Equatorial plasma bubbles (EPBs) can cause rapid fluctuations in amplitude and phase of radio signals traversing the ionosphere and in turn produce serious ionospheric scintillations and disrupt satellite-based communication links. Whereas numerous studies on the generation and evolution of EPBs have been performed, the prediction of EPB and ionospheric scintillation occurrences still remains unresolved. The generalized Rayleigh–Taylor (R–T) instability has been widely accepted as the physical mechanism responsible for the generation of EPBs. But how the factors, which seed the development of R–T instability and control the dynamics of EPBs and resultant ionospheric scintillations, change on a short-term basis are not clear. In the East and Southeast Asia, there exist significant differences in the generation rates of EPBs at closely located stations, for example, Kototabang (0.2°S, 100.3°E) and Sanya (18.3°N, 109.6°E), indicating that the decorrelation distance of EPB generation is small (hundreds of kilometers) in longitude. In contrast, after the initial generation of EPBs at one longitude, they can drift zonally more than 2000 km and extend from the magnetic equator to middle latitudes of 40° or higher under some conditions. These features make it difficult to identify the possible seeding sources for the EPBs and to accurately predict their occurrence, especially when the onset locations of EPBs are far outside the observation sector. This paper presents a review on the current knowledge of EPBs and ionospheric scintillations in the East and Southeast Asia, including their generation mechanism and occurrence morphology, and discusses some unresolved issues related to their short-term forecasting, including (1) what factors control the generation of EPBs, its day-to-day variability and storm-time behavior, (2) what factors control the evolution and lifetime of EPBs, and (3) how to accurately determine ionospheric scintillation from EPB measurements. Special focus is given to the whole process of the EPB generation, development and disruption. The current observing capabilities, future new facilities and campaign observations in the East and Southeast Asia in helping to better understand the short-term variability of EPBs and ionospheric scintillations are outlined.

Challenges to Equatorial Plasma Bubble and Ionospheric Scintillation Short-Term Forecasting and Future Aspects in East and Southeast Asia

Abstract A statistical study of L-band amplitude scintillations and zonal drift velocity of Fresnel-scale ionospheric irregularities is presented. Ground-based global positioning system (GPS) data acquired at the equatorial station of Sao Luis (2.33°S, 44.21°W, dip latitude 1.3°S), Brazil, during the solar maximum period from March 2001 to February 2002 are used in the analysis. The variation of scintillations and irregularity drift velocities with local time, season and magnetic activity are reported. The results reveal that for the near overhead ionosphere (satellite elevation angle >45°) a broad maximum in the occurrence of scintillation is seen from October to February. In general, weak scintillations (S 4 90%) during equinox (March–April; September–October) and December solstice (November–February) quiet time conditions and, many of the scintillations, occurred during pre-midnight hours. The mean zonal velocities of the irregularities are seen to be ∼30 m s −1 larger near December solstice, while during the equinoctial period the velocities decay faster and the scintillations tend to cease earlier. On geomagnetically disturbed nights, scintillation activity seems to be strongly affected by the prompt penetration of magnetospheric electric fields and disturbance dynamo effects. On disturbed days, during the equinox and December solstice seasons, the scintillations tend to be suppressed in the pre-midnight hours, whereas during June solstice months (May–August) the effect is opposite. In the post-midnight period, the mostly marked increase in the scintillation occurrence is observed during the equinox months. The results show that during disturbed conditions only one type of storm (when the main phase maximum takes place during the daytime hours) agrees with the Aarons’ description, that is the suppression of L-band scintillations in the first recovery phase night. The results also reveal that the storm-time irregularity drifts become more spread in velocity and occasionally may present westward drift. The present work is important to evaluate the behavior of the ionospheric irregularities at equatorial latitudes under geomagnetically quiet and disturbed conditions, which is one of the most relevant themes in the space weather studies.

Occurrence and zonal drifts of small-scale ionospheric irregularities over an equatorial station during solar maximum

. In this study the climatology of ionospheric scintillations and the zonal drift velocities of scintillation-producing irregularities are depicted for a station located under the southern crest of the equatorial ionization anomaly. Then, the α − μ ionospheric fading model is used for the first- and second-order statistical characterization of amplitude scintillations. In the statistical analyzes, data are used from single-frequency GPS receivers acquired during ∼ 17 years (September 1997–November 2014) at Cachoeira Paulista (22.4° S; 45.0° W), Brazil. The results reveal that the nocturnal occurrence of scintillations follows the seasonal distribution of plasma bubble irregularities observed in the longitudinal sector of eastern South America. In addition to the solar cycle dependence, the results suggest that the occurrence climatology of scintillations is also modulated by the secular variation in the dip latitude of Cachoeira Paulista, since the maximum occurrence of scintillations during the peak of solar cycle 24 was ∼ 20 % lower than that observed during the maximum of solar cycle 23. The dynamics of the irregularities throughout a solar cycle, as investigated from the estimates of the mean zonal drift velocities, presented a good correlation with the EUV and F10.7 cm solar fluxes. Meanwhile, the seasonal behavior showed that the magnitude of the zonal drift velocities is larger during the December solstice months than during the equinoxes. In terms of modeling, the results for the α − μ distribution fit quite well with the experimental data and with the temporal characteristics of fading events independently of the solar activity level.

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Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

We present a study on the effects of ionospheric scintillation on BeiDou Navigation Satellite System (BDS) precise point positioning (PPP) at low-latitude regions. The analysis was carried out using BDS data collected by a newly installed ionospheric scintillation monitoring receiver located at Sha Tin of Hong Kong and 15 Hong Kong Satellite Positioning Reference Station Network (SatRef) stations from October 6, 2015, to November 17, 2015. The rate of total electron content index (ROTI) derived from BDS data is shown to be a good indicator in observing the ionospheric scintillation. The analysis indicates that the correlation coefficient between ROTI and $$S_{4}$$
 /
 $$\sigma_{\varphi }$$
 is about 0.7. Under scintillation activity, the time series of positioning results for BDS static PPP show a stable variation, but the irregularities are reflected in the time series of code and phase residuals with the maximum values as 7.096 and − 0.469 m, respectively. Further, under scintillation condition it is found that positioning results for BDS kinematic PPP vary significantly and the range can reach several meters in the east, north and up directions. The statistical results show that the three-dimensional root-mean-square of BDS PPP is 1.842 m under scintillation condition, which is much larger than that for non-scintillation condition as 0.155 m.

Investigation of ionospheric scintillation effects on BDS precise point positioning at low-latitude regions

Two widely used scintillation indexes $$ S_{4} $$ and $$ \sigma_{\varphi } $$ are generated by dedicated ionospheric scintillation monitoring receivers (ISMRs), which typically have 50-Hz temporal resolution and thus require substantial memory capabilities. Taking into consideration the huge number of common Global Navigation Satellite System (GNSS) receivers, the derivation of a GNSS receiver-based scintillation index as a supplement to the ISMR indexes is expected to improve the study of ionospheric scintillation. We developed an amplitude scintillation index, $$ S_{{4{\text{c}}}} $$, which is derived from the carrier-to-noise density ratio ($$ C/N_{0} $$) data released by common geodetic GNSS receivers operating at 1-Hz. The reliability of the $$ S_{{4{\text{c}}}} $$ index is compared with the typical scintillation index $$ S_{4} $$ of three ISMRs located in Hong Kong and Brazil. The statistics indicate that during scintillation activity, the correlation coefficient between $$ S_{{4{\text{c}}}} $$ (derived from common receivers) and $$ S_{4} $$ (generated by ISMRs) is generally higher than 0.9. The reliability of $$ S_{{4{\text{c}}}} $$ was also verified based on 1-year observations from two adjacent stations in Hong Kong, which are equipped with Leica GR50 and Septentrio PolaRxS Pro receivers, respectively. Long-term scintillation occurrence ($$ S_{{4{\text{c}}}} $$ > 0.2 vs. $$ S_{4} $$ > 0.2) rates show good agreement between $$ S_{{4{\text{c}}}} $$ and $$ S_{4} $$. In addition, two-dimensional $$ S_{{4{\text{c}}}} $$ maps (1° × 1°) generated by GPS L1 and BDS B1 signals data collected at 117 continuous operation tracking stations in China clearly show post-sunset super plasma bubbles as the source of ionospheric scintillation during the main phase of the intense storm that occurred on September 8, 2017. These results demonstrate the feasibility of using the $$ S_{{4{\text{c}}}} $$ index derived from the large volume of GNSS observations recorded by non-scintillation GNSS receivers for the study and monitoring of ionospheric scintillation.

Hongke Li

Papers

Statistical characteristics of low-latitude ionospheric scintillation over China