Chapter 7: Sun, Solar Wind, and Magnetic Fields

"All magnetospheres also contain large numbers of electrons; on average, magnetospheric plasma is approximately _____________ in charge."

neutral

What is a heliosphere?

A magnetic cavity formed by the Sun which resembles a bubble 'blown' into the interstellar medium by the solar wind. Within this bubble, the solar wind flows around and interacts with the magnetic fields surrounding the Earth, the giant planets and mercury. The fields are generated in these planets' interiors via a dynamo process. Venus, Mars, and comets are surrounded by magnetic structures that are induced by the interaction of the solar wind with their ionospheres. Mars, the Moon, and some asteroids show evidence of large scale remanent magnetism.

What are sources of plasma?

Charged particles can originate in cosmic rays, the soar wind, or the planet's ionosphere, or on satellites/rings that are partially or entirely embedded in the magnetosphere. Although ionospheric particles are usually gravitationally bound to the planet, some charged particles escape along magnetic field lines into the magnetosphere.

How does the solar minima and maxima affect solar winds?

During solar minima, there are large coronal holes near the Sun's poles from which the wind emanates; at these times, the speed is typically 750-800 km/s at higher solar latitudes.

What are the inner parts of a sunspot?

Each sunspot shows a dark center, the umbra, surrounded by a lighter, radially striated penumbra.

How is energy transported out of the Sun?

Energy is transported outwards via radiation in the radiative zone and via convection in the outer third of the Sun, the convection zone.

What are solar flares?

Events during which the coronal X-ray and ultraviolet (UV) emissions suddenly intensify by several orders of magnitude in a relatively localized region in the low corona and chromosphere. Major solar flares typically occur approximately one per week during years of maximum sunspot activity, with weak flares and CMEs happening a few times daily. During years of minimum solar activity, such weaker events may happen once a week.

In what ways can solar wind-interactions vary?

For bodies without intrinsic magnetic fields, the interaction depends on the conductivity of the body, and/or its atmosphere. Poor conductors --> the solar wind particles hit the body directly and are absorbed. The interplanetary magnetic field lines simply diffuse through the body. If a planetary body is highly conductive, the interplanetary magnetic field lines drape around teh body because the plasma flows around the conductor. If a poorly conducting body has an atmosphere but no internal magnetic field, the solar wind interacts with the atmosphere. The interaction is mainly between charged particles, i.e. with a planet's or satellite's ionosphere, or in the case of comets, with the outflowing gases after they are ionized.

What does the size of a planet's magnetosphere depend on?

It depends on the planet's magnetic dipole moment and the local strength of the solar wind.

How can magnetospheric plasma be lost?

Moons, rings, and atmospheres are both sources and sinks of magnetospheric plasma. articles that hit the surface of a solid body are generally absorbed andlost from the magnetosphere.

Other than the heliosphere, what are the largest structures in the solar system?

Planetary magnetospheres.

What are active regions?

Sunspots usually come in pairs, and some sunspots occur in complex groups, called active regions. The two spots in each pair of sunspots show opposite magnetic polarity, with the field lines either pointing in or out of the spots.

What is the solar corona?

The corona consists of highly variable magnetically controlled loops and streamers.

What are sunspots?

The dark 'blemishes' on the Sun. Sunspots appear dark because their temperature is lower (around 4500K) than the average photospheric temperature (around 5800K). In contrast, the magnetic field strength in sunspots is higher than in the surrounding regions, such that there is approximate pressure equilibrium between the spots and the surrounding region.

What are coronoal holes?

The loops and streamers in the solar corona contain hot plasma that is visible at EUV and X-ray wavelengths. The dark regions largely devoid of hot X-ray--emitting plasma. Magnetic field lines in these regions have opened up into interplanetary space, so that particles can freely escape into space, forming the solar wind.

What is the photosphere of the sun?

The photosphere is the lowest layer of the solar atmosphere. It is essentially the solar "surface" that we see when we look at the Sun in "white" (i.e. regular, or visible) light.

What happens to the Sun every 11 years?

The polarity of the overall magnetic field of the SUn reverses. At the beginning of the 11-year cycle, sunspots appear at high solar latitudes. New sunspots appear at lower and lower latitudes as the cycle progresses, so that over time a butterfly pattern is formed on the plot.

What is the outward acceleration of the solar wind primarily caused by?

The pressure difference between the corona and the interplanetary medium. Eugene Parker predicted the existence of the continuous solar wind flow, assuming that particles flowed radially outward from the Sun, carrying the solar magnetic field as if it were 'frozen in'.

What is a magnetosphere?

The region surrounding the earth or another astronomical body in which its magnetic field is the predominant effective magnetic field.

What is space weather?

The response of Earth's environment to solar activity and the continuously varying interplanetary medium. The effects of CMEs and solar flares on the interplanetary medium and Earth's environment are referred to as space weather storms.

What is the solar maximum and solar minimum?

The solar maximum is the maximum number of sunspots during a solar cycle. Because sunspots lower the total luminosity of the Sun by only ~0.15% at solar maximum, this has a negligible effect on the climate on Earth. The extreme ultraviolet radiation from the sun, however, which also displays an 11-year solar cycle, may influence Earth's climate because this radiation affects the ionization in a planet's ionosphere.

What does a solar wind mostly consist of?

The solar wind consists of a roughly equal mixture of protons and electrons, with a minor fraction of heavier ions. The density decreases roughly as the inverse square of the heliocentric distance.

What determines the shape and size of a planet's magnetosphere?

They are determined by the strength and orientation of its magnetic field, the solar wind flow past the field, and the motion of charged particles within the magnetosphere.

Are charged particles present in all magnetospheres?

Yes, although the density and composition vary from planet to planet. That particles may originate in the solar wind, in the planet's ionosphere, or on satellites or ring particles whose orbits are partly or entirely within the planet's magnetic field.

What is the Sun's chromosphere?

a reddish gaseous layer immediately above the photosphere of the sun or another star. Together with the corona, it constitutes the star's outer atmosphere.