พุธ, 12 พฤษภาคม 2021, 5:07AM
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อภิธานศัพท์: อภิธานศัพท์ฟิสิกส์ (อวกาศ)
F

#### foEs

The maximum ORDINARY MODE radiowave frequency capable of reflec- tion from the SPORADIC E REGION of the IONOSPHERE.

#### foF2

The maximum ORDINARY MODE radiowave frequency capable of reflec- tion from the F2 REGION of the IONOSPHERE.

#### FORBUSH DECREASE

An abrupt decrease, of at least 10%, of the background galactic COSMIC RAY intensity as observed by neutron monitors.
G

#### GAMMA

A unit of magnetic field intensity equal to 1 x 10.0E-05 GAUSS, also equal to 1 NANOTESLA.

#### GAMMA RAYS

High energy radiation (energies in excess of 100 keV) observed during large, extremely energetic solar FLARES.

#### GAUSS

The unit of magnetic induction in the cgs (centimeter-gram- second) system.

#### GEOMAGNETIC ELEMENTS

The components of the geomagnetic field at the sur- face of the earth. In SESC use, the northward and eastward components are often called the H and D components, where the D component is expressed in gammas and is derived from D (the declination angle) using the small angle approximation.

#### GEOMAGNETIC FIELD

The magnetic field observed in and around the earth. The intensity of the magnetic field at the earth's surface is approximately 0.32 gauss at the equator and 0.62 gauss at the north pole.

#### GEOMAGNETIC STORM

A worldwide disturbance of the earth's magnetic field, distinct from regular diurnal variations. Minor Geomagnetic Storm: A storm for which the Ap index was greater than 29 and less than 50. Major Geomagnetic Storm: A storm for which the Ap index was greater than 49 and less than 100. Severe Geomagnetic Storm: A storm for which the Ap index was 100 or more. Initial Phase: Of a geomagnetic storm, that period when there may be an increase of the MIDDLE-LATITUDE horizontal intensity (H). Main Phase: Of a geomagnetic storm, that period when the hori- zontal magnetic field at middle latitudes is generally decreasing. Recovery Phase: Of a geomagnetic storm, that period when the depressed northward field component returns to normal levels.

#### GEOPHYSICAL EVENTS

Flares (Importance two or larger) with Centimetric Outbursts (maximum of the flux higher than the Quiet Sun flux, duration longer 10 minutes) and/or strong SID. Sometimes these flares are followed by Geomagnetic Storms or small PCA. (Class M Flares)

#### GEOSYNCHRONOUS

Term applied to any equatorial satellite with an orbital velocity equal to the rotational velocity of the earth. The net effect is that the satellite is virtually motionless with respect to an observer on the ground.

#### GMT

Greenwich Mean Time. (See COORDINATED UNIVERSAL TIME.)

The commencement of a geomagnetic storm that has no well-defined onset.

#### GRANULATION

Cellular structure of the PHOTOSPHERE visible at high spatial resolution.

#### GREEN LINE

The green line is one of the strongest (and first-recognized) visible coronal lines. It identifies moderate temperature regions of the CORONA.