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

Wavelike oscillation of the stableinterface (tropopause)resulting inpropagating waves (AGWs)Penetrative convectionFig. 4 Schematics of penetration of a pileus (funnel) of hot and moist airthrough an interface (region of high static stability). This penetration cancause atmospheric gravity waves. The right-hand photo shows such a funnelobserved over the Chung-Li VHF Radar.The upper panel of Fig. 3 shows the turbulent velocity, which was extremely strong at about3 m/s (with short peaks at 5 m/s) during the updraft of the funnel and slowly decreased thereafterin the downdraft. Because these turbulent velocities are really large and the horizontal wind wassmall (≈ 10 m/s), we can in a first approach neglect the effect of beam-width broadening. Weshould also note that the apparently large turbulent velocities in the region below 6 km are due tospectrum widening by precipitation. This had not been eliminated in these analyses, whichconcentrates on the region above this level. The precipitation also can be noticed in the reflectivityincrease in the upper panel, and in the downward velocity bursts in theConclusionThe Chung-Li VHF Radar showed its capabilities of long runs to study typhoon passages. For thefirst time a clear event of very deep convection was observed when the typhoon Lekima passedTaiwan end of September 2001. This penetrative convection event generated a clear gravity waveoscillation. Besides this presented event, several further high reaching convective updrafts wereobserved during this typhoon passage. We regard these observations as proof that a VHF radar iscapable to properly study convection processes, which can create gravity waves.Reference:Röttger, J., C.J. Pan, C.H. Liu, and S.Y. Su, Wind field and reflectivity variations investigatedwith the Chung-Li VHF Radar during typhoon passage, Proc. Int'l. Conf. Mesoscale Meteor., Met.Soc. ROC and AMS, Taipei, 3-6 Dec. 1991, 737-379, 1991.188