Analysis and trends of atmospheric turbidity parameters over Cairo |
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Authors: | F M El-Hussainy M A Omran |
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Institution: | (1) Present address: Department of Astronomy and Meteorology, Faculty of Science, Al-Azhar University, P. N. Box, 11884 Nasr-City, Cairo, Egypt |
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Abstract: | Summary This work deals with the Linke turbidity factor, based on total spectrum observations of the direct solar beam and aerosol turbidity parametersa
a
, , and based on observations in broad spectral bands. Diurnal and seasonal variations of these turbidity parameters were analyzed for the period 1975 to 1991.Annual variations of these parameters show low values in winter and high values in both spring and summer. The extinction coefficients decrease with increase of both wavelength and optical airmass. Trend analysis shows an increase in aerosol extinction coefficient below 0.63 m, and a slight decrease for longer wave-lengths.Linear regression relations are also constructed to estimate botha
a
and whenT
L
is available. The relations show thata
a
can be estimated with errors below 20%. The relation with the parameter, may give better results when it is estimated by assigning a fixed value of .Nomenclature AV
Monthly and total average of the measured parameter
-
a
Atmospheric optical thicknes
-
a
a
Aerosol optical thickness
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a
r
Mean value of optical thickness of. Rayleigh atmosphere over all wavelengths
-
a
o
Ozone optical thickness
-
a
o
Ozone absorption coefficient
-
a
w
Water vapor optical thickness
- COR
Correlation coefficient of the linear relation in percentage
- Ex1, Ex2, Ex3
Aerosol extinction coefficients in the bands .2–.53, .53–.63, .63–.695, respectively
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I
(o)
Normal incident direct solar radiation, under clear sky condition
-
I
o
Extraterrestrial insolation at normal incidence
-
m
r
Relative (optical) air mass
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NO
Number of the observations used in either making the relation or the verification
- RMSE
Root mean square error of the linear relation
- RMSE%
Percentage value of the root mean square error relative to the average measured value AV
-
T
L
Linke turbidity factor
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T
Dry bulb temperature in °C
-
u
o
Ozone layer thickness, cm
-
Z
Zenith angle
-
Ångström wavelength exponent
-
Ångström turbidity coefficient
-
Wavelength
-
Y
The year number after 1975
With 5 Figures |
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Keywords: | |
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