A model study of the downstream variation of the lower trade-wind circulation

The downstream variations of the macro-structure of the undisturbed lower tradewind circulation such as the thickness of the layer, the pressure, temperature and velocity are measurable important quantities. BOMEX data during an undisturbed period was used to estimate the upward slope of the inversion base in the downstream direction. The interrelationships among these properties were examined with a simple model. By using the characteristic values of the horizontal velocity, the thickness, the net diabatic heating rate in the layer and the inversion strength, a scale analysis was found useful for simplifying the governing equations. Layer-averaged properties were then deduced by solving those simplified equations. An explicit expression for the slope of the inversion base was obtained in terms of the small-scale turbulent fluxes, diabatic heating rates and the inversion strength. A quantitative theoretical value of the slope was also computed using published empirical values of the parameters for the BOMEX region. Reasonable agreement between this value and the observed value indicates that a steady upward slope of the inversion base would result when the heat loss in the inversion layer is too large to be compensated by the adiabatic warming of the subsident motion, and when a horizontal flow associated with the one in response to the small scale turbulent and diabatie processes within the trade-wind layer can provide the necessary additional adiabatic warming. Other features of the theoretical results will also be discussed.