P1.40 Numerical Experiment Comparing the Efficacies of Dryice Pellets and Liquid Carbon Dioxide for Cloud Seeding Operation

Monday, 28 June 2010
Exhibit Hall (DoubleTree by Hilton Portland)
Akihiro Hashimoto, MRI, Tsukuba,Ibaraki,, Japan; and M. Murakami

Water shortage is one of the most serious problems in many countries and areas in the world and its extent may be escalated in the future by global warming. In Japan, although there is much amount of yearly precipitation more than thousand mm, serious water shortage occurs once for several years. Meteorological Research Institute has been studying the weather modification with cloud seeding for the orographic snow clouds which form above the Echigo mountains. The snowpack produced there by the snow clouds during winter is essential to the steady water resource for the metropolitan area vicinity of Tokyo. For better cloud seeding experiment, it is important to make a good choice of seeding agent. We are investigating the efficacies of dryice pellet (DIP) and liquid carbon dioxide (LCO) in airborne cloud seeding. In the seeding operation using DIP, the airplane fling near the cloud top successively drops the DIPs, which generate ice crystals along their fall streaks, forming a curtain of ice crystals in the cloud. On the other hand, LCO is spouted out from the airplane fling near the cloud base, forming a thin streak of ice crystals in the cloud. We performed several numerical simulations in order to examine the seeding effects using those substances. The domain size is 12 km x 16 km in horizontal and 5 km in vertical. The grid size is 50 m. We assumed horizontally uniform temperature and humidity profiles, and the super-cooled cloud layer with two kilometers depth as the initial condition. In the numerical experiments, the seeding airplane is assumed to fly once at the speed of 100 m/s along the 4-km straight path. The seeding rate of 50 g/sec is adopted for the simulation with DIP. We set the seeding rate of LCO to be the same as that of DIP so that new ice crystals are created in same order of magnitude of number concentration among the different seeding agents, although this is unusually large rate compared to the rate adopted in the actual operation using LCO. As the result of the simulations, it is found that the cloud seeding with DIP is able to process a super-cooled cloud more quickly than that with LCO in the initially calm environment. The effect on the precipitation on the ground appears faster in the case of using DIP. After a couple of hours, the difference in the accumulated precipitation amount between the simulations with DIP and with LCO becomes unclear. The similar results are obtained also for the initial environments with and without warm bubbles in vertically sheared wind profile. It is also planned to perform the simulations with realistic seeding rate of LCO. The presenter would like to discuss on which substance is effective according to the environment and available resources for the cloud seeding operations.
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