Cirriform cloud observation in the tropics by VHF wind profiler and 95-GHz cloud radar

Vertical air motions and their effects on particle falling velocities in tropical cirriform clouds are presented using data derived from VHF wind profiler operated at 47 MHz (the Equatorial Atmosphere Radar; hereafter EAR) and cloud radar operated at 95 GHz. Observations were carried out at the Equatorial Atmosphere Observatory (0.2degS, 100.32degE), Sumatra, Indonesia. A case on 14 November 2005 has been investigated in detail.

Vertical air motions in cirriform clouds observed by the EAR oscillated with a time scale shorter than several tens of minutes. Similar oscillatory features were seen in the reflectivity-weighted particle falling velocities observed by the 95-GHz cloud radar. Detailed comparison of vertical air motions and reflectivity-weighted particle falling velocities showed that reflectivity-weighted particle falling velocities are composed of inherent parts determined by the shape and size of particles and fluctuating parts which showed consistent changes with vertical air motions. This result indicates that a measurement of vertical air motions in cirriform clouds can contribute to a better retrieval of microphysical properties of cirriform clouds, especially when a retrieval is carried out with a time resolution shorter than several tens of minutes.