The Solar Wind
The Solar Wind parameters are derived from the ACE satellite, this satellite is situated on 1/100 of the Sun - Earth distance. The measurements from the ACE satellite reach us in about an hour.
The Speed of the Solar Wind
The Speed of the solar wind is very important, if the speed is too low there will be no chances
to see some aurora. The normal solar wind speed is arround 300km/sec but increases when a coronal
hole or CME shock (coronal mass ejection plasma cloud) arrives. Depending of the speed of impact the
solar wind can jump to 500 or 700km/sec or even 1000km/sec.
For the Middle Latitudes a good speed
is required and should be arround 700km/sec, but it can also happen that aurora can form with lower
speeds (depends on the strength of the Interplanetary Magnetic Field).
On the data plots you can easely see when a CME shock has arrived, the solar wind increases immediatly
with sometimes several 100km/sec. When a shock arrives, it's time to look at the IMF parameters and
the magnetometers. Keep in mind that when the shock arives at the ACE satellite it takes about an
hour to reach earth. Below a good example of an arrival of a CME shock of 2006:
The Solar Wind Density
This parameter measures the proton density in the Solar Wind. How more protons in the solar wind how more chances we get for aurora. The scale, used in the plots, is protones per cubic cm or p/cm³. A value above 50 is positive but is no garantee that we'll see the aurora. It often happens that at impact the density is high but then collapses to nearly zero, don't let it fool you.