Proceedings with Extended Abstracts (single PDF file) - Radio ...

Typhoon LekimaFig. 2 Typhoon Lekima passing Taiwan on 28 September 2001VHF radar reflectivity and velocity in vertical beamAfter two days of operation during the departure of typhoon Nari (Fig. 1) the Chung-Li VHFradar was operated continuously over about 130 hours between 24 September 2001, 14 LT(UTC+8), and 30 September 2001, 02 LT, with two short interruptions. Fig. 2 shows the radarobservations and a map with track of the eye of typhoon Lekima and the location of the Chung-LiVHF Radar. This figure shows the radar reflectivity (lower panel) and mean vertical velocity(upper panel) during this period. On 24 September the eye was about 800 km south of the radar.During this time the troposphere up to about 10 km altitude showed a very enhanced reflectivity,where a separate layer even moved upward to 12 km altitude. The typhoon moved northward thefollowing day and the reflectivity decreased but the convective activity increased. The latter canbe seen in the almost vertical streaks of upward motion (green) at time scales of less than a fewhours, which are dominating against the downward motions (red). On 25 and 26 September,when the typhoon moved further towards the island several broader layers of reflectivity movedupward to the 10 km level. They comprise boundaries of different air. Since they are separated bysome 4 -12 hours, they could be attributed to meso-scale disturbances embedded in the largerscaletyphoon circulation system. Those meso-scale structures can also be seen in the satellitecloud structure records. The reflectivity layer at constant height of about 6-7 km is close to themelting layer where precipitation was formed. We assume that it results from temperaturegradients occurring in such conditions. On 26-27 September precipitation can be recognized inthe velocity plot as an increase of the downward velocity. Between 6 and 7 km the scatter signalfrom precipitation dominates the velocity estimate, which therefore is biased downward (due tothe falling hydrometeors, which scatter the radar signal). We checked the Doppler spectracarefully and notice that only in the regions of strong downward velocity (red) around 7 km thegiven estimate is not representing the vertical air velocity. Thus, on 26-27 September the upwardstreaks above this altitude are clearly showing many events of deep convection. These werereaching altitudes as high as 12 km.In the second part of 27 September, when the typhoon had its closest distance to the radarlocation the mean vertical velocity was fairly small without indications of convection and thereflectivity showed mostly short living layers. When the typhoon was departing, strong275