On the Occurrence of Atmospheric States that are Non-Elliptic for the Balance Equation

Abstract

The origins of atmospheric states that are non-elliptic for the height constrained balance equation are examined from observational perspectives. Such states are commonly present in the deep tropics in Objectively analyzed data sets. In order to analyze the source of this phenomenon, we compute terms of the divergence equation (from which the balance equation derives) for disturbed periods of the GATE experiment. Meaningful residuals cannot be obtained because they are obscured by observational uncertainty of the geopotential gradients that are calculated from the hydrostatic equation using temperature observations. The geopotential fields recomputed from the divergence equation using observed wind data appear to be much better determined, but they still produce fields that are non-elliptic for the height constrained nondivergent balance equation. For the convective GATE cases, it appears that the essential balance of the divergence equation is between divergent accelerations, deforming accelerations, the divergent pressure form field and friction, while centripetal accelerations (including the Coriolis is effect) are secondary. Thus, the underlying assumption of solenoidal flow in the balance equation is fundamentally wrong in regions of tropical convection. This appears to be the physical source of the poorly posed balance equation in many non-elliptic cases.