The Earth's Ionosphere And Terrestrial Radio Communications

The Earth's ionosphere and terrestrial radio Communications

  The Earth's ionosphere and terrestrial radio communications are disrupted by flare X-rays. The solar ultraviolet radiation is greatly enhanced during solar flares. Sometimes, a single flare may outshine the entire Sun in ultraviolet radiation. Ultraviolet lines are generally enhanced but the L line remains remarkably unchanged during flares. It is interpreted that this line probably is radiated from the entire chromosphere. The Sun is the nearest source of cosmic rays. 

During large flares some of the solar (protons, eiectrons and heavier nuciei) are accelerated to very high energies-particles with energies even higher than 100 eV have been observed The highest flux of particles occurs, of course, in the MeV range. These high energy rays whose composition has been found not to differ significantly from the normal composition of the Sun itself. The most abundant particles are protons. Next comes the Alpha particles, and so on. The fraction of the flare energy contained in the flare cosmic ra s is, of course, quite small, usually less than one per cent. The particles are believed to be accelerated in regions of high magnetic field gradient but no entirely convincing explanation of the origin of solar cosmic rays has yet been established.

 Several theories have been proposed by various authors to explain the origin of solar flares. Flares have been speculated as manifestations of clectrical discharge. It has also been conjectured that flare energy might be produced by nuclear reactions in the surface layer of the Sun. Since both these theories have later been shown to be highly improbable, we shall particles are the solar cosmic not discuss these any further. Although none of the flare theories so far proposed appear completely satisfactory, we shafl briefly discuss two of the theories which can explain manyat the observed charactenstics of flares. Both these theories are based on the high magnetic Kelds in sunspot regions.

 Observationally, it is found that flares occur mostly in regions of complex spot groups, where magnetic fields are high. Magnetic fields of a few hundred gauss can supply energy of the order of a few times 10 erg cm, as flares are observed to possess (using E = B-18 TC). But the theory must also explain the extreme suddenness of the release of this energy. Severny proposed that flares originate as a result of magrnetic discharge near an X-type neutral point which may arise by interaction of fields of two neighbouring bimmagnetic spots in a complex spot group.

 The magnet field gradient is very high near neutral points. The intermetion of spot groups may initiate a kind of perturbation, which may trigger the magnetic discharge. thereby suddenly dissipating large amount of magnetic energy and neutralizing.