TURBULENT COMPRESSIBLE CONVECTION WITH ROTATION .1. FLOW STRUCTURE AND EVOLUTION

The effects of Coriolis forces on compressible convection are studied using three-dimensional numerical simulations carried out within a loc al modified f-plane model. The physics is simplified by considering a perfect gas occupying a rectilinear domain placed tangentially to a ro tating sphere at various latitudes, through which a destabilizing heat flux is driven. The resulting convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers, evaluating c onditions where the influence of rotation is both weak and strong. Giv en the computational demands of these high-resolution simulations, the parameter space is explored sparsely to ascertain the differences bet ween laminar and turbulent rotating convection. The first paper in thi s series examines the effects of rotation on the flow structure within the convection, its evolution, and some consequences for mixing. Subs equent papers consider the large-scale mean shear flows that are gener ated by the convection, and the effects of rotation on the convective energetics and transport properties. It is found here that the structu re of rotating turbulent convection is similar to earlier nonrotating studies, with a laminar, cellular surface network disguising a fully t urbulent interior punctuated by vertically coherent structures. Howeve r, the temporal signature of the surface flows is modified by inertial motions to yield new cellular evolution patterns and an overall incre ase in the mobility of the network. The turbulent convection contains vortex tubes of many scales, including large-scale coherent structures spanning the full vertical extent of the domain involving multiple de nsity scale heights. Remarkably, such structures align with the rotati on vector via the influence of Coriolis forces on turbulent motions, i n contrast with the zonal tilting of streamlines found in laminar flow s. Such novel turbulent mechanisms alter the correlations which drive mean shearing flows and affect the convective transport properties. In contrast to this large-scale anisotropy, small-scale vortex tubes at greater depths are randomly orientated by the rotational mixing of mom entum, leading to an increased degree of isotropy on the medium to sma ll scales of motion there. Rotation also influences the thermodynamic mixing properties of the convection. In particular, interaction of the larger coherent vortices causes a loss of correlation between the ver tical velocity and the temperature leaving a mean stratification which is not isentropic.