Extrapolation of solar wind parameters in three-dimensions in the inner heliosphere

Solar wind parameters, such as the velocity, density or pressure of the solar wind, are one of the most important factors in space physics, and their knowledge at as many points in the heliosphere as possible contributes to a broader understanding of our solar system.

Solar wind parameters at various points in the inner heliosphere are estimated using extrapolation methods. Currently, all spacecraft measuring solar wind parameters are in the ecliptic plane, thus it is enough to extrapolate the data from space probes to other spacecraft or celestial bodies near the ecliptic. Solar Orbiter, on the other hand, will soon leave the ecliptic and reach heliocentric latitudes of 34 degrees by the end of the mission, opening a new perspective.

The ballistic method extrapolates solar wind parameters in one dimension from the point of measurement to a chosen heliospheric position. The simple ballistic model considers the average rotation period of the Sun for the extrapolation in longitude while assuming a constant solar wind velocity during radial propagation. Our improved solar wind propagation model takes into account the interaction of slow and fast solar wind by applying a pressure correction during the extrapolation.

Applying this pressure-corrected ballistic method to data from solar corona models, we determined the solar wind parameters in the heliosphere in three dimensions. The advantage of our pressure-corrected ballistic method is that it is simple, it requires little calculation and it can be easily applied to the data of solar corona models in order to obtain a fast and efficient prediction in three dimensions.