Cloud seeding impact on precipitation as revealed by cloud-resolving mesoscale model

Abstract

A cloud-resolving mesoscale model has been used to investigate the effects of cloud seeding by silver-iodide (AgI) if the seeding is performed at cold part of a long-lasting convective cloud. Our motivation for this research was to answer the principle question: where, when and what amount of silver-iodide lead to optimum effects of seeding: rain precipitation enhancement and reduction of hail. The bulk two-moment microphysical scheme and the new software package for silver-iodide are incorporated in the model. The new saturation-adjustment scheme is introduced to include the effect of seeding agent particles as deposition nuclei. Sensitivity tests with respect to seeding agent amount, location, time and dynamics of seeding are performed. Our principal findings are as follows: The accumulated hail and rain precipitation at the surface are significantly reduced (-6.47%) or increased (8.43%) if the seeding zone in form of a circular sector is seeded at early stage of cloud development (5.4 min of simulated time) for the largest seeding agent amount used. The greatest increase in corresponding rain precipitation (8.75%) is occurred if the circle ring is seeded under the same other conditions as in previous case. The greatest reduction of the accumulated hail precipitation at the surface (-7.10%) and 9.55% of rain increase is occurred if the total number concentration of active deposition nuclei is decreased. Increased hail melting is the most important mechanism for increasing of rain after seeding. Changes in rates by which hail accretes cloud water in dry growth regime and snow accretes rain mostly contributed to hail reduction at the surface. © Springer-Verlag 2006.