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 — such as speed, temperature, density, magnetic field strength, and angle — are measured by satellites like DSCOVR and ACE, both located at the L1 Lagrange point, 1.5 million kilometers from Earth. These parameters are published in real-time by NOAA's Space Weather Prediction Center. Whether the solar wind disturbs the Earth's magnetic field and causes the aurora depends on these parameters. However, not all of them are equally important for predicting the aurora.
The most important ones
The OVATION Prime Model, a widely used and highly regarded tool for predicting visible auroras, primarily relies on three solar wind parameters: speed, magnetic field strength, and magnetic field angle. Among these, the magnetic field angle, particularly the Bz component, is generally the most critical parameter, followed by solar wind speed and 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, allowing more solar wind energy to be transferred. 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 over time, which increases your chances of seeing the aurora. Solar wind speed also indicates how long it will take for the measured solar wind to reach Earth. For example, if it's 400 km/s, the solar wind will take about an hour to travel from the DSCOVR satellite, 1.5 million km away, 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 energy is transferred from the solar wind into the magnetosphere, again increasing your chances of seeing the aurora.
Solar Wind Density
Solar wind density refers to how many particles are in the solar wind. While it's important, the OVATION model doesn’t use it directly to predict auroras. However, density does have an indirect effect. It can influence how the magnetic field behaves, which in turn affects how much energy is transferred to Earth’s magnetosphere. So, even though density isn’t directly used in the model, it still plays a role through its impact on the magnetic field.
What values are considered good
For a good chance of seeing the aurora, look for a negative Bz, ideally around -2nT, -5nT, or even -10nT. A solar wind speed above 400 km/s is favorable, with 600 km/s or 800 km/s being perfect. Ideally, these conditions should persist for an hour or two, rather than for a short period of time.
Do you really need to know them?
While the OVATION model provides an excellent forecast, having some awareness of real-time solar wind parameters can be useful for understanding the underlying processes behind the aurora. This knowledge can enhance your overall experience and help you make informed decisions, especially when conditions are changing.
However, it’s easy to become overly focused on checking these parameters constantly. Instead, once you have a good forecast, it’s often more productive to concentrate on your photography setup and composition. This approach is more likely to lead to better aurora photos, as the OVATION model already incorporates the necessary data for a reliable forecast.
