อภิธานศัพท์ฟิสิกส์ (อวกาศ)


อภิธานศัพท์ฟิสิกส์ (อวกาศ)
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S

SECTOR BOUNDARY

In the SOLAR WIND, the area of demarcation between sec- tors, which are large-scale features distinguished by the predominant direction of the interplanetary magnetic field, toward or away from the sun.
Entry link: SECTOR BOUNDARY

SHORT WAVE FADE (SWF)

A particular ionospheric solar flare effect under the broad category of sudden ionospheric disturbances (SIDs) whereby short-wavelength radio transmissions, VLF, through HF, are absorbed for a period of minutes to hours.
Entry link: SHORT WAVE FADE (SWF)

SMOOTHED SUNSPOT NUMBER

An average of 13 monthly RI numbers, centered on the month of concern.
Entry link: SMOOTHED SUNSPOT NUMBER

SOLAR COORDINATES

Central Meridian Distance (CMD). The angular distance in solar longitude measured from the central meridian.
Entry link: SOLAR COORDINATES

SOLAR CYCLE

The approximately 11-year quasi-periodic variation in frequency or number of solar active events.
Entry link: SOLAR CYCLE

SOLAR MAXIMUM

The month(s) during the SOLAR CYCLE when the 12-month mean of monthly average SUNSPOT NUMBERS reaches a maximum. The most recent solar maximum occurred in July 1989.
Entry link: SOLAR MAXIMUM

SOLAR MINIMUM

The month(s) during the SOLAR CYCLE when the 12-month mean of monthly average SUNSPOT NUMBERS reaches a minimum. the most recent minimum occurred in September 1986.
Entry link: SOLAR MINIMUM

SOLAR SECTOR BOUNDARY (SSB)

The apparent solar origin, or base, of the interplanetary SECTOR BOUNDARY marked by the larger-scale polarity inversion lines.
Entry link: SOLAR SECTOR BOUNDARY (SSB)

SOLAR WIND

The outward flux of solar particles and magnetic fields from the sun. Typically, solar wind velocities are near 350 km/s.
Entry link: SOLAR WIND

SPORADIC E

A phenomenon occurring in the E REGION of the IONOSPHERE, which significantly affects HF radiowave propagation. Sporadic E can occur during daytime or nighttime and it varies markedly with latitude.
Entry link: SPORADIC E

SPOTNIL

Spotless disk
Entry link: SPOTNIL

SUDDEN COMMENCEMENT(SC, or SSC for Storm Sudden Commencement)

An abrupt increase or decrease in the northward component of the geomagnetic field, which marks the beginning of a GEOMAGNETIC STORM.
Entry link: SUDDEN COMMENCEMENT(SC, or SSC for Storm Sudden Commencement)

SUDDEN IMPULSE (SI+ or SI-)

A sudden perturbation of several gammas in the northward component of the low-latitude geomagnetic field, not associated with a following GEOMAGNETIC STORM. (An SI becomes an SC if a storm follows.)
Entry link: SUDDEN IMPULSE (SI+ or SI-)

SUDDEN IONOSPHERIC DISTURBANCE (SID)

HF propagation anomalies due to ionospheric changes resulting from solar FLAREs, PROTON EVENTs and GEOMAGNETIC STORMs.
Entry link: SUDDEN IONOSPHERIC DISTURBANCE (SID)

SUNSPOT

An area seen as a dark spot on the PHOTOSPHERE of the sun. Sunspots are concentrations of magnetic flux, typically occurring in bipolar clusters or groups. They appear dark because they are cooler than the surrounding photosphere.
Entry link: SUNSPOT


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