NUMERICAL-SIMULATION OF THERMAL-CONVECTION IN A ROTATING SPHERICAL FLUID SHELL AT HIGH TAYLOR AND RAYLEIGH NUMBERS

In this study, we carry out numerical simulations of thermal convectio n in a rapidly rotating spherical fluid shell at high Taylor number Ta and Rayleigh number R with a nonlinear; three-dimensional time-depend ent, spectral-transform code. The parameters used in the simulations a re chosen to be in a range which allows us to study two different type s of convection, i.e., single column and multi-layered types, and the transition between them. Numerical solutions feature highly time-depen dent north-south open columnar convective cells. The cells occur irreg ularly in longitude, are quasi-layered in cylindrical radius, and main tain alternating bands of mean zonal flow. The complex convective stru cture and the banded mean zonal flow are results of the high Taylor an d Rayleigh numbers. The transition between the two types of convection appears to occur gradually with increasing Rayleigh and Taylor number s. At a Taylor number of 10(7) the differential rotation pattern consi sts of an inner cylindrical region of subrotation and an outer cylindr ical shell of superrotation manifest at the outer boundary as an equat orial superrotation and a high latitude subrotation. The differential rotation pattern is similar at Ta = 10(8) and low Rayleigh number, Cyl indrical shells of alternately directed mean zonal how begin to develo p at Ta = 10(8) and R = 50R(c) and at Ta = 10(9) and R = 25R(c). This pattern is seen pn the outer surface as a latitudinally-banded zonal f low consisting of an equatorial superrotation, a-middle and high latit ude subrotation, and a polar superrotation. At Ta = 10(9) and R = 50R( c) the differential rotation appears at the surface as a broad eastwar d how in the equatorial region with alternating bands of westward and eastward how at high latitudes. (C) 1995 American Institute of Physics .