a INDEX. A 3-hourly "equivalent amplitude" index of local geomagnetic activity; "a" is related to the 3-hourly K INDEX according to the following scale: K 0 1 2 3 4 5 6 7 8 9 a 0 3 7 15 27 48 80 140 240 400
A INDEX. A daily index of geomagnetic activity derived as the average of the eight 3-hourly a indices.
ACTIVE (GEOMAGNETIC). Geomagnetic levels such that 15 is less than Ap which is less than 29.
AFRED. Abbreviation for the A INDEX for Fredericksburg.
Ap INDEX. An averaged planetary A INDEX based on data from aset of specific stations.
CONJUGATE POINTS. Two points on the earth's surface, at opposite ends of a geomagnetic field line.
COORDINATED UNIVERSAL TIME. By international agreement, the local time at the prime meridian, which passes through Greenwich, England. Therefore, it is also known as GREENWICH MEAN TIME, or some times simply UNIVERSAL TIME.
CORIOLIS ACCELERATION. An aparent acceleration necessary in the momentum equqtions written in a noninertial frame of reference.
COSMIC RAY. An extremely energetic (relativistic) charged particle.
D REGION. A daytime layer of the earth's IONOSPHERE approximately 50 to 90 km in altitude.
Dst INDEX. A geomagnetic index describing variations in the equatorial ringcurrent.
E REGION. A daytime layer of the earth's ionosphere roughly between the altitudes of 85 and 140 km.
EXTREME ULTRAVIOLET (EUV). A portion of the electromagnetic s pectrum from approximately 100 to 1000 angstroms.
F REGION. The upper layer of the IONOSPHERE, approximately 120 to 1500 km in altitude. The F region is subdivided into the F1 and F2 regions. The F2 region is the most dense and peaks at altitudes between 200 and 600 km. The F1 region is a smaller peak in electron density, which forms at lower altitudes in the daytime.
IONOSPHERIC CONVECTION. The movement of a plasma parcel un der the influence of electric and magnetic fields.
FLUENCE. Time integrated flux.
FLUX. The rate of flow of a physical quantitiy through a reference surface.
fMIN. The lowest radiowave frequency that can be reflected from the IONOSPHERE.
foF2. The maximum ORDINARY MODE radiowave frequency capable of reflec-tion from the F2 REGION of the IONOSPHERE.
GEOMAGNETIC STORM. A worldwide disturbance of the earth's magne tic field, distinct from regular diurnal variations.
GMT. Greenwich Mean Time. (See COORDINATED UNIVERSAL TIME.)
HIGH LATITUDES. With specific reference to zones of geomagnetic a ctivity, "high latitudes" refers to 50o to 80o geomagnetic.
INFRARED RADIATION. Electromagnetic radiation with wavelength between 10e-6 and 10e-3 m.
INTERPLANETARY MAGNETIC FIELD (IMF). The magnetic fi eld carried with the SOLAR WIND.
ION DRAG. A momentum transfer coefficient. Often refered to as a force on the neutral atmosphere due to collisions with ions.
IONOSPHERE. The region of the earth's upper atmosphere containing a small percentage of free electrons and ions produced by photoioniza- tion of the constituents of the atmosphere by solar ultraviolet radiation at very short wavelengths (l.t.1000 angstroms). The ionosphere significantly influences radiowave propagation of fre-quencies less than about 30 MHz.
IONOSPHERIC STORM. A disturbance in the F REGION of the IONOSPHERE, which occurs in connection with geomagnetic activity.
JOULE HEATING. Heating of the neutral gas that results from collisi ons with charged particles that are moving under the influence of an electromagnetic field.
K INDEX. A 3-hourly quasi-logarithmic local index of geomagnetic activity relative to an assumed quiet-day curve for the recording site. Range is from 0 to 9. The K index measures the deviation of the most disturbed horizontal component.
KELVIN. A unit of absolute temperature.
Kp INDEX. A 3-hourly planetary geomagnetic index of activity generated in Gottingen, Germany, based on the K INDEX from 12 or 13 stations distributed around the world.
MAGNETOPAUSE. The boundary layer between the SOLAR WIND and the MAGNETOSPHERE.
MAGNETOSPHERE. The magnetic cavity surrounding the earth, carved o ut of the passing SOLAR WIND by virtue of the geomagnetic field which prevents, or at least impedes, the direct entry of the SOLAR WIND PLASMA into the cavity.
MIDDLE LATITUDES. With specific reference to zones of geomagnetic activity, "middle latitudes" refers to 30 deg. to 50 deg. geomagnetic.
PLASMA. Any ionized gas, that is, any gas containing ions and free elect rons.
PLASMASPHERE. The inner region of the Earth's magnetosphere in which ions and electrons are constrained to closed field lines.
SOLAR CYCLE. The approximately 11-year quasi-periodic variation in f requency or number of solar active events.
SOLAR MAXIMUM. The month(s) during the SOLAR CYCLE when the 12-month mean of monthly average sunspot number reaches a maximum. The most recent solar maximum occurred in July 1989.
SOLAR MINIMUM. The month(s) during the SOLAR CYCLE when the 12-month mean of monthly average unspot number reaches a minimum. The most recent minimum occurred in September 1986.
SOLAR WIND.The outward flux of solar particles and magnetic fields from the sun. Typically, solar wind velocities are near 350 km/s but can reach 800 -1000km/s at 1 AU.
THERMOSPHERE. The region of the atmosphere between about 80 and 50 0 km where the neutral temperature increases asymptotically from a minimum at the mesopause twoard a maximum called the exospheric temperature.
TIDES. Global waves with periods of one solar day or an integer fraction of one day.
UNIVERSAL TIME (UT). See COORDINATED UNIVERSAL TIME.
Developed by Mihail.Codrescu