Spatial and temporal variation of rainwater stable isotopes in Egypt and the east Mediterranean

By analyzing normalized variables, it was found that the latitudinal secular variations of the rainwater deuterium fractionation ratio super(2)H, oxygen fractionation ratio super(18)O, 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 degree S than to the north of 45 degree N. In the east Mediterranean, the rate of change of super(18)O with height was found to be-.2ppm per 100 m and that of super(2)H is comparable with the dry lapse rate in the atmosphere. Analysis of the annual time series of super(2)H 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 super(2)H or super(18)O 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 super(2)H and share 68% of the seasonal variation of super(18)O. Share of variances of monthly EOF in the months of the year indicate that the main underlying factors that cause fractionation processes for super(2)H and super(18)O are similar across the east Mediterranean especially in late winter and early spring.