Abstract: With Doppler radar data from Shantou and Xiamen and NCEP/NCAR reanalysis data,characteristics of a short-time super heavy rainstorm on 17 May 2006 caused by Typhoon Chanchu are studied.Doppler radar data indicate that during the period from 18:00 to 19:00 on May 17th,the azimuthal phases of the positive and negative radial wind maximums are asymmetric around the core radius of Typhoon Chanchu,i.e.,the radial wind on the left side of the track is anomalously larger than that on the right side.Studies show that it is induced by the intruding of cold air(northeasterly wind) which primarily locates at the mid-lower layers lower than 4 km,and it is because of the intruding cold air that can force the atmosphere to uplift,enhance releases of instability energy and finally trigger the heavy precipitation.Dkuring the late stage of the cold air activity,the typhoon is weakened rapidly.Consistent with the observed intrusion of cold air by radars,the NCEP/NCAR reanalysis wind data also show that there are obvious large scalar wind values at the mid-lower layers(1～3 km or so) to the left of typhoon center at 18:00 on May 17th,and in all regions except those affected by the intruding cold air the wind speeds at all the layers on the right side of the track remain larger than those on the left side.Furthermore,the Rankine model results confirm the fact of northeasterly cold air intruding into the typhoon at the mid-lower layers to the left of the track.Calculations also point out that there exists a frontal zone with high θ_se which tilts from southeast to northwest with height,and the super heavy rainstorm occurring in the south of Fujian province lies just near the front zone.