Hi
from the Norwegian magnetometers I deduct that a large substorm is in progress over Norway.
I'd say northern lights can be visible now up to 35 degrees from northern Germany.
Amsterdam 8/8
JanL
http://geo.phys.uit.no/stack/stackH.html
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jan lameer
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Ulrich Rieth
SUBJECT>Re: 21:20 UT substorm Norway >500nT
Hi Jan!
: I'd say northern lights can be visible now up to 35 degrees from
: northern Germany.
I don't think so.
The drop in the H component of the Norwegian magnetometers was just way too slow. It took more than an hour to reach those -500nT (e.g. in Kiruna).
If such a -500nT in X/H together with a rise in Z happens within minutes, you might be right with the 35 degree elevation display, but with such a slow decline I would not expect any sighting possibility from a location south of Stockholm or even furthern north.
The solar wind is just too slow to give us a good auroral display.
If you take a look at the Sodankylä all-sky camera, you will see, that the substorm was really bright, but you will also see, that it "only" reached the zenith up there. For a display visible in lower mid latitudes the main activity in Sodankylä has to happen in the southern part of the all-sky image.
Clear skies!
Ulrich
Hi Jan!
: I'd say northern lights can be visible now up to 35 degrees from
: northern Germany.
I don't think so.
The drop in the H component of the Norwegian magnetometers was just way too slow. It took more than an hour to reach those -500nT (e.g. in Kiruna).
If such a -500nT in X/H together with a rise in Z happens within minutes, you might be right with the 35 degree elevation display, but with such a slow decline I would not expect any sighting possibility from a location south of Stockholm or even furthern north.
The solar wind is just too slow to give us a good auroral display.
If you take a look at the Sodankylä all-sky camera, you will see, that the substorm was really bright, but you will also see, that it "only" reached the zenith up there. For a display visible in lower mid latitudes the main activity in Sodankylä has to happen in the southern part of the all-sky image.
Clear skies!
Ulrich
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jan lameer
SUBJECT>Re: 21:20 UT substorm Norway >500nT *LINK*
Hi Ulrich !
Ah, your explanation makes sense.
But I still think this would mean at least photographic aurora from Terschelling. Red arc with occasional yellow beams low over the horizon.
I wish I was there now with the camera to empirically prove it ...
But I've archived the magnetometer diagram and will compare it sometime in the future with the nights that I recorded photographic aurora.
It's a pity I cannot make it to the AKM weekend.
We had a Dutch polar meeting in December last year, it was very nice (I gave a half hour talk on aurora from the Netherlands) but it only was one afternoon, which was way to short.
Ehm, question: when ACE measures Bz as -10nT and 300 km/s, how does this relate to -10nT and 600 km/s ?
Velocity squared, velocity linear or velocity independent ?
greetings, JanL
Hi Ulrich !
Ah, your explanation makes sense.
But I still think this would mean at least photographic aurora from Terschelling. Red arc with occasional yellow beams low over the horizon.
I wish I was there now with the camera to empirically prove it ...
But I've archived the magnetometer diagram and will compare it sometime in the future with the nights that I recorded photographic aurora.
It's a pity I cannot make it to the AKM weekend.
We had a Dutch polar meeting in December last year, it was very nice (I gave a half hour talk on aurora from the Netherlands) but it only was one afternoon, which was way to short.
Ehm, question: when ACE measures Bz as -10nT and 300 km/s, how does this relate to -10nT and 600 km/s ?
Velocity squared, velocity linear or velocity independent ?
greetings, JanL
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Dirk
SUBJECT>Re: 21:20 UT substorm Norway >500nT *LINK*
: Ehm, question: when ACE measures Bz as -10nT and 300 km/s, how does
: this relate to -10nT and 600 km/s ?
: Velocity squared, velocity linear or velocity independent ?
This was one of the first questions that people working on substroms asked themselves after Syun Akasofu "discovered" the substrom. Back then there wasn't a satellite in the solar wind, of course. But when satellite measurements of the solar wind became available, and theories about how substroms work became better, several people came up with simple formulas to estimate the energy transfer from the solar wind to the magnetosphere. One of the most persistent formulas for this is the "epsilon parameter" which Syun Akasofu devised in 1978 (actually, it was his student, Perrault, who did the work). This is essentially
v B2 sin4(theta/2)
where the angle theta is measured between By and Bz. However, a shortened epsilon, just v B2 also works fine (for Bz negative only).
--Dirk
: Ehm, question: when ACE measures Bz as -10nT and 300 km/s, how does
: this relate to -10nT and 600 km/s ?
: Velocity squared, velocity linear or velocity independent ?
This was one of the first questions that people working on substroms asked themselves after Syun Akasofu "discovered" the substrom. Back then there wasn't a satellite in the solar wind, of course. But when satellite measurements of the solar wind became available, and theories about how substroms work became better, several people came up with simple formulas to estimate the energy transfer from the solar wind to the magnetosphere. One of the most persistent formulas for this is the "epsilon parameter" which Syun Akasofu devised in 1978 (actually, it was his student, Perrault, who did the work). This is essentially
v B2 sin4(theta/2)
where the angle theta is measured between By and Bz. However, a shortened epsilon, just v B2 also works fine (for Bz negative only).
--Dirk
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jan lameer
SUBJECT>Re: 21:20 UT substorm Norway >500nT
Thanks Dirk !
So it figures out that Ulrich was right in his theoretical prediction (v low so no substorms likely) and I was right in my empirically prediction (widespread disturbance over Norway >500nT, so weak aurora up to 35 degrees should be visible from Terschelling, Netherlands and Schottland under very dark skies, confirmed by 2 observations from Schotland; Netherlands under thick cloudcover).
I've a couple of "proceedings" at home about the solar wind ('70-s, Spacelab sat. obs.) that I bought for little money from the Amsterdam U. Pannekoek Astronomy. One line was said a few times then: "How do we relate this mysterious Bz measured, to what we observe on earth ?".
New to me is the idea that Cary Oler (STD) revealed on his www.spacew.com forum that in spring and autumn substorms are more likely because both the northern and southern hemisphere have half night and day. Makes a lot of sense, when thinking of currents flowing through the atmosphere.
But when digging into this matter, I always end up with quite difficult charged particle fluid flowing dynamics that has only a few solutions here and there.
Visual aurora is only one of those solutions, photographic or radio aurora another etc.
Oh well, greetings,
Jan Lameer
Thanks Dirk !
So it figures out that Ulrich was right in his theoretical prediction (v low so no substorms likely) and I was right in my empirically prediction (widespread disturbance over Norway >500nT, so weak aurora up to 35 degrees should be visible from Terschelling, Netherlands and Schottland under very dark skies, confirmed by 2 observations from Schotland; Netherlands under thick cloudcover).
I've a couple of "proceedings" at home about the solar wind ('70-s, Spacelab sat. obs.) that I bought for little money from the Amsterdam U. Pannekoek Astronomy. One line was said a few times then: "How do we relate this mysterious Bz measured, to what we observe on earth ?".
New to me is the idea that Cary Oler (STD) revealed on his www.spacew.com forum that in spring and autumn substorms are more likely because both the northern and southern hemisphere have half night and day. Makes a lot of sense, when thinking of currents flowing through the atmosphere.
But when digging into this matter, I always end up with quite difficult charged particle fluid flowing dynamics that has only a few solutions here and there.
Visual aurora is only one of those solutions, photographic or radio aurora another etc.
Oh well, greetings,
Jan Lameer
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