Cirrus clouds are generally one of the most occurring cloud types in Thailand and worldwide and play a considerable role in the global heat balance. The knowledge of their information about the habits of microphysical properties is essential for parameterization of particle habits in radiation transfer, weather and climate modeling and in remote sensing retrievals. The state-of-science airborne instrumentation of department of royal rain-making and agricultural aviation (DRRAA) was used to

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... re the shape and size distribution of cloud particles in case of tropical cirrus. The observation was carried out on 7 September 2011 over three provinces of central Thailand. Four samples of cirrus clouds totaling to 54.2 km of cloud penetration. The samples consist of two cirrostratus (Cs) and two Cirrus (Ci) with temperature between -8°C and 21°C at four different altitudes from 6 km to 10 km. Particle number size distribution (PNSD) between 0.47 µm to 19,200 µm were also constructed with combining measurements from the fast-forward scattering spectrometer probe (Fast-FSSP), two dimensional spectrometer (2-DS) and high volume precipitation spectrometer (HVPS). Images of ice crystals were measured with cloud particle imager (CPI). It was found that the PNSD in Cs clouds clearly exhibit continuously wider spectra with higher total number concentration than Ci clouds. Conversely, Ci clouds contain larger particle diameters, with dominated size around 300 to 500 µm, comparing to particles in Cs clouds which is approximately 10 µm. CPI was used to capture 31,233 images of ice crystals. The analysis shows average maximum aspect ratio (AR) of all sampled cirrus cloud particles ranging from 4.9 to 11. The Cs clouds evidently illustrate a larger AR than the Ci clouds. The proportion of spherical particles in cirrus clouds was found to be approximately 8.45%. Moreover, the study shows that the ratio of spheroids and ice particles in both cirrus types tends to be steady as the temperature cool down beyond -16°C. The analysis of particle sizes and behaviors showed that the cirrus clouds are essentially formed from irregular ice crystals and the pristine ice crystals are rare. Also, the irregular shape particles are evenly distributed in all size categories and usually trend to be a small ice particles of approximately 90 µm.