Effect on Near-Earth Space (Space Weather)
[19] The full chain of disturbances from in an individual large flare
event can be represented in three separate stages of the effect (http://sec.noaa.gov/NOAAscales):
Electromagnetic shock
[20] reaches near-Earth space at the speed of
light, i.e., at the instant of the development of a solar flare.
During its effect in short-wave ranges of electromagnetic
radiation the flux increases by several orders of magnitude
relative to the background values. For instance, in soft X rays
(1-8 Å, 12.5-1 keV) the flux increase can reach four orders.
As a consequence, immediately at the instant of of a flare development
(timescale of the disturbance development is a few
minutes after the beginning of the flare) sudden ionospheric
disturbances develop in near-Earth space, causing a complete radio
silence in the range of high frequencies at the dayside of the
Earth; its duration reaches several hours, upsetting the radio
communication with ships and airplanes. In the range of low
frequencies at the dayside of the planet, errors in positioning
systems of ground-based objects and satellites sharply increase
and are accumulated during many hours. At present, a five-grade
scale for the assessment of this kind of disturbances has been
introduced: from R1 for flares with an X-ray importance
of M (up to 950 events per cycle) to R5 for the most
powerful flares with an X-ray importance of
X17.5 (1-6 times per cycle).
Ejection of energetic solar particles
[21] (protons, electrons, neutrons),
which, reaching NES, cause solar proton events (SPE).
Invasions of high-energy solar particles ( Epr>10 Å)
sharply raise the level of radiation hazard to astronauts, crews
and passengers of high-altitude airplanes at high latitudes,
result in losses of satellites and in failures of scientific and
navigation instruments on space objects, interrupt short-wave
communication in subauroral regions, and provoke a sharp increase
in positioning system errors. This results in serious problems in
positioning of ground-based and space objects. The timescale of
the SPE onset with respect to the beginning of a proton flare is
a few hours, though particles with GeV energies arrive
to the Earth at the speed of light. To describe SPE in near-Earth
space, a five-grade scale of the protons flux assessment
with energies
E> 10 MeV has also been introduced: from
S1 for a proton flux of 10 particles per second per
steradian per square centimeter (up to 50 events per cycle) to
S5 for a proton flux by four orders of magnitude greater
(less than one event per cycle).
Plasma shock:
[22] interplanetary shocks and flows of solar plasma
with enhanced density and/or speed (transient structures,
high-speed solar wind flows) cause magnetic and ionospheric
disturbances in near-Earth space. For disturbances of the
geomagnetic field of the Earth with the intensity exceeding the
threshold of magnetic storms, a five-grade system of their
estimation has also been introduced: from G1 for
disturbances in which at least one three-hour Kp index has
reached 5 (~900 days per solar cycle) to G5 with
Kp = 9 (1-5 days per cycle). It should be kept in mind
that this scale estimates the intensity of a geomagnetic
disturbance; it is quite possible to imagine a situation when the
disturbance has an importance G1 or G2, but in fact there is no
magnetic storm, and the diurnal geomagnetic index Ap is
much lower than the magnetic storm threshold. Certainly, it is a
problem of definition of "MAGNETIC STORM''--magnetic
disturbance with a duration not shorter than 12 hours and with a
mean Ap-index not lower than 27 (in western countries the
threshold value is Ap = 30).
[23] At present the problem of reflection of the situation in
near-Earth space and estimation of its state is solved by "space weather'' services,
which have been created in leading institutes
and organizations all over the world (more than 40 URLs); the main
ones are:
- USA (NOAA SEC, http://www.swpc.noaa.gov);
- Europe (ESA, http://www.esa-spaceweather.net/spweather/current_sw/index.html);
- World Data Center, solar activity indices, Brussels, (http://sidc.oma.be/html/LatestSWData.html);
- Japan (http://hiraiso.nict.go.jp);
- Australia (http://www.ips.gov.au/);
- Russia: Space Research Institute, Russian Academy of Sciences, (http://www.iki.rssi.ru/sw.htm);
- Institute of a terrestrial magnetism, ionosphere and radiowave propagation, Russian Academy of Sciences, (http://www.izmiran.ru).
[24] Their task is to give in real time the main characteristics of
phenomena determining the NES state and the indices describing
the state of the magnetosphere, ionosphere, and other layers of
the Earth's atmosphere. The most informative Web pages of the
space weather state are granted by the Space Weather Prediction
Center of the National Oceanic and Atmospheric Administration
(SWPC, NOAA, USA) (http://www.swpc.noaa.gov/).
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