地上気圧変化量を用いたσ-面上の水平流および鉛直流の変分法による解析

Abstract

The validity of surface pressure tendencies included in the SYNOP and the SHIP obser- vations is investigated. The variational technique under the strong constraint of the continuity equation is proposed to analyze the mass-adjusted three dimensional wind fields in the σ-coordinate system from the observational data of surface pressure tendency and wind. Dividing the wind field into the vertically averaged mean and the deviation field, two differential equations to be solved for Lagrange multipliers are introduced.One case is treated as the numerical example. On that occasion, in place of surface pressure tendencies, 12 hours surface pressure changes are used. It is demonstrated that the original fields of horizontal wind and 12 hours surface pressure change are modified largely so as to satisfy the continuity equation in the vicinity of large scale orographies such as Tibetan Plateau, Rocky Mountains and Greenland, and of strong cyclones. And it is also shown that the patterns of induced vertical velocity are in good correspondence with the surface pressure distribution and large scale orographies. On the other hand, the magnitudes of it in the high and the middle latitude are much smaller but in the low latitude they are considerably larger than those obtained by the conventional initialization scheme.By making use of these mass-adjusted three-dimensional wind fields as the initial ones, the 48 hours prediction with the 5-level primitive equation model is performed, and the results are compared with those predicted with the same model but starting from the initial fields derived by the conventional initialization scheme. It is concluded that noises created by gravity waves become remarkably small if we use these adjusted fields as the initial ones.The problem to select the most suitable value for the weight relating to the error variance of the observation data is also discussed.