Unstable Ridges and Creation of Kinetic Energy in the Atmosphere

[摘要]  When height contours on a high level constant pressure (say the 300 mb.) chart exhibit a strongly curved anticyclonic ridge, air parcels moving even with the maximum possible gradient wind, namely twice the geostrophic wind, cannot follow the contours and instead will be forced to move from higher to lower contours and thereby acquire appreciable amounts of kinetic energy. Studies with the machine processed daily wind data of the northern hemisphere for January and February, 1949, has enabled the author to compute the day-to-day net production of large-scale-eddy kinetic energy in complete zonal belts around the globe, allowing for (a) the convergence of the flux of the eddy kinetic energy across the latitudinal walls and (b) the conversion of the eddy kinetic energy into the mean zonal kinetic energy by the action of the eddy stresses. On a few instances of very large net production of largescale-eddy kinetic energy at the 300 mb level, at latitude 45°N, it was found that nearly a third of it was accountable by the cross-contour flow necessitated by a well marked anticyclonic ridge near the Canadian-Pacific coast. It is likely that such unstable ridges play a role in the generation of ‘velocity maxima’along the meandering axis of a well-developed ‘stream’ of the middle latitudes.

[学科分类] 大气科学