The Evolution And Mechanisms Of Catastrophic Mesoscale System In The Outer Rainbands Of Typhoon Mujigae(1522)

The landed typhoon system is one of the most catastrophic weather system in the world,ordinarily,it is composed of the eye,the eye wall and the outer spiral rainbands.Both the eye wall and outer rainbands are composed of many strong storms,which are the important part of showing the powerfull damages of typhoon system.The development mechanism and the analysis and prediction of typhoon system and its subsystems have always been one of the most concerned fields in the science of atmospheric science.The analysis and research of catastrophic mesoscale weather system in the outer rainbands of a strong typhoon named Mujigae(1522)which landed Zhanjiang Guangdong province of China in the late fall were finished in this paper.The evolution characteristics of severe stroms were established,The possible distribution mechanism of typhoon spiral rainband and the possible formation mechnasims of echo hook were deduced,which are available for reference.(1).During the landing of Mujigae,Many supercells appeared with catastrophic disasters,which enhanced from severe stroms in the outer rainbands at first quadrant about 300-500km away from the center of typhoon.One waterspout appeared in the offshore of Haifeng district of Shanwei city,one tornado appeared in Shunde district of Foshan city and one tornado appeared in Panyu district of Guangzhou city.Take the eye and eye wall of Mujigae as one part-the inner core,the velocity of the tangential wind first increase with the increase the distance away from inner core,and then the velocity would decrease after the distance reaches a proper value.The strong wind would motivate and enhance the development of severe storms in the out spiral rainbands at the proper distance.Therefore,the Rankine vortex model can explained the formation mechanisms of the strong wind and spiral rainbands with severe strom far away from the center of Mujigae.(2).Mesocyclones in the strong rainbands in different stages had different characteristics.For the uncorrelated shear(UNC-SHR)type,the values of average base height(BASE),top height(TOP),and shear maximum height(SHRHGT)were 1.5 km at both stations.For the 3 dimension correlated shear(3DC-SHR)type,the three parameters(BASE,TOP,and SHRHGT)at Guangzhou station were 1.8,3,and 2.5 km,respectively,and at Shanwei station they were 1.8,3.1,and 1.8 km,respectively.The SHRHGT at Shanwei was lower by approximately 0.7 km than that at Guangzhou.For the Mesocyclone(M)type,the three parameters at Guangzhou station were 1.1,2.4,and 1.7 km,respectively,and at Shanwei station they were 1.3,2.7,and 2.1 km,respectively.The values at Shanwei were higher than those at Guangzhou by approximately 0.2,0.3,and 0.4 km.The characteristics of the radial diameter(DIAMRAD)of the two stations were big-small-big,while those of azimuthal diameter(DIAMAZ)were small-big-small,for the three different types,respectively.The average wind shear(SHEAR)was approximately 0.01 s-1 at the two stations,and the average value for the M type was larger than that for the UNC-SHR and 3D-SHR types.(3).According to the criteria of mesocyclone duration,the duration of 3 supercells induced tornadoes were approximately 1.5-1.6 hours,which belonged to the short-lived supercells.According to the criteria of mesocyclone recognition guidelines,-the maximum rotational velocity of the mesocyclone induced waterspout in Shanwei was 19.5m/s classified into moderate mesocyclone,and the velocity of the two mesocyclones induced tornadoes in Guanzhou are more than 27m/s classified into strong mesocyclone.The data of 3 automatic weather station which the 3 supercell passed showed that the wind direction changed 180°and all of them were heavy precipitation above 20mm.(4).The velocity spectrum width has the precursor significance in the development of the severe storm stage-the supercell stage-the tornadonic stage,which provides the early warning function for the development of the early discovery of the strong convection.Taking the location of the three supercell induced tornadoes as the center,the Doppler radar spectrum were examined carefully by times and layers.It is shownded that the varieties of Doppler radar spectrum width could give an early indication approximately 10-30 minutes of the emergences and evolutions of mesocyclones and tornadoes in the three supercells,and the relationships about spectrum width and mesocyclones and tornadoes in supercells was discovered depended on the relationship of speed width and turbulence dissipation rate.A conceptual model of the effect of the evolution of velocity spectrum width on the strong convection storm monomer is established.When the velocity spectrum is widing,the strong convective storm is at the stage of development(or weakened),while when the velocity spectrum is reducing,the strong convective storm is in the stable period of each stage.(5).The three supercells induced tornadoes formed in the end of the each part they belonged to.From the detailed analysis of echoes above 50dBZ of 3 supercells,the 3-dimensional evolution characteristics of echo structure were revealed,and the formation mechanism of the hook echo were deduced and tested.The supercells in Shanwei and Foshan absorbed and combined the nearby weak storms during its growing process.The rotation located near the domed echo and the hanging echo in the supercell phase,and showed obviously "Vortex tube" shape tilted toward the moving direction.Bernoulli's principle can explain the formation mechanism of hook echo in supercell,and the principle could reasonable explain the formation process of the hook echo in the supercell in westerlies or easterlies in the northern hemisphere.The evolution mechanism of supercells would help further understanding of causing severe-weather process.