The solar wind speed is the speed at which particles from the Sun are moving through the solar system and, in our case, specifically toward Earth. This wind speed is measured in kilometers per second (km/s). When measured at the L1 orbit, it can take anywhere from 15 minutes to just over an hour for particles from the Sun to reach Earth based entirely on this wind speed. Knowing this information is important to know when the density of particles and the north or south orientation of the Bz field will reach Earth’s magnetosphere. The app uses this speed to tell you approximately when to expect all of these values to cause an impact and, in our hopes, aurora activity.
The higher the solar wind speed, the more impact there is on aurora activity. As the solar wind speed increases, it causes the magnetosphere to bend and flux. This bending and fluxing causes chaotic turbulence in the Earth’s magnetic field and leads to an increase in the chances of seeing aurora activity. You can still see aurora activity with lower wind speeds, but the displays will tend to move less and be less vibrant than displays with higher wind speeds. Additionally, aurora activity may be confined to higher latitudes with lower wind speeds due to the lack of bending and fluxing in the magnetosphere.
Free Versus Subscription
The free version of the app gives you approximately two hours and 30 minutes of solar wind speed data: the previous 90 minutes plus the next hour. The subscription version lets you go back and look at solar wind speed data for the past 36 hours in 6-hour increments.