{"id":1877,"date":"2022-08-02T05:50:41","date_gmt":"2022-08-02T05:50:41","guid":{"rendered":"https:\/\/aurorasaurudev.wpengine.com\/?p=1877"},"modified":"2023-12-15T22:02:22","modified_gmt":"2023-12-15T22:02:22","slug":"what-is-discrete-aurora-its-not-discreet","status":"publish","type":"post","link":"https:\/\/blog.aurorasaurus.org\/?p=1877","title":{"rendered":"What Is Discrete Aurora? (It\u2019s Not Discreet!)"},"content":{"rendered":"
\"\"<\/a>
Photo by Donna Lach showing discrete and diffuse aurora together, taken facing east-northeast at about 6:30 am on November 4, 2021 near Plumas, Manitoba. Note that the discrete aurora on the left of the photo shows vertical, fine-line \u201cfilament\u201d structures and tall rays, while a dimmer, cloudlike, diffuse aurora is visible on the right of the photo.<\/figcaption><\/figure>\n

While \u201cdiscreet\u201d means something that is a little bit secretive or unobtrusive, \u201cdiscrete\u201d auroras are distinct, bright, narrow bands\u2014most commonly, photos of auroras are of this type. They typically have a definite lower border and can stretch high into the sky, like curtains, when viewed from the side. From below they are very narrow. They can wave slowly or race across the sky.. They are broadest, brightest, and\/or most active around midnight local time. (By contrast, \u201cdiffuse\u201d aurora <\/span>usually have<\/span><\/a> little motion, are quite dim, and might even be confused with clouds.)<\/span><\/p>\n

In this post, we\u2019ll talk from a Western science perspective (which is one of <\/span>many<\/span><\/a>) about some of the characteristics of these showy, dancing ribbons in the sky.\u00a0<\/span><\/p>\n

How do we know about discrete aurora?<\/b><\/h2>\n

Want to learn more? Check out our Journal Club <\/span><\/i>reading<\/span><\/i><\/a> video of the classic article \u201c<\/span><\/i>Observed Characteristics of Auroral Forms<\/span><\/i><\/a>\u201d by T. Neil Davis<\/span><\/i><\/p>\n

People have observed the aurora and <\/span>developed knowledge<\/span><\/a> about it for millennia. Relatively recently, videography and satellite observations have added additional perspectives. In the 1970s, around the same time that scientists were beginning to be able to film aurora from the ground, the satellites <\/span>Isis II<\/span><\/a>\u00a0and DMSP were some of the first to be able to take photos from space of auroras shining over wide areas. Looking at images from Isis 2, scientists noticed bright, ribbonlike auroras toward the poles, and dimmer, foggy, cloudlike auroras toward the equator. They named the bright ribbons \u201cdiscrete auroras,\u201d and the cloudlike lights \u201cdiffuse auroras\u201d. Since then, other rockets, planes, and spacecraft have taken to the skies, with different instruments that measure aurora in different ways. These measurements can be paired with ground-based photographs to analyze auroral structures\u2014but this is extremely difficult to do because with an ever-changing aurora, the timing needs to be very exact.<\/span><\/p>\n

\"Satellite<\/a>
Satellite image<\/a> by the Suomi NPP satellite showing bright discrete aurora with fainter diffuse aurora to the south. Note that the discrete auroras are thin across the arc and long along a continental scale.<\/figcaption><\/figure>\n

What are some characteristics of discrete aurora?<\/b><\/h2>\n

The distinctive appearance of discrete aurora generally graces the most impressive aurora photos. Important characteristics include:<\/span><\/p>\n