Project to increase rainfall in the Republic of Cuba

   The lack of rainfall, which regularly occurs in Cuba, significantly affects the development of the national economy and, in particular, the yield of crops, citrus fruits, and tobacco. Despite the construction in Cuba of numerous reservoirs designed to supply water to the population, industrial enterprises and agriculture, during dry periods they do not satisfy water needs. In this regard, starting from 1979, the Institute of Meteorology of the Cuban Academy of Sciences, within the framework of the Cuban Program of Active Influence on the Weather (Programa Cubano de Modificación Artificial del Tiempo (PCMAT) and within the framework of Soviet-Cuban scientific and technical cooperation, began work on artificially increasing precipitation in Cuba.At the first stage of work, climatological studies of cloud resources were carried out in 1979-1981 in order to select the territory and the most favorable period for conducting cloud seeding experiments.As a result of the analysis of climatological material and experimental aircraft and radar studies of clouds and precipitation, the territory in the province of Camagüey was chosen for the experiments.

   At the second stage (1982-1984) the following was carried out: 1) the equipment of the Camaguey meteorological polygon (KMP) was carried out with an information-measuring system (IMS), which includes two radars — ARS-3 and a two-wave meteorological radar MRL-5, equipped with a digital system ADSORS, point of radio sounding of the atmosphere, point of reception of synoptic, satellite and prognostic information, and a specialized network of rain gauges; 2) prepared two aircraft — An-26 and Il-14, equipped with equipment for studying the microphysical and thermodynamic characteristics of the atmosphere and clouds, as well as with means for seeding clouds by firing squibs with silver iodide from the An-26 aircraft; 3) pilot experiments on the effects on clouds were carried out in order to prepare for a research experiment on the ILC. In June-August 1985, a randomized research experiment was conducted at the ILC, during which the hypothesis of dynamic cloud seeding to increase precipitation was tested and the method of influencing tropical convective clouds was tested. During this period, the main attention was paid to the definition of a set of criteria for the suitability of isolated convective clouds for seeding with an ice-forming agent and the establishment of reagent consumption rates and methods for introducing it into the clouds.

   To carry out research and carry out cloud seeding at the ILC, two Cuban aircraft were mainly used: An-26 and Il-14. In addition to them, the Russian LSU Il-18 «Cyclone» (in 1986-1987) and An-12 «Cyclone» (in 1988-1990) were also used in the work.

   Taking into account the results of preliminary studies of clouds and precipitation at the ILC in 1982-1986. complex experiments were carried out to study tropical clouds in Cuba with experimental seeding of convective clouds of various forms with silver iodide aerosols and using aircraft and radar controls. During this period, about 200 experiments were carried out with clouds having heights from 5.5 to 10 km and temperatures at the level of the upper limit from -4.5 to -35 °C. During the experiments, visual and instrumental observations of the evolution of clouds were carried out from the boards of the LSU An-26 and Il-14 and radar observations using the ARS-3 and MRL-5 radars equipped with an automated digital processing of radar signals (ADSORS). As a result of radar and aircraft studies of clouds and precipitation at the ILC in 1984-1986. preliminary criteria were established for the suitability of clouds for seeding in order to obtain additional precipitation.

   In 1986-1990. the confirmation phase of a randomized experiment on seeding of convective clouds was carried out at the KMP. At the same time, along with isolated clouds, cloud clusters were seeded, which are mesoscale cloud formations on an area of ​​400-600 km², and, as studies have shown, give 20-25% of the amount of precipitation on the ILC, in contrast to the 3% contribution of isolated clouds. In total for the period 1986-1990. data were analyzed for 46 isolated clouds (24 seeded and 22 control) and 82 cloud clusters (42 seeded and 40 control). Table 1 shows the data used to analyze the results of seeding isolated clouds. The following radar parameters of the clouds were used as the main characteristics for the analysis: Ho is the height of the radio echo of the cloud at the time of its first crossing by an aircraft, Т is the time interval between the moments of the appearance of the first radio echo of the cloud and the first crossing of the cloud by an aircraft, Zо is the maximum reflectivity of the radio echo of precipitation at the time of the first crossing , So is the area of ​​radio echo of precipitation at the time of the first flight of the aircraft through the cloud, T is the period of existence of the radio echo (the “lifetime” of the cloud), Q is the amount of precipitation that fell from the cloud, Hmax is the maximum height of the radio echo cloud over the entire period of its existence, S is the total area of precipitation during the lifetime of the cloud, Zmax is the maximum radar reflectivity of precipitation, Smax is the maximum area of precipitation during the lifetime of the cloud.

Table 1

Average values of radar parameters of seeded and control isolated experimental clouds in the seasons 1986-1988.

   As a result of the analysis, it was shown that when considering the entire set of seeded and control isolated clouds without stratification of experiments, a positive effect is observed in all analyzed parameters. So seeded single clouds existed on average 5.4 min longer, had a 4% higher radio echo height, 4% more radar reflectivity and 21% more precipitation area, and also gave 41% more precipitation compared to control clouds. Unlike isolated clouds, mesoscale cloud systems (cloud clusters) provide 20-25% of the amount of precipitation on the ILC and, therefore, are more favorable objects for seeding in order to artificially increase precipitation on the polygon area. In the seasons 1986÷1989. data were obtained for 82 cloud clusters (42 seeded and 40 controls). Table 2 shows the main results of comparing the data obtained for seeded and control clusters.

table 2

Average values of radar parameters of seeded and control cells of cloud clusters in seasons 1986-1989

   When comparing the final parameters of seeded and control cells of clusters without stratification of experiments, a positive seeding effect is observed for all analyzed parameters.

   Thus, as a result of the analysis of the experimental material obtained during the period of the experiment on the seeding of convective clouds in order to increase precipitation at the KMP, the possibility of modifying isolated convective clouds and cloud cluster cells by dynamic seeding was quite convincingly demonstrated. Thus, the seeding of growing convective cells with a temperature at the level of the upper boundary in the range of –10 °С ÷ –20 °С is accompanied by their large vertical growth, an increase in the lifetime, the area of ​​radio echo of precipitation, their reflectivity and, as a consequence of these changes, an increase (on average, almost 2 times) precipitation from seeded single clouds and cluster cells compared to unseeded ones.