冬季南西諸島海域における層状雲の雲物理学的性質

Abstract

Microphysical properties of stratiform clouds were observed over the Southwest Islands Area as a part of intensive field observations of Western North-Pacific Cloud-Radiation Experiments (WENPEX). The observation was made under the weak outbreak of cold airmass in January 1991. The observed clouds were mainly stratocumulus clouds, whose cloud depths were about 0.5 to 1.2 Km. A strong temperature inversion was always observed near the cloud tops, above which there was a stable dry layer. The air temperature near cloud tops reached values lower than 0°C for some clouds (minimum temperature: -5°C). The clouds consisted mainly of cloud droplets and they were non-precipitating clouds. The clouds showed considerable horizontal inhomogeneity and vertical changes. The number concentration of cloud droplets in the central parts of clouds showed a tendency to be constant with height. The mean concentration reached approximately 500 to 800 cm -3 as a result of a high CCN concentration. Mean droplet radius rose from about 3 μm near cloud base to 7 μm near cloud top. The vertical profiles of liquid water content (LWC) indicated that the values increased with height as a result of an increase in droplet size rather than concentration. The peak LWC reached about 1.0 g/m 3 in the thick clouds. The envelope of maximum LWC was generally smaller than the adiabatic values. Effective radius changed from about 3 μm near cloud base to 6 μm near cloud top. The characteristics of the stratocumulus clouds over the Southwest Islands Area in Japan is discussed from the microphysical standpoint, as compared with the stratiform clouds observed in geographically different areas.