ORIGINAL PAPER The Temperature–Humidity Covariance in the Marine Surface Layer: A One-dimensional Analytical Model

Abstract An analytical model that predicts how much of the temperature–humidity covari-ance within the marine atmospheric surface layer (ASL) originates just above the ASL and just near the surface is proposed and tested using observations from the Risø Air Sea Experi-ment (RASEX). The model is based on a simplified budget for the two-scalar covariance that retains three basic terms: production, dissipation, and vertical transport. Standard second-order closure formulations are employed for the triple moments and the dissipation terms, and the canonical mixing length for the closure model is assumed linear with height (z) from the surface. Despite the poor performance of the gradient–diffusion closure in reproduc-ing the measured triple moment, the overall covariance model was shown to be sufficiently robust to these assumptions. One of the main findings from the analytical treatment is the origin of the asymmetry in how the top and bottom boundary conditions affect the two-scalar covariance in the ASL. The analytical model reveals that ‘bottom-up ’ boundary-condition variations scale with z− a, while ‘top-down ’ variations scale with z a, where a is a constant that can be derived from similarity and closure constants. The genesis of this asymmetr