Characteri sticanalysis of the strengthening spiral bands and the preceding squall lines in association with the 0509 Typhoon “Matsa"

The spacetime characteristics of clouds, wind, and rainfall of the landfallin g spiral bands of the 0509 Typhoon “Matsa" were analyzed quantitatively based o n the FY-2C satellite, Doppler radar, wind profiler and auto weather station (A WS) observation data. The analysis shows there were six outer and inner spiral bands landfalling in East China. The spiral bands strengthened obviously with the minimum cloud top black body temperature declined by about 20.2℃ on average.The time span of the spiral bands from landfall to weakening was about 12.8 h a nd the interval between landfalls of the spiral bands was about 8.6 hours. When the outer spiral bands made the landfall, wind speed strengthened by about 2.0 m/s. The outer spiral bands brought about precipitation of averagely 19 mm and 75 mm in maximum. The inner spiral bands contributed to precipitation of about 139.6-174.2 mm and 396 mm in maximum. The wind speed strengthened by about 4.1m /s evenly and 9.0 m/s in maximum during the landfall of the inner spiral bands.Several squall lines formed and separated from the front of the spiral bands during their landfall. The width of the squall lines was about 5 km with a large -gradient, and the length varied from tens to hundreds kilometer. The echo reflec tivity of the squall lines strengthened by about 5-10 dBz during landfall. The m oving direction of the squall lines was the same as the typhoon, and the moving speed was about 46 km, 2.5 times of the typhoon. The squall line appeared like a n arc with two or several chains in the radar echo, and the chains combined to b e a large arc when the squall lines made landfall. There was slow wind with an i nverse “V" or “S" shape in the radial velocity distribution of the Doppler rad ar echo. A confluence line between southeast and northeast winds appeared in the smallscale surface wind field. When the squall line passed through, the wind speed doubled and the wind direction changed by 47°-135°.It contributed to 6.9-29.1mm precipitation and 90 mm maximum precipitation. The wind speed stre ngthened by about 4 m/s on average and 10 m/s in maximum. The maximum gust speed was about 26.4 m/s. The wind speed above 500 meter height was twice of that at ground surface. The gust zone can extend into the upper levels of the troposphere.