NOAA / Space Weather Prediction Center

SWPC Frequently Asked Questions

General Space Weather | Effects on Earth | Noaa Space Weather Scales | ACE Real-Time Solar Wind


NOAA Space Weather Scales

1. What is the difference between the number of events per cycle and the days per cycle.

The number of days per cycle means the number of days on which one or more of that particular event occurred, whereas the number of events per cycle is a total count of all events. For example, we could have 7 days of minor radio blackout activity (R1) which consisted of several dozen R1 events.--CB

2. How would one find out how many of each event have occurred in the current cycle?

The National Geophysical Data Center (NGDC) has the archival responsibility for all of the events that occur during a cycle. You should be able to get some information from the NGDC web site ( --CB

3. At what point is a cycle considered ended and a new cycle has begun?

Traditionally the end and start of the cycle is marked by the smoothed sunspot number (you can get details about the sunspot number from the sunspot index data center

4. What are the effects on mid-latitude power systems from Geomagnetic Storms?

There are two things to consider to evaluate the local interaction with any power grid. The first is a question of the local natural earth-conductivity. Areas that permit natural currents to flow are not very likely to be affected, whereas areas with poor natural conductivity provide a possible opportunity for currents to get into the grid through grounded neutrals of transformers. The other consideration is your proximity to the auroral electrojet. Under G2 conditions the aurora will have expanded somewhat, but not down to mid-latitudes. A G3 storm begins to move the aurora down to lower latitudes to the point where mid-latitude affects are possible. One complication to this is that lines of magnetic latitude do not map exactly with the geographic latitude. Thus, one tends to worry more about the East coast geographic mid-latitudes than the West coast geographic mid-latitudes because the former are closer to the magnetic pole. If you want to see a map of this, look at the relation between Kp and the aurora on our web page (/info/kp-aurora.html) --CB

5. What are the units for flux levels in Solar Radiation Storms?

"ster" stands for ster-radian, which is a unit of "solid angle." The reason that this is done used is because the instrument samples particles only over a limited angular volume. One takes the particle counts and divides by the solid angle subtended by the instrument to normalize the measurement per solid angle unit. To convert to the equivalent flux that one would expect in all directions, multiply by 4 x pi. Note that this is valid, however, only if the particle trajectories are uniformly distributed over all possible directions. --CB

6. What type of particles are measured for Solar Radiation Storms?


7. Do the effects of Solar Radiation Storms differ based on latitude?

Solar radiation storms are the result of energetic particles produced by solar activity. These particles have a very difficult time making it to the ground due to their interaction with the Earth's magnetic field and with the Earth's atmosphere. We hardly see anything at the ground at all, except very near to the magnetic poles. From a practical point of view, solar radiation storms are mainly a concern for spacecraft and astronauts, particularly if they are far above the stronger parts of the geomagnetic field and above the atmosphere. --CB

8. How are the three NOAA scales related?

The answer is complicated. The radio blackouts are a result of solar flares, a solar phenomena that has been known for a good 150 years or so. Solar flares are also associated with the radiation storms and can sometimes be followed by a geomagnetic storm a day or so later. However, as have learned more over the years, we have discovered some things that have modified the view:

1. The energetic particles that lead to radiation storms can be accelerated by flares or by interplanetary shocks. Interplanetary shocks occur when the Sun energetically ejects material into space, a phenomena known as a coronal mass ejection. Both types of mechanisms can contribute to energetic particles and consequently, radiation storms.

2. Geomagnetic storms are caused either by the interaction of a coronal mass ejection with the earth or by another solar phenomena called a high-speed stream, emanating from what is called a coronal hole. A coronal mass ejection is sometimes associated with a flare, but not always. As for cause and effect, it is now widely thought that the Sun's magnetic fields drive the mass ejection, rather than the radiative energy released from a flare. One often does have a coronal mass ejection that is associated with a flare, but it is not always the case. Coronal holes are regions of open coronal magnetic fields. In these voids of the sun's atmosphere, material flows rapidly away from the sun (more than it does over the closed field regions) and a high-speed stream of solar wind forms in interplanetary space. When the high speed stream interacts with the Earth we can often see a geomagnetic storm result.

3. A final complication is that geomagnetic storms end up driving the ionosphere, and can also wreak havoc on radio communications. Thus, independent of the flare effect for radio blackouts one also has radio blackouts originating from geomagnetic storms.--CB


General Space Weather | Effects on Earth | Noaa Space Weather Scales | ACE Real-Time Solar Wind