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

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

Spectral region wavelength energy
Infrared gt700 nm 49.4
visible 400-700 nm 42.3
UV-A 400-315 nm 6.3
UV-B 315-280 nm 1.5
UV-C lt280 nm 0.5
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 researchs 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-A 94 -- 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
Dependence of UV on ozone and other trace gases
UVD Cont

• 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

Dependence on Aerosols!

• They attenuate UV flux through the atmosphere
  aerosol optical depth (AOD) and the average
  column value of the single scattering albedo

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 from ISCCP (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 through Brewer-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

• Latitudinal Comparison of UV, ozone and Aerosol
  Index

Due to the Saharan and Arabian Deserts
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
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 lt100 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)