Abstract
A detailed analysis of the dynamics and thermodynamics responsible for the structure, growth and propagation of an orogenic mesoscale convective system simulated in two dimensions is made. The process of scale interaction is addressed through Fourier analysis and Reynolds averaging analysis of representative predicted variables, diabatic forcing and momentum acceleration terms. Additional dynamical analysis is accomplished through sensitivity experiments in which Coriolis, diabatic heating and ambient airflow are varied.
The general conclusion is that the simulated orogenic development is a geostrophic adjustment process to convective heating which is itself modulated and maintained by orographically induced flow systems. The heating scales range over a nearly continuous spectrum ranging from 10–250 km. The heating occurs in response to primary advective gravity modes. The larger-scale gravity-wave disturbances modulate the smaller scales by organizing mean upward vertical motion patterns. The largest gravity-wave modes are modulated by constraints of the slope flow circulation, namely a phasing of an advective mode with a localized break in the plains inversion.
The simulated growth to mesoα-scale proportions occurs from the horizontal expansion of the disturbance through interaction with the mountain-plains scale slope flow circulation. Similar to upscale two-dimensional turbulence cascade, the mountain plains solenoid deforms thermal patterns, increasing their scale. As the scale reaches mesoα-scale proportions, geostrophic adjustment frequencies are sufficient to allow the thermal fields to persist. Implications to the problem of cumulus parameterization and limitations of the two-dimensional framework of this numerical study are discussed.
