I might be stupid, but still the passion to learn...

[JPMK]

Hello! 

I'm a long time lurker trying to decrypt what you guys are writing and everytime I visit the forums I learn something new. 

I have read the FAQ / HELP on SWL atleast 10 times and I still dont understand the graphs well enough to make "educated" guesses. The purpose of me learning this is my passion for stars, night skies and the aurora. What I seem to not understand is what impact every parameter has on the strength of the aurora. I think I have watched every youtube video, read every FAQ/Help forum there is, read ALOT of threads on forums and generally just trying to discover more about the aurora all the time. Still no success. 

 

So, here's to my request. Is there anyone out there wiling to explain this to me in a more "educated" way, ELI5 almost  

Top of mind right now:

• How does the density impact the strength of the aurora
• How does the speed impact the aurora(I read sometimes that the speed should be high, and sometimes I read that the speed does not need to be high to get a visible aurora)
• Is it possible to follow the storm? e.g. Lets say that it's been M activity from the sun and the activity starts as a C flare at 10:00 01-01-2022 UTC and M flare at 17:00 01-01-2022UTC. Is it possible somehow to "translate" those hours to earths hours? I understand that we need to get info on if the flare is earth directed(?), when it's confirmed to be earth directed we have the ACE satelite to measure data from. Lets say that the C flare reaches ACE at 15:00 03-01-2022, can we say with certainty when the M flare will reach? Or is it just a waiting game? 
• Are ACE the only indication on plausible aurora activity?
• Is it possible to determine the color of the aurora?

You see, I have many questions yet so little answers....

I'm living in the southern parts of Sweden with alot of sightings recently, super glad for that! 

The photo is from 5th march 2022! 

[KW2P]

I look forward to responses to your questions from people who know more than I.  I've been watching the sun's behavior for decades but with a very narrow and simplistic interest: radio propagation.  Only recently have I taken an interest in the how and why, not just the what.  Thank you for asking those questions because I don't know the answers.

/phil

 

[Sam Warfel]

8 hours ago, JPMK said:

How does the density impact the strength of the aurora

How does the speed impact the aurora

Density, along with speed, are simply the amount of charged particles in the solar wind, and how fast they are flowing.  Because those charged particles are what create aurora, the lights can be stronger if one or both are higher.  That being said, these are not the only important parameters.  Many different factors work together in concert to determine the strength of the auroras, namely the solar wind (speed and density, as discussed), and the IMF, or Interplanetary Magnetic Field.  The IMF parameters such as Bt (magnetic field strength) and Bz (magnetic field direction) are also very important.  No one factor can make or break a display all by itself, you need to consider them together.  For example, consider a CME that boosts the solar wind speed to a fast 700 and density to 40.  This could power a strong display.  But if the Bz is oriented northward, strong auroras will not develop, even with this high speed and density.  If the Bz is southward and strongly so, then combined with the high speed and density a strong aurora will develop.  However, an aurora can develop if the Bz is southward even when the SW speed and density are not as high.
Basically, they all work together.  The more that are the favorable the better, but they don't all have to be.

Quote

Is it possible to follow the storm? e.g. Lets say that it's been M activity from the sun and the activity starts as a C flare at 10:00 01-01-2022 UTC and M flare at 17:00 01-01-2022UTC. Is it possible somehow to "translate" those hours to earths hours? I understand that we need to get info on if the flare is earth directed(?), when it's confirmed to be earth directed we have the ACE satelite to measure data from. Lets say that the C flare reaches ACE at 15:00 03-01-2022, can we say with certainty when the M flare will reach? Or is it just a waiting game? 

I think by "flare" you mean a CME, the cloud of charged particles often propelled by a flare.  In the solar wind, think of a CME as a big gust or puff of wind.  If we see a flare on the sun, as measured by the amount of X-rays it gives off (C-class, M-class, X-class, etc.) we can see how powerful a flare was.  This is seen in close to real time, as it takes 5 minutes for the x-rays to travel from the sun to earth at the speed of light.
Now, sometimes a flare launches a CME.  It doesn't always do it, but in general, the stronger the flare, the better the odds, and the stronger the CME.  The CMEs are what we're interested in, because they cause the largest displays of the Aurora here on Earth.  CMEs travel much slower than the speed of light, about 600 to 1500+ km/s, on average.  This means they take a few days to travel from the sun to the Earth.

Predicting the arrival time is difficult, because we cannot tell for sure how fast a CME was going when it left the sun, nor how much it will slow down on the way to Earth.  In fact, we can't always tell if it's going to hit Earth or not.  Our only monitoring data comes from spacecraft at L1 (google if you want), which is so close to Earth it only gives us data about a half hour to an hour ahead of Earth.  If we could measure a CME somewhere closer to the Sun we could make more precise estimates of when it will arrive at Earth, but we don't have spacecraft for that right now.  Orbital mechanics makes it difficult.

You mentioned using a previous flare (by which you probably mean CME) to guess at the travel time of a following one.  Unfortunately, all CMEs are different and launched differently, so we can't really correlate them directly.

Quote

Are ACE the only indication on plausible aurora activity?

Our main data actually comes from DSCOVR, a similar spacecraft to ACE but newer, more reliable, and higher quality, positioned in the same general area as ACE.  ACE continues to function as a backup.
Yes, this data (solar wind speed and density, IMF strength and direction) is the main indicators of aurora visibility.  This is what the Auroral Oval and Hemispheric Power models use to calculate their predictions of aurora strength/visibility, and are the main thing I look at to determine if I should look for the Aurora.  That being said, it's not the only data, the magnetometers located on the ground on Earth can also indicate geomagnetic activity in the same general area as the magnetometer doing the measuring.  This can help predict auroras, if the magnetometer is close to you, but it does have the downside of not offering any lead time, as the data from DSCOVR at L1 does (30-60 mins).  Mostly, I look at the DSCOVR data.

Quote

Is it possible to determine the color of the aurora?

Not predict per se, but we do know some of what influences it.  Green is the typical color, caused by exciting oxygen molecules at a certain altitude. The other colors, especially red and pink, are caused by exciting of oxygen at different altitudes.  In general, only the stronger storms produce these colors, it takes more energy in those charged particles to excite the red color, or them to penetrate deeper in the atmosphere.  So we can't predict it, but we can say that if there's a strong storm going on, the odds of getting colors other than green are higher than they would be normally, although we can't say they will be there for sure.

 

I hope all that helps!  Kind of a lot to read.

[JPMK]

2 hours ago, Orneno said:

Density, along with speed, are simply the amount of charged particles in the solar wind, and how fast they are flowing.  Because those charged particles are what create aurora, the lights can be stronger if one or both are higher.  That being said, these are not the only important parameters.  Many different factors work together in concert to determine the strength of the auroras, namely the solar wind (speed and density, as discussed), and the IMF, or Interplanetary Magnetic Field.  The IMF parameters such as Bt (magnetic field strength) and Bz (magnetic field direction) are also very important.  No one factor can make or break a display all by itself, you need to consider them together.  For example, consider a CME that boosts the solar wind speed to a fast 700 and density to 40.  This could power a strong display.  But if the Bz is oriented northward, strong auroras will not develop, even with this high speed and density.  If the Bz is southward and strongly so, then combined with the high speed and density a strong aurora will develop.  However, an aurora can develop if the Bz is southward even when the SW speed and density are not as high.
Basically, they all work together.  The more that are the favorable the better, but they don't all have to be.

 

I think by "flare" you mean a CME, the cloud of charged particles often propelled by a flare.  In the solar wind, think of a CME as a big gust or puff of wind.  If we see a flare on the sun, as measured by the amount of X-rays it gives off (C-class, M-class, X-class, etc.) we can see how powerful a flare was.  This is seen in close to real time, as it takes 5 minutes for the x-rays to travel from the sun to earth at the speed of light.
Now, sometimes a flare launches a CME.  It doesn't always do it, but in general, the stronger the flare, the better the odds, and the stronger the CME.  The CMEs are what we're interested in, because they cause the largest displays of the Aurora here on Earth.  CMEs travel much slower than the speed of light, about 600 to 1500+ km/s, on average.  This means they take a few days to travel from the sun to the Earth.

Predicting the arrival time is difficult, because we cannot tell for sure how fast a CME was going when it left the sun, nor how much it will slow down on the way to Earth.  In fact, we can't always tell if it's going to hit Earth or not.  Our only monitoring data comes from spacecraft at L1 (google if you want), which is so close to Earth it only gives us data about a half hour to an hour ahead of Earth.  If we could measure a CME somewhere closer to the Sun we could make more precise estimates of when it will arrive at Earth, but we don't have spacecraft for that right now.  Orbital mechanics makes it difficult.

You mentioned using a previous flare (by which you probably mean CME) to guess at the travel time of a following one.  Unfortunately, all CMEs are different and launched differently, so we can't really correlate them directly.

 

Our main data actually comes from DSCOVR, a similar spacecraft to ACE but newer, more reliable, and higher quality, positioned in the same general area as ACE.  ACE continues to function as a backup.
Yes, this data (solar wind speed and density, IMF strength and direction) is the main indicators of aurora visibility.  This is what the Auroral Oval and Hemispheric Power models use to calculate their predictions of aurora strength/visibility, and are the main thing I look at to determine if I should look for the Aurora.  That being said, it's not the only data, the magnetometers located on the ground on Earth can also indicate geomagnetic activity in the same general area as the magnetometer doing the measuring.  This can help predict auroras, if the magnetometer is close to you, but it does have the downside of not offering any lead time, as the data from DSCOVR at L1 does (30-60 mins).  Mostly, I look at the DSCOVR data.

Not predict per se, but we do know some of what influences it.  Green is the typical color, caused by exciting oxygen molecules at a certain altitude. The other colors, especially red and pink, are caused by exciting of oxygen at different altitudes.  In general, only the stronger storms produce these colors, it takes more energy in those charged particles to excite the red color, or them to penetrate deeper in the atmosphere.  So we can't predict it, but we can say that if there's a strong storm going on, the odds of getting colors other than green are higher than they would be normally, although we can't say they will be there for sure.

 

I hope all that helps!  Kind of a lot to read.

WOW! Im blown away. Thank you very much for taking time to respond. 
 

I still have a question unanswered: Is it possible to follow the storm? e.g. Lets say that it's been M activity from the sun and the activity starts as a C flare at 10:00 01-01-2022 UTC and M flare at 17:00 01-01-2022UTC. Is it possible somehow to "translate" those hours to earths hours? I understand that we need to get info on if the flare is earth directed(?), when it's confirmed to be earth directed we have the ACE satelite to measure data from. Lets say that the C flare reaches ACE at 15:00 03-01-2022, can we say with certainty when the M flare will reach? Or is it just a waiting game? 

 

I think I mean that if we see that DISCOVR gets data that a CME is on its way can we predict the strength  of the Aurora due to the different Gusts the C/M gusts. 
 

C-Class 2.5 01-01-2022 - 08:35

C-Class 1.5 01-01-2022 - 10:20

C-Class 0.8 01-01-2022 - 13:00

M-Class 9.1 01-01-2022 - 15:00

X-Class 10.7 01-01-2022 - 17:00

DISCOVR picks up data, can we see which one of these gusts it is? So let’s say that we pick up data and it indicates that it’s the C class 2.5. Can we then say that the northern lights will be amazing at 9 hours later because we had X-Class 9 hours delayed from first C-Class. 

[hamateur 1953]

wow Im guessing Orneno has seen the magnetometer display by now I hope I hope Dr Tamitiha Skov space weather woman just uploaded a beautiful video and coming attractions FY all of y’all Information!! 

oops yet again. let me state most emphatically, I only know of Dr Skov by virtue of discovery through this site alone. No shill or relative of hers am I ( though wish I were younger hah!) 

[Sam Warfel]

6 hours ago, JPMK said:

DISCOVR picks up data, can we see which one of these gusts it is? So let’s say that we pick up data and it indicates that it’s the C class 2.5. Can we then say that the northern lights will be amazing at 9 hours later because we had X-Class 9 hours delayed from first C-Class. 

No, it doesn’t really work that way. Because each CME is different, just because a CME from a flare two hours before another flare/CME was launched doesn’t mean that CME will arrive two hours after the first. They all travel at different speeds, and different directions, many don’t even hit earth at all. So, if the second CME was faster, it could overtake and swallow the earlier one and get there sooner, or if it was slower, it could arrive way more than two hours after the first, or if it’s not quite Earth directed it may never arrive at all. We can’t tell until it reaches DSCOVR/ACE, only less than an hour out from Earth. 

[JPMK]

17 minutes ago, Orneno said:

No, it doesn’t really work that way. Because each CME is different, just because a CME from a flare two hours before another flare/CME was launched doesn’t mean that CME will arrive two hours after the first. They all travel at different speeds, and different directions, many don’t even hit earth at all. So, if the second CME was faster, it could overtake and swallow the earlier one and get there sooner, or if it was slower, it could arrive way more than two hours after the first, or if it’s not quite Earth directed it may never arrive at all. We can’t tell until it reaches DSCOVR/ACE, only less than an hour out from Earth. 

That's super helpful! Again, thank you very much!!

[Cat Perkinton]

Thanks @JPMK for asking the questions & @Orneno for answering so succintly. Good to know some things I did not & also to have some things I thought I knew confirmed too. Hurrah for "Things & the knowing"!