Solar wind parameters and aurora
What are solar wind parameters? How do they affect the aurora and your chances of seeing it? Which are essential, and do you really need to know them?
The OVATION Model precisely forecasted a fantastic aurora on February 28, 2019
Solar wind parameters
The parameters describing solar wind are speed, temperature, density, magnetic field strength, and angle. These parameters are measured by the DSCOVR satellite, which is 1.5 million kilometers from Earth, and published in real-time by NOAA Space Weather Prediction Center. Whether or not the solar wind disturbs the Earth's magnetic field and causes the aurora depends on its parameters. But not all of them are equally important for predicting the aurora.
The most important ones
The best model that predicts the visible aurora with 86% accuracy is the OVATION Prime Model. The model is a function of three solar wind parameters: speed, magnetic field strength, and magnetic field angle. These three parameters have different weights. Based on the solar wind coupling function that the OVATION Prime Model uses, the magnetic field angle is twice more important than solar wind speed and 4 times more important than the strength of the magnetic field.
Magnetic field angle
When the solar wind's magnetic field is opposite to the Earth's, the solar wind is "pulled" into the Earth's magnetosphere, and more solar wind energy is transferred. Otherwise, the solar wind is pushed away. In practice, you need the Bz component of the solar wind magnetic field to be negative for some time to see the aurora.
Solar wind speed
The second most important parameter is solar wind speed. Typically it's about 375 km/s. As it increases, more energy can be transferred per time. That grows your chances of seeing the aurora.
Also, solar wind speed can tell you how long does in take for just measured solar wind to reach the Earth. For example, if it's 400 km/s, solar wind will take about an hour to travel from DSCOVR satellite 1.5 million km to Earth.
Strength of the magnetic field
The least influential but still essential parameter is the strength of the magnetic field. The stronger it is, the more effectively the energy is transferred from the solar wind into the magnetosphere. Which again increases your chances of seeing the aurora.
What values are considered good
As discussed earlier, you are looking for the negative Bz, say -2nT, -5nT, or even -10nT. And the solar wind speed is higher than 400 km/s, or better, 600 km/s, or 800 km/s. And not just for a few minutes, but for an hour or two.
Do you really need to know them?
Actually not. Even if you are a highly experienced aurora photographer, you can't compete with the OVATION model in forecasting the aurora. The model uses formulas to calculate all the necessary parameters with the proper weights. It accumulates the data for the last 4 hours and uses specific coefficients for each hour. Also, the model makes adjustments and corrections only possible with the computer.
It could be addictive to constantly check the solar wind parameters while waiting for the aurora. Still, it's much better to use the OVATION forecast and spend time thinking about composition. It will definitely pay off and improve your aurora photography.
