Frequently Asked Questions about Space Weather (FAQ) - Glossary

Auroral Zone
Canada has three zones of geomagnetic activity: the polar cap zone, the auroral zone, and the sub-auroral zone. The greatest geomagnetic disturbances are observed in the auroral zone. The aurora is most frequently observed in the auroral zone. Current and forecast conditions for the auroral zone apply to the region of Canadian territory extending between 63 and 77 degrees magnetic latitude.

Corona
The corona is the outermost region of the Sun’s atmosphere that extends millions of kilometres out and is visible as a faint halo during a solar eclipse. The corona consists of ionized gas at a temperature of 1 million degrees Celsius. Because of its high temperature, the corona produces a continual flow of electrically charged particles called the solar wind.

Coronal Mass Ejections (CME)
CMEs are ejections of plasma from the corona of the Sun. Their arrival at Earth is the main cause for large geomagnetic disturbances. CMEs travel at speeds from 400 to 2000 km/second and their travel time to Earth varies from 1 to 4 days. CMEs are often associated with solar flares

Coronal Holes
Coronal holes are regions in the corona where the magnetic field lines are open to space allowing high speed streams of plasma to escape from the Sun. High speed streams interacting with the Earth are the cause of long lasting (3 or 4 days) periods of geomagnetic activity, particularly in the auroral zone.

Electron fluence
Electron fluence refers to the total number of energetic electrons with energies >2 MeV passing through a given area in a day. Electron fluence is measured in units of electrons per square centimetre per steradian per day (electrons / cm2-sr-day). To determine electron fluence over 1 day, flux measurements made at a geosynchronous orbit of 6.6 Earth radii are taken at 5 minute intervals and summed over a 24 hour period. The fluence value of 5.0 E10+07 electrons / cm2-sr-day is considered as a threshold level for possible adverse space weather conditions hazardous to geostationary satellites. Possible impacts are provided here.

Geomagnetic Activity
Geomagnetic activity is derived from measurements made at magnetic observatories located in the polar cap, auroral, and sub-auroral zones. The data are processed to produce an hourly range index to characterize the range of magnetic field variations measured during one hour at ground level. Hourly range indices are divided into 5 activity levels: classified as quiet, unsettled, active, stormy, and major storm. Hourly range values corresponding to different activity levels depend on observatory locations and can be found at http://www.spaceweather.gc.ca/forecast-prevision/short-court/sfst-5-en.php by clicking on each observatory. For more information about the Earth’s magnetic field, see http://www.geomag.nrcan.gc.ca/. Possible impacts for each activity level are provided here.

Geomagnetic Disturbances
Geomagnetic disturbances are produced by electric currents in the ionosphere and magnetosphere. These currents are generated by the interaction of CMEs or high speed streams with the Earth’s magnetic field. The strongest currents are associated with the aurora.

Geomagnetically Induced Current (GIC)
During a geomagnetic storm, currents in the ionosphere become irregularly enhanced. The fluctuating current causes a fluctuating magnetic field which in turn causes currents to be induced in the ground. The induced current is called a geomagnetically induced current (GIC) and can also be induced in long conductors like pipelines and power lines.

Geostationary
A satellite in a geostationary orbit is located at an altitude of ~35900 km above the Earth at the equator and has an angular velocity equal to that of the Earth so that the position of the satellite is fixed with respect to the Earth.

Geostationary Satellite Environment
Geostationary Satellite environment refers to energetic electron fluence measured at a geostationary orbit (~35900 km altitude) which influences the operation of satellites in a fixed position in this orbit.

Interplanetary Magnetic Field (IMF)
The IMF is the solar magnetic field carried out into interplanetary space by the solar wind. The north-south component of the IMF, Bz, has a strong influence on the occurrence of geomagnetic activity; geomagnetic conditions are generally more disturbed when Bz is negative. Prolonged period of negative Bz are often associated with increased levels of geomagnetic activity.

Ionosphere
The ionosphere is a layer of the upper atmosphere that is ionized by solar radiation. It is made up of several ionized layers and extends from about 70 to 1000 km above the Earth’s surface.

Ionospheric Absorption
Ionospheric absorption is the loss in signal strength or attenuation of radio waves as they propagate through the ionosphere. Precipitating electrons and protons are the main causes of strong ionospheric absorption. During the daytime, ionization of the ionosphere by solar radiation is also a source of ionospheric absorption.

Ionospheric Disturbances
Ionospheric disturbances are produced by charged particles precipitating into the ionosphere. These particles create extra ionization that causes absorption of radio waves.

Major Storm Watch
A major storm watch is issued to indicate that major storm conditions have been observed by multiple observatories during the same period. These conditions are likely to continue to be observed by more than one observatory for at least the next few hours. The space weather watch is either limited to the auroral zone if such conditions have only been observed in that zone or applies to all of Canada if major storm conditions have been observed in both the auroral zone and the sub-auroral zone.

Magnetosphere
The magnetosphere is an asymmetrical region surrounding the Earth in which charged particles are trapped and their behaviour is dominated by the Earth’s magnetic field. The magnetosphere extends from one hundred to several thousand kilometres above the surface of the Earth

Polar Cap Absorption
Polar Cap Absorption is a term given to a type of ionospheric absorption that is caused by the precipitation of energetic protons into the auroral and polar regions. The energetic protons react with the particles of the lower ionosphere and during sunlit conditions cause severe attenuation of radio waves for magnetic latitudes greater than 63 degrees. During periods when the ionosphere is dark, the attenuation is substantially reduced.

Polar Cap Zone
The region poleward of the auroral oval. Current and forecast conditions for the polar cap zone apply to the region of Canadian territory extending between 77 and 90 degrees magnetic latitude.

Solar X-ray Flare
A solar x-ray flare is a burst of electromagnetic radiation across the electromagnetic spectrum, notably in visible light, and x-rays that can last from a few minutes to a few hours. Long duration flares can last for more than 3 hours. Flares are one indicator of possible solar plasma eruptions, and can be classified according to x-ray intensities into 4 categories: B (very low), C (low), M (medium), and X (large). Each category (except X) has 9 subdivisions ranging from, e.g., M1 to M9. The scaling is defined so that an M2 x-ray flare is twice as powerful as an M1 flare. X class flares >9 are possible.

Solar Wind
The solar wind is a continuous stream of charged particles flowing outward from the Sun. Typical speeds are 300 – 400 km/second.

Space Weather
Space Weather refers to changes in the space environment and geomagnetic disturbances resulting from eruptions on the Sun. Space weather ultimately affects human activities and technologies on Earth and in space.

Sub-Auroral Zone
The region equatorward of the auroral oval. Current and forecast conditions for the sub-auroral zone apply to the region of Canadian territory extending between 49 and 63 degrees magnetic latitude.