Observational study on cirriform clouds in the tropical upper troposphere

存在于对流层上部的环形云(卷云、卷层云、卷积云)几乎全部由冰粒组成，在调节地球-大气系统的辐射平衡方面发挥着重要作用。然而，由于热带地区观测资料的匮乏，控制热带环状云产生、维持和消散的机制还不是很清楚。本研究项目在印度尼西亚西苏门答腊岛的科托塔邦(南纬0.2度，东经100.32度)，利用甚高频风廓线仪观测垂直风，用W波段多普勒雷达观测云中冰粒的下落速度，用激光雷达观测小冰粒，用天气雷达观测降水粒子，用无线电探空仪观测垂直温度和湿度的垂直廓线，进行了环状云观测活动。在此基础上，详细研究了垂直风对环形云中粒子下落速度的影响。利用安装在科托塔邦的甚高频风廓线仪(赤道大气雷达)观测到的垂直风资料，研究并发表了与东移天气尺度积云活动有关的对流层中上层垂直风变化(Yamamoto等人，出版社)、降水层状区垂直风的精细时间-高度变化(Nishi等人，2007)和对流层中层环状云的垂直运动(Seto等人，2006)。这项研究项目已经证明，将甚高频风廓线仪和其他仪器结合起来观测环形云内部是有用的，以观测与这类云有关的过程。

Cirriform clouds (cirrus, cirrostratus, cirrocumulus) existing in the upper part of the troposphere consist almost entirely of ice particles, and are known to play a significant role in regulating the radiation balance of the earth-atmosphere system. However, mechanisms which control generation, maintenance, and dissipation of cirriform clouds in the tropics are not well understood due to a scarcity of observations in the region. In this research project, an observation campaign of cirriform clouds using VHF wind profiler to observe vertical wind, W-band Doppler radar to observe falling velocity of ice particles in clouds, lidar to observe small-sized ice particles, weather radar to observe precipitating particles, and radiosonde to observe vertical profiles of temperature and humidity has been carried out at Kototabang, West Sumatra, Indonesia (at latitude 0.2 degrees south and longitude 100.32 degrees east).From detailed data analysis using data derived from the observation campaign, time-altitude variations of vertical wind in and around tropical cirriform clouds has been shown for the first time. Further, effects of vertical wind on particle falling velocity in cirriform clouds are studied in detail. Using vertical wind data observed by a VHF wind profiler installed at Kototabang (the Equatorial Atmosphere radar), vertical wind changes in the middle and upper troposphere associated with eastward-moving synoptic-scale cumulus activity (Yamamoto et al., in press), fine time-altitude variations of vertical wind in the precipitating stratiform region (Nishi et al., 2007) and vertical motion of cirriform clouds in the middle troposphere (Seto et al., 2006) have been studied and published. This research project has demonstrated that a combination of VHF wind profiler and other instruments to observe inside of cirriform clouds is useful to observe processes related to such clouds.