A stochastic model for diagnosing humidity dynamics with stable isotopologues of water vapor

Abstract:

The humidity of the free troposphere can be modeled, to first order, in terms of cold-point dehydration, followed by moistening via mixing with boundary layer air. The relative balance between these processes is of prime interest for understanding interannual variability of humidity and for understanding the water vapor feedback. Measurements of water vapor isotopic composition can provide quantitative constraints on these processes. We developed a stochastic model that parameterizes water vapor isotopic composition in terms of these processes and fit the model parameters to data from the Chajnantor Plateau, Chile (23S). The results show that the observed moistening in 2014, relative to 2012, required increases in both the last-saturation mixing ratio and the post-condensation moistening and illustrate the utility of isotopic measurements for constraining the processes governing the humidity of the troposphere.