Spectacular rippling waves spread out in the atmosphere above Australia last week, showing off a little-known phenomenon known as gravity waves.
Gravity waves are very different to gravitational waves - the ripples from distant collisions in space captured by detectors on Earth - and refer to waves in our atmosphere.
They’re often caused by collisions between air masses of different temperatures, creating ‘ripples’ that can be seen by satellites.
More atmospheric gravity waves. Triggered, in this case, by outflow from isolated thunderstorms over eastern NSW this afternoon. pic.twitter.com/tE5OQDouHB— Andrew Miskelly (@andrewmiskelly) October 24, 2019
Atmospheric gravity waves over the Coral Sea this morning. pic.twitter.com/hVKTbw12Z0— Andrew Miskelly (@andrewmiskelly) October 9, 2019
Weather expert Andrew Miskelly said: ‘More atmospheric gravity waves. Triggered, in this case, by outflow from isolated thunderstorms over eastern NSW this afternoon.’
Adam Morgan of the Australian Bureau of Meteorology told ABC: ‘There was a big thunderstorm over the north-west of Western Australia and the disturbance in this case was the cold air falling out of the thunderstorm and into the warmer air near the surface.
‘The difference in density there causes the disturbance and then the gravity wave can travel out as the cold air spreads out.
‘The disturbance will exist until everything rebalances itself, that's why they can travel a long way.’
The waves are known as ‘gravity waves’ because they are rebalanced by gravity.
According to Jacques Descloitres, who works at the MODIS Rapid Response system, which provides real-time images updates from the Terra Satellite, the waves create thin ripples, such as those that occur when a pebble is thrown into still water.
“These gravity waves sometimes happen when the stable air masses on which these clouds float are disturbed by some sort of terrain, thunderstorm updraft, or vertical wind shear. The patterns the waves form in the clouds are reflected on the ocean surface where the waves have reached down and left their impression on the water.”