Enstrophy bounds and the range of space-time scales in the hydrostatic primitive equations

Abstract

The hydrostatic primitive equations (HPEs) form the basis of most numerical weather, climate, and global ocean circulation models. Analytical (not statistical) methods are used to find a scaling proportional to ${\left(\mathrm{Nu}\phantom{\rule{0.16em}{0ex}}\mathrm{Ra}\phantom{\rule{0.16em}{0ex}}\mathrm{Re}\right)}^{1/4}$ for the range of horizontal spatial sizes in HPE solutions, which is much broader than is currently achievable computationally. The range of scales for the HPE is determined from an analytical bound on the time-averaged enstrophy of the horizontal circulation. This bound allows the formation of very small spatial scales, whose existence would excite unphysically large linear oscillation frequencies and gravity wave speeds.