Relative amplitude of the variations of the total electron content according to the data of the GPS global network

Institute of Solar-Terrestrial Physics, Irkutsk, Russia

Abstract

[1]  A method is developed that makes it possible to estimate the relative amplitude dI/I of the variations of the total electron content (TEC) corresponding to the mean (MS) and intermediate (IS) scales of ionospheric irregularities (from 300 to 30 km). This method is based on the evaluation of TEC variations from the data of the global GPS network. The results of the analysis of the diurnal and latitudinal dependencies of dI/I and distribution probability P(dI/I) for 52 days with different level of geomagnetic activity are presented. The statistical estimates were obtained from the analysis of 10⁶ samples of 2-hour-long TEC series. To obtain statistically significant results, we have chosen three latitudinal zones provided on the Web by the maximum number of GPS sites: high-latitudinal zone of the Northern America (50-80^oN, 200-300^oE; 59 stations), midlatitude zone of the Northern America (20-50^oN, 200-300^oE; 817 stations), and the equatorial zone (20^oS-20^oN, 0-360^oE; 76 stations). It was found that on the average the relative amplitude of the TEC variations varies within the range 0-10% proportionally to the value of the Kp geomagnetic index. This dependence is best 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 value by a factor of 3-5 at low and high latitudes and by a factor of 2 at middle latitudes. At a high level of magnetic field disturbances, the geomagnetic control of the amplitude of TEC variations at high and middle latitudes is much more significant than the regular diurnal variations. At the equator, on the average, the amplitude of both MS and IS variations in quiet and disturbed periods almost does not differ. At high latitudes one can note insignificant difference in the TEC variations amplitude both for MS and IS travelling ionospheric disturbances (TID) (by not more than a factor of 2). At middle latitudes the difference may reach an order of magnitude. This indicates that there is a cardinal depletion of the slope of the power spectrum of TEC disturbances because of a decrease of the amplitude of the small-scale parts of the spectrum. The amplitude of TEC variations almost does not depend on solar activity index F_10.7. The obtained results do not always agree with the known mechanisms of generation and propagation of ionospheric irregularities at various latitudes and may be useful for development of the theory.

Received 20 December 2005; revised 16 November 2006; accepted 20 February 2007; published 27 April 2007.

Keywords: transionospheric propagation; GPS system; ionospheric behavior.

Index Terms: 2439 Ionosphere: Ionospheric irregularities; 2427 Ionosphere: Ionosphere/atmosphere interactions; 6964 Radio Science: Radio wave propagation.