Wait a minute... maybe we WILL see a little aurora tonight, March 13-14

A series of rays or pillars with pink tops and green bottoms dance along the northern horizon Friday night, March 12, 2021. Both colors are caused by the excitation of oxygen atoms as they're bombarded by solar electrons. It's a battle out there! Bob King


The northern border states may been in for another, albeit small, aurora display tonight, March 13-14. The latest 3-day forecast from NOAA's space weather gurus fires my optimism.

Over the years, I've used Kp 5 as the minimum indicator of magnetic hullabaloo that has to occur before the aurora shows up in the Duluth, Minn. region, but lately I've noticed that sometimes we'll get good activity — low bright arcs and faint rays — when Kp = 4. Just to refresh, Kp is a number from 0 to 9 that indicates how disturbed Earth's magnetic field becomes when it's affected by particle blasts from the sun. Those include material ejected during solar flare eruptions and from coronal holes.

Kp is an index of activity in Earth's magnetic bubble called the magnetosphere. It's measured by multiple magnetometers at different locations around the planet. NOAA

Kp = 1 indicates calm, while 5 means a minor geomagnetic storm is underway. As you can imagine, a Kp 9 is serious event with extensive auroras. One such storm in 1989 created an auroral tsunami that brought the northern lights all the way down to Cuba.

Faint rays appear above a set of brighter ones during last night's aurora. Cameras record auroral colors vividly. With the eye alone the arc appeared pale green, while the rays were colorless. Bob King

Although last night's aurora was originally forecast to be a Kp 5 or minor geomagnetic storm event, it was downgraded to a 4. Yet the aurora was still a wonderful sight from the countryside. Earlier this afternoon, the NOAA forecast predicted a peak Kp of just 3 for this evening (March 13). But the latest forecast tonight was just upgraded to Kp 4 between 9 p.m. and midnight Central Standard Time. Daylight Saving Time begins at 2 a.m. Sunday, March 14.

So maybe, just maybe observers in the northern U.S. will get treated to another small but pretty display of northern lights Saturday night (March 13). I hope it happens, and I hope you see it!

Comments

  1. ClarenceMarch 13, 2021 at 7:15 PM

    Hello, Mr. King. I hope you and yours are doing well. I’m also hoping I can articulate my question well enough for you to answer it. My question is about the map image available at

    https://services.swpc.noaa.gov/images/aurora-forecast-northern-hemisphere.jpg

    I’m wondering: Does the map mark places on Earth’s surface (places on the ground) from which the aurora might be visible, or does the map mark places above Earth’s surface where the aurora itself might be located? If the latter, does the aurora’s luminosity tend to emanate from altitudes that would allow it to be visible from significantly south of the areas marked on the map? I’m ultimately asking if the western tip of Lake Superior needs to be covered/colored on this map for someone to have a chance to see the aurora from Duluth, or if instead the map functions such that someone in Duluth would have a chance to see the aurora if the covered/colored area of the map makes it down, say, toward the U.S.-Canada border.

    ReplyDelete
    Replies
    1. Bob KingMay 27, 2021 at 7:37 AM

      Hi Clarence,
      I apologize for not seeing your comment until now. The map shows where the aurora is located above the Earth's surface, but since it's so high, it can be hovering over southern Canada and still be visible from western Lake Superior. That means that the aurora doesn't have to be directly over Duluth, say, in order to see it. There are times however when it is directly over Duluth. Those times it fills both the northern and southern sky.

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