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Weather Wise: What's causing the purple sunsets?

Posted at 10:06 AM, Sep 03, 2019
and last updated 2019-09-03 12:59:18-04

You may have noticed a few things regarding the sunset recently: it's happening earlier and earlier, and the color often has a purple hue.

In this week's Weather Wise, the unusual color we've seen here in Montana has been shared throughout the northern hemisphere.

Big sky sunsets have been even more spectacular than normal recently as purple shades join or even dominate the normal yellows, oranges and reds. For the cause we need to look to the pacific ocean as two volcanoes have erupted this summer. The raikoke volcano between japan and russia and the ulawun volcano in new guinea erupted and punched through to the stratosphere, sending material as high as 60,000 feet. Volcanic ash rarely reaches this height but when it does it, it creates an unusual sunset color. The purple-ish hue is produced when fine volcanic aerosols reach the stratosphere and scatter blue light, which when mixed with ordinary sunset red, produces a violet tone. The purple color is often preceded by a yellow arch hugging the horizon. As teh sun sets, violet beams emerge from the yellow, overlapping to fill teh western sky with a soft purple glow. Sky watchers shouldn't expect to see purple every night as the volcanic gas is patchily distributed bringing beautiful violet shades on some nights, not all.