Have you ever seen a ‘rain bomb’?
They’re not so uncommon so it’s quite possible you have at some point. But in this era where so many of us carry sophisticated recording devices in our pockets, capturing spectacular weather events on your smartphone’s camera or video (and often sharing it on Facebook!) has become a bit of a hobby. And it’s turning some of us into keen – or accidental – amateur storm chasers.
An interesting weather event recently captured in both still images and video on a Queensland farmer’s iPhone made it to an international science blog and multiple media websites around the world.
As reported by ABC News online (28 January), the event was witnessed on Sunday 25 January by grazier, Peter Thompson, who was working on his property just outside Roma in south west Queensland.
He describes seeing a big grey ball of cloud forming and then dropping to the ground and rolling outwards. Have a look at the video here.
The Bureau of Meteorology (BOM) describes Mr Thompson’s rain bomb as a type of downburst known as a ‘microburst’ that is associated with severe thunderstorms.
The BOM website says, http://www.bom.gov.au/aviation/data/education/thunderstorms.pdf “The name given to an intense thunderstorm downdraught concentrated on a small area is a microburst.”
“A downburst is a concentrated downdraft, typically lasting five to fifteen minutes, and is of unusually high speed such that it can cause damage on, or near, the ground. The term microburst is used to describe a downburst which causes damage over an area with horizontal dimensions of less than four kilometres.
Microbursts can be wet or dry too. It gets a bit more complicated at this point but you can find out all about them and more here.
Microbursts can be devastating to aviation and prior to a deadly passenger plane disaster in the United States in 1985, were little understood. The US Federal Aviation Administration website has a section reporting on aviation accidents and the lessons learned where you can read about Delta Airlines Flight 191’s tragic 1985 encounter with a microburst on approach to Dallas Fort Worth airport.
Using the information from the plane’s flight recorder, the Smithsonian Institution in Washington has produced a video recreating the final moments of Delta 191’s attempted landing and fatal crash due to the microburst, which you can see here. It also includes interviews with NASA and weather and aviation experts.
Dr John McCarthy , a meteorologist and aviation weather expert, describes a microburst as similar to what happens when you turn the tap on hard in your kitchen sink and the water shoots straight down and splashes out in all directions.
“It’s a tiny thing,” he says, “meteorologicaly speaking, compared to a big storm or a snow storm or a hurricane – it’s like a needle in a haystack.”
“Except that it is extremely bad news if you are an aeroplane flying through it,” he says.
If you’re interested in weather events like microbursts, you might like to have look at BOM’s Storm Spotter’s Handbook.