Space weather predictions
Particle flux from the Sun interacts with the Earth's magnetic field and causes short term variations of it. These variations cause the Aurora.
The National Oceanic and Atmospheric Administration of the United States (NOAA) operates several satellites that monitor the Sun and particle fluxes heading for Earth. These include satellites that observe both the front and back side of the Sun in visible light and various wavelengths of light outside the visible spectrum. The satellites also include sensors for particle fluxes from the Sun. This data is combined with numerical simulations to predict particle fluxes to Earth.
The aurora forecasts of the Icelandic Meteorological Office are expressed on the Kp-index. The Kp-index is a numerical scale from 0 to 9 which describes 3 hr variations of the Earth's magnetic field. The lowest numbers of the Kp-index are frequent: The Kp-index is 0-4 about 90% of the time and the highest values are very rare, 7-9 only appear about 1% of the time.
Seen from Earth the Sun rotates about its axis in about 27 days, and therefore some disturbances in the solar wind are repeated every 27 days. Changes in the Sun on such timescales may vary this. The particles of the solar wind are mainly protons and electrons travelling from the Sun at speeds of several hundred kilometers per second. At this speed it takes about 1-3 days to reach Earth if the particles are heading our way. Because of this it is usually possible to predict major geomagnetic storms.
Figure 1 shows the Sun earlier today: 1a shows the Sun in visible light, and 1b is a thermal image of extreme ultraviolet light where material in the solar corona needs to be at about 2 million °C to shine at these low wavelengths.
Space weather prediction graphs
Figures 2-4 show space weather prediction graphs with variable range, from a few hours to two weeks. The left part of the graphs shows measured variations of the Earth's magnetic field (blue), while the right part shows the predictions (red). The variations are all shown on the scale of the Kp-index, 0-9 which describes 3 hr variations of the Earth's magnetic field.
Figure 2 shows 1-4 hr space weather predictions. Vertical gray line indicates the time of prediction (now). This forecast shows both 1 hr (red line with dots) and 4 hr (orange line). The shorter forecast is considered more reliable because it is based on measurements of particle flux from the Sun at the ACE-satellite. Previous 1 hr forecasts are also shown (pink). The particle flux hits the satellite about 1 hr before it hits Earth.
Figure 3 shows a three day space weather prediction. A vertical gray line is set at last midnight, the time of the forecast. The left part of the figure shows measurements of Earth's magnetic field variations (blue) and predictions for today and next two days (red). The 1 day forecasts of the previous four days is also shown (pink). The activity is expressed as Kp-index which describes magnetic field variations.
Figure 4 shows the space weather outlook for the next two weeks. The horizontal time-axis shows 22 days where the date is written under middle of each day. The graph shows measurements of the magnetic field variations during the past one week (blue), the 3 day prediction (red) and the two week outlook (orange). Also the 1 day forecasts of the past week are shown (pink).