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Surface solar ultraviolet irradiance andtotal ozone during summertimeC. Varotsos a , C. Tzanis b , S. Tsitomeneas c , M‐N.

Assimakopoulos a & A. Mammis aa Department of Applied Physics , University of Athens ,Panepistimiopolis Build. Phys. 5, 15784, Athens, Greeceb Department of Energy Technology , Technological EducationInstitute of Athens , Ag. Spyridonos Str., 12210, Athens, Greecec Department of Electronics , Technological Education Institutionof Piraeus , 250 Thivon & P. Ralli, Aigaleo‐12244, GreecePublished online: 25 Apr 2008.

To cite this article: C. Varotsos , C. Tzanis , S. Tsitomeneas , M‐N. Assimakopoulos & A. Mammis(2008) Surface solar ultraviolet irradiance and total ozone during summertime, InternationalJournal of Remote Sensing, 29:9, 2667-2673, DOI: 10.1080/01431160701767567

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Surface solar ultraviolet irradiance and total ozone during summertime

C. VAROTSOS{, C. TZANIS{, S. TSITOMENEAS*§,

M-N ASSIMAKOPOULOS{ and A. MAMMIS{{Department of Applied Physics, University of Athens, Panepistimiopolis Build. Phys. 5,

15784, Athens, Greece

{Department of Energy Technology, Technological Education Institute of Athens, Ag.

Spyridonos Str., 12210, Athens, Greece

§Department of Electronics, Technological Education Institution of Piraeus, 250 Thivon

& P. Ralli, Aigaleo-12244, Greece

An anticorrelation between total ozone and UV-B radiation was observed in

Athens, Greece (35.59uN, 23.44uE) for clear-sky conditions during the

summertime period 1993–2006. The UV-B radiation (290–320 nm) was measured

using a UV-B pyranometer, and the total ozone column data were obtained using

the Dobson No. 118 spectrophotometer. In addition, a parametric model has

been used for the calculation of the direct and diffuse solar ultraviolet radiation

reaching the Earth’s surface. Finally, the total ozone observations made by the

satellite-borne instrument Scanning Imaging Absorption Spectrometer for

Atmospheric Chartography were used in order to confirm the results obtained

from the Dobson measurements. The main finding which stems from these data

is that there is no significant seasonality in the radiation amplification factor of

UV-B, broadband UV, and the erythemally weighted UV, whereas the enhanced

UV-B generates intensive air-pollution episodes, which subsequently attenuate

the surface UV-B irradiance. Furthermore, these findings may be used for the

prediction of the propagation parameters of the microwaves, mm-waves and

optical telecommunication signals over the Athens Metropolitan Area.

1. Introduction

The anticorrelation between total ozone content (TOC) and surface UV radiation is

a complex function of many variables, including the solar zenith angle, surfaceelevation, cloud cover, aerosol loading, and optical properties such as surface albedo

and vertical profile of ozone (Madronich 1993, Varotsos et al. 1995, 2001a,b, 2004,

Varotsos 2005, Efstathiou et al. 2003).

The oldest measuring device for the TOC content in the atmosphere is the Dobson

spectrophotometer, which was developed in 1924 by G. M. B. Dobson (Komhyr

1980, Bojkov et al. 1993, Varotsos and Cracknell 1993, 1994a, b). The instrument

uses a quartz double monochromator, and it has been used to monitor TOC since its

development. One monochromator is used to disperse the radiation and the secondto reject interfering scattered radiation. The operation principle of the instrument is

based on taking TOC measurements in the Huggins bands by measuring the

difference between the intensity of solar light at certain wavelength pairs. These

pairs are selected in such a manner that the difference in the ozone absorption

*Corresponding author. Email: stsit@teipir.gr

International Journal of Remote Sensing

Vol. 29, No. 9, 10 May 2008, 2667–2673

International Journal of Remote SensingISSN 0143-1161 print/ISSN 1366-5901 online # 2008 Taylor & Francis

http://www.tandf.co.uk/journalsDOI: 10.1080/01431160701767567

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coefficient for each pair is as large as possible, while the difference between the

corresponding wavelengths remains small. By using one pair of wavelengths, a

differential measurement is made. One is absorbed by ozone while the other passes

through a variable optical wedge. This measured difference combined with the

extraterrestrial constant and the ozone absorption spectrum provides the TOC value

(Varotsos et al. 2000, Efstathiou et al. 2003).

The high-frequency electromagnetic waves from spectrum bands, not as high as

the UV, interact also with the molecules of the atmospheric gases. Therefore, the

propagation parameters of the microwaves (MW), mm-waves and optical

communication signals, depend on the concentration and other characteristics of

the atmospheric gases (International Telecommunication Union 1997). The power

losses, due to absorption phenomena, are presented as a prediction of signal

attenuation as a function of frequency, elevation of the path, propagation altitude,

gas molecule density, air temperature and pressure. Attenuation is not the only

important parameter, but also the degradation in coherence, the depolarization, and

the time/frequency dispersion.

The remote sensing and modern telecommunication applications, such as the

broadcasting of digital satellite or terrestrial Radio-TV, or the broadcasting of laser,

Radio, TV, and Teletext (Tsitomeneas and Voglis 1998) over capital cities such as

Athens, may face design obstacles, related to atmospheric gases, such as the diurnal

and seasonal phenomena from low- and high-altitude ozone (Reid et al. 1994).

Therefore, the transmitter’s power, receiver’s sensitivity with the antenna, or

photodiode characteristics must be assessed to accommodate the data and expecta-

tions for the worst-case meteorological situation through which the atmospheric

communication application expected to operate.

This paper presents the results obtained from measurements of ultraviolet

irradiance carried out in the Department of Applied Physics, University of Athens,

Greece. The frequent ability of clear skies, with a long sunshine duration, at this site

provides the opportunity to monitor cloud-free relationships between UV exposure

and TOC.

It is important to note that this investigation allows us to study over a long period

(summer period 1993–2006) the fluctuation of UV-B radiation and total ozone

column over Athens, a city that represents a tourist destination for people around

the globe each summer. Furthermore, the opposite behaviour between TOC and

UV-B radiation will be shown.

2. Data and analysis

Varotsos (1994) proposed a simple parametric model for the calculation of direct

and diffuse SUVR reaching the Earth’s surface under different atmospheric

conditions depending on time and geographic location (1993–1995). The employ-

ment of the daily total ozone values at the above-mentioned model allows the

detection of mean monthly UV-B irradiance fluctuation for the summer months of

the time period 1993–2006.

The daily UV-B measurements for the period 1996–2006 deduced from a UV-B

pyranometer located at the University of Athens in Greece were recorded on tapes.

The processing of these tapes allows us to measure the amount of UV-B irradiance

reaching the surface on clear-sky days.

TOZ measurements for the period 1993–2006 were obtained from the Dobson

No. 118 spectrophotometer, operating in Athens University, since 1989. TOC is

2668 C. Varotsos et al.

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expressed in terms of the equivalent thickness of the ozone layer at standard

temperature and pressure (Dobson Units; 1 D.U.51025 m).

Additionally, the TOZ measurements derived from SCIAMACHY (SCanning

Imaging Absorption spectroMeter for Atmospheric CHartographY) observations

that referred to the greater Athens area were also used in order to confirm the results

obtained from the Dobson measurements. SCIAMACHY is an instrument installed

on board the European Space Agency (ESA) Environmental Satellite (ENVISAT).

This instrument was designed and built as a joint German/Dutch project funded by

the German and Dutch national agencies (with a contribution from Belgium) and

launched on March 2002. The SCIAMACHY primary mission objective is to

perform global measurements of trace gases in the troposphere and stratosphere

(Kondratyev and Varotsos 1995, 2001a, b, 2002). The satellite is equipped with two

radars, three spectrophotometers, two radiometers, and two instruments which

indicate the satellite orbit. The SCIAMACHY instrument measures the spectra in a

wide wavelength range, from the ultraviolet (UV: 240 nm) into 1700 nm and 2 mm to

2.4 mm. This instrument has the possibility to take measurements in three different

ways (nadir, limb, and occultation). By using the nadir and limb process,

SCIAMACHY observes the whole atmosphere, while the occultation process

confirms the measurements taken by the limb method. It is worth noting here that

the TOZ observations derived from the Dobson No. 118 spectrophotometer

installed at the Athens ozone station compare well with TOZ observations with

the satellite-borne instrument SCIAMACHY.

Due to the fact that the TOZ measurements derived from SCIAMACHY

observations were only available for the short time period 2002–2006, the figures

shown in this paper come from TOZ data obtained using the Dobson instrument.

3. Discussion and results

In figure 1, the temporal variation of TOZ and broadband UV-B is depicted. The

anticorrelation behaviour between TOZ and UV-B is obvious, corresponding to a

Figure 1. Monthly mean TOZ and UV-B values over Athens for the summertime period in1993–2006.

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statistically significant correlation coefficient of 0.65. For example, in June 2005, a

high TOZ value equal to 338 D.U. corresponds to a low UV-B intensity value equal

to 21.1 W m22, whereas in July 1996 a low TOZ value equal to 294 D.U.

corresponds to a high UV-B intensity value equal to 24.2 W m22. The average values

of TOZ and UV-B are about 311 D.U. and 22.6 W m22, respectively.

A similar analysis to that described above was also repeated using TOZ

observations conducted using the SCIAMACHY instrument throughout the period

2002–2006. This analysis confirmed the above-mentioned results. As to the TOZ

peculiarities in 2002, these are extensively described in Varotsos (2002, 2003, 2004).

In the following, the radiation amplification factor (RAF) was calculated using

the in-field observations and the theoretically derived values (erythemathy weighted

UV) of the UV-A, UV-B and broadband UV during the summertime periods in

Figure 2. Monthly mean radiation amplification factor (RAF) values of the (a) UV-B, (b)broadband UV, and (c) erythemally weighted UV over Athens for summertime period 1993–2006.

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1993–2006. The latter, were calculated by employing the model proposed by

Varotsos (1994). The results obtained are shown in figure 2, which shows that there

is no significant seasonal variability in RAF.

Finally, the influence of the local air pollution effect on the attenuation of the

surface solar ultraviolet irradiance is illustrated in figure 3. More specifically,

figure 3 shows the temporal variability of the measured UV-B as a function of the

surface ozone concentration. Inspection of this figure shows that a high UV-B dosereveals enhanced photochemical smog, and subsequently the latter acts as a filter of

the UV-B reaching the surface. Also, the effect of clouds on the surface UV-B dose is

important when the clouds are thin (such a high level cirrus or solid crystals of

various compounds). The absorbing and scattering properties of the solid crystals

are strong functions of their mechanical properties and the wavelength of the solar

radiation (Lazaridou et al. 1985).

4. Conclusions

The main conclusions deduced from the above-mentioned discussion on theassociation between UV, TOC and air-pollution during the summertime period

1993–2006 in Athens, are as follows:

1. The variability in the monthly mean values of the observed UV-B during the

summertime period is strongly anticorrelated with that in the observed TOC

values.

2. There is no significant seasonality in the radiation amplification factor of UV-

B, broadband UV, and the erythemally weighted UV.

3. The enhanced UV-B reveals intensive air-pollution episodes, which subse-

quently attenuate the surface UV-B irradiance.

The ozone values, extracted from the above UV measurements, may be used forlocalized prediction of the propagation parameters and degradation quality of the

broadband laser, mm-W, and MW communication signals, transmitted at different

Figure 3. Monthly mean values of the surface ozone concentration at a highly pollutedlocation in the greater Athens area (Marousi) versus the corresponding values of the surfaceUV-B for the summertime period in 1993–2006.

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altitudes and elevation angles (from horizontal up to vertical path) in the Athens

atmosphere. The latter is the subject of our future work on the field.

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