Atmospheric Chemistry and Physics Discussions
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10.5194/acpd-7-1595-2007
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http://www.atmos-chem-phys-discuss.net/7/1595/2007/acpd-7-1595-2007.pdf
1595
1622
2007-01-31
Characteristics of particle size distributions in the tropical tropopause based on optical particle counter and lidar measurements
S. Iwasaki
K. Maruyama
M. Hayashi
S. Y. Ogino
H. Ishimoto
Y. Tachibana
A. Shimizu
I. Matsui
N. Sugimoto
K. Yamashita
K. Saga
K. Iwamoto
Y. Kamiakito
A. Chabangborn
B. Thana
M. Hashizume
T. Koike
T. Oki
Dept. of Earth and Ocean Sciences, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan.
Dept. of Information and Systems Engineering, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
Dept. of Earth System Science, Fukuoka University, 8-19-1 Nanakuma, Jonan, Fukuoka 814-0180, Japan
Inst. of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka 237-0061, Japan.
Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052, Japan
Graduate School of Earth and Environmental Science, Tokai University, 1117 Kitakaname, Hiratsuka 259-1292, Japan
National Inst. for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan
National Research Inst. for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba 305-0006, Japan
Graduate School of Science, Tokai University, 1117 Kitakaname, Hiratsuka 259-1292, Japan
Faculty of Science, Chulalongkorn University, 254 Phyathai Road, Patumwan, Bangkok 10330, Thailand
School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo 113-0033, Japan
Inst. of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro 153-8505, Japan
An optical particle counter (OPC) is used in conjunction with lidar
measurements to examine the characteristics of the particle size
distribution in cirrus cloud at the tropical tropopause (TT) over Thailand.
Of 11 OPC launches, cirrus cloud was detected at 10–15 km high on 7
occasions, cirrus was detected at the TT in 6 cases, and simultaneous OPC
and lidar measurements were made on two occasions. Comparison of lidar and
OPC measurements reveal that the cloud height of cirrus in the TT varies by
several hundred meters over distances of tens kilometers; hence the height
is not horizontally uniform. The mode radii of particles constituting the
clouds are estimated by lidar and OPC measurements to be less than
approximately 10 μm. The regression lines of the particle size
distribution with and without cirrus cloud exhibit similar features at
equivalent radii of <0.7 μm. Enhancement in the integrated number
concentration at radii greater than 0.7 μm indicates that liquid
particles tend to be frozen at a radius of 0.7 μm, with cirrus clouds
above 10 km exhibiting similar features. In addition, common features of
cirrus clouds at the TT include a local maximum in the particle size
distribution at 2.0 μm and a peak between 0.5 μm and 1.7 μm
in the ratio of the standard deviation of count values to that of the
Poisson distribution of the averaged count values. Each feature implies that
all ice particles in the clouds may be nucleated by the same mechanism and
particles in this size range are actively frozen at the TT. These parameters
are thus good indicators for checking the results of cirrus cloud models in
the TT.
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