: -clear skies -using ozone column (DU) average (1979-1989)

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