V. A. Anufriev

Sporadic structures and small-scale irregularity in the nighttime polar ionosphere in the period of high solar activity according to the data of radio occultation measurements on satellite-to-satellite paths

Results of the analysis of 327 sessions of radio occultation on satellite-to-satellite paths are presented. The data are taken in the nighttime polar ionosphere in the regions with latitudes of 67°–88°, and in the period of high solar activity from October 26, 2003 to November 9, 2003. Typical ionospheric changes in the amplitude and phase of decimeter radio waves on paths GPS satellites-CHAMP satellite are presented. It is demonstrated that these data make it possible to determine characteristics of the sporadic Es structures in the lower ionosphere at heights of 75–120 km. Histograms of distribution of the lower and upper boundaries, thickness, and intensity of the Es structures are presented. Dispersion and spectra of amplitude fluctuations of decimeter radio waves caused by small-scale irregularity of the ionospheric plasma are analyzed. The relation of the polar Es structures and intensity of small-scale plasma irregularity to various manifestations of solar activity is discussed. The efficiency of monitoring the ionospheric disturbances caused by shock waves of the solar wind by the radio occultation method on satellite-to-satellite paths is demonstrated.

Effect of the solar-wind shock wave on the polar ionosphere according to the radio occultation data on satellite-to-satellite paths

The polar lower ionosphere is distinguished by its variability due to various effects of solar activity. They result in the appearance of sporadic E S structures, in excitation of the broad spectrum of plasma inhomogeneities, and in variations of the electron concentration. The goal of the present study is to reveal regularities in the variations of the night-side polar lower ionosphere on the basis of radio wave measurements on links from navigation GPS satellites to CHAMP satellite. These ionosphere variations are stipulated by the effect of the flare solar activity. To this end, it was necessary to determine the altitude profiles of the electron concentration N e ( h ) and to find the characteristics of both sporadic E S structures and plasma inhomogeneities. We used the data of 327 radio occultation events of the night side polar ionosphere in regions of latitudes higher than 65° N for the time period from October 25 to November 9, 2003, when particularly strong solar activity was observed. In the radio occultation events of the ionosphere, we have registered the amplitude E and the increments of the phase path ψ for two coherent signals with the frequencies of f 1 = 1.5 GHz and f 2 = 1.2 GHz [1‐3]. In order to determine the excitation degree for small-scale inhomogeneity of the ionosphere plasma, we analyzed random fluctuations of the radio-wave amplitude δ E . These fluctuations were subjected to the standard procedure of statistical processing in order to obtain the root-mean-square amplitude deviation σ . The fluctuations δ E are caused mostly by plasma inhomogeneities located in the ionosphere F region at altitudes h ≈ 200–300 km. The analysis of these fluctuations has shown that the quantity σ is subjected to variations with the minimum values being σ min ≈ 1 .5% and with the maximum fluctuation level attaining 20%. In Fig. 1, dots indicate values of root-mean-square deviations σ for the fluctuations of the amplitude E , which were registered within the period of October 26 to November 9, 2003 (measurement dates are indicated at the horizontal axis). In the beginning of this period, the fluctuation intensity attained σ ≈ 2%, whereas later, on October 27, an increase in the fluctuations was observed. The maximum of the field-intensity fluctuations took place on October 29, 30, and 31 when σ attained 10‐14%. Starting from November 1, the fluctuation intensity began to decrease, and on November 4, elevated values of σ were recorded again. In order to determine the amplitude fluctuations σ A more objectively, we have excluded the slight effect of continually present small fluctuations with σ min = 1.5%. We have used here the relationship = σ 2 – and have realized smoothing the dependence as a function of time by the sliding mean technique with time interval 6-hour.