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 geq 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:

[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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