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17 April 2009

A Couple Model of Droplet Growth Above Bandung

By: Plato Martuani Siregar
S2 - Oceanography and Atmospheric Sciences
Supervisors :
Prof. Dr. The Houw Liong
Dr. Bayong Tj H K

Convection process, cloud droplet

A couple model of droplet growth is developed by three kinds of processes, which are dynamic, thermodynamic, and cloud physics that assume water vapor is present between ground surface and tropopause layer. Updraft in boundary condition is zero. Factor of convergence, lateral advection, turbulent motion, updraft vorticity, and ice phase are neglected, then developed numerical modeling in one dimension of the formation, of droplet growth. This model is very sensitive to initial conditions.

The formation of droplet growth requires high supersaturated vapor to oppose curvature term. For the saturation ratio at relative humidities less than 100 %, droplet growth will be blocked by curvature term, so it needs addition of ammonium sulfate solution to an air parcel until droplet radius 0.13 micrometer, after critical saturation ratio is formed, droplet will grow although relative humidities approach one. On the other hand,solution effect growth is increased by heat conduction and vapor diffusion becomes droplet of radius around 10 micrometer.
A major part of solar radiation have absorbed by the surface of the earth. The atmosphere then becomes unstable due to the heating around ground,and thus convection is generated in the troposphere. The temperature of an air parcel moving upward decreases because of the adiabatic expansion,while water vapor in the air is warmed when it condenses. The temperature lapse rate in the troposphere is thus determined by balance of water vapor in the atmosphere. Using radiosonde data at LAPAN Bandung period in the 1992-1996 to optimize model trend and do verification, after that modeling can be used to estimate updraft rate, parcel temperature, rain mixing ratio, and mixing ratio of the condensed water in the atmosphere.

Convection process is determined in cloud droplet growth. The formation of cloud causes give temperature variations and mixing ratio in atmosphere. It can be seen that temperature variations in the level of 1500m above Bandung is larger than near ground. In this level, the cloud will be formed to absorb solar radiation, current air in cloud and separation of electrical dipole of water molecules which will give temperature variation of air parcel.

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