From Glossary of Meteorology
The water vapor storage equation as applied to the atmosphere.
The general form of the equation is written
where I is the atmospheric moisture inflow, E the evapotranspiration from the ground, O the atmospheric moisture outflow, P precipitation, and dS/dt the time rate of change of moisture storage in the portion of the atmosphere under consideration. In practice the equation is more commonly applied to a finite interval of time and the various terms become mean values in this interval.
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