Tuesday, October 22nd 2019, 5:00 pm - How one dust storm made a 400 km-long arch in Australia.
With desert making up 35 per cent of the continent, it may be no surprise that dust storms are a fact of life in much of Australia. Dust storm 'season' for the country tends to correspond to the Southern Hemisphere spring -- happening now -- as cold fronts dive out of arid central Australia and push toward the ocean.
These storms are often massive in scale, but an image like the one captured by the Himawari8 satellite really puts it in perspective.
Image courtesy CIRA/RAMMB.
In the image above, you can see the sprawling cloud arch on the leading edge of the storm as it pushes offshore, along with the reddish smear of the dust itself spreading over the Indian Ocean. Comparing it to the coast of Australia, that cloud arch looks to stretch at least 400 km long.
After sunrise, you can see a pattern of cloudy and clear streaks following the leading cloud (they look a bit like echoes). It's gravity waves that cause these lines in the clouds -- rising and falling air bumping up against the tropopause. We see clouds where the air is rising, and clear where it's falling, making for the striped pattern.
Looking at the satellite image, the arch (not unlike those that form with chinooks here in Canada) seems to have formed in part due to the interaction of two fronts off to the east. You can just make them out on the overnight cloud image.
The yellow arrows indicate the leading edges of the two air masses, about to collide. Image courtesy CIRA/RAMMB.
Even though it's still dark out, you can also pick out the leading edge of the outflow boundary as it pushes offshore as the satellite picks up the highest clouds.
The yellow arrows show the leading edge of the cloud arch developing along the outflow boundary. Image courtesy CIRA/RAMMB.
Then sunrise reveals the entire picture, dust cloud and all. Even several days later, it's still possible to see the lingering dust in the atmosphere off the coast, though it's lost much of its red tinge.
The city of Broome recorded gusts of up to 80 km/h as the dust swept through on Sunday. The dust storm wasn't the only exceptional weather event the area has seen in the last week, either. The Bureau of Meteorology reported Broome hit the highest temperature for October in the past two years on Monday, as the temperature climbed to a scorching 42.6ºC.
Broome has just recorded its hottest Oct day in 2 years with the mercury climbing to 42.6°, almost 10° above the Oct Average.Our heatwave product shows that parts of the west Kimberley have experienced low to severe intensity heatwave conditions over the past 3 daysBureau of Meteorology, Western Australia on Twitter