Temperature: This trace shows a 50,000 K dip in the temperature of the leading edge of the cloud between January 10 and January 11. This is followed by a sharp rise in the gas temperature inside the cloud, which then decreased the farther the leading edge of the CME cloud was from the satellite. The typical solar wind temperature is about 100,000 K.
Density: There was little change in the density of the gas near the satellite until January 11. When the satellites encountered the interior of the CME, just behind the leading edge, it appears there was a 'wall 'of high density gas. Directly behind this wall is a low density cavity which contained nearly half the density of the gas typically detected in the solar wind.
Speed: The satellites detected the steady flow of the solar wind at about 450 km/sec. Once the satellites were inside the main body of the CME cloud on January 11, they encountered the fast moving gas with speeds of 600 km/sec. This continued to be the case until the back of the cloud passed the satellites on January 12. Then, the contact with the slower moving, normal solar wind was re-established.
Magnetic Field: Before January 10, the satellites were in contact with the solar wind's magnetic field which had a strength of about 5 nT (The unit 'nT' means nanoTesla and is a measure of magnetic field strength. The Earth's magnetic field is about 50,000 nT at the surface). As the satellites encountered the leading edge of the CME between January 10 and 11, the magnetic field tripled in strength. It then returned to the normal solar wind level after the back-side of the CME Front was encountered on January 11.
COMBINING THE CLUES:
Once the students have interpreted each trace, we can then combine them into a simple model of the CME cloud, but not what the entire cloud looks like in three dimensions.
The solar wind, in this instance, has a temperature near 100,000 K, a density of about 10 particles per cubic centimeter, a speed near 400 km/sec, and a magnetic field strength of 5 nT.
The leading edge of the CME contains a strong magnetic field. Although there is no change in the gas density and the solar wind speed, the entire magnetic field of the CME seems to be concentrated there. The magnetic field is responsible for the drop in the solar wind temperature in this region. Scientists call this the CME 'magnetic cloud' region.
The back edge of this 'magnetic cloud' coincides with a sharp increase in gas density and temperature which define the CME boundary in what scientists call the 'shock front'. Behind this shock front there is a fast moving, but low density gas. In the interior of the CME cloud 'bubble' region, the gas density decreases with distance from the shock front, until it eventually returns to the temperature of the solar wind. Behind the fast moving interior bubble is the back-side of the CME which is where the conditions have returned to those of the normal solar wind.
Traveling at a top speed of 500 km/sec, the entire cloud took 2 days to pass the satellites. This means the thickness of the CME was about 86 million kilometers (500 km/sec x 2 days x 86,400 sec/day). This is about half the distance between the Sun and the Earth. Since the satellites were located about 2 million kilometers from the Earth, it took the cloud only about 30 minutes to reach the Earth on January 12.
The NASA Goddard Space Flight Center's National Space Science Data Center has a massive archive of satellite data on solar storms that you can access via the CDAWeb Interface. If you select the 'WIND' satellite, and 'Magnetic Fields' through their forms interface, CDAWeb will let you select a time and date range to plot the data that the WIND satellite collected with its magnetometer. There are many investigations similar to this exercise that you can have the students carry out by getting their own satellite data to study.