Questions about solar wind

[LunarLights58]

Why does the solar wind have so much variation in Bz? How does it flip so much on short timescales and why is it so hard to predict if it will be positive or negative in the near future? I would think that the magnetic fields would simply cancel out instead of doing this ⬇️

[Jesterface23]

The IMF flows with the solar wind and is a river that always changes its path. It can't be told if the river will be rough or calm for any amount of time. It can't cancel its self out if it can't reach what is ahead or behind it, but may only influence it to a small degree.

[Newbie]

10 hours ago, LunarLights58 said:

Why does the solar wind have so much variation in Bz? How does it flip so much on short timescales and why is it so hard to predict if it will be positive or negative in the near future? I would think that the magnetic fields would simply cancel out instead of doing this ⬇️

Earth has a magnetic field. It forms a bubble around our planet called the magnetosphere, which deflects solar wind gusts. Earth's magnetic field and the IMF (Interplanetary Magnetic Field) come into contact at the magnetopause: a place where the magnetosphere meets the solar wind. Earth's magnetic field points north at the magnetopause. The IMF is a three dimensional vector Bt with components Bx, By and Bz. Most interest lies with Bz as an indicator of auroral activity. When the IMF points south, a condition scientists call 'southward Bz' then the IMF can partially cancel Earth's magnetic field at the point of contact.

When Bz is south, that is, opposite Earth's magnetic field, the two fields link up, you can then follow a field line from Earth directly into the solar wind or from the solar wind to Earth. South-pointing Bz's open a door through which energy from the solar wind can reach Earth's atmosphere.

Southward Bz's often herald widespread auroras, triggered by solar wind gusts or coronal mass ejections that are able to inject energy into the Earth's magnetosphere.

The solar wind is created by the outward expansion of plasma (a collection of charged particles) from the Sun's corona (outermost atmosphere)

When the solar wind plasma leaves the Sun's corona, it carries with it some of the Sun's magnetic field. This extension of the Sun's magnetic field into space greatly influences the manner in which the solar wind interacts with the Earth and eventually, the interstellar medium. It is these embedded 'chunks' of magnetic field which exhibit different properties of magnetism. Consider negative or positive and handedness, left or right twisting. Very little is understood of the make up of these embedded magnetic fields and it is only when the solar wind passes the monitoring satellites that the IMF can be measured. The very nature of the solar wind is what makes it so unpredictable. 

Newbie. 

[Strom]

So, if the satellite that measures Bz measures  -8 in the solar flow as it passes the satellite, when that section of the solar flow reaches earth, would you expect it to be at a  -8Bz?

[Jesterface23]

27 minutes ago, Strom said:

So, if the satellite that measures Bz measures  -8 in the solar flow as it passes the satellite, when that section of the solar flow reaches earth, would you expect it to be at a  -8Bz?

The nT strength of the IMF components would lower very slightly from the satellites in orbit around the L1 position to Earth at 1 AU, given a satellite and Earth are in perfect alignment.

[Sam Warfel]

46 minutes ago, Strom said:

So, if the satellite that measures Bz measures  -8 in the solar flow as it passes the satellite, when that section of the solar flow reaches earth, would you expect it to be at a  -8Bz?

For all practical intents and purposes, yes, if the satellite is at L1 directly between the sun and earth.

[Archmonoth]

1 hour ago, Strom said:

So, if the satellite that measures Bz measures  -8 in the solar flow as it passes the satellite, when that section of the solar flow reaches earth, would you expect it to be at a  -8Bz?

I think so, solar wind contains/is plasma, which generally has an equal charge when measured altogether, but regions will have a variety of charge. Also, the solar wind spreads out as it travels away from the Sun, so regions might reduce/change their charge as it brushes against Earth's magnetic field. 

Edited September 5, 2022 by Archmonoth