[2] Study of ionospheric irregularities is one of the important problems of the geophysics and radiophysics. Ionospheric irregularities influence radio wave propagation within the broad radio wave range from hundreds of meters to tens of centimeters used in radiocommunication, radiolocation, and radioastronomy [Afraimovich and Karachentsev, 2003; Afraimovich et al., 1992, 1994, 1999; Lawrence et al., 1964; Spoelstra and Kelder, 1984].
[3] The middle-scale (MS) irregularities with a typical period of 20-60 min are manifested in the form of middle-scale and large-scale (depending on the propagation velocity) travelling ionospheric disturbances (TID) and are an ionospheric response of acoustic gravity waves (AGW) [Afraimovich et al., 2000a; Hines, 1960; Hocke and Schlegel, 1996; Hunsucker, 1982; Oliver et al., 1997]. TID produce refractive distortions of transionospheric radio signals [Afraimovich et al., 1992, 1994, 1999; Jacobson et al., 1995; Lawrence et al., 1964; Spoelstra and Kelder, 1984].
[4] Intermediate-scale irregularities (IS) with a period of 2-10 min and dimensions of 10-30 km are usually associated with the spread F [Bowman, 1990, 1991, 1992] and by size are close to small-scale irregularities causing scintillations of transionospheric signals [Yeh and Liu, 1982].
[5] The experimental study of the ionospheric irregularities is based on the use of radiophysical methods of ionospheric sounding. Recently, considerable progress has been achieved in the study of ionospheric irregularities using the new technology of radio sounding by signals of the satellite navigation system GPS [Davies and Hartmann, 1997]. This technology allows us to obtain data on variations of the total electron content (TEC) in the ionosphere with high spatial and time resolution in various regions of the globe. Advancements in the development of this technology enabled study of characteristics of wide range of the ionospheric irregularities as a function of local time, latitude, geomagnetic field disturbances, and other geophysical factors.
[6] The goal of this paper is a complex study of spatial and temporal characteristics of the absolute ( dI ) and relative ( dI/I ) amplitudes of TEC variations in quiet and disturbed geomagnetic conditions.
[7] Section 2 contains general information on the experiment. Section 3 is dedicated to the description of the method of data processing. The main results of the analysis of the diurnal dependence and statistical characteristics of the amplitude of TEC variations as a function of the Kp and F10.7 indices are described in sections 4 and 5. The problem on the correspondence between TEC amplitude characteristics and parameters of local irregularities of the electron density is discussed in section 6. The obtained results are discussed in section 7.
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