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Solar Data Description
2800 MHz Solar Flux
The sun emits radio energy with a slowly varying intensity. This radio flux,
which originates from atmospheric layers high in the sun's chromosphere and low
in its corona, changes gradually from day-to-day, in response to the number of
spot groups on the disk. Radio intensity levels consist of emission from three
sources: from the undisturbed solar surface, from developing active regions,
and from short-lived enhancements above the daily level. Solar flux density at
2800 megaHertz has been recorded routinely by radio telescope near Ottawa since
February 14, 1947. Each day, levels are determined at local noon (1700 GMT)
and then corrected to within a few percent for factors such as antenna gain,
atmospheric absorption, bursts in progress, and background sky temperature.
Beginning in June 1991, the solar flux density measurement source is Penticton,
B.C., Canada.
The data contain fluxes from the entire solar disk at a frequency of 2800
megaHertz in units of 10 to the -22 Joules/second/square meter/Hertz. Each
number has been multiplied by 10 to suppress the decimal point. Three sets of
fluxes - the observed, the adjusted, and the absolute - are summarized. Of the
three, the observed numbers are the least refined, since they contain fluctuations as large as 7% that arise
from the changing sun-earth distance. In contrast, adjusted fluxes have this variation removed; the numbers
in these tables
equal the energy flux received by a detector located at the mean distance between sun and earth. Finally, the absolute
levels carry the error reduction
one step further; here each adjusted value is multiplied by 0.90 to compensate
for uncertainties in antenna gain and in waves reflected from the ground.
Missing data will be represented as ---. The data are displayed as the
flux value multiplied by ten (same as the table format). For example,
1324 converts to 132.4 solar flux units for Jan 1, 1950.
Relative Sunspot Number
The relative sunspot number is an index of
the
activity of the entire visible disk of the Sun. It is determined each day
without reference to preceding days. Each isolated cluster of sunspots is
termed a sunspot group, and it may consist of one or a large number of
distinct spots whose size can range from 10 or more square degrees of the
solar surface down to the limit of resolution (e.g., 1/25 square degree). The
relative sunspot number is defined as R = K (10g + s), where g is the number
of sunspot groups and s is the total number of distinct spots. The scale
factor K (usually less than unity) depends on the observer and is intended to
effect the conversion to the scale originated by Wolf.
Group Sunspot Numbers (Rg)
Rg values were derived to provide
a homogeneous record of solar activity
from 1610 to 1995. Care was taken that the long-term changes are
more self-consistent than are the changes using the Wolf Sunspot Numbers.
Standard deviations
Contains daily standard deviations of the Group Sunspot
Numbers for 1610 to 1995. These numbers represent the random errors in the daily means.
Number of observations
The daily average number of observations per
day used in forming the daily means.
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