Coronal holes are natural openings in the solar atmosphere that allow fast flowing streams of solar wind to fan out. When these streams hit the earth they squish our magnetic field and can cause auroral displays. There is a correlation between the size of a coronal hole and the intensity of the solar wind hitting the Earth. At Dunedin Aurora, we have created a computer program that calculates this relationship between coronal hole size to solar wind speed. Once we know this, we can calculate the arrival time of any space weather strong enough to cause an aurora.
Linear approximation is: Predicted windspeed = 428.27 + 1393.7 * coronal hole area on meridian
Pearsons correlation |r| = 0.5663
Average Windspeed is 408.9km/s
Space weather transit time is 4.2 days