Abstracts for the 5th International GAME Conf.
3-5 October 2001
Aichi Trade Center
Nagoya Japan
Cloud behavior in rainy season in Thailand observed by a lidar
Nobuo Takeuchi (1), Teruyuki Nakajima (2), Tamio Takamura (1), Wawyu Widada (1)
(1) CEReS, Chiba University
(2) CCSR, University of Tokyo
@As one of the GAME activity, a micro-pulse lidar (MPL) was installed at Sri Samrong (17:09N, 99:57E), 500 km north of Bangkok, Thailand, a radiation observation site of GAME-AAN. It worked to monitor the cloud height to estimate the effect to the radiative forcing. This lidar suffered with a lot of troubles. However it fortunately provides a continuous half year cloud data from July 1997 to January 1998. This period corresponds to the rainy season to the beginning of the dry season. MPL was developed by NASA and was manufactured by SESI Inc, USA. It consists of a diode-pumped high-repetitive-pulse solid-state laser and a Cassegrain type telescope. The repetition frequency of MPL is 2500 Hz and the interval of the successive pulses corresponds to 60 km in light traveling distance. As the power is very small, the photon counting method is used for detection, and to obtain enough S/N, the signal is integrated over 20 or 30 sec to obtain one vertical profile. The data is stored in a hard disk and then transferred to a MO for further analysis. Since the detector is fragile to the direct incidence of the solar radiation, the lidar attitude was tilted to the north by 19 deg.
From the monitored data, the cloud altitude is determined by taking the derivative of lidar signal. The point to become positive is taken as the cloud base, zero crossing point from positive to negative is the apparent cloud peak, and the point to approach zero is the cloud top. The histogram of cloud base height shows that the most frequent altitude of cloud base is 1.5 km, which extends to more than 10 km in rainy season, and with decrease of frequency a dip at 3.5 km appears. With the start of dry season, the weight of lower cloud decreases and the relative weight of cloud higher than at 7 km increases. In July and August, the cloud is detected in 90 % of the data. In a data with one hour averaging time, the convective cloud shows ascending motion appearing at 1.5 km and disappearing at 7 or 8 km. It ascends quickly with the speed of 3 - 5 km/day below 5 km in altitude, and above 5 km, the ascending speed of the cloud slows down to 1 to 3 km/day. This kind of stability of cloud was found from the lidar data.
Submittal Information
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1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 | |
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takeuchi@ceres.cr.chiba-u.ac.jp | |