On the Quantitative Tripartite Allocation of the Atmospheric Vapor, Oqtav

Abstract

The quantitative distribution of AVM into three distinguished vapor endmembers is lacking in the literature. This work fills such a gap. The isotope ratio, δ18OL, of rainwater in Winter, and artificial condensates in Summer, gave the 18OV contents of the AVMs at temperature-dependent equilibrium, downtown Cairo city, Nile Delta apex. We used our models, TIMAM, CLAW, and SIGNALS to process the δ18OV and the commensurate S values in several AVM data sets for determining the percent and mass contributions of three moisture origins and their temporal waveforms. The proportions revealed the Marine vapor dominance, followed by Evapotranspiration contribution. By far, the free Troposphere source showed a slight input. The quota of each constituent manifests a delayed waveform vs. the δ18OV influx, which shows a diurnal peak and a nocturnal tunnel. The moderate ET percent inputs in Winter, and by daytime, impose significant AVM 18O enrichment. In contrast, the high Maritime vapor inputs in Summer, and by night, stand behind the depleted AVM 18O content. The relationship between the mass input of each source and the AVM isotope ratio show significant dispersion for the negative trend of the diurnal-nocturnal Marine vapor in the two seasons. Such a high scattering is due to the mingling of the diurnal northern wind-gust convection (marked by low Marine vapor input) and the nocturnal steady advection (characterized by high Marine vapor input). Marine vapor waveform has a 12-hour time-lag by the intertwining of turbulent diurnal transmission, and steady nocturnal transport, via the long trajectory (180 km) from the Mediterranean coast to Cairo. In contrast, the relationships between ET mass input and AVM isotope ratio, on the one hand, and between the Troposphere vapor mass input and AVM isotope ratio, on the other hand, manifest low-dispersion positive and negative regressions, respectively. Such a low dispersion is due to short transport pathway, narrow range of the biological input (that increases only during daytime), and Troposphere downdraft (moving northward in Winter but southward in Summer). The ET waveform has a Zero-hour time-lag, like that of the Troposphere vapor. Albeit the low S value of the Troposphere vapor, its impact on the AVM isotopic depletion is significant due to its extremely shallow 18O content. The Troposphere input increase, at low S values of the AVM, is related to regional drought, as expected. The high S values, of Marine and biotic origins, usually go with temperature apogees, especially in Summer, as anticipated. The used models help in improving the time-series simulation of evaporation runs, since using seasonal δ18OV and S markers is better than using a snapshot. The ternary-vapor-source allocation procedure is a breakthrough in isotope hydrology. This thoroughly useful procedure will prove its ultimate benefits when the users get CRDS laser-controlled devices for the continuous measurements of the isotopic ratios in the local AVMs.