Do northern lights (aurora borealis) show the same visual activity all along their visible latitude range?

[mason]

Hello,

probability aside regarding their visibility (I did read on Neil Davies Aurora watcher's handbook that probability is highest in the middle of thieir latitude range called aurora oval, lowering both north and south of it), do they show the same visual effects all along their latitude range?

Is it just the angle compared to the viewer that would change (closer to the middle of their range = seeing them overhead, farther from the middle range = seeing them across the horizon)?

 

For example, during a geomagnetic storm that NOAA classifies as 3 (Kp=7), what would be the visual difference between a viewer located at the limiting visibility latitude of Kp=5 and Kp=3?

Would the visibility oval shift southward instead of increasing in width and hence also shift the middle of its visibility latitude range southwards?
Animations I have seen on NOAA 30 minutes forecast seem to support the latter, however it was just eyeballed and not quantitatively assessed.

Weather conditions all the same, is the best viewing line in the middle of the latitude range or is it simply the most probable line in which it'd be visible? Or would it have added benefits other than probability?

Thank you

[Christopher S.]

The latitude does not necessarily determine the colors of the Aurora, if that is what you are asking. Look over this informational PDF: https://pwg.gsfc.nasa.gov/polar/telecons/archive/PR_E-PO/Aurora_flyer/aurora-flyer_p2.doc.pdf

The perspective of the Aurora is the only thing that changes with viewing angle; There is no redshift from different angles, and no extra stage of refraction to an observer far away from the visible Aurora. The parts of the Aurora you see from your viewing angle may reveal features that are not visible from another person's viewing angle, since this phenomenon occurs in three-dimensional space.

The colors depicted in "Auroral Ovals" represent probability of the Aurora being visible, not actually the colors of the Aurora itself.

[mason]

2 hours ago, Christopher S. said:

The latitude does not necessarily determine the colors of the Aurora, if that is what you are asking. Look over this informational PDF: https://pwg.gsfc.nasa.gov/polar/telecons/archive/PR_E-PO/Aurora_flyer/aurora-flyer_p2.doc.pdf

The perspective of the Aurora is the only thing that changes with viewing angle; There is no redshift from different angles, and no extra stage of refraction to an observer far away from the visible Aurora. The parts of the Aurora you see from your viewing angle may reveal features that are not visible from another person's viewing angle, since this phenomenon occurs in three-dimensional space.

The colors depicted in "Auroral Ovals" represent probability of the Aurora being visible, not actually the colors of the Aurora itself.

I see, thank you. What about shapes, brightness and shapeshifting speed? Would these vary at different viewing latitudes or would they just relate to solar wind speed and storm intensity?

[Vancanneyt Sander]

I live in the lower middle latitude, meaning i need at least Kp 7/8 to have a little chance of seeing it. If the magnetometers readings are good for my location i would be able to see it near the northern horizon but nothing fancy. For my location the display is more red than green because that part is still below horizon. Even in a huge event, i would still look from the side so i won't be able to see the curtains but it does give more colors.

Few examples from the Netherlands:

 

[Christopher S.]

Ah, so I suppose when the aurora is near the horizon, it can blue- or red-shift.

[Marcel de Bont]

8 uren geleden, Christopher S. zei:

Ah, so I suppose when the aurora is near the horizon, it can blue- or red-shift.

I dont think so. The colour just depends on at what altitude the aurora is occurring. I am not 100% sure about the exact altitudes but I think its below 85 kilometers for purple. Between like 85 kilometers and 200 kilometers for green and above that red. A quick Google search should give you exact numbers I might be wrong about the exact altitudes. If the aurora is extremely bright some of the greens can become almost white from my experience but this lasts at most seconds. I haven't seen blue aurora but heard reports about it. The aurora can absolutely be more intense from one place to another. Local stronger geomagnetic disturbances are not uncommon. Also keep in mind the auroral oval is at its thickest and this stretches to lower latitudes near magnetic midnight.

[Christopher S.]

3 hours ago, Marcel de Bont said:

I dont think so. The colour just depends on at what altitude the aurora is occurring. I am not 100% sure about the exact altitudes but I think its below 85 kilometers for purple. Between like 85 kilometers and 200 kilometers for green and above that red. A quick Google search should give you exact numbers I might be wrong about the exact altitudes. If the aurora is extremely bright some of the greens can become almost white from my experience but this lasts at most seconds. I haven't seen blue aurora but heard reports about it. The aurora can absolutely be more intense from one place to another. Local stronger geomagnetic disturbances are not uncommon. Also keep in mind the auroral oval is at its thickest and this stretches to lower latitudes near magnetic midnight.

In the PDF I linked, sourced directly from NASA, the colors indicate the kinds of gas particles that are being excited. Are you sure about what you're saying?

Also, it isn't a question of where the aurora itself is occurring which determines what an observer sees, it is an observers location relative to the aurora.

[Jeremiah in AK]

There isn't much consistent in anything about the aurora so simplifying any prediction to fit an entire latitude seems very unlikely. 

45 minutes ago, Christopher S. said:

In the PDF I linked, sourced directly from NASA, the colors indicate the kinds of gas particles that are being excited. Are you sure about what you're saying?

Also, it isn't a question of where the aurora itself is occurring which determines what an observer sees, it is an observers location relative to the aurora.

The altitude does in fact have an impact on the colors and yes he's right, it has to do with which elements are present, namely oxygen and nitrogen, and the reason the altitude has an effect is because different levels o the atmosphere have different compositions. A quote from wikipedia: "This is why there is a color differential with altitude; at high altitudes oxygen red dominates, then oxygen green and nitrogen blue/purple/red, then finally nitrogen blue/purple/red when collisions prevent oxygen from emitting anything. Green is the most common color. Then comes pink, a mixture of light green and red, followed by pure red, then yellow (a mixture of red and green), and finally, pure blue." 
 

So yes, it's all about the altitude of where the solar wind is interacting with the atmosphere and nothing to do with its relative position related to the horizon.
 

[Christopher S.]

14 hours ago, Jeremiah in AK said:

There isn't much consistent in anything about the aurora so simplifying any prediction to fit an entire latitude seems very unlikely. 

The altitude does in fact have an impact on the colors and yes he's right, it has to do with which elements are present, namely oxygen and nitrogen, and the reason the altitude has an effect is because different levels o the atmosphere have different compositions. A quote from wikipedia: "This is why there is a color differential with altitude; at high altitudes oxygen red dominates, then oxygen green and nitrogen blue/purple/red, then finally nitrogen blue/purple/red when collisions prevent oxygen from emitting anything. Green is the most common color. Then comes pink, a mixture of light green and red, followed by pure red, then yellow (a mixture of red and green), and finally, pure blue." 
 

So yes, it's all about the altitude of where the solar wind is interacting with the atmosphere and nothing to do with its relative position related to the horizon.
 

I'm not the one asking if latitude determines what an observer sees - see first two posts. Altitude does not necessarily determine the colors of the aurora, it is the gaseous composition at those altitudes which is the main factor. It is subject to change with meteorological phenomenon.

[Marcel de Bont]

15 uren geleden, Jeremiah in AK zei:

There isn't much consistent in anything about the aurora so simplifying any prediction to fit an entire latitude seems very unlikely. 

The altitude does in fact have an impact on the colors and yes he's right, it has to do with which elements are present, namely oxygen and nitrogen, and the reason the altitude has an effect is because different levels o the atmosphere have different compositions. A quote from wikipedia: "This is why there is a color differential with altitude; at high altitudes oxygen red dominates, then oxygen green and nitrogen blue/purple/red, then finally nitrogen blue/purple/red when collisions prevent oxygen from emitting anything. Green is the most common color. Then comes pink, a mixture of light green and red, followed by pure red, then yellow (a mixture of red and green), and finally, pure blue." 
 

So yes, it's all about the altitude of where the solar wind is interacting with the atmosphere and nothing to do with its relative position related to the horizon.
 

You are very much correct. Also keep in mind that due to the curvature of our planet, if you look from very far away (thus the aurora is low on the horizon for the observer) you will more likely see the top of the aurora: the red colours. These are also harder to spot for the naked eye than greens but with a DSLR you will more easily see the aurora. When the aurora comes closer and closer to the observers position you will start to see the greens.

You are right that the gaseous composition determines the colors of the aurora but Earth's weather is not a factor at such high altitudes. We are talking about the edge of space and space itself. What angle you are watching the aurora from should not cause it to shift in color from one observer to the other.

[northwind-adventurer]

 

On 2/10/2020 at 10:57 AM, mason said:

 

For example, during a geomagnetic storm that NOAA classifies as 3 (Kp=7), what would be the visual difference between a viewer located at the limiting visibility latitude of Kp=5 and Kp=3?

 

Most likely, the viewer standing at the KP5 location, given clear skies, would see bright aurora spread across most of the sky, whereas the viewer at the KP3 location would see aurora across most of the sky, but tending towards the equator-ward direction. Sometimes this might mean that in the northern hemisphere during a KP7 storm someone at this location would see northern lights entirely in the southern sky.

It's also worth noting that along with angles/colours, a stronger geomagnetic storm (higher KP) will generally mean more active displays and the potential for faster movement and greater 'brightness' regardless of which latitude you watch it from.

To give an example of a relevant situation, the below image shows the auroral oval by VIIRS satellite over North America on 9 September 2015, during a KP6 Geomagnetic storm. You can see that the aurora is pretty much overhead at the KP5 line, but someone from the KP6 or KP7 line would definitely be able to see the aurora if they have clear skies.