In this study, a one-dimensional transient cumulonimbus cloud is modeled to be seeded by liquid CO 2 . The model includes microphysical and dynamical processes associated with glaciogenic seeding by homogenous ice nucleation and two thermal terms associated with seeding by -90 8C liquid CO 2 . For this model, the study concentrates on five types of hydrometeors, namely, cloud droplet, cloud ice, snow, hail/graupel, and rain. Point and horizontal seeding methods are implemented to observe their implications for rainfall enhancement, amount of hail/graupel production, vertical cloud extension, and radar's reflectivity. In addition, the seeding temperature effects on the rainfall and microphysical processes are investigated. The results of the study show that, the rainfall enhancement and rainfall intensity in the point seeding case are more than those in the horizontal seeding. Moreover, the study reveals that, there is a vertical cloud extension enhancement of 0.5 km for clouds with top height of 10.5 km. The most important sources of the rain water production are found to be the accretion of cloud water by rain (P RACW ) and by snow (P SACW ), and for the graupel production is dry growth of the graupel (P GDRY ). The results of this study are confirmed by the results of other investigators and are found to be comparable with the recorded data at rain gauge stations.
In this work, a comparative study of liquid carbon dioxide versus silver iodide seeding effects on a one-dimensional transient cumulonimbus cloud model is made. The over-riding concern is to figure out the implications of different seeding methods and agents for rainfall enhancement and hail suppression in cumulonimbus clouds. Based on the model results, it may be inferred that for the liquid carbon dioxide seeding, the seedability temperature limit is wider and the dynamic effects and precipitations are stronger compared to those of the silver iodide seeding. In addition, based on the model results, the rainfall enhancement can augment to 52 % for liquid carbon dioxide as the cloud top level increases. However, this rainfall enhancement can augment to only 19 % in the case of silver iodide seeding. Also, the model results show that for clouds with cloud top level less than 7 km, the cumulative rainfall for the point seeding is less than that for the horizontal seeding, but for clouds with cloud top level more than 9 km, the rainfall amount for the point seeding is more than that for the horizontal seeding. The results also show that there exist two threshold temperatures for the silver iodide seeding methods. The model results also indicate that the silver iodide seeding in the mixed clouds can be used for the cloud seeding with the aim of hail suppression. In general, the obtained results from this model show to be comparable with the recorded data at rain gauge stations.
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