Guo-jun Wang

Relationship between strong range spread F and ionospheric scintillations observed in Hainan from 2003 to 2007

Data from a DPS-4 Digisonde and an ionospheric scintillation monitor, both located at the low-latitude station Hainan (109.1 degrees E, 19.5 degrees N; dip latitude 9 degrees N), were analyzed to study the strong range spread F (SSF) and its correlation with ionospheric scintillations observed in the period of declining solar cycle 23 from 2003 to 2007. The results show that the maximum and minimum of the occurrence of SSF appeared in nearly the same months as those of the GPS L band scintillations. The variations in SSF occurrence were also similar to those of the scintillations. From 2003 to 2007, both the SSF and the scintillation occurrences decreased from the high solar activity year to the low solar activity year. The correlation coefficient between the occurrences of the SSF and the GPS L band scintillation was as high as 0.93, suggesting associated mechanisms producing SSF and scintillations. Electron density depletions extending from the bottomside to the topside ionosphere are the likely cause explaining the high correlation.

Ionospheric plasma bubbles observed concurrently by multi‐instruments over low‐latitude station Hainan

Previous studies have shown that the ionospheric “strong range spread F” (SSF) closely correlates with the occurrence of scintillations caused by equatorial plasma bubbles. However, there is no report on concurrent observations of SSF and bubbles with in situ measurement. This paper discusses two cases of concurrent observations with a DPS4 Digisonde and a collocated scintillation monitor at the low-latitude station Hainan (19.5°N, 109.1°E), and with in situ ion density measurements made by the ROCSAT-1 satellite. Two case studies were made for 10 and 23 April 2004, respectively. In both cases, the SSF occurred before midnight and lasted more than 3.5 h. The scintillations were accompanied with strong range SF. Concurrently, the ROCSAT-1 satellite observed plasma bubbles over Hainan station. In the first case, two bubbles were observed by the satellite with east-west sizes of more than ~200 km over Hainan station. Two bubbles were also observed in the second case with east-west extensions of about 220 km and 35 km, respectively. For the first time, direct observational evidence is provided for the causal relationship between equatorial plasma bubbles with in situ measurement and the concurrent occurrence of SSF and strong scintillations.

Correlation between ionospheric strong range spread F and scintillations observed in Vanimo station

Data from the ionospheric scintillation monitor and ionosonde at the low-latitude station Vanimo (2.7 degrees S, 141.3 degrees E; dip latitude 11 degrees S) in the Southern Hemisphere in 2003 were statistically analyzed to study the correlation between scintillations and strong range spread F (SSF). The results showed that the observed SF had four types: frequency spread F, mixed spread F, range spread F (RSF), and strong range spread F (SSF). SSF and scintillations usually occurred simultaneously and had nearly the same periods and similar trends. Only the SSF had a high correlation (coefficient 0.7199) with the scintillation, while the other three types of SF were uncorrelated with the scintillation. This implies that the SSF has a different physical mechanism from the RSF, and both the SSF and the scintillation are caused by equatorial plasma bubbles. This is important for us to understand the physical mechanisms of the irregularities in the low-latitude ionosphere.

A case study on ionospheric scintillations at low latitude associated with a plasma blob observed in situ

In general, ionospheric scintillations at low latitude are considered as signatures of equatorial plasma bubbles (depletions). However, some authors considered that scintillations may also be associated with plasma blobs (enhancements), but there was no in situ measurement hitherto to confirm it. We performed a case study on the concurrent observation of an ionospheric plasma blob with in situ measurements by ROCSAT-1 (i.e. Formosa satellite-1) and of GPS amplitude scintillations in the low-latitude ionosphere on 1 June 2003. The blob measured in situ had a scale size of about 800 km in the F layer, and the ion density inside the blob was severely disturbed. Amplitude scintillation with S-4>0.3 was observed concurrently in the same longitude range as the blob measured. This case study provides evidence of simultaneously observed GPS amplitude scintillations and a blob in situ, and it confirms that scintillations can be associated with plasma blobs in the low-latitude ionosphere.

Characteristics of low altitude ionospheric electric field over Hainan Island, China

A sounding rocket experiment undertaken by the Chinese Meridian Project from a low latitude station on Hainan Island (19.5°N, 109.1°E), China, measured the DC electric field during 05:45–05:52 LT on April 5, 2013. The data observed using a set of electric field double probes, as part of the rocket’s scientific payload, revealed the special profile of how the vectors of the DC electric field vary with altitude between 130 and 190 km. During the experiment, the vertical electric field was downward, and the maximum vertical electric field was nearly 5.1 mV/m near the altitude of 176 km. The zonal electric field was eastward and slightly less than 0.6 mV/m. The plasma drift velocity was estimated from the E×B motion, and the zonal drift velocity was eastward and of the order of 100 m/s. The zonal wind velocity was also estimated using the drift velocity near the maximum density height in the F1-region, and it was found to be nearly 120 m/s. This work constituted the first in situ measurement of the DC electric field conducted within the F1-region (between 130 and 190 km) in the East Asian Sector.

Seasonal variation of GPSTEC at low latitude station

Measurements of GPS STEC carried out at Hainan station, are used to derive vertical total electron content (VTEC). The ionospheric variability of TEC for different seasons is discussed; GPS TEC is compared with the NeQuick model. We have found that the diurnal variation of TEC for different seasons shows the winter anomaly and semiannual anomaly; in general the diurnal maximum is the highest in equinox months, the least in summer months; The TEC of NeQuick model underestimates the TEC during night-time and overestimates it during daytime independent of the season.