Three-Dimensional Modelling of Precipitation Enhancement by Cloud Seeding in Three Different Climate Zones

This study numerically investigates precipitation enhancement from cumuliform clouds in three different climate regions: (1) Arid climate of the United Arab Emirates (UAE); (2) maritime climate of Thailand; and (3) continental climate of Serbia. Recently developed core/shell sodium chloride (NaCl)/titanium dioxide (TiO2) nanostructure (CSNT) aerosol was tested as a precipitation enhancer in all three climate regions. Previous experimental studies in cloud chambers and idealized numerical simulations demonstrated that CSNT is a significantly more effective precipitation enhancer than the traditional NaCl. Here, CSNT and NaCl seeding agents are incorporated into the WRF (Weather Research and Forecasting) model microphysics with explicate treatment of aerosol. Our results show that CSNT is a profoundly more effective precipitation enhancer in the case of arid climate characterized with low humidity. The accumulated surface precipitation in the arid test was 1.4 times larger if CSNT seeding agent was used instead of NaCl. The smallest difference in the effectiveness between CSNT and NaCl was observed in the maritime case due to their similar activation properties at high values of relative humidity.

ANALISIS KEMUNCULAN AWAN HUJAN BERDASARKAN JENISNYA UNTUK MENDUKUNG KEGIATAN MODIFIKASI CUACA

Untuk memenuhi kebutuhan cadangan air di tiga danau yang ada di DAS Larona, telah beberapa kali dilakukan penyemaian awan dengan menggunakan Teknologi Hujan Buatan. Teknologi yang selama ini dilakukan adalah penyemaian awan dari udara dengan menggunakan pesawat terbang sebagai sarana penghantar bahan semainya. Namun akhir-akhir ini di Balai Teknologi Modifikasi Cuaca, BPPT telah mulai dikembangkan teknologi penyemaian awan dari darat yang menggunakan menara. Penempatan menara ini perlu mempertimbangkan unsur meteorologi agar bahan semai secara efektif dapat masuk ke dalam awan yang potensial menghasilkan hujan. Dari data satelit dan penakar hujan didapatkan gambaran secara umum sebaran awan hujan. Dengan melakukan analisis reflektifitas radar diperoleh sebaran awan hujan berdasarkan jenis awan hujannya. Dengan metoda ini diketahui bahwa awan-awan hujan yang muncul di Matano, Timampu dan Tokalimbo kebanyakan awan hujan jenis shallow convective. Awan hujan shallow convective dan convective pada bulan Januari-Maret lebih banyak tumbuh di bagian Utara dan Timur DAS. Di bagian tengah DAS, kemunculan awan hujan lebih sedikit.Kata Kunci: radar, awan hujan, sorowako, modifikasi cuacaCloud seeding project has been carried out in Larona watershed to enhanced the rainfall in this area. Until now the cloud seeding technology has been done by delivering the seeding material directly to the cloud by aircraft. But recently, the National Laboratory of Weather Modification Technology of Indonesia is developing a new method of ground based seeding by building some towers for delivering the seeding agent to the cloud. Location of the tower should consider elements of Meteorology in order for the seeding materials can effectively enter into cloud which potentially produce rain. By doing an analysis of the radar reflectivity obtained the distribution of clouds based on the type of precipitation cloud. With this method it is known that rain clouds that appeared in Matano, Timampu and Tokalimbo are mostly shallow convective clouds. In January-March, shallow convective clouds and convective grew more in the North and East of the Larona watershed. In the central part of the watershed, there is less precipitating clouds appear.Keywords: radar, rain cloud, sorowako, weather modification

STUDI MODEL UNTUK PENINGKATAN PRESIPITASI AWAN KONVEKTIF DENGAN BUBUK GARAM

Sebuah studi tentang penggunaan garam serbuk polidispersi sebagai bahan semaitelah dilaksanakan dengan memakai model 1-dimensi. Dalam studi ini pengaruhpenambahan serbuk garam tersebut terhadap distribusi tetes awan dan jumlah penambahan presipitasi telah dilakukan, serta hasilnya telah dianalisa dan dibandingkan dengan hasil yang diperoleh pada pemakaian partikel higroskopis yang diperoleh dari flare piroteknik. Kondisi awan yang dipelajari terdiri dari beberapa macam ketinggian, updraft dan konsentrasi inti kondensasi atmosfer semula. Hasil studi menunjukkan bahwa bubuk garam polidisperse dapat dipakai untuk menghasilkan presipitasi dari awan marginal yang biasanya tidak mampu menghasilkan presipitasi.A study of use of polydisperse salt as seeding agent in cloud modification was conducted using 1-dimensional model. In this study the effects of introduction of the salt powder to cloud droplet distribution and the amount of precipitation enhancement were analyzed and compared to the results obtained by introduction of hygroscopic particles from pyrotechnic flares at various cloud media conditions such as cloud thickness, updraft, and original atmospheric condensation nuclei. This study reveals that polydisperse salt powder is usable to obtain precipitation from marginal cloud that usually can not produce precipitation.

A Quest for Effective Hygroscopic Cloud Seeding

It is shown here that hygroscopic seeding requires two orders of magnitude more hygroscopic agent than can be delivered by flare technology for producing raindrop embryos in concentrations to detect by cloud physics aircraft the microphysical signature of rain initiation. An alternative method of finely milled salt powder is shown to be capable of achieving this goal. During field experiments the use of a sulfur hexafluoride (SF6) gas tracer to identify the exact seeded cloud volume and to quantify dilution of the seeding agent showed that the seeding agent dilutes to the order of 10−10 of its released concentration in updrafts at a height of ≥1 km above cloud base. This means that the theoretically expected changes in the cloud drop size distribution (DSD) would not be detectable with a cloud droplet spectrometer in a measurement volume collected during the several seconds that the seeded volume is traversed by an aircraft. The actual measurements failed to identify a clear microphysical seeding signature from the burning of hygroscopic flares within the seeded convective clouds. This uncertainty with respect to hygroscopic flare–seeding experiments prompted an experimental and theoretical search for optimal hygroscopic seeding materials. This search culminated in the production of a salt powder having 2–5-μm-diameter particle sizes that are optimal according to model simulations, and can be distributed from a crop duster aircraft. Such particles act as giant cloud condensation nuclei (GCCN). Any potential broadening of the DSD at cloud base by the competition effect (i.e., when the seeded aerosols compete with the natural ambient aerosols for water vapor) occurs when the seeding agent has not been substantially diluted, and hence affects only a very small cloud volume that dilutes quickly. Therefore, the main expected effect of the GCCN is probably to serve as raindrop embryos. The salt powder–seeding method is more productive by two orders of magnitude than the hygroscopic flares in producing GCCN that can initiate rain in clouds with naturally suppressed warm rain processes, because of a combination of change in the particle size distribution and the greater seeding rate that is practical with the powder. Experimental seeding of salt powder in conjunction with the simultaneous release of an SF6 gas tracer produced strong seeding signatures, indicating that the methodology works as hypothesized. The efficacy of the accelerated warm rain processes in altering rainfall amounts may vary under different conditions, and requires additional research that involves both observations and simulations.