Hi Glenn,

In many ways the solar wind is like a wind in that it is a gas that moves quickly in a particular direction. It differs from standard gas (and terrestrial wind) in that it is very tenuous (only one particle in a cubic-centimeter, typically, as compared to about 30,000,000,000,000,000,000 particles for air at the Earth's surface) and it is completely ionized (meaning all the atoms have had their electrons removed which move around separately). It also moves much more quickly than most wind we have on Earth; typical speeds are 1 million miles per hour.

The reason why it pushes the Earth's magnetic field around is because along with the particles in the solar wind, there is a magnetic field in there which has been pulled outwards from the Sun. This field is what pushes up against the Earth's magnetic field and deforms it from a nice symmetric shape like the field around a dipole magnet. When the solar wind has a particularly strong 'gust' (a period where the speed is much higher than normal and the density of particles increases and the magnetic field increases) and that hits the Earth's magnetic field, the distortions can be so significant that it is called a geomagnetic storm and has all kinds of effects on Earth.

-Christina