The Study of Precipitable Water and its use in CloudSeeding with thermodynamic diagrams and ModisSatellite in Western Iran

The study of Precipitable water (PW) and determining the cloud seeding threshold areof great importance in reducing the considerable cost of unsuccessful seeding or overseeding which well result in a decrease in rainfall potentiality. The present study wascarried out within a four-year period covering from 2000 to 2003 where the amount ofrainfall in Tabriz and Kermanshah was recorded by precipitation stations. instabilityindices, PW were calculated using the data obtained through radiosonde,thermodynamic diagram, and Modis satellite. Using the curve and upon choosing thePW and the rainfall average as dependent variable, from among the PW, the suitablecloud seeding threshold was estimated.The thresholds obtained through Modis and radiosonde for cloud seeding and PWwere compared across 21 cases. The two methods employed showed high correlation.The thresholds obtained through Modis in East Azerbaijan and Kermanshah were 7mm and 12 mm respectively, while the thresholds obtained through radiosonde on thesame days for PW were 9 mm in East Azerbaijan and 15 mm in Kermanshah. Ingeneral, the amount of PW obtained through radiosonde proved to be greater thanthose achieved through Modis. It is mainly due to the fact that the clouds’ build uptime and satellite picturing were not synchronous; moreover, the Modis had highersensitivity to the back scattering of the infrared waves by heavy clouds and, at thesame time, and the low sensitivity in fogy condition on earth.