Hi,

The Sun's magnetic field is a very complicated beast - in fact, it varies dramatically in strength and polarity on small scales, for example, sunspots are areas of more intense magnetic field. It also varies with time both over long and short time periods. The long term global variation is the basis of the 11-year solar cycle where the solar magnetic field changes from being fairly ordered and somewhat well behaved (like a bar magnet with north and south ends) to being somewhat chaotic and very complicated and then back to simple again (but with the north and south poles reversed). In the short term, the Sun often sends out big loops of magnetic field (and plasma) called coronal mass ejections.

The Sun's magnetic field reaches throughout our solar system to the heliopause, where the interstellar magnetic field and plasma begins to dominate the space. The changes in the solar magnetic field affect all the planets (as well as particles that are coming into our system from interstellar space). For planets like Earth and Jupiter that have their own strong magnetic field, the interaction between changes in the solar magnetic field (for example when a coronal mass ejection reaches the planet) and the planetary magnetic field can cause all kinds of interesting effects. One of these effects is a geomagnetic storm where the Earth's magnetic field is significantly (but temporarily) altered by the interaction. Related symptoms are the aurora, communication problems, and increased number of particles in the Earth's radiation belts.

Understanding the changes in the Sun's magnetic field is a huge area of space physics and there is still a lot we don't understand.

-Christina

Hello! You ask excellent questions! I will answer the last two, because these are the questions I know the most about. Hopefully one of the solar physicists will answer your first two questions.

How far can it reach?
The region of space affected by the Sun's magnetic field and the solar wind is called the heliosphere. The boundary between the heliosphere and interstellar space is called the heliopause. My colleagues at the University of Iowa built an instrument to measure radio and plasma waves for the Voyager 1 spacecraft, which was launched 40 years ago in 1977. Using this instrument (it still works!!!), they observed a special kind of plasma wave, called an electron plasma oscillation that indicated Voyager had reached the heliopause in 2012. Voyager 1 was located at a distance of about 121 AU (AU=Astronomical Unit, or 93 million miles, the distance between the Earth and the Sun). At 121 times further away than the distance between the Earth and the Sun, sunlight takes more than 16 hours to reach Voyager 1. That's really, really, really far away. You can listen to what the signals picked up by Voyager 1 at the heliopause sound like here - http://www-pw.physics.uio...nterstellar_epo.html

How does it interact with the Earth's magnetic field or does only plasma from the the solar wind interact?
Both the Sun's magnetic field and the solar wind plasma interact with Earth's magnetic field (the magnetosphere). Both the strength and direction of the solar wind magnetic field are very important. When the solar wind magnetic field points in the opposite direction to the Earth's magnetic field, a process called magnetic reconnection will happen on the day side of the Earth. Magnetic reconnection allows solar wind plasma to enter the magnetosphere, and is an important way that energy is transferred between the solar wind and magnetosphere. When the solar wind magnetic field points southward, or opposite to the Earth's northward magnetic field, for an hour or two, and then suddenly turns northward, people at high latitudes might be able to see beautiful displays of aurora. If the solar wind magnetic field points southward for several hours, and there are higher than normal solar wind speeds and higher than normal solar wind plasma densities, there could be a geomagnetic storm. One of the satellite missions I work on is called Magnetospheric Multiscale (MMS) and its main goal is to study magnetic reconnection. Another satellite mission I work on is called the Van Allen Probes, and its main goal is to study what happens to the radiation belts during geomagnetic storms. When scientists try to understand what they see in MMS and Van Allen Probes data, they will often look at what the solar wind magnetic field is doing to place their observations in the proper space weather context.