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Glossary of Solar Terrestrial Terms
A-B|
C|
D|
E|
F|
G|
H|
I-J|
K|
L|
M|
N|
O|
P-Q|
R|
S|
T|
U|
V|
W|
X-Y|
Z|
Daylight Fadeout
When flares occur, increased absorption of a radio wave in the D region may
make part of the HF spectrum unusable. At times, the whole HF spectrum is affected, but
normally the lower frequencies are affected most. Only those circuits with daylight sectors may
be affected.
Decile
If a set of numerical values is ordered from lowest to highest and divided into ten
equal parts, then the values separating the ten parts are called deciles. Hence, there
are nine deciles which separate the ten sections. The upper and lower deciles have
90% and 10% of the values below them, respectively.
Deviative Absorption
Absorption of a radio wave near the point of refraction.
Differential Solar Rotation
Refers to the fact that the rotation of the Sun varies with latitude. Rotation of plasma near
the equator of the Sun is generally faster.
Disc/Disk
When referring to the Sun, it is the visible hemisphere.
Diurnal
Through the day.
D region
The lowest region of the ionosphere where most HF absorption occurs. Present during
daylight hours only. This region does not refract HF radio waves but does attenuate them.
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Educational 
MAG: Normal
ION: Moderate