Shown above is the latest forecast of conditions in the solar wind, as predicted by the WSA-Enlil model. The solar wind is a fast-moving stream of charged particles emanating from the Sun and moving outwards towards the Earth and planets. During “fair-weather” conditions the solar wind still contains significant variations in density and speed which originate at the solar surface and are imparted with a spiral appearance due to the Sun's roughly 27 day rotation.
At irregular intervals the “fair-weather” is interrupted by major solar eruptions known as Coronal Mass Ejections (CMEs) which are propelled outwards into the background wind. Variations in the plasma density and speed within these solar storms can be much more dramatic than during quiet conditions. For both “fair-weather” and “storm” conditions, predicting the arrival at Earth of variations in the solar wind is important because these can lead to geomagnetic storms.
The top row plots show predictions of the solar wind density. The bottom row plots show solar wind velocity.
The circular plots on the left are a view from above the North Pole of the Sun and Earth, as if looking down from above. The Sun is the yellow dot in the center and the Earth is the green dot on the right. Also shown are the locations of the two STEREO satellites. These plots often depict spiral structures, due to solar rotation, as described above.
The wedge-shaped plots in the center provide a side view, with north at the top and south at the bottom.
The graphs on the right show the model predictions for the time evolution of density and velocity at the locations of Earth and of the two STEREO spacecraft. The yellow vertical line is in sync with the movies on the left, so it is possible to see how values of density and velocity correspond to particular solar wind structures.
A “model run mode” for WSA-Enlil is indicated at the bottom: “Ambient” means that the model has been run in the quiet, “fair-weather”, mode while “CME” indicates a dynamic model run containing a prediction of one or multiple CMEs which may be directed towards Earth, or “Geo-effective”.