Diagnostic analysis of a case on interaction between landed typhoon and Northwest China vortex

Based on conventional surface and upper data and NCEP/NCAR 6-hourly reanalysis with 1°×1° resolution, taking a regional rainstorm event which occurred in eastern Shaanxi, eastern Gansu and the junction of southern Shaanxi and Sichuan on 23 July 2010 as an example,we make a diagnostic analysis of the interaction between a remote landed typhoon and Northwest China vortex and its influence on the development of Northwest China vortex and rainstorms. The results indicate that (1) the interaction between remote landed typhoon and Northwest China vortex changes the baroclinic, temperature-humidity and momentum structure of Northwest China vortex, and strengthens convective instability and dynamic uplift effect near the Northwest China vortex. (2) Theimprovement of center intensity of Northwest China vortex and the ambient field in its surrounding areas has a positive feedback on the originating and strengthening of rainstorm. Namely, it extends the water-vapor transportation established by typhoon and subtropical high over the West Pacific, and strengths the dynamic uplift in the low-level over rainstorm area, which results in increasing the area and intensity of rainstorm. (3) While the interaction between remote landed typhoon and Northwest China vortex occurs, the low level jet is established, which have a certain indicative significance to the position and intensityof the broad-scale but short-term severe precipitation.