What Does Unusual Auroral Activity Mean in Astronomy?

[CallMeSusan]

Hi,

I am a newbie trying out astronomy after two decades of politics, but I was hoping if someone could help translate the following statement for me (I am not a student, so your not answering an essay question or anything);

We report unusual auroral features observed by the DMSP-F6 satellite on January 10 and 11. These features include the shift of the most active region to the morning sector, the shift of the polar cap center toward the evening sector, a large number of sun-earth aligned arcs and the oval-shaped diffuse glow without bright oval arcs. The simultaneous magnetic field observations by the ISEE-3 and IMP-8 satellites, together with a simple magnetospheric modeling result, suggest that the unusual features result from both the unusually large BY and a large positive Bz component of the IMF.

The italic/bold section confuses me somewhat. The answer (the last sentence) doesn't really explain it.

 

[jim mcnamara]

Welcome to Physics Forums.

A page that explains the Interplanetary Magnetic field

http://www.spaceweatherlive.com/en/help/the-interplanetary-magnetic-field-imf

The aurora we see on Earth is the result of "stuff" that is ejected from the sun interacting, way up high, with atoms in Earth's atmosphere. The atoms become excited and give off light. The "stuff" is made of charged particles. The particles, because they have a charge, are affected by Earth's magnetic field and the IMF.

What the bold part talks about, in part, is the areas of the auroral glow are not where they usually are. The morning sector is the area where sunrise is happening on Earth -- looking down onto the North (or South Pole). The polar sector is directly over the pole. You can guess what the evening sector is.

The auroral display has features like arcs, glow, striations. If you have not been to the far North or South you probably have not seen them. They are wonderful.
http://en.wikipedia.org/wiki/Aurora_(astronomy )

The bold section is talking about displays that are out of the ordinary and are in places where they may not normally be seen.

The Bx, By, and Bz are vector components (think of a vector as direction and velocity like your car on the highway) that make up the IMF. The vector has 3 dimensions: (B)x,(B)y and (B)z. The article is saying that changes in magnitudes of Bz and By caused the unusual aurora.

Space Weather (the charged particles, and the IMF) is very important to satellite communications.

 

[CallMeSusan]

Thanks Jim, I appreciate the clarity. I understand that the date of the journal article is quite old (1983) - would you know, by any chance, whether activity such as this often occurs, or was it quite unique for that day/moment (as in the shift of the most active region to the morning sector etc)? I only ask this because I am confused as to why this is "unusual".

 

[jim mcnamara]

Space Weather is a fairly young, evolving science, so some of their observations and goals have been moving targets, so to speak. I do not know whether this was a one time anomaly or not. As a guess I would say no.

The current Maunder cycle -- 24 -- (sunspot cycles influence aurora intensity) is weak, so if there are going to be anomalies, this may be a chance to see them. According to the report:

http://solarscience.msfc.nasa.gov/SunspotCycle.shtmlSunspot numbers and solar output appear to be declining. The report makes an analogy between the current trend and sunspot numbers in the late 17th Century.

 

[pmacias]

Hello,

Unusual auroral activity refers to a rare occurrence of auroras, also known as the Northern or Southern Lights, which are caused by charged particles from the sun interacting with the Earth's atmosphere. In this case, the DMSP-F6 satellite observed unusual features on January 10 and 11, including a shift in the most active region to the morning sector, a shift in the polar cap center towards the evening sector, and a large number of sun-earth aligned arcs. Additionally, there was a diffuse glow without the presence of bright oval arcs. These features were likely caused by a combination of two factors: an unusually large BY component of the Earth's magnetic field and a large positive Bz component of the interplanetary magnetic field (IMF). The magnetic field observations from the ISEE-3 and IMP-8 satellites, along with a simple model of the magnetosphere, support this explanation. Essentially, the unusual features in the aurora were a result of the unique magnetic conditions in the Earth's environment at that time. I hope this helps clarify the statement for you.