عنوان مقاله [English]
نویسنده [English]چکیده [English]
The study of Precipitable water (PW) and determining the cloud seeding threshold are
of great importance in reducing the considerable cost of unsuccessful seeding or over
seeding which well result in a decrease in rainfall potentiality. The present study was
carried out within a four-year period covering from 2000 to 2003 where the amount of
rainfall in Tabriz and Kermanshah was recorded by precipitation stations. instability
indices, PW were calculated using the data obtained through radiosonde,
thermodynamic diagram, and Modis satellite. Using the curve and upon choosing the
PW and the rainfall average as dependent variable, from among the PW, the suitable
cloud seeding threshold was estimated.
The thresholds obtained through Modis and radiosonde for cloud seeding and PW
were compared across 21 cases. The two methods employed showed high correlation.
The thresholds obtained through Modis in East Azerbaijan and Kermanshah were 7
mm and 12 mm respectively, while the thresholds obtained through radiosonde on the
same days for PW were 9 mm in East Azerbaijan and 15 mm in Kermanshah. In
general, the amount of PW obtained through radiosonde proved to be greater than
those achieved through Modis. It is mainly due to the fact that the clouds’ build up
time and satellite picturing were not synchronous; moreover, the Modis had higher
sensitivity to the back scattering of the infrared waves by heavy clouds and, at the
same time, and the low sensitivity in fogy condition on earth.