Monday, October 26, 2015
Cloud Seeding in Malaysia
Baru-baru ini berlaku sedikit kekecohan di Whatsapp apabila terdapat mesej yang viral mengatakan bahawa proses pembenihan awan yang dilakukan ketika musim jerebu mengandungi bahan chemical. Ini semua tiada asas kerana pembenihan awan dijalankan menggunakan garam sahaja yang dibancuh dengan air. Seingat saya, proses ini telah pun didokumentasikan di dalam rancangan TV. The Star pada 25 Oktober telah memuatkan sekali lagi satu artikel berkenaan dengan proses pembenihan awan ini. Bagi sesiapa yang malas membaca artikel di bawah, ringkasan isi kandungannya adalah mudah iaitu, pembenihan awan menggunakan garam biasa sahaja.
An as-salt on the clouds
The Star Malaysia
25 October 2015
THERE’S a viral message going around on social media that cloud seeding is being done using “strong chemicals”.
It’s wrong. There’s no exotic chemical. “Wet” cloud-seeding is done using salt. Common table salt. Sodium chloride. And water. There is also a “dry” cloud-seeding method, which also uses table salt and functions on the same principle as “wet”, but that uses a different delivery method and a different aircraft.
To drive home the point, the Malaysian Meteorology Department (MMD) decided to invite the media to see exactly what goes on in a cloud-seeding operation.
“Actually, there is no difference between cloud-seeding and the natural method of cloud-forming from seawater. We are just enhancing the natural process,” said MMD’s director-general Datuk Che Gayah Ismail.
First, Met Department personnel put in eight bags of salt, each weighing 25kg, into a 1,800-litre stainless steel tank.
This is then followed by 1,500 litres of water and a laborious effort mixing the two together to make sure the 200kg of salt is dispersed throughout the water.
The Royal Malaysian Air Force (RMAF) C-130 aircraft carries four of these stainless steel tanks totalling about 6.8 tonnes in weight.
“Once the aircraft reaches the area we’re targeting for cloud seeding, we start disbursing the saline solution in very small droplets, almost like a mist. “The salt particle is what we call a cloud condensation nuclei (CCN), and it will attract more and more water molecules over the target area, until you get precipitation, meaning rainfall,” Che Gayah said. The ideal cloud formations MMD hopes to help create through the seeding process is called “towering cumulus”, which are dense enough so that they won’t get dispersed easily by wind.
Rainfall could come within two to three hours, or even as soon as 30 minutes, depending on the size of the CCNs. On average, conducting a wet-seeding operation costs about RM50,000 to RM70,000 per mission.
“The salt and water doesn’t cost a lot, the main expenditure is for the aircraft, the aircrew, fuel and maintenance,” said Che Gayah. By comparison, a dry-seeding operation, which uses a smaller Cessna, is cheaper in terms of aircraft and fuel, although the dry cloud-seeding capsules are more expensive, and flight time is shorter.
Each sodium chloride-potassium chloride flare costs about RM450, the director-general said. These flares are fitted on a rack fitted to the Cessna’s wings, and upon reaching the target area, the pilot would activate the flares.
“We mainly use the Cessna and flares for smaller target areas, especially when we’re aiming to precipitate over dams facing water shortage, like what was done in Johor recently,” Che Gayah said. By contrast, the C-130H’s four turbo-prop engines allow the plane to cover longer distances, a longer loiter time, and consequently the aircrew can disperse the saline solution over a much larger area. So far, cloud-seeding has had about a 70%-80% success rate.
Sometimes, while the air crew managed to successfully disperse their saltwater solution, the clouds formed are not large and heavy enough to precipitate as rain. Instead, these nascent cumulus formations get blown off course, and the mission is considered unsuccessful. Safety is also a concern, and Rainmaker missions have been aborted in the past because of poor visibility, which is a danger for the aircrew considering the low altitude they’re flying at. While other aircraft usually avoid cloud formations, the C-130 heads into such formations to help increase cloud size for rainfall. “Flying at low altitude, around 1,500m to 2,500m, is also a concern because of the Titiwangsa range,” said RMAF co-pilot Captain Ruzanna Md Nasir, who has logged 1,700 hours on the aircraft.