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20 4 4 4 . . . . II II II . II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Task 2 - Implement algorithms simulating cloud seeding generators as sources of IFN at specified ground-based sites The CSU RAMS was used to provide real-time forecast support during portions of the OW 2003-2004 Program's winter orographic cloud-seeding activities. The model physics explicitly represent orographic clouds and precipitation processes in mixed.phase clouds. A two. moment microphysics scheme was used, in which mixing ratios and concentrations are predicted for seven hydrometeor categories. Through the course of the 2003-2004 winter season, evaluation of the model's real-time forecast performance led to a series of adjustments in the simulation design. The model was extended to include seeding effects in order to evaluate the no-seed vs. seed precipitation simulated by RAMS. Algorithms were added to RAMS simulating sources of IFN from cloud-seeding generators (low-level model grid points). The extended model simulated sources of silver iodide (Agl) released at each generator as recorded in WlNC's operational cloud-seeding logs. The Agl was treated as a second predictive IFN field with its own activation characteristics. The Agl activation law was based on laboratory experiments that used the same types of generators and Agl materials as used by WlNC on the OW Program. (WlNC used a 4% Agl solution with sodium iodide as a carrier in acetone along with 1 % moth balls to improve nuclei activation between -2.5'C and -a.OoC.) As with the standard IFN category. the number of seeded IFN that is activated becomes a source of pristine ice crystals in equal numbers and a corresponding sink of IFN that is available for subsequent activation. The RAMS seeding simulations were set up identically as the control runs, except for the addltionallFN category and the seeded Agl. Simulated 24-hr precipitation in the seeded runs replaced the amounts from the corresponding non- seeded control runs to form complete daily, event. monthly and seasonal simulated precipitation totals that include all cloud-seeding operations. The CSU Team originally intended to use a seeding event selected from the OW 2002-2003 Program's operational season as a test case for the RAMS model seeding code, in order to develop the code and have it ready when the OW 2003-2004 Program's cloud-seeding data became available. OW Program seeding contractor Larry Hjermstad (WlNC) chose the February 4, 2003 seeding event for this test case and provided the seeding data. However, several factors delayed the test case experiment, including the delayed acquisition of the computer cluster, uncertainties in generator identification and location for the previous season, and shifted priority to current season cases as those seeding data became available. Thus this test case study was not completed until early May 2004. where it was used as one of the seeding sensitivity studies for Task 4 in the research project. The primary sensitivity explored with this test case involved reducing the initial background or naturallFN concentration to 40% of that used in the standard code. for both control and seeding runs. The February 4. 2003 seeding test case summary is in Appendix 3.