Atmospheric turbidity of urban and desert areas of the Nile Basin in the aftermath of Mt. Pinatubo’s eruption |
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Authors: | S A El-Wakil M El-Metwally C Gueymard |
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Institution: | (1) Physics Department, Faculty of Science, Mansoura University, Mansoura, Egypt, EG;(2) The Egyptian Meteorological Authority, Cairo, Egypt, EG;(3) Edgewater, FL, USA, US |
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Abstract: | Summary The Linke T
L
, ?ngstr?m β and Unsworth-Monteith δ
a
turbidity parameters are investigated for two sites in Egypt: Cairo, a densely populated urban area, and Aswan, an arid unpolluted
area. These three turbidity parameters are calculated from broadband pyrheliometric measurements recorded hourly over the
period 1992–96. Monthly averages of T
L
, β and δ
a
show relatively flat and identical seasonal variations with a marked main maxima during spring at both sites, due to Khamsin
depressions coming from the Great Sahara. A secondary maximum is observed at Aswan in summer, due to dust haze which prevails
during that season, and at Cairo in autumn, due to the northern extension of the Sudan monsoon trough, which is accompanied
by small scale depressions with dust particles. Annual mean values of T
L
, β and δ
a
(5.59, 0.250 and 0.372, respectively) at Cairo are larger than at Aswan (3.89, 0.139 and 0.213, respectively). In the same
way, the seasonal mean values of T
L
, β and δ
a
at Cairo are larger than at Aswan. More generally, the monthly and yearly average turbidity values are significantly larger
in Cairo than in Aswan for the whole period 1992–96, which is attributable in part to the urbanization/industrialization effect
of Cairo. An estimate of the corresponding overburden is obtained by comparison between the present data and older T
L
data from 1922–27. It is also shown that turbidity over both sites is largest during 1992, just after the eruption of Mount
Pinatubo in 1991. The dependence of β on some meteorological parameters such as wind speed and direction, precipitable water,
relative humidity, temperature and visibility, is also analyzed. This reveals in particular that visibility is not a good
predictor of turbidity at either site. Conversely, the wind direction and speed have a definite effect on turbidity, and consequently,
largest turbidities occur when the wind carries aerosols from the main industrial particle source areas around Cairo. For
any season of the year, the average turbidity at the latter site is larger than that at other big cities such as Athens, Rome,
and Toronto, but is lower than at Dhahran, Saudi Arabia.
Received February 3, 2000 Revised August 25, 2000 |
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Keywords: | |
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