In article , "starman"
wrote:

Great report. Are these events more likely to happen during the decline
of a solar cycle?

Yes. In the declining part of the cycle flares are generally less frequent
but more energetic.

--
| John Doty "You can't confuse me, that's my job."
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John Doty wrote:

In article , "starman"
wrote:

Great report. Are these events more likely to happen during the decline
of a solar cycle?

Yes. In the declining part of the cycle flares are generally less frequent
but more energetic.

Is that because the magnetic field lines become more 'twisted' (for lack
of a better word) during the declining phase of the cycle?


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In article , "starman"
wrote:

John Doty wrote:

In article , "starman"
wrote:

Great report. Are these events more likely to happen during the
decline of a solar cycle?

Yes. In the declining part of the cycle flares are generally less
frequent but more energetic.

Is that because the magnetic field lines become more 'twisted' (for lack
of a better word) during the declining phase of the cycle?
---

Other way around. The field is less tangled, so there are fewer
opportunities for reconnection. However, this also means that if
reconnection occurs, it can rearrange the field on a large scale,
releasing a lot of energy.

--
John Doty "You can't confuse me, that's my job."
Home:
Work:

John Doty wrote:

In article , "starman"
wrote:

John Doty wrote:

In article , "starman"
wrote:

Great report. Are these events more likely to happen during the
decline of a solar cycle?

Yes. In the declining part of the cycle flares are generally less
frequent but more energetic.

Is that because the magnetic field lines become more 'twisted' (for lack
of a better word) during the declining phase of the cycle?
---

Other way around. The field is less tangled, so there are fewer
opportunities for reconnection. However, this also means that if
reconnection occurs, it can rearrange the field on a large scale,
releasing a lot of energy.

--
John Doty

I thought the solar cycle is primarily driven by the effect of the sun's
differential rotation on it's magnetic field. If this is correct, how
does it relate to what you say (above) about the field lines becoming
less 'twisted' during the declining phase of the cycle?


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In article , "starman"
wrote:

I thought the solar cycle is primarily driven by the effect of the sun's
differential rotation on it's magnetic field. If this is correct, how
does it relate to what you say (above) about the field lines becoming
less 'twisted' during the declining phase of the cycle?

Differential rotation winds the field up. When the fields get really wound
up and tangled, reconnection becomes more frequent, breaking long tangled
field lines into shorter loops. Solar flares are the result of
reconnection events. If you see them, the field is untangling.

--
| John Doty "You can't confuse me, that's my job."
| Home:
| Work:

John Doty wrote:
Differential rotation winds the field up. When the fields get really wound
up and tangled, reconnection becomes more frequent, breaking long tangled
field lines into shorter loops. Solar flares are the result of
reconnection events. If you see them, the field is untangling.

Reconnection comes from resistance, which produces heating. Without dissipation
charged particles cannot cross field lines (actually reversing cause and effect
here; the field lines take into account charged particles not crossing them; their
motion is a current. The prohibition of crossing field lines disappears if the
particle velocities can be interrupted by something other than electrical effects,
like collisions. This produces heating. The sharp turns in the field lines then
can ``drag'' through the particles and become less sharp.)
--
Ron Hardin


On the internet, nobody knows you're a jerk.

In article , "Ron Hardin"
wrote:

John Doty wrote:
Differential rotation winds the field up. When the fields get really
wound up and tangled, reconnection becomes more frequent, breaking long
tangled field lines into shorter loops. Solar flares are the result of
reconnection events. If you see them, the field is untangling.

Reconnection comes from resistance, which produces heating.

That's the magnetohydrodynamic story. The trouble is that MHD is a poor
model for real plasmas. Also, the resistivity of astrophysical plasmas is
much too low to produce the reconnection phenomena we see.

Without
dissipation charged particles cannot cross field lines (actually
reversing cause and effect here; the field lines take into account
charged particles not crossing them; their motion is a current.

On the scale of the cyclotron radius they cross field lines all the time.
In a uniform magnetic field, with no electric field, the motion is helical
with the axis parallel to the field, so a particle must stay *near* a
particular field line. This is the sense in which "particles don't cross
field lines". However, if the field isn't uniform on the scale of the
cyclotron radius a particle can readily move away from a particular field
line.

The
prohibition of crossing field lines disappears if the particle
velocities can be interrupted by something other than electrical
effects, like collisions. This produces heating.

In astrophysical plasmas particle collisions are generally too infrequent
to have an effect. Wave-particle interactions are much more important.
These tend not to be very effective at entropy generation, but they can
exchange free energy between the particles and waves in the plasma.
Laser-like phenomena can occur: the presence of waves stimulates the
emission of more wave energy. Wave amplitudes can grow until the helical
motion of the particles is severely disturbed. The macroscopic effect is
similar to collisions (look up "Bohm diffusion" in your favorite plasma
physics text). There's not as much heat as collisions would produce,
however: the energy tends to wind up in waves and accelerated particles.

--
| John Doty "You can't confuse me, that's my job."
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