Solar Steph Space Weather Dashboard

The solar wind is the stream of charged particles flowing from the Sun. It is often around 300 to 450 km/s. Speeds above about 500 km/s count as fast, and these streams often come from coronal holes. A sudden jump in density or speed can mean a disturbance such as the edge of a fast stream or a coronal mass ejection (CME) is passing the spacecraft.

Bt is the total strength of the magnetic field carried by the solar wind, usually a few nT. Bz is its north-south part. When Bz points south (negative), the solar wind connects more easily to Earth's magnetic field, so geomagnetic activity and aurora become more likely. Strongly negative Bz (around −5 nT or lower) lasting for hours matters most, especially with fast wind.

Kp is a 0 to 9 measure of how disturbed Earth's magnetic field is, updated every three hours. Kp 5 is a minor geomagnetic storm (G1), Kp 6 is G2, 7 is G3, 8 is G4, and 9 is G5. Aurora is usually seen at higher latitudes first. In the UK it is more often seen from the north at Kp 5 or above, and further south as Kp rises. Clear, dark skies matter as much as the number.

Solar flares are ranked by their peak X-ray brightness: A, B, C, M and X, each ten times stronger than the one before. The number is a multiplier, so an X2 is twice an X1. C-class flares are common and usually have little effect at Earth. M and X flares can cause radio blackouts on the sunlit side of Earth: M1 is R1, M5 is R2, X1 is R3, X10 is R4 and X20 is R5.

Protons accelerated by flares and CMEs can reach Earth within minutes to hours. A radiation storm (S1 or above) begins when the flux of protons above 10 MeV reaches 10 pfu (particles per cm² per second per steradian). S2 is 100, S3 is 1,000, S4 is 10,000 and S5 is 100,000. These mostly matter for satellites, astronauts and high-latitude flights, rather than for people on the ground. The S-level only looks at protons above 10 MeV. Studies of ground-level enhancements describe how hard the spectrum is with a spectral index: the slope of a power law, J(E) ∝ E^−γ, fitted to the differential proton flux in the channels above about 40 MeV. A smaller γ means a harder spectrum, which can matter more for aircraft and ground-level effects than the S-level alone suggests. The value changes through an event, and is usually flattest early on. The words hard, typical and soft are a rough guide and not an agreed standard. They split at the midpoints between published averages: ground-level events average a slope of about 3.2 above 40 MeV, while event-integrated 10–100 MeV studies give about 2.7 for GLEs, 3.8 for regular large SEP events and 4.9 for filament-eruption events. So below 3.2 is called hard, and above 4.4 soft. The fit uses only channels that are clearly above their quiet-time level, so it is shown only during a significant event. NOAA issues its own alert when the ≥100 MeV flux reaches 1 pfu.

Active regions are the Sun's sunspot groups. NOAA gives each a number (for example AR4560) and, for groups with sunspots, a magnetic class based on how the magnetic polarities are arranged. α (alpha) is a single dominant polarity, β (beta) is a simple pair of opposite polarities, γ (gamma) is a tangled mix with no clear dividing line, and δ (delta) has opposite polarities packed inside one sunspot. Combined names such as β-γ or β-γ-δ are more complex. Simple groups (α, β) rarely produce big flares, while the more complex classes are more likely to, although most regions never produce a large flare. Regions with no spots, only bright plage, have no class. Where a region sits on the disc also matters. Flares and CMEs from regions near the centre are more likely to be aimed at Earth.

The Open field button shades the parts of the Sun's surface where the model's magnetic field lines reach the outer boundary instead of looping back down. That open field is what the solar wind flows out along, so these areas are the model's version of coronal holes. Pink is field pointing away from the Sun and blue is field pointing towards it. They are not expected to match the dark patches in the pictures exactly, because the model is simplified and is built from a map that is not perfectly up to date, so treat any difference as a sign of the model's limits.

The Field lines button draws a computer model of the Sun's magnetic field over the picture. It is a potential field source surface (PFSS) model, built from the latest HMI magnetic map. It assumes there are no electric currents between the surface and an outer boundary at 2.5 solar radii, which makes it a simplified picture and not a measurement. White lines leave the Sun and come back down, so they are closed loops. Pink and blue lines reach the outer boundary and are open, so they carry the solar wind outwards, pink where the field points away from the Sun and blue where it points towards it, and only their roots are drawn. Open lines gather above coronal holes. The lines turn with the Sun, but the model is only rebuilt when a new map is made, so it can miss changes such as new regions.

The Sun's atmosphere gives off light at different wavelengths depending on its temperature. The 193 Å view shows the corona at about a million degrees, where coronal holes look dark, and it is the one used for the outlines. The 304 Å view shows cooler gas in the chromosphere, so filaments appear as dark threads and prominences as bright loops, and an erupting filament can launch a CME. The 131 Å view picks out very hot plasma, so flares appear as brilliant patches, but it looks grainy on quiet days. Use the buttons at the top of the Sun panel to switch between them and the magnetogram.

A magnetogram maps the Sun's magnetic field along our line of sight, measured by the HMI instrument on NASA's Solar Dynamics Observatory. White is field pointing towards us (positive) and black is field pointing away (negative), with grey where the field is weak. Active regions show up as close pairs of white and black patches. Coronal holes are regions where the field mostly points one way, which is why the outlines on the pictures are coloured pink for positive and blue for negative. The data used here arrive about an hour after they are measured.

Coronal holes are the dark patches in the AIA 193 Å image. The Sun's magnetic field is open there, so fast solar wind streams out. A hole facing Earth can send a fast stream that typically arrives a few days later. On the picture the outline colour shows the hole's magnetic polarity: pink is positive (field pointing outward) and blue is negative. Holes are labelled by where they sit on the disc.

The auroral oval is the ring around the magnetic pole where aurora is most likely. It grows and moves towards the equator when geomagnetic activity rises. On the map the colour shows the forecast chance of aurora, with the ring pink on the map marking the UK. Because aurora is high up, it can sometimes be seen low on the northern horizon from further south than the band itself, in dark and clear skies. Cloud and moonlight matter as much as the forecast.

The corona is the Sun's outer atmosphere, which is far fainter than the Sun's disc. A coronagraph blocks the disc so the corona shows up. A coronal mass ejection (CME) appears as a cloud that brightens and moves outward over several frames. Whether it is aimed at Earth is hard to tell from one view. Forecasters combine coronagraph images with other data to judge that, and a CME that is Earth-directed usually takes a day or more to arrive. The corona panel can show NOAA's CCOR-2 or the older SOHO LASCO C2 and C3 coronagraphs. C2 looks close to the Sun, and C3 looks much further out, so a CME can be followed for longer. SOHO's pictures can be delayed because its data arrive in contacts with ground stations.

It shows where on the Sun the solar wind reaching Earth most likely came from. The wind measured at L1 is traced back along the Sun's magnetic field using a computer model. The white outlines mark where most of the traced field lines land, and the confidence label is a rough guide to how tightly they cluster. It is a research-style estimate, not a measurement, so treat it with care.

L1 is a point about 1.5 million km from Earth towards the Sun, where spacecraft measure the solar wind before it reaches us. At typical speeds that gives roughly an hour of warning, which is why the numbers at the top are a nowcast and not a forecast.