Understanding the Physics Behind Rising Atmospheric Air Parcels
Well known is that wide parcels of air accelerate more slowly than narrow parcels, and the effect is stronger when the parcel is near the surface. These effects are simulated crudely in climate models, which have coarse resolutions and thus cannot simulate narrow parcels and their vigorous vertical motion; such models are operating in the hydrostatic limit. Although this effect is well-known, it has not been well-quantified nor understood.
A recent study supported by the Department of Energy derives theoretical equations to explain the physics behind these phenomena, by finding mathematical formulae for the acceleration of buoyant parcels as functions of both parcel aspect ratio (width/height) and surface proximity. These formulae may be especially useful both in gaining physical insight into atmospheric convective systems, and in mapping out the gray zone of numerical modeling, as limitations of hydrostatic effect are reached and non-hydrostatic effects become important.
Jeevanjee, N., and D. M. Romps. 2015. “Effective Buoyancy at the Surface and Aloft,” Quarterly Journal of the Royal Meteorological Society 142(695), 811-20. DOI: 10.1002/qj.2683.