Sudden Increase Of Total Electron Content Research Articles

Some statistics of Ionospheric total electron content variations at mid-latitude zones of Mongolia

This work is focused on the correlation of ionosphere total electron content (TEC) with solar and geomagnetic activities of the space weather at mid-latitude zone. In our analysis, we investigate the TEC time series obtained from dual-frequency GNSS (Global Navigation Satellite System) observations at three continuous GPS/GNSS stations HOVD (48.00N, 91.66E), CHOB (48.08N, 114.53E) and DALN (43.56N, 104.42) for 2013. The statistical analyses are performed on 15 minute averaged yearly TEC values, which reveal the semi-annual anomaly and high correlation with the activities of the Sun and the rotation of the Earth. Phase overlapping seasonal variations of TEC and Sunspot, and Solar flux (10.7) indices, and Earth rotations (LOD) and Atmospheric angular moment (AAM) are observed in our data analyses. Sudden ionospheric storm changes in TEC with geomagnetic storm induced by the extreme solar flare and 2013 events were investigated. The result shows that GPS derived TEC behaves as an indicator of these events showing sudden increase in TEC during the event.

Investigation of Solar Flares Impact on GPS/BDS/GALILEO Broadcast Ionospheric Models

AbstractThe ionosphere is significant to solar‐terrestrial space environment, and the ionospheric delay is considered as one main error source in Global Navigation Satellite System (GNSS). For GNSS single‐frequency users, broadcast ionospheric models (BIMs) play an important role in mitigating the ionospheric delay. Solar activity induces ionospheric disturbances, which can reduce the performance of GNSS. In this study, solar flares impact on Global Positioning System/BeiDou satellite navigation System/Galileo (GPS/BDS/GALILEO) BIMs was investigated in the Asia‐Pacific region. Twelve X‐class and M‐class large solar flares were selected for this study. Total electron content (TEC) derived from selected International GNSS Service and Crustal Movement Observation Network of China (CMONOC) were used to analyze the TEC anomalies and the adaptability of the GPS/BDS/GALILEO BIMs during sample solar flare events. It is verified that very noticeable sudden increase in TEC clearly took place during solar flares. The temporal variation of rate of TEC is more pronounced and rapid with respect to that of TEC. Especially, solar flares impact on the correction accuracy of the GPS/BDS/GALILEO BIMs is significant, as illustrated by a noticeable decrease in relative difference between the observed and modeled TEC values of the GPS/BDS/GALILEO BIMs occurred during the events. Through our investigation, we found that the adaptability of BDS BIM is better than GPS and GALILEO BIMs under solar flare conditions because its coefficients were updated more frequently, while the accuracy of the GALILEO BIM is the highest among current GPS/BDS/GALILEO BIMs in general.

Precise point positioning performance in the presence of the 28 October 2003 sudden increase in total electron content

AbstractIntense disturbances in the ionosphere may produce perturbations in Global Navigation Satellite Systems (GNSS) radio signals that in the most severe cases produce receiver tracking problems, which in turn impact on GNSS positioning accuracy. In this paper we present a case study related to the sudden increase in total electron content (SITEC) induced by the X17.2 solar flare that occurred on 28 October 2003. This is the largest SITEC ever recorded by means of the rate of change of total electron content. A solar radio burst (SRB) occurred in the same period which caused GNSS signal fading and in some cases complete signal loss. Although SITEC contribution to the signal noise cannot be separated from that of SRB, in this paper we show that accuracy degradation may happen in kinematic precise point positioning (PPP) in several stations of the sunlit hemisphere when 30 s sampling rate data are analyzed. The observed errors in the position are the result of the difficulties that cycle slip (CS) detection strategies have to deal with the observables that have been affected by the SITEC.

Study of ionospheric disturbances during solar flare events using the SuperDARN Hokkaido radar

It is well known that many types of ionospheric disturbances occur during solar flare events. The sudden increase in total electron content (SITEC) has been studied for several decades, but total electron content (TEC) data do not provide information on the altitudinal distribution of electron density changes. Previous studies used HF Doppler system data to investigate the contributions of the D-region and F-region ionospheric electron density changes by examining the HF radio wave frequency dependence on the Doppler shift values. In this study we examined the dependence of the elevation angle of the Doppler shift of ground scatter echoes using the SuperDARN Hokkaido radar. We analyzed solar flare events from Dec 2006 to Mar 2012. A sudden fade-out of echoes was observed in almost all the events we analyzed, which was the result of the radio absorption associated with a significant increase in electron density within the D-region ionosphere. In addition, we discovered positive Doppler shifts just before the sudden fade-out of echoes. The Doppler shift is negatively correlated with the elevation angle of received radar waves. It indicates that variation of electron density in the D-region ionosphere is dominant during solar flare events. This result is consistent with a previous study. We also compared the irradiation by X-ray and extreme ultra violet rays observed by the GOES-14 and GOES-15 satellites, which generated Doppler shifts. A positive Doppler shift is consistent with a change of X-ray flux.

GPS Ionospheric Total Electron Content and Scintillation Measurements during the October 2003 Magnetic Storm

Problem Statement: Ionospheric scintillations, cause significant effects on satellite signals for communication and navigation in equatorial region and polar regions mainly during sever magnetic storms periods. This phenomenon is not fully understood due to few studies performed. The study investigates variability of Total Electron Content (TEC) and ionospheric scintillation during October 2003 magnetic storm over Antarctica using ground based GPS technique. Approach: The TEC/scintillation measuring system at Scott Base station, consists of Trimble TS5700 24-channel (a high-precision dual-frequency GPS receiver), a Trimble Zephyr Geodetic antenna and a notebook computer for data logging. The absolute GPS TEC was calculated from differential phase advance GPS observables (1-L2). The GPS signal-to-noise ratios (C/No) and 1/L2 carrier frequencies were employed to determine the scintillation index S4 every 60 s, amplitude scintillation (in dB-Hz) and phase scintillation. Results: The GPS measurements during storm periods at Scott Base show pronounced phase and amplitude scintillation activities, sudden increase in TEC followed by trough-like figure depletions. The maximum value of phase scintillation during the main phase of third episode was 8.3 times the value during Sudden Storm Commencement (SSC) period. Measured amplitude scintillation and S4 index on both 1 and L2 signals are >15dB-Hz and >0.4dB-Hz respectively. Conclusion/Recommendation: The timing and intensity of TEC and scintillation measurements during the storm event were are in a good agreement with WDC measurements. For this particular event, the duration of enhanced periods were approximately 12 h while periods of TEC depletions were more than 30 h. This value implies better understanding of the polar ionospheric response to magnetic storm and eases efforts for better space weather prediction in this region.

Summer‐winter hemispheric asymmetry of the sudden increase in ionospheric total electron content and of the O/N2 ratio: Solar activity dependence

The solar activity dependence of the summer‐winter hemispheric asymmetry (SWHA) of the sudden increase in total electron content (SITEC) due to solar flares and of the O/N2 ratio is statistically analyzed using global GPS‐total electron content data and TIMED Global Ultraviolet Imager column O/N2 ratio data. We focus on observations with nonnegligible residuals of the solar zenith angle (SZA) dependency of SITEC. We examined 109 SITEC events associated with flares larger than M5 X‐ray class flare from 2000 through 2006 and compared the residual SITEC (δ) to the O/N2 ratio. We observed that the latitude gradient of δ has not only an annual variation but also a year‐to‐year variation that is similar to those of the O/N2 ratio. The SWHA magnitude (defined as the annual maximum of latitude gradient) of both δ and O/N2 decreases as the solar activity declines toward its minimum. The correlation coefficient between the annual SWHA magnitudes of δ and those of O/N2 is 0.92, indicating strongly that the SWHA of O/N2 is responsible for that of SITEC in both the annual and year‐to‐year variations. The X‐ray classes of the solar flares have no clear correlation with the solar activity, F10.7 index. We observe that the SWHA magnitude of δ does not depend on the magnitude of solar flare but rather on the background solar activity through the SWHA magnitude of the O/N2.

Summer‐winter hemispheric asymmetry of sudden increase in ionospheric total electron content induced by solar flares: A role of O/N2 ratio

Latitudinal and local time dependences of the sudden increase in total electron content (SITEC) of the ionosphere induced by solar flares were statistically studied. We analyzed 91 SITEC events associated with solar flares larger than M5 X‐ray class from January 2000 to May 2005. Global total electron content (TEC) data from the Scripps Orbit and Permanent Array Center (SOPAC) GPS networks and X‐ray flux data obtained by the Geosynchronous Operational Environmental Satellites (GOES) were used in this study. The global TEC maps revealed that the SITEC value basically depends on the cosine of solar zenith angle (SZA). However, we found that there were significant residuals δ from the linear fitting to the SZA for almost all the flare events. The value of δ is statistically larger in the winter hemisphere than in the summer hemisphere. The latitudinal difference of δ is ∼0.5 TECU between 50°N and 50°S in the solstice. On the other hand, there was not a clear statistical difference in δ between the morning and evening sectors. The similar summer‐winter hemispheric asymmetry was also seen in the daytime distribution of the F region O/N2 density ratio in the MSISE‐90 model. This result indicates that the SITEC phenomena induced by solar flares depend not only on the SZA but also on the O/N2 density ratio. The daytime F region electron density and the background TEC is well known to be determined basically by the O/N2 ratio. It is reasonable that the O/N2 ratio affects the sudden increase in TEC in the same sense as it determines the background TEC.

The sudden increase in ionospheric total electron content caused by the very intense solar flare on july 14, 2000

The present paper studies the sudden increase in total electron content (SITEC) on the ionosphere caused by the very intense solar flare on July 14, 2000. According to the well-known Chapman theory of ionization, we derive the relationship between the temporal variation rate, partial derivativeTEC/partial derivativet, of the total electron content (TEC) and the flare parameters. It is shown that partial derivativeTEC/partial derivativet is proportional to the effective flare radiation flux, I-f, and inversely proportional to the Chapman function, ch(chi), of the zenith angle chi. TEC data observed by the GPS networks located in China, Southeast Asia and Australia during the very intense solar flare on July 14, 2000 are used to statistically investigate the relation between the observed partial derivativeTEC/partial derivativet and ch(chi). The analyses show that the two quantities are inversely proportional to each other, as the theory predicted. The present work shows that GIPS observation is a powerful tool for studying solar flare effects on the ionosphere, i.e. the sudden ionospheric disturbances (SIDs). Because of its advantages of high precision, large geographical distribution and good temporal resolution, GPS TEC observation may reveal quantitatively the process of ionospheric disturbances caused by solar flares. Therefore, our results are of significance in the space weather research.