What is Space Weather?
Space weather is a term that refers to the physical conditions that begin at the sun, ultimately reach earth, and have an effect on us and our atmosphere. There are various conditions that contribute to space weather though the largest contributing factors to the effects we see on Earth are:
Solar wind: A constant stream of protons and electrons that flow from the sun to earth. This flow of charged particles varies in speed and intensity and so does its effects.
Solar Flares: A sudden release of magnetic energy from the sun’s surface. This release sends radiation through space and when the flare occurs on the side of the sun facing Earth these will head towards Earth.
Coronal Mass Ejection (CME): A massive release of charged gases and magnetic field that often (but not always) accompany strong solar flares. The products of a CME are released into the solar wind and can make their way to Earth.
The Above picture show the areas of life that Solar Flares can affect
(Govt of Canada Website)
All of these conditions listed above contribute to changes in Earth’s magnetic field and ionosphere which have an effect on GPS signals.
How Does Space Weather Affect GPS?
The ionosphere is in the upper part of our atmosphere and is constantly being ionized by solar radiation. The ionosphere bends radio waves in the same manner that water bends visible light. During periods of low solar activity the changes in the ionospheric conditions are gradual and easy to take into account when calculating RTK corrections.
When solar activity is high the ionosphere becomes unstable and the changes can be large and rapidly changing. These rapid changes in the ionosphere make it difficult to model and therefore difficult to account for when calculating RTK corrections. The degree of distortion (scintillation) of a radio wave by the ionosphere depends on the signal frequency. That is why GPS-RTK receivers are usually “dual frequency” receivers using signals at 1575.42 MHz (L1) and 1227.6 MHz (L2). This allows the receiver to compare the signal at the 2 frequencies and help take into account some of the scintillation errors.
The ionosphere over the poles is less stable than other areas. Major space weather events can push the disturbed polar ionosphere 10° to 30° of latitude toward the equator into the areas above where we are. These events can cause large ionospheric gradients (unstable and rapidly changing) at mid and low latitude. Both of these factors can distort GPS signals and make calculating RTK corrections difficult.