Researched For A Tropical Cyclone Remote Precipitation In The Huaihe River Basin

This work analyzes a process of heavy rain in the Huaihe River region caused by a remote tropical cyclone on August26,2012. Mainly from the following several aspects,water vapor condition, water vapor transmission, the thermal conditions and dynamic conditions, the mesoscale features and structure, and the removed the typhoon and weakened subtropical high sensitivity experiment.By this work,for the occurrence mechanism of tropical cyclone remote precipitation have a comprehensive understanding, the main conclusions is give the follow.In this process the water vapor was transported from the Yellow Sea area mainly below the level of700hPa. When the heavy rain occurred the water vapor was net inflow, but before and after the precipitation process the water vapor was net outflow. Under the joint guidance of the circulation of the typhoon and subtropical high, the water vapor was transferred from the east into the heavy rain area, as indicated by the motion trajectory of air parcels in a channel of water vapor. The water vapor absorbed by air parcels moving over the surface of the Yellow Sea is the main source of water vapor in this process.First attack of the cold air from the high beginning, precipitation area in front of the precipi-tation in the upper for cold advection lower for warm advection, cold advection gradually ex-tends to the lower level, in the cold advection struck down front.ln the process of invasion of cold air downward to the southeast, due to the fluctuation on the potential temperature for cold with warm situation, formation of unstable energy.Regions of precipitation for positive vorticity in precipitation occurs at the bottom of the upper negative vorticity, and to convergence at the bottom of the top for radial and high-level divergence strength is greater than the underlying convergence intensity, high-level process of strong divergence is beneficial to take the latent heat of condensation precipitation over the area to maintain the unstable situation, makes the convec-tion movement to keep, continue to produce rain.The mesoscale vortex in the first place in the middle, with cold air downward leads to the underlying instability energy release, mesoscale-Vortex also strengthened, when cold air occupy the bottom of the warm air transport is cut off, potential unstable situation be changed, the mesoscale vortex weakens disappear.The distance the tropical cyclone torrential rain process generated by the four Chinese beta scale convection system,≥5mm/h precipitation only in TBB≤-42℃area covered with clouds, the lower the TBB value, the greater the rainfall intensity. In the mesoscale cyclone occurs at the top of a potential vortex downlink and lower troposphere are common and strengthen the mesoscale vortex induced potential temperature anomalies. Small scale potential vortex anomaly area is easy to cause the mesoscale cyclone, and large scale potential vortex disturbance is not easy to cause the mesoscale cyclone instead. When the westerly trough eastward, Ahead of its have cold air invading down, polite to the east by the sea by the cold air in the air to produce up-ward movement, slot before cold air intrusion is small so formed several mesoscale cyclone. Af-ter the westerly trough eastward movement deepened, cold air occupy lower after orthotopic temperature anomaly is abate, unable to induce and maintain the lower mesoscale cyclone enough strength. From the three dimensional flow field in the precipitation region, the east low laminar flow field is mainly affected by the West Paeific West Paeific Subtropical high is the an-ticyclonic type, top is mainly affected by the westerly trough; As the typhoon come on closer, shrinkage of West Paeific Subtropical high flow towards the northeast, southeast of precipitation area flow into the bottom of the original by the wind flow field influence to southwest outflow; West and lower in the westerly trough under is massive potential vortex anomaly, and that the mesoscale cyclone is not easy to produce precipitation is also weakened so stop.In the process of water vapor transmission, the typhoon and the role of the subtropical high is equally important. The typhoon change the intensity and position of subtropical high, between the typhoon and the subtropical high winds are both contain, subtropical high strength increase after the airflow guide role to strengthen to the north, making water vapor transmission Delivery to the north, with the north after the water vapour met westerly trough more prone to conver-gence caused heavy rain; When the subtropical high is weakened the typhoon to strengthen the guide function of airflow makes the water vapor transport more straight east-west or has a southward component, the conveying direction unfavorable to produce convergence to the west wind trough, so the precipitation is weaked. Westerly trough as a large scale background field, carried by the air under the guidance of the westerly trough, the cold air from high-level to low-level intrusion, at the same time due to the low level there is a typhoon,and the subtropical high conveying warm moist air flows, in warm wet upper lower under the configuration of dry and convective instability, trigger upward movement after disturbance. At the same time at a high level due to the existence of the westerly trough the high-rise high-altitude westerly jet in the air in the precipitation process of condensation latent heat away, thus keeping the precipitation over the unstable situation, makes the convection movement to keep, continue to produce heavy rains.