Nadir Jeevanjee is awarded the James R. Holton Award for his groundbreaking contributions to atmospheric sciences, in particular, to the fundamental understanding of convection.
Although the notion of Archimedean buoyancy is among the classics in science, the idealized concept of buoyant accelerations as driven by local density variations suffers important limitations. First, the motion of a buoyant plume induces a response in the environment through which the plume moves, establishing a nonhydrostatic vertical pressure gradient. Second, environmental fluid surrounding the plumes is mixed, or entrained, into the plume. Both reduce the acceleration of the plume. Nadir’s studies of effective buoyancy have provided a robust interpretation of the environmental pressure gradients associated with buoyant plumes. The roles of buoyancy and turbulence in entrainment are a more recent focus of these studies.
Nadir has connected his findings on plume dynamics with cold pools and convective organization, both areas currently receiving extensive attention in studies of convection. His incisive analysis of the sources of acceleration in convection showed the importance of mechanical forcing to the initiation of deep convection. As with his results on the effective buoyancy of plumes, these results have important implications for the parameterization of convection in complex Earth system models. Nadir’s powerful application of analytic methods in his studies has imbued these results with physical intuition, but he has also explored numerical models of convection. In addition to proving consistent with analytic results, these studies have produced important results in their own right, for example, by illuminating the “gray zone,” where models begin to resolve motions parameterized at coarser resolutions. Other innovative studies are providing new insights on fundamentals of radiative transfer, including its relationship to precipitation changes in warming climates as well as cooling to space.
—Leo Donner, Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, Princeton, N.J.