Studies On Monitoring,Analysis And Application Of Chinese Mid-and Low Latitude Ionospheric Scintillation

Ionospheric scintillation is a rapid change in the amplitude and phase of a radio signal as it passes through small-scale plasma density irregularities in the ionosphere. The scintillation may cause problems such as signal power fading, phase cycle slips, receiver loss of lock, etc., and degrade the quality of satellite navigation systems. Being concerned about these effects, ionospheric irregularities/scintillations have become a key component of space weather. By using the GPS ionospheric scintillation/TEC and Beidou ionospheric scintillation measurements over Wuhan (30.6°N, 114.4°E) and Sanya (18.3o N, 109.5o E), a statistical analysis of ionospheric scintillations and transverse drift velocities of irregularities, effects of geomagnetic storm on ionospheric scintillations, and scintillation effects on communication system have been performed. Main results are outlined as follows.First, the scintillation index computation, the principles of ionospheric scintillation monitoring, and the hardware design of GPS/Beidou ionospheric scintillation monitoring system are introduced. Based on the hardware system, several programs have been developed under Windows operating system, which includes a real-time GPS/Beidou ionospheric scintillation monitoring software for measuring and displaying scintillation (when ionospheric scintillation occurs, the raw amplitude and phase data can be saved automatically), data transferring, data processing etc. The realization of these programs provides a basis for obtaining the ionospheric scintillation data and the nowcasting of ionospheric scintillation.Next, automatic recorded raw digital scintillation data are analyzed to obtain the spectral characteristics of irregularities producing ionospheric scintillations, the transverse drift velocities of irregularities during geomagnetic quiet days (Kp<4) and the correlation between amplitude scintillation and power spectral density are estimated. The statistical results reveal that amplitude scintillations mainly occur from postsunset to near midnight or post-midnight. The occurrence rate and intensity of amplitude scintillations are evidently enhanced in equinox months and reduced in winter and summer months. In comparison with amplitude scintillation, the variation of phase scintillation doesn't have these regular variations. Within the period of Year 2005-2006, the simultaneous GPS and Beidou scintillation measurements show that GPS and Beidou amplitude scintillations nearly occur at the same time, but GPS scintillation is stronger than scintillation observed by Beidou. For the analysed dataset, no strong Beidou amplitude scintillation (S4>0.6) is observed. Since the power spectra of scintillation event contain information about the irregularities that produce the scintillation, automatic recorded raw digital scintillation data are analyzed to obtain the spectral characteristics. The statistical results of S4 indices and power spectral indices indicate that the power spectral indices show a linear change with weak amplitude scintillation indices (0.1≤S4<0.3). They increase toward the generation phase of amplitude scintillation activities, and decrease toward the decay phase. But for moderate and strong amplitude scintillations (S4≥0.3), the spectral indices tend to be saturated. The spectral indices range 1.0 to 6.4 with mean value of 3.6. The correlation between estimated transverse drift velocities and LT probably demonstrated that the motion of the irregularities which cause scintillations is highly variable in the initial phase of irregularity development on geomagnetic quiet days. After about 22:00 LT, the estimated velocity tends to follow the same pattern on different days.Finally, we investigate the effects (trigger or inhibit/not trigger) of geomagnetic storms on ionospheric scintillations at Wuhan and Sanya. Magnetometer data, Digisonde data and topside plasma data are also used to help elucidate the possible mechanisms responsible for the effects. The results show that the storm effects on scintillation depend on the maximum dDst/dt determined local time sector. When the determined time is close to postsunset, the enhanced eastward electric field sets the plasma into motion via the vertical ExB drift, which causes the Rayleigh-Taylor mode becomes unstable, and leads to the development of irregularities (spread F and plasma bubbles) producing scintillation. Also, the sporadic E layer played a role in the generation of ionospheric scintillation through changing the Pederson conductivity ratio and suppressing the upward plasma drift, thus reducing the growth rate of irregularities associated with spread-F.Furthermore, the paper presents the statistical analysis of the effects of ionospheric scintillation on fade duration and message reliability. If the fade duration is longer than the message length and the fade depth is below the system threshold, the information can be lost fully or partially. The investigation of the scintillation effects will help engineers to determine margins necessary for communication systems during times of severe ionospheric scintillations.