Spatial and temporal variation of rainwater stable isotopes in Egypt and the east Mediterranean |
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| Authors: | A M El-Asrag S A Al-Gamal A Youssef D M Ahmed |
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| Institution: | (1) Research Department, The Egyptian Meteorological Authority, Egypt, EG;(2) Egyptian Atomic Energy Authority, Nasr City, Egypt, EG |
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| Abstract: | Summary ?By analyzing normalized variables, it was found that the latitudinal secular variations of the rainwater deuterium fractionation
ratio δ2H, oxygen fractionation ratio δ18O, vapor pressure, and surface temperature were almost non-linear, occurred in parallel, and decreased with latitude. The
rate of depletion around the equator is asymmetric and smaller to the south of 45° S than to the north of 45° N. In the east
Mediterranean, the rate of change of δ18O with height was found to be −.2‰ per 100 m and that of δ2H is comparable with the dry lapse rate in the atmosphere.
Analysis of the annual time series of δ2H at Alexandria has indicated that variations show sinusoidal waveform with a major cycle of two years that accounts for 68%
of the total variance. Although the quasi-biannual cycle in the atmosphere has small amplitude in the lower layers of the
atmosphere at East Mediterranean latitudes, the major cycle in annual series of δ2H or δ18O may be linked to the quasi-biannual oscillation in the atmosphere.
It was also found that the first three Empirical Orthogonal Functions (EOF) account for 72% of the seasonal variation of δ2H and share 68% of the seasonal variation of δ18O. Share of variances of monthly EOF in the months of the year indicate that the main underlying factors that cause fractionation
processes for δ2H and δ18O are similar across the east Mediterranean especially in late winter and early spring.
Received May 13, 2002; revised July 8, 2002; accepted August 6, 2002 |
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