The Temperature-Humidity Covariance Budget in the Convective Boundary Layer

Abstract

The behavior of the temperature-humidity covariance (θ_q) budget in the convectively driven boundary layer is determined through analysis of data from AMTEX and (to a lesser extent) Kansas and Minnesota. In the near-neutral surface layer a balance is found between production and molecular destruction; in the mixed layer, transport is also important. We extend the Corrsin theory for inertial subrange scalar spectral behavior to the temperature-humidity cospectrum, and thus relate the molecular destruction rate of θ_q to its inertial range level. Destruction rates inferred from AMTEX cospectra agree with those found from the imbalance of production and transport terms. The budgets within the surface layer and the mixed layer are parameterized separately with appropriate scales. Both temperature and humidity fluctuations contribute to the small-scale refractive index variations which affect acoustic and electromagnetic wave propagation in the atmosphere. Our results indicate that their joint contribution C_Tq to the refractive index structure parameter is directly related to the molecular destruction rate of θ_q. The results provide a basis for understanding and predicting the behavior of C_Tq in the convective boundary layer.