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

attribute this to a strong deep and very localized convection event. It is actually possible to tracethis funnel back to its likely origin height around 6 km by inspecting the reflectivity plot. Withinabout 20 minutes it reached the altitude of 14 km. If this event would have occurred locally overthe radar the convection funnel must have moved upward with a velocity of up to 4 m/s. Thereflectivity plot shows that the updraft actually accelerated quickly in its lowest altitudes and thenmoved upward with fairly constant velocity.Fig. 2 The funnel event observed with the Chung-Li VHF Radar between08:07 and 10:35 LT on 28 September 2001. Left-hand panel: spectral plot asfunction of height at the end of this event (the negative spectra parts below 4 kmare due to precipitation; centre panel: radar reflectivity; right-hand panel: aphoto of an equivalent deep convection event, taken from aircraft.The altitudes around 6 km are about the height were precipitation is formed at about 08:30 LT.This can clearly be determined from the spectra (see example in the left-hand panel of Fig. 2).We can assume that the heat released hereby caused the convection to start. From the inspectionof Doppler spectra we note that actually the precipitation echo formed and separated clearly fromthe air echo around these altitudes. This provides further prove that this strong convection eventwas initiated by heat release during the formation of precipitation. Heated and moist air result inan increase of radar reflectivity, which we observed (see figures).Looking up the temperature profile, measured with radiosonde, we recognize that the regionabove about 9 km is getting close to becoming convectively unstable, which must have supportedthe convective process to grow, accelerate and move up to larger altitudes.In Fig. 3 we have shown the height-time-intensity plots of reflectivity, vertical velocity andturbulent velocity. We again note the sudden increase in reflectivity above 6 km around 08:40.This is the birth of the convective cell, which then moved upward. quickly. The radial velocity isshown in the centre panel, which is a good estimate of the vertical velocity. Since its magnitude isfairly large we can neglect a significant leakage of a horizontal component. In the origin region ofthe funnel the vertical velocity is about +1 m/s (upward) and it increases within the funnel tomore than +3 m/s. This is consistent with the observed motion of the reflectivity structure (upperpanel in Fig. 3). It is well noticeable that around 09:18 at about 11 km the vertical velocity rapid-186