Lynch Rocket Laboratory - Dartmouth College

Another exceedingly quiet night with practically no aurora. What little aurora there was was very far to the north and very faint. The problem is that the solar wind pressure on the Earth's space environment is very very small right now, so not much energy is stored in the magnetosphere and auroras are not triggered.

You can see in the pictures the difference between a weak period and an active one. What the plots show is a measurement by the GOES satellite.

GOES is a geosynchronous spacecraft, which means it has a 24-hour orbit and sits above the same place on Earth all the time. The blue trace is the GOES satellite that is nearest our longitude. Each day, the GOES satellite moves from the dayside (between the earth and the sun) to the nightside (behind the earth) and back. The trace shows the GOES measurement of the Earth's magnetic field with time. On the dayside, where the solar wind pushes on the Earth's dipole field, the field is compressed and strengthened. On the nightside, where the solar wind pulls the tail out to many Earth radii, the field is stretched and turned, and GOES measures a smaller signal. When energy is stored in the tail, the tail is stretched out even farther, and the GOES signal drops well below the oscillating daily sinusoid. When the tail is stretched too far, and too much energy is stored, there is a release which triggers aurora. So each sharp upturn in the GOES signal on the nightside corresponds to a nightside aurora at that (our) local time.

If you compare the two plots, you see one is a clean quiet sinusoid: that's a boring quiet time. The other has lots of dropouts and sharp recoveries: that's an active time. The two plots are from the week which is one solar rotation before now. You can see that 27 days ago, we moved from a fairly quiet time to a quite active time, so there is a lot of hope that in the next few days we should see quite an increase in the activity. NOAA space weather predictions say that the activity increase should be on Saturday; the straight 27-day cycle puts it on Friday night; we'll wait and see. The weather remains clear, and the rocket is happy: all we need is some aurora!