THE DIURNAL PRESSURE OSCILLATION ON A HEATED MOUNTAIN ISLAND

Abstract

A theory is developed for the 24-hr component of the diurnal pressure oscillation and compared with observations on Haleakala Mountain, Hawaii. Using the linearized hydrodynamic equations, the theory for flow over an unheated mountain is combined with the theory for flow over a flat heated island and applied to a diurnally heated mountain ridge of infinite extent perpendicular to an undisturbed current. An appropriate heating function is deduced whose variation in the vertical embodies the eddy conduction of heat. The development is also applied to an infinite ridge oriented parallel to the undisturbed current. The two ridge models are then superposed to obtain a surface more closely approximating an isolated mountain, and the distribution of the pressure perturbation over this surface is calculated. Measurements of the 24-hr component of the diurnal pressure oscillation at ten stations on Haleakala are presented. It is demonstrated that an accurate measure of the 24-hr component may be obtained from only two weeks of continuous pressure data. Except near the trade inversion, the time-dependent portion of the pressure perturbation predicted by theory agrees closely with the Haleakala observations on both the order of magnitude and the smaller features of the distribution of the 24-hr component. The elevation at which the phase changes abruptly by 180 deg is excellently predicted.