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AN OVERVIEW OF THE GREEK HAIL SUPPRESSION PROJECT
The Greek National Hail Suppression Program (GNHSP) was established in 1984 under the auspices of the National Agricultural Insurance Organization know named as ELGA. The primary goal of the program is to reduce hail damage to agricultural crops in a selected project area of central Macedonia, in northern Greece, using airborne cloud seeding technology. The project area is situated in the agricultural area northeast of the city of Thessaloniki.
Hail Suppression Hypothesis and Seeding Criteria
The hail suppression cloud seeding hypothesis of the GNHSP is based on the cloud microphysical concept of beneficial competition theory. This hypothesis assumes a lack of natural ice nuclei in the storm environment and that the injection of artificial nuclei of AgI (silver iodide) will increase the total ice nuclei in thunderstorm clouds. Hence, the available supercooled water to each embryo is limited and the hailstones that are formed will be smaller and produce less damage if they reach the ground.
The seeding criteria in the GNHSP requires that seeding must be conducted on every storm reaching a radar intensity of 35 dBZ or greater, at altitutes between the -5 and -30 C levels while these storms are within the project area or within a 20 minute-upwind buffer of the project area.
Program Operations
The program operations have started on 15 April 1997 and will continue up to 30 September 1997 covering an agricultural area of about 2,340 Sq. km. Cloud seeding is conducted using two light twin aircrafts (Piper Cheyenne II) equipped with seeding racks containing both droppable and end-burning silver iodide flares.
Weather forecasting is conducted using weather analysis and prognostic charts, sounding data, satellite pictures, radar maps and weather infromation bulletins. The Convective Day Category (CDC) developed by Strong (1979) is used to categorize the cloud conditions and the probability of hail for the day. Aircrew readiness for take off is 15 or 45 minutes based mainly on forecasted CDC. Daily weather forecasts and operations briefings are conducted at 9.30 UTC.
Weather surveillance is provided by an Enterprise WSR74 10-cm S-band weather radar located at Macedonia International Airport in Thessaloniki. A routine 20-hour a day radar operation is conducted based on scheduled shifts, that is extented to 24-hour a day in the case that continued storm activity threatens the project area. Support to ELGA is provided by the companies General Aviation 3D and Weather Modification Inc.
A network of 140 hailpads (and raingauges) is operated in the project area to provide quantitative measurements of hailfalls. Hailpad data are used as a primary database for evaluation of the cloud seeding effect and also for an adequate sampling of hailfalls and fine analysis scale of hailswaths. Hailpad network operations include maintenance, hailpad service, post storm hailpad change, and total rainfall recording.
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