(note: we conclude our series featuring Dr. Beyulev's report on Russia's weather modification projects with this interesting perspective on stopping rain. for complete series, click Russia/BERYULEV link)
WEATHER MODIFICATION BY AIRCRAFT CLOUD SEEDING
BERYULEV G.P. Head,
Department of Cloud Physics and Weather Modification
Central Aerological Observatory
Rosgidromet, Russian Federation
Improving Weather Conditions
To crystallize one cubic km of [a] supercooled cloud, it is usually enough to seed it by several hundred grams of dry ice or [with] several grams of silver iodide.
After seeding a cloud or fog by ice particles in favorable conditions, an intensive cloud crystallization process begins, and in 5-10 minutes ice crystals are observed to fall out of the cloud.
In this case, one passage of a seeding airplane results in producing a dissipation zone with an average 3-5 km width. (image right from traudtaerial.com)
The full clearing of the target site from cloud drops and precipitation particles occurs in 35-50 minutes after seeding.
The methods to destroy developing convective clouds differing in intensity, from cumulus congestus to cumulonimbus, using a dynamic technique, i.e. artificially generated downdrafts, were theoretically justified by scientists from the Russian Institute of Applied Geophysics and thoroughly tested under laboratory and field conditions by specialists from the CAO.
It has been found out that downdrafts in the upper cloud part can be produced by an artificial air jet directed downward, through seeding powders or dispersing water mass in it.
Also, downdrafts in a cumulonimbus congestus can be generated by enhancing precipitation falling into them from aloft.
The dynamic destruction of cumulonimbi through seeding their tops by powdery material has proved sufficiently effective.
Thus, the seeding of single-cell isolated air-mass clouds and frontal clouds accounts for a 90% and 60-65% score, respectively.
The seeding of 30 kg or more of coarse-dispersion powders (per cloud top) resulted in the destruction of single-cell isolated clouds within 10-20 minutes and frontal ones within 30-35 minutes.
The other two methods out of the four mentioned at the beginning of this section use weather modification techniques similar to that employed in the first method aimed at the dissipation of clouds and fogs.
In both cases it is possible to estimate the distance of advance seeding relative to the protected territory so as to prevent undesirable clouds and precipitation from reaching it.
In some synoptic situations, overseeding may prove to be the most appropriate procedure. This is due to its capability to reduce precipitation significantly and to its faster action facilitating the production of an artificial crystallization zone (with reduced or not precipitation) over a protected territory, which is especially important in conditions of a complex and variable wind field.
All the procedures and technical aids described above were employed successfully in the activities associated with eliminating the consequences of [the] Chernobyl disaster and improving weather conditions[s] in Moscow (November 7, 1984; May 8-9, 1995, September 5-7, 1997, July 13 and 19, 1998, May 9, 2000, September 2-3, 2000, September 1-2, 2001, June 12 and 15, 2004; August 31 and September 1, 2002), Tashkent (1994-2002) and Astana (June 9-10, 1998).