摘要
With Doppler radar data from Shantou and Xiamen and the National Centers for Environmental Prediction and the National Center for Atmospheric Research （NCEP/NCAR） reanalysis data, the characteristics of a short-term heavy rainstorm on 17 May 2006 caused by Typhoon Chanchu are studied. Doppler radar data indicates that during the period from 1800 to 1900 May 17, the azimuthal phases of the positive and negative radial wind maximums are asymmetric around the core radius of the typhoon, i.e., the radial wind on the left side of the track is anomalously larger than that on the right side. Studies show that this is induced by the intrusion of cold air （northeasterly wind）, which is primarily located at the mid-lower layers, lower than 4 kin; this is due to the intruding cold air that forces the atmosphere to uplift, enhancing the release of instability energy, which triggers the heavy precipitation. During the late stage of the cold air activity, the typhoon is rapidly weakened. Consistent with the radar-observed intrusion of cold air, the NCEP/NCAR reanalysis of wind data also shows that there are obvious large scalar wind values at the mid-lower layers （approximately 1-3 km） to the left of the typhoon center （1800 May 17）, and in all regions--except those affected by the intruding cold air--the wind speeds on the right side of the track remain larger than those on the left side. Furthermore, the Rankine model results confirm that northeasterly cold air is introduced to 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 θse that tilts from southeast to northwest with height and the super heavy rainstorm occurring in the south of Fujian province lies just near the fxontal zone.
With Doppler radar data from Shantou and Xiamen and the National Centers for Environmental Prediction and the National Center for Atmospheric Research(NCEP/NCAR) reanalysis data,the characteristics of a short-term heavy rainstorm on 17 May 2006 caused by Typhoon Chanchu are studied.Doppler radar data indicates that during the period from 1800 to 1900 May 17,the azimuthal phases of the positive and negative radial wind maximums are asymmetric around the core radius of the typhoon,i.e.,the radial wind on the left side of the track is anomalously larger than that on the right side.Studies show that this is induced by the intrusion of cold air(northeasterly wind),which is primarily located at the mid-lower layers,lower than 4 km;this is due to the intruding cold air that forces the atmosphere to uplift,enhancing the release of instability energy,which triggers the heavy precipitation.During the late stage of the cold air activity,the typhoon is rapidly weakened.Consistent with the radar-observed intrusion of cold air,the NCEP/NCAR reanalysis of wind data also shows that there are obvious large scalar wind values at the mid-lower layers(approximately 1-3 km) to the left of the typhoon center(1800 May 17),and in all regions—except those affected by the intruding cold air—the wind speeds on the right side of the track remain larger than those on the left side.Furthermore,the Rankine model results confirm that northeasterly cold air is introduced to 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 θse that tilts from southeast to northwest with height and the super heavy rainstorm occurring in the south of Fujian province lies just near the frontal zone.
基金
Project for Social Development from Xiamen Science and Technology Bureau (3502Z20052010
3502Z20064022)
