Determination of effective droplet radius and optical depth of liquid water clouds over a tropical site in northern Thailand using passive microwave soundings, aircraft measurements and spectral irradiance data

• Published in: Journal of atmospheric and solar-terrestrial physics 2017-08, Vol.161, p.8-18
• Main Authors: Nimnuan, P., Janjai, S., Nunez, M., Pratummasoot, N., Buntoung, S., Charuchittipan, D., Chanyatham, T., Chantraket, P., Tantiplubthong, N.
• Format: Article
• Language: English
• Subjects: Cloud effective radius; Cloud optical depth; Liquid water clouds; Thailand; Tropics
• ISSN: 1364-6826; 1879-1824
• DOI: 10.1016/j.jastp.2017.06.002

This paper presents an algorithm for deriving the effective droplet radius and optical depth of liquid water clouds using ground-based measurements, aircraft observations and an adiabatic model of cloud liquid water. The algorithm derives cloud effective radius and cloud optical depth over a tropical site at Omkoi (17.80°N, 98.43°E), Thailand. Monthly averages of cloud optical depth are highest in April (54.5), which is the month with the lowest average cloud effective radius (4.2 μm), both occurring before the start of the rainy season and at the end of the high contamination period. By contrast, the monsoon period extending from May to October brings higher cloud effective radius and lower cloud optical depth to the region on average. At the diurnal scale there is a gradual increase in average cloud optical depth and decrease in cloud effective radius as the day progresses. •An algorithm is used for deriving tropical cloud optical depth, effective droplet radius, and liquid water path.•Liquid water path is a linear function of cloud thickness.•Monthly averages of cloud optical depth are highest in April and decrease during the monsoon months from May to October.•Monthly averages of effective radius are lowest in April and increase during the monsoon months.•On average, cloud optical depth increases during the day as the effective droplet radius decreases.