Quantitative Analyses of Several Q Vectors

Considering a typical Jiang-Huai Meiyu rainstorm event during 5-6 July, 1991 and the operational requirements, the differences of the capability of reflecting precipitation area among quasi-geostropic-, semi-geostrophic-, ageostrophic- and wet-Q vector divergence fields at 850 hPa, 700 hPa and 500 hPa are examined in detail; in the meanwhile, the capability of reflecting precipitation area for each Q vector itself in the divergence fields at the three layers is analyzed. On a quantitative comparison basis, the diagnostic features of the four Q vectors are obtained: (1) quasi-geostropic- and semi-geostrophic-Q vector divergence fields at the three layers respond less obviously to the synchronous rainfall, while ageostrophic- and wet-Q vector divergence fields are better than previous two; especially, the diagnostic capability of the wet-Q vector divergence field at each layer is greater than those of the others throughout the Meiyu-front rainstorm. (2) As far as each Q vector is concerned, the 700 hPa convergence field basically has good capability of reflecting precipitation area than those at the other two layers; in particular, the convergence of the wet-Q vector divergence at 700 hPa serves as a good indicator of precipitation intensity and fallout region. At last, the diagnostic property of each Q vector is documented on a theoretical basis, and not only the theoretical differences among four Q vectors are depicted in full but the results form the quantitative comparison are confirmed theoretically as well.