[58] We have developed the method of estimation of relative amplitude dI/I of TEC variations from the GPS data and also the results of the analysis of the dI/I dependence on local time and latitude.
[59] We have found that on average, the relative amplitude of the TEC variations varies within the range from 0% to 10% proportional to the value of the geomagnetic index Kp. This dependence is most pronounced at high latitudes (the proportionality coefficient k=0.37 ), is weaker at middle latitudes ( k=0.2 ), and is the weakest at the equator ( k<0.1 ). In quiet conditions the nighttime dI/I values significantly exceed the daytime ones (by a factor of 3-5 at low and high latitudes and by a factor of 2 at middle latitudes). At high levels of the magnetic field disturbance, the geomagnetic control of the amplitude of TEC variations is more important than regular diurnal variations.
[60] At high latitudes one can note insignificant difference of the amplitude of TEC variations for MS and IS ionospheric irregularities (not more than by a factor of 2; while at middle latitudes this factor reaches 10). This manifests a cardinal decrease of the power spectrum of TEC disturbances due to increase of the small-scale part of the spectrum.
[61] The analysis of the corresponding amplitude characteristics of TEC variations and parameters of local irregularities of the electron density showed that recalculation of these characteristics is possible only in the scope of some model of irregularity. In any case the relative amplitude of local electron density disturbances is higher than the amplitude of TEC variations.
[62] The obtained results are not always in accordance with the known mechanisms of generation and propagation of ionospheric irregularity at various latitudes and can be useful for development of the theory.
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