how fast is the solar wind flowing?

How do we know it’s blowing that fast?

We can measure the solar wind speed by using special instruments on spacecraft. Here's a graph of the speed of the solar wind measured by a spacecraft called Ulysses during two months of observations in 1992 - 1993.

Notice that the speed of the solar wind goes up and down in a regular pattern. That’s because the Sun, like the Earth, is rotating.

Where do these winds come from?

The fast and slow wind come from different places on the Sun. The fast wind comes from coronal holes while the slow solar wind probably comes from streamers