COMPUTATION OF DYNAMIC FACTORS OF PRECIPITATION GENERATION FROM OBJECTIVE ANALYSIS DATA

N. P. Shakina, E. N. Skriptunova, and A. R. Ivanova

Results of diagnostic computations are analyzed for five calendar seasons using data of objective analysis operatively performed at the Hydrometeorological Center of Russia. The computed diagnostics (frontal parameter as a measure of baroclinicity and cyclonicity, frontogenetic function and tropopause height as indicators of nonlinear interactions and vertical transverse circulations in baroclinic zones, and convection height) are compared against 12-h precipitation amounts considered as an integral indicator of ascending motions. It is shown that the frontal parameter, implicitly containing most of information on frontogenesis and frontolysis nonlinear effects, is related to the precipitation occurrence frequency by a monotonous dependence and represents a primary characteristic of precipitation dynamic forcing. The secondary forcing factor is represented by convective instability estimated at the objective analysis grid points. Convective instability is, to a large extent, forced: its generation and release are much more active at the fronts than outside them. The tropopause height is a significant indicator of a transverse circulation, which represents the third forcing factor: a primary maximum of the precipitation occurrence frequency corresponds to high tropopause and frontogenesis, while a secondary maximum is associated with low tropopause and frontolysis. It is concluded that precipitation localization and intensity are largely determined by dynamic forcing.