An Overview of Atmospheric Convection

The nature of atmospheric convection is briefly reviewed. We can assess the stability of a single air parcel with respect to vertical displacements by comparing the lapse rate of the parcel’s environment to the rate of temperature change within the displaced parcel owing to adiabatic expansion or compression and latent heating or chilling. We also can examine the tendency for convective overturning in a global sense, when buoyancy sources are distributed over a large area and the entire fluid is engaged in convective overturning. In this case, the onset of global dry convection due to thermal instability is determined by the Rayleigh number. Within the atmospheric boundary layer on a sunny day, the Rayleigh number is several orders of magnitude larger than the critical Rayleigh number; thus, convective overturning is a ubiquitous characteristic of the atmospheric boundary layer in sunny conditions. The structure of dry atmospheric convection depends to a large degree on the vertical wind shear within the atmospheric boundary layer, and quite possibly also is sensitive to surface characteristics and mean vertical motions.