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protuberances are referred to as mammatus cloud, whose generation mechanisms still remain
to be discussed (Schultz et al., 2006). Brightness showed an increase around the cloud border
due to the turbulence generation by KH instability. Vertical wind velocity showed oscillations
exceeding ±3 m s
-1
in magnitude due to KH instability, and played a role in producing
protuberances of clouds through its downward motions. Luce et al. (2010a) suggested that the
reduction of static stability at the interface between the clear air and cloud provided the
favorable condition for triggering KH instabilities. Using the MU radar and a lidar (Behrendt
et al., 2004), Luce et al. (2010b) also showed a correspondence between protuberances of clouds
and vertical wind disturbances caused by atmospheric instability. Using the MU radar and a
scanning millimeter-wave radar (Hamazu et al., 2003), Wada et al. (2005) showed a 3-D cell
structure of cirrus clouds generated by KH instability, and the cell structures have greater
vertical extension in the presence of upward vertical wind.
Fig. 8. Time-altitude plot of (upper) brightness and (lower) vertical wind velocity measured
by the vertical beam of the MU radar operated with the RIM measurement mode (Luce et
al., 2010a). Thick black curve shows a contour of -6 dBZ
e
equivalent radar reflectivity factor
measured by a millimeter-wave radar. Numbers 1-6 shown in the upper panel indicate
protuberances of clouds. Yamamoto et al. (2011b) describe details of the millimeter-wave
radar.
