A Severe Convective Weather In Gansu Province To The Formation Mechanism Of Analysis And Research

The heavy convective storms such as heavy rain, hail, squall line, tornado and thunder etc. are disastrous weather, which endanger not only agriculture but also the building and highway. Because the heavy convective storms have small spatial and time scale, it hard to predict them exactly. We selected the hail as emphases, studied a heavy convective storm occurred northeast of the Qinghai-Tibet Plateau (the hail was on southwest Gansu province). By using the diagnostic analysis of the non-hydrostastic model numerical simulation result the cause of heavy convective storm. The result shows that the conveyance of vapour for a long time in the warm area and moisture field with dry at high levels and wet at low levels were found to prepare the instability strata condition for the severe convective storm formation while the Siberian cold—cyclone moves slowly eastward. The severe convective storm was generated by the mesoscale convergence flow fields and the downdraft divergent outflow under the cumulus bus is the mechanism of the convective storm propagation. The convective of the hail region developed higher than that of normal thunder region and the instability energy is greater. Second, the dry cold tongue play an important role on the hail coming into being, the enhance of moist baroclinic instability could indicate the hail. At last, the mesoscale mountain has significant influence on the location and intensity of the heavy storm. Analysis off numerical simulation of NHT shows that the steep topography enables the upflow reach higher level easily; a wavy terrain could enhance raising current on specific regions and nonuniform the kinetic energy. The Qilian Mountain resists some south wind and then enables the convergence near the ground develope more quickly.