Year-round Occurrence Frequency of Seedable Clouds over Ogouchi Dam West of Tokyo

MRI, in cooperation with Bureau of Waterworks of Tokyo Metropolitan Government, is carrying out the Tokyo Weather Modification Pilot Project. The objectives of the project are 1) to evaluate occurrence frequency of seedable clouds, 2) to optimize characteristics of seeding materials (AgI and hygroscopic particles), 3) to investigate possible seeding methods and their optimal conditions, and 4) to estimate seeding effect all the year around. In this paper, we present year-round occurrence frequencies of seedable clouds evaluated using three different methods. For the first method, which is applicable to any region without special observation facility before starting a weather modification project, seedable clouds are evaluated using GSM satellite data and classified into water clouds with top temperature warmer than -5 C (suitable for hygroscopic seeding), supercooled clouds with top temperature colder than -5 C (suitable for glaciogenic seeding) and ice clouds. For the second methods, seedable clouds are evaluated using data from various kinds of ground-based active (X-, K- nad Ka-band Doppler radars and passive (multi wavelength microwave radiometer) remote sensors and are classified into water clouds with top temperature warmer than -5 C and LWP > 0.5 mm (suitable for hygroscopic seeding), supercooled clouds with top temperature colder than -5 C and supercooled LWP > 0.2 mm (suitable for glaciogenic seeding). For the third method, seedable clouds are evaluated using a non-hydrostatic model (NHM) with horizontal resolution of 1 km and are classified in the same way as for the second method. The three methods showed a similar seasonal variation in occurrence frequency of seedable clouds; their occurrence frequencies of clouds suitable for both glaciogenic and hygroscopic seeding are high ( ~ 10% in time) in early summer and very low in mid-winter. Detailed differences in the occurrence frequencies among the three methods are discussed.