FACTORS AFFECTING SYNOPTIC-SCALE VERTICAL MOTIONS - A STATISTICAL STUDY USING A GENERALIZED OMEGA-EQUATION

Processes affecting synoptic-scale vertical motions are investigated u sing as the main tool a generalized omega equation that assumes only h ydrostatic balance. This equation and the adiabatic quasigeostrophic ( QG) omega equation were solved in a global domain for six synoptic tim es in February 1979 using spectral truncation T63. The results are por trayed in the form of statistical quantities calculated for four latit ude belts in the Northern Hemisphere and Tropics. In the mid- and uppe r troposphere, the average correlation between the QG and generalized vertical motions is near 0.85 in high latitudes (60 degrees-90 degrees N), roughly 0.7 in midlatitudes (30 degrees-60 degrees N), and slight ly over 0.6 in the subtropics (15 degrees-30 degrees N). In these zone s, ageostrophic temperature and vorticity advections explain an apprec iable part of the nonquasigeostrophic vertical motions. In the Tropics (15 degrees S-15 degrees N), where the role of diabatic heating is do minant, the QG and generalized solutions correlate only very weakly. I n the mid- and high latitudes, the omega components associated with vo rticity advection and thermal advection clearly are more important tha n the other three components calculated with the generalized omega equ ation, and this also holds for the subtropics above 600 hPa. However, the effect of diabatic heating is far from negligible in midlatitudes and subtropics. The relative influence of friction is largest in high latitudes, but even there it is important only in the lower tropospher e. In midlatitudes, vorticity advection and thermal advection are of r oughly equal importance at resolution T63. For the large-scale vertica l motions resolvable with truncation T21, however, the role of vortici ty advection is clearly dominant in the lower and midtroposphere.