A Monitoring Study of the 1998 Rainstorm along the Yangtze River of China by Using TIPEX Data

By using data from the Secondary Tibetan Plateau Science Experiment (TIPEX) in 1998, includingenhanced soundings, surface observations, data from captive balloons, remote sensing, and Doppler radar(China and Japan cooperative study of GAME/Tibet), a monitoring study on the generation and movingtrack of the cumulus convective systems over the Tibetan Plateau is made, and the relationship between theevolution of cloud systems over the Tibetan Plateau and 1998 flooding in China is studied. The results areas follows. 1) Analyzing the image animation and Hovmoller diagram of satellite TBB data shows that therainstorms for the Yangtze River in the last ten days of July 1998 can be tracked regionally to the TibetanPlateau. 2) For the period of cloud clusters passing through the Amdo station (18-19 July), monitoringobservations by Doppler radar is made. The monitoring of radar echoes shows that the developing, eastwardmotion, and strengthening of the echoes can be frequently observed in the middle of the Tibetan Plateau.An integrated analysis and tracking of the generation, disappearance, development, and eastward motionof these convective systems by using multiple instruments is very valuable for diagnosing and predicting theinfluence of the plateau systems on the downstream weather situation. 3) The integrated analysis of space-time cross sections of the enhanced upper air and surface observations from TIPEX during the intensifiedobservation period shows that the frequent development of convective clouds over the Tibetan Plateauis related with the quasi-stationary convergence of surface winds. The dynamic convergence of surfacewinds, the vertical shear in the upper air, and transportation of water vapor due to increasing humidityover the Tibetan Plateau played an important role in the developing and strengthening of rainstorms overthe Yangtze River in 1998. 4) Meso-sale filtration analysis of the vertical distribution of water vapor overthe Tibetan Plateau indicates that alternating changes of high and low water vapor distribution over theTibetan Plateau reveals clearly that the sub-synoptic scale waves exist, whose lifetime is on the order ofthe hours. The revelation of the eastward motion of mesoscale waves from the Tibetan Plateau indicatesthat the plateau systems obviously influenced the rainstorms over the Yangtze River valley in 1998.