Relationships Between Inversion Strength, Lower‐Tropospheric Moistening, and Low‐Cloud Fraction in the Subtropical Southeast Pacific Derived From Stable Isotopologues of Water Vapor

Abstract

AbstractQuantitative, observational constraints on lower‐tropospheric mixing are crucial for improved models of low‐cloud feedbacks, and analysis of water vapor isotopic composition provides an independent means for generating such constraints. In situ measurements of water vapor isotopic composition from the Chajnantor Plateau, in northern Chile, are merged with sounding data from Antofagasta and satellite measurements of cloud fraction (CF) from the SE Pacific to show an inverse relationship between the estimated inversion strength (EIS) and water vapor export from the marine boundary layer into the free troposphere. When merged with results from the subtropical northern Pacific, the relationship between EIS and water vapor transport is found to be exponential across EIS values ranging from 0 to 15.6 K. The data from Chile are stratified into terciles of EIS with average EIS values of 9, 12.6 and 15.6 K. We show positive relationships between EIS, cloud fraction, and the mixing diagnostic δDv−δDr and negative relationships between EIS and the observed mixing ratios and water vapor δD values at Chajnantor, all of which are consistent with an inverse relationship between inversion strength and water vapor export from the marine boundary layer. Inverse modeling of the isotopic data using a simple process model shows that the average mixing ratios at Chajnantor derived from the marine boundary layer are estimated to be 2.1, 1.15, and 0.84 g/kg, respectively, for the lowest, middle, and highest terciles of EIS. These results can be used to constrain convective parameterizations and models of low‐cloud feedbacks.