A Numerical Model To Investigate Optimum Liquid Carbon Dioxide Seeding Rate in Weather Modification Projects

Atmosphere is a dynamic fluid in which natural processes such as movementof air mass, formation of natural cloud and precipitation occur, and whereweather modification is focused on possibility of control on natural processesof atmosphere. cloud models have different types of application in operationalweather modification programs such as; hypothesis development, assessment ofseedability, experimental design, operational decisions, project evaluation, aswell as understanding of seeding effects. therefore, in this research, numericalmodeling for optimal utilization of phase change energy in ice thermal inducedby liquid carbon dioxide (lcd) in supercooled cloud seeding as suggestedin javanmard et al. (1998a) has been applied. in this article, after a shortreview on application of numerical modeling in weather modification activities,numerical modeling of the roll-up expansion of twin horizontal ice crystalthermal (rethit) process which forms in lcd seeding has been presented.it includes the dynamics, microphysics, and procedure of calculation of themodel. then in order to assess optimal seeding rate in supercooled cloud seedingusing lcd, the above mentioned rethit numerical model which is writtenin fortran language has been applied. the model has been run for the threeseeding rates of (pl) 40 gis, 100 gis, and 260 g/s. finally, the output resultsof the microphysic and dynarn.ic parameters of the formed ice thermal has beendiscussed.the above mentioned results of the numerical model has shown that thearriving time of ice thermal at the cloud top is about 16 min in pl=40, 15.4min in pl=100, and 17.2 min in pl=260. which is very close to the lcdseeding experiment results which have been obtained by tomine et al. (1998);they ere also in accordance with the metaldehyde seeding experiment resultsobtained by fukuta (1972). as a result, the calculated optimum seeding rateby lcd seeding model is 40 s/». which could help in determining the thresholdvalue of seeding rate, and which avoids overseeding effects as well as economicbenefits.