A large, greyish white cloud appeared on Sunday morning over Meulaboh in Aceh province to shock the city’s residents, some of whom thought that the low-lying, horizontal cloud formation resembled a tsunami.
Videos and photos of the strange cloud made their rounds on social media, sparking some concerns among local residents.
Twitter user Arief Arbianto tweeted using the handle @masawep on Monday morning: “Let us pray that Meulaboh city will be all right. A view of a this morning’s cloud above Meulaboh, West Aceh regency.”
Meanwhile, user Agus Maulana (@a_mantu71) posted a video clip to his account on Monday afternoon, calling the “uncommon phenomenon” a “tsunami cloud”.
Weather forecast and early warning head Miming Saepudin of the Meteorology, Climatology and Geophysics Agency (BMKG) identified the rare weather phenomenon spotted over Meulaboh.
“It is a relatively rare phenomenon called an arcus cloud,” Miming said on Monday as reported by kompas.com.
Miming said that arcus clouds formed as a result of atmospheric instability caused when air masses of different temperatures and humidity met
“The cooler air masses push the warmer air up to form horizontal clouds,” he said, adding that an arcus cloud could be a sign of bad weather in the area where it appeared, such as strong winds and thunderstorms.
“So we urge all residents to stay alert, especially fishermen, as the cloud could cause strong winds and heavy rainstorms accompanied by thunder,” he said.
Miming debunked suggestions by several social media users that the cloud signified an impending earthquake or tsunami.
“Such a cloud is purely a [natural weather] phenomenon due to atmospheric dynamics and has nothing to do with potential earthquakes or tsunamis or mystical things,” he stressed.