Atmospheric and Climate Sciences, 2011, 1, 55-60
doi: 10.4236/acs.2011.12006 Published Online April 2011 (http://www.SciRP.org/journal/acs)
Correlative Study between UV Irradiance and TOC
Using AURA OMI at Kannur (12.3N, 75.4E)
Nishanth T.*, Sheela M. Joseph, Praseed K. M., M. K. Satheesh Kumar
Department of Atmospheric Science, Kannur University, Kannur, Kerala, India
Received February 25 , 20 1 1; revis ed Marc h 8, 2011; Accepted March 15, 2011
Abstract
The solar UV radiation has prominent impacts on human life, animals and plants with positive and negative
effects. Atmospheric ozone, which is formed from the photodissociation of molecular oxygen mainly in the
stratosphere, absorbs a significant factor of solar UV radiation. The ozone in the stratosphere acts as a pro-
tective layer to prevent UV radiation reaching on the surface of the earth. Hence the intensity of solar UV
radiation on the surface has a strong dependence on the Total Ozone Column (TOC). The UV irradiance on
earth surface depends on geometrical factors such as solar zenith angle, altitude, latitude and other atmos-
pheric parameters as well. This is an attempt to study the variation of solar UV flux at its four discrete wave-
lengths ranging from 305 - 380 nm at Kannur, which is located in the north of Kerala in India. Hence such a
correlation of TOC and UV irradiance is relevant to realize the radiation budget at this location (12.3N,
75.4E) using AURA OMI data. This paper reveals the correlation of day to day, month to month temporal
variation of total ozone column (in DU) and UV irradiance (w/m2). From the analysis, the anti-correlation
between UV and TOC is revealed and its impact in the solar radiation budget is established.
Keywords: UV Irradiance, Aura OMI, Total Ozone Column, Sun Burn
1. Introduction
Ozone is an important atmospheric constituent, because
it absorbs the part of solar radiation that is deleterious to
biological life on earth [1]. It is also widely accepted that
although UV irradiance represents a small portion of the
solar spectrum, its spatial and temporal availability is of
great importance [2]. This is because UV is responsible
for a variety of familiar photochemical reactions, includ-
ing photochemical smog in polluted urban areas, bleach-
ing of paints, decay of plastics and other detrimental ef-
fects on the earth’s ecosystems [3-6]. The solar UV ra-
diation is classified as UV-A (320 - 400 nm), UV-B (280
- 320 nm) and UV-C (200 - 280 nm), based on the wave-
length of the radiation. While the UV-C radiation is
completely absorbed by the atmospheric ozone, most of
the UV-A radiation reaches the earth’s surface. The
UV-A radiation is however, not harmful to biological life
on earth [7]. UVB (spectral range 280 - 320 nm) still
reaches ground level it is strongly absorbed by strato-
spheric ozone. UV- B radiation is effectively attenuated
by the stratospheric ozone layer, it is no t fully blocked. It
is very strongly absorbed in tissues and penetrates only
superficially into the body; thus it directly affects only
the eye and the skin. Detrimental consequences for the
eye could include impaired vision, since UV radiation
has been reported to cause opacification of the lens
(cataract), losses of productivity and other destructive
effects in plants [8-12]. Quite apart from its damaging
effects, the UVB can also be beneficial; it initiates the
production of vitamin D that helps build and maintain
human bones as well as it may prevent against certain
types of cancer [4, 13]. Although UVB comprises the
most energetic wavelengths, several studies showed that
UVA is also hazardous, producing skin damage and
premature skin photo-ageing and wrinkling as well as
eye damage.
The total column ozone at a location is known to vary
from day to day, seasonally and annually. Periodicity
related to quasi-biennial and solar cycles has also been
associated with the total column ozone variation [14].
UV-B radiation is strongly absorbed by stratospheric
ozone, and its intensity at the surface depends on the
ozone layer concentration [15, 16].
Studies on stratospheric ozone depletion at many loca-
tions on the globe are being made using instruments like

56 T. NISHANTH ET AL.
the Dobson spectrophotometer, Brewer spectrophotome-
ter etc. In addition to these ground based ozone meas-
urements, which have limited spatial coverage, meas-
urements done by Total Ozone Mapping Spectrometer
(TOMS) aboard Nimbus-7 Satellite provide a good da-
tabase for the long-term monitoring of column ozone
with extensive spatial coverage. Krishna Prasad and
Niranjan [17] made an attempt to study the correlation
between solar UVB irradiance and total column ozone
with TOMS data. They made regression model for esti-
mating UV-B irradiance from TOMS ozone, air-mass,
sun-earth distance correction and solar zenith angle at
Vishakhapatnam. In addition to this, they studied a
long-term variation of incoming UV-B irradiance for the
period 1978-1993 using TOMS ozone. The main objec-
tive of this work is to analyze the correlation between
clear sky UV irradiance and total ozone column using
AURA OMI over Kannur at different season of 2009.
2. Results and Discussion
2.1 Ultra Violet (UV) Irradiance and Total
Ozone Column (TOC)
The UV irradiance and TOC data sets consists of obser-
vations carried out by satellite borne instrumentation
(TOMS and OMI). The Total Ozone Mapping spec-
trometer (TOMS) launched on board the Earth Probe
satellite of NASA in Ju ly 1996 is still con tinuing by long
term daily mapping of the global distribution of the dis-
tribution of ozone over a column of atmosphere. The
Ozone Monitoring Instrument (OMI) has been operating
since July 2004 on board EOS Aura which is a nadir
viewing imaging spectrograph that measures solar radia-
tion back scattered by earth atmosphere and surface over
the wavelength range from 300 nm to 500 nm with a
spectral resolution of about 0.5 nm. In this study, data
were retrieved only at cloudless, blue-sky conditions at
similar solar zenith angles to eliminate much of the in-
fluences of non- ozone parameters described earlier. The
UV irradiance and TOC were analyzed at pre monsoon
(May), monsoon (June), post monsoon (October) and
winter (December) seasons in Kannur. The relation con-
necting solar irradiance and total ozone column is de-
picted in the Figure 1. The data is taken in a clear sky
days of the months of May 2009 for a wavelength of 305
nm with a solar zenith angles of 25.07, 22.33, 24.02, and
30. From the figure, it is clearly seen that both solar ir-
radiance and total ozone column are anti correlating with
each other.
The data correspond to 305 nm solar irradiance and
respective total ozone column were analyzed in detail in
a pre-monsoon (May), post monsoon (October), mon-
soon (June) and winter (December) season of 2009 and is
shown in the follo wing Figures 2-5.
Figure 1.Variation of clear sky irradiance with TOC.
Figure 2. Correlation between TOC and CS irradiance for
305 nm in pre monsoon months (May) 2009.
Figure 3. Correlation between TOC and CS irradiance for
305 nm in post monsoon months (October) 2009.

T. NISHANTH ET AL.
57
Figure 4. Correlation between TOC and CS irradiance for
305 nm in monsoon months (June) 2009.
Figure 5. Correlation between TOC and CS irradiance for
305 nm in winter months (December) 2009.
In the Figure 2, it is seen that the CS irradiance and
total ozone column are anti correlate with each other and
the correlation coefficient is –0.958. The squared corre-
lation between clear sky irradiance and total column
ozone for 305 nm is 0.944.
In the Figure 3 it is clear that the effective UVB and
total ozone column are anti correlate with each other and
the correlation coefficient (r = –0.972) is statistically
significant, probably due to the same aerosol optical
thickness. The squared correlation between clear sky
irradiance and total column ozone for 305 nm is 0.986.
This means that a change in 100DU ozone produces
about 70 mw/m2 effective UV.
In the Figure 4, the effective UVB and total ozone
column are anti correlate with each other and the correla-
tion coefficient (r = –0.92) is statistically significant but
the squared correlation (R2 = 0.876) is not good. This
may be due to the aerosol optical thickness effect or due
to the cloud effect or humidity. This means that a change
in 100 DU ozone produces about 200 mw/m2 effective
UV. The correlation is not good.
In the Figure 5, the effective UVB and total ozone
column are still anti correlate with each other and the
correlation coefficient (r = –0.999) is statistically sig-
nificant probably due to the same aerosol optical thick-
ness. The squared correlation is also statistically impor-
tant (R2 = 0.998) this means a change in 100 DU ozone
column reduces about 110 mw/m2 effective UV.
Table 1 shows the correlation coefficient and the
squared correlation between clear sky irradiance and
total ozone column for 305 nm for different seasons of
observation.
2.2 Total Ozone Column over Kannur
The monthly mean value of total ozone column over
Kannur was retrieved from TOMS and is plotted against
the months for the year Jan 2000 to February 2010. The
variation of total ozone column over Kannur during
2000-2010 is shown in the Figure 6.
Total ozone columns are generally measured in Dob-
son Unit . One Dobson is 2.69 × 1016 ozone molecules/cm2.
When the total ozone column is less than 220 DU, ther e i s
chance for the production of ozone hole in that location.
Table1. Seasonal variation of correlation coefficient and R2.
Season Correlation
coefficient Squared correlation (R2)
Pre monsoon–0.958 0.954
Monsoon –0.921 0.876
Post monsoon–0.972 0.986
Winter –0.999 0.998
Figure 6. Variation of total ozone column over Kannur
during 2000-2010.

58 T. NISHANTH ET AL.
From the figure it is clear that the total ozone concentra-
tion is found to be high in May and June. It decreases
during monsoon and becomes very low in December and
January. Thereafter it gradually increases throughout the
winter reaches a peak in summer. This trend is consis-
tently observed in all the years from 2000 to 2010. The
amount of ozone in the troposphere and lower strato-
sphere in general depends on both dynamics and chemis-
try of the atmosphere. The dynamical influences include
wave driving of the stratospheric circulation and tro-
popause folds. The only mechanism of ozone production
is the recombination of atomic oxygen with oxygen
molecules. In the troposphere the energetically excited
oxygen atom is comes from the photodissociation of NO2,
whereas in the stratosphere it comes from the dissocia-
tion of oxygen molecules. There is a sharp decrease in
total ozone column was observed in the year 2005. This
may be due to the fact that the year 2005 was the hottest
year of this decade. Subsequently, the convectiv e activity
increases and the ozone are removed from the atmos-
phere due to this enhanced convective activity.
2.3 Tropospheric Ozone over Kannur
Even if about 90% of atmospheric ozone molecules re-
side in the stratosphere, tropospheric ozone strongly in-
fluences the radiative budget of the atmosphere and the
oxidation capacity of the troposphere. Due to its high
chemical reactivity in the lower troposphere, ozone is
considered a dangerous pollutant, causing harm to hu-
man health and ecosystems. Figure 7 shows the variation
of troposph eric ozone over Kannur during 2005 to 2010,
retrieved from Aur a O MI.
From the figure it is clear that tropospheric ozone
concentration is high during summer (March, April, May)
and low during monsoon (July, August, September)
Figure 7. Variation of tropospheric ozone over Kannur
during 2005-2005.
seasons. Maximum concentration of 59.4 DU is observed
in April 2006 and a minimum of 34 DU is observed in
August 2007.During the period of observation it is found
that an increase of 4.17% of tropospheric ozone over
Kannur.
2.4 Uv Index During Sun Burn
The UV index is an international standard measurement
of how strong is the ultraviolet (UV) radiation from the
sun at a particular place on a particular day. It is a num-
ber linearly related to the intensity of UV radiation
reaching the surface of the earth at a given point. It can-
not be simply related to the irradiance (measured in
W/m2) because the UV of concern occupies a spectrum
of wavelength from 295 nm to 325 nm and shorter wave-
lengths have already been absorbed a great deal when
they arrive at the Earth’s surface. Skin damage, however,
is related to wavelength, the shorter wavelengths being
much more significant. Variation of Erythemal UV over
Kannur is shown in the Figure 8.
The monthly mean UV values have been retrieved
over Kannur from the TOMS EP data and from OMI
Aura. Data are plotted against months for the years
January 2000 to February2010. It shows a clear seasonal
variation that is repeated consistently year after year. It is
further observed that the UV at Kannur has increased
consistently from 2000 to 2010. There is a sharp increase
in UV In the year 2005. This shows that total ozone
column has a significant effect on the UV radiation. Ta-
ble 2 shows the average value of total ozone column ob-
served during the month of March 2005-2010 at Kannur
and Palakkad in Kerala, India where the sun burn was
reported in month of Mar ch 2010.
From the above table, it is clear that the total ozone
column during March is quite low as compared other
Figure 8. Variation of Erythemal UV over Kannur.

T. NISHANTH ET AL.
59
Table 2. Variation of TOC over Kannur and Palakkad.
Location where sun burn reported
Year Kannur (TOC DU) Palakkad (TOC DU)
2005 259 257
2006 254 253
2007 255 254
2008 251 250
2009 260 260
2010 250 246
months in Kannur. Generally, TOC over Palakkad is
lesser than that of Kannur. Comparing to other year,
during 2010 total ozone column is very low over Kannur
and Palakkad. This may be the prime reason for the sun
burn reported in these two locations.
3. Conclusions
The solar UV irradiance on clear sky days during
pre-monsoon, monsoon, post-monsoon and winter sea-
sons has been successfully retrieved from OMI and this
has been correlated with total ozon e column over Kannur.
As expected a negative correlation is obtained between
UVB and TOC in all season. Howev er, the correlation is
much strong during post-monsoon and winter days due
to relatively clean atmosphere after severe south west
monsoon activity in Kannur. During the pre monsoon
and monsoon period, the atmosphere becomes quite tur-
bid due to heavy winds that transport aerosols and trace
gases that make the degree of correlation relatively poor.
Thus it is evident that the correlation of solar UV irradi-
ance with changes in TOC becomes more accurate dur-
ing post monsoon and winter months over Kannur. The
extended study revealed a significant reduction in TOC
over some regions in Kerala from where few cases of sun
burn have been reported during March. This reduction of
total ozone column enhanced the amount of UVB flux
more than the normal dose and this is the prominent
cause for the sunburn cases reported from these locations
in the state.
4. Acknowledgements
Authors acknowledge their deep sense of gratitude to
Kannur University for providing all support to material-
ize this target. One of the authors Sheela M Joseph ex-
presses her sincere thanks to Dr.Suriya Ahmad, NASA
and Dr.Anitti Arola, Finland Meteorological Institute,
Finland for their help and support received in retrieving
and analyzing TOMS data.
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