Vertical air motion in midlevel shallow‐layer clouds observed by 47‐MHz wind profiler and 532‐nm Mie lidar: Initial results

Abstract

Variations of vertical air velocity (W) in the midlevel shallow‐layer clouds are described by a case study observed at West Sumatra, Indonesia (0.2°S, 100.32°E), in the nighttime between 8 and 9 May 2004. By receiving echoes from refractive index irregularities, W and spectral width (σW), used as a proxy of W turbulence, were observed both in clear and cloud regions using frequency power spectrum obtained by a 47‐MHz wind profiler with 150‐m vertical and 166‐s time resolutions. Using altitude profiles of received signal intensity of a 532‐nm Mie lidar (Plidar), altitudes with significantly larger Plidar than below (or above) were considered as cloud regions. Most of the shallow‐layer clouds were observed between 6.0 and 8.5 km. In the top part of clouds (∼0–500 m below the estimated cloud tops), downward W up to ∼0.2–0.3 m s−1 and σW up to ∼0.5–0.6 m s−1 were observed. In the middle part of clouds (∼500–1000 m below the estimated cloud tops), W showed large variations. Both the standard deviation of W during the observation period and σW were large (∼0.5–0.7 m s−1). These results demonstrate that a combination of VHF wind profiler and lidar is useful to observe wind variations in and around midlevel shallow‐layer clouds with high time and vertical resolutions. Altitude profiles of temperature observed by radiosondes showed that the air was absolutely stable near the top part of clouds and conditionally stable below. Possible relationship between W and temperature is discussed.