High-latitude GPS TEC changes associated with a sudden magnetospheric compression (original) (raw)
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The global evolution of two major ionospheric storms, occurring on November 4, 1993 and November 26, 1994, respectively, is studied using measurements of total electron content (TEC) obtained from a worldwide network of ground-based GPS receivers. The time-dependent features of ionospheric storms are identified on a global scale using TEC difference maps based on the percent change of TEC during storm time relative to quiet time. The onset of each ionospheric storm is indicated by the appearance of auroralhubauroral TEC enhancements which occur within one hour of the beginning of the geomagnetic storm main phase. Significant TEC enhancements (> 100%) are observed in the winter northern hemisphere. The rate at which TEC enhancements appear is found to correlate with gradients in the Dst index. The large scale ionospheric structures identified during the storms are: (1) nightside auroral/subauroral enhancements which surround the auroral oval; (2) dayside (around noon) high latitude and middle latitude enhancements associated with traveling ionospheric disturbances, and (3) conjugate latitudinal enhancements. For the November 93 storm, a short positive phase (about 15 hours) is followed by a long negative phase (-60 hours). In the November 94 storm, we have identified the clear signature of a traveling ionospheric disturbance (TID) which propagated at a speed of-460 m/s from-70" N to-50" N. The motion of this disturbance appears to conserve angular momentum.
Journal of Atmospheric and Solar-Terrestrial Physics, 2013
The intensity of large-scale traveling ionospheric disturbances (LS TIDs), registered using measurements of total electron content (TEC) during the magnetic storms on October 29-31, 2003, and on November 7-11, 2004, had been compared with that of local electron density disturbances. The data of TEC measurements at ground-based GPS receivers located near the ionospheric stations and the corresponding values of the critical frequency of the ionospheric F region f o F2 were used for this purpose. The variations of TEC and f o F2 were similar for all events mentioned above. The previous assumption that the ionospheric region with vertical extension from 150 to 200 km located near the F-layer maximum mainly contributes to the TEC variations was confirmed for the cases when the electron density disturbance at the F region maximum was not more than 50%. However, this region probably becomes vertically more extended when the electron density disturbance in the ionospheric F region is about 85%.
American Journal of Engineering and Applied Sciences, 2011
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 S 4 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.
Annales Geophysicae, 2009
Measurements of total electron content (TEC) using 263 GPS receivers located in the North and South America continents are presented to demonstrate the simultaneous existence of traveling ionospheric disturbances (TID) at high, mid, and low latitudes, and in both Northern and Southern Hemispheres. The TID observations pertain to the magnetically disturbed period of 29-30 October 2003 also known as the Halloween storm. The excellent quality of the TEC measurements makes it possible to calculate and remove the diurnal variability of TEC and then estimate the amplitude, wavelength, spectral characteristics of the perturbations, and the approximate velocity of the AGW. On 29 October 2003 between 17:00 and 19:00 UT, there existed a sequence of TEC perturbations (TECP), which were associated with the transit of atmospheric gravity waves (AGW) propagating from both auroral regions toward the geographic equator. A marked difference was found between the northern and southern perturbations. In the Northern Hemisphere, the preferred horizontal wavelength varies between 1500 and 1800 km; the propagation velocity is near 700 m/s and the perturbation amplitude about 1 TEC unit (TECu). South of the geographic equator the wavelength of the TECP is as large as 2700 km, the velocity is about 550 m/s, and the TECP amplitude is 3 TECu. Concurrently with our observations, the Jicamarca digisonde observed virtual height traces that exhibited typical features that are associated with TIDs. Here, it is suggested that differences in the local conductivity between northern and southern auroral ovals create a different Joule heating energy term. The quality of these observations illustrates the merits of GPS receivers to probe the ionosphere and thermosphere.
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2010
Positive ionospheric anomalies induced in the polar cap region by co-rotating interaction region (CIR)- and coronal mass ejection (CME)-driven geomagnetic storms are analysed using four-dimensional tomographic reconstructions of the ionospheric plasma density based on measurements of the total electron content along ray paths of GPS signals. The results of GPS tomography are compared with ground-based observations of F region plasma density by digital ionosondes located in the Canadian Arctic. It is demonstrated that CIR- and CME-driven storms can produce large-scale polar cap anomalies of similar morphology in the form of the tongue of ionization (TOI) that appears on the poleward edge of the mid-latitude dayside storm-enhanced densities in positive ionospheric storms. The CIR-driven event of 14–16 October 2002 was able to produce ionospheric anomalies (TOI) comparable to those produced by the CME-driven storms of greater Dst magnitude. From the comparison of tomographic reconstruc...
Geophysical Research Letters, 2007
Nighttime and daytime medium-scale traveling ionospheric disturbances (MSTIDs) are detected with dense and wide detrended total electron content (TEC) maps over North America using multiple GPS receiver networks. The TEC maps cover a wide region of 60-130°W and 24-54°N (30-65°N in geomagnetic latitude), and have a spatial resolution of 1.05°Â 1.05°in latitude and longitude (0.15°Â 0.15°with 7 Â 7 pixel smoothing) and a temporal resolution of 30 seconds. The TEC maps reveal, for the first time, that the nighttime MSTIDs propagate southwestward with 200-500 km wavelengths over North America and have wavefronts longer than $2,000 km. We also observe that daytime MSTIDs with 300-1,000 km wavelengths propagate southeastward until mid-afternoon and southwestward in the late afternoon. In the mid-to-late afternoon, these MSTIDs propagating in the different directions are superimposed. The TEC maps can be a new powerful tool to investigate the MSTIDs.
Annales Geophysicae, 2011
Arrays of GPS Ionospheric Scintillation and TEC Monitors (GISTMs) are used in a comparative scintillation study focusing on quasi-conjugate pairs of GPS receivers in the Arctic and Antarctic. Intense GPS phase scintillation and rapid variations in ionospheric total electron content (TEC) that can result in cycle slips were observed at high latitudes with dual-frequency GPS receivers during the first significant geomagnetic storm of solar cycle 24 on 5-7 April 2010. The impact of a bipolar magnetic cloud of north-south (NS) type embedded in high speed solar wind from a coronal hole caused a geomagnetic storm with maximum 3-hourly Kp = 8and hourly ring current Dst = −73 nT. The interhemispheric comparison of phase scintillation reveals similarities but also asymmetries of the ionospheric response in the northern and southern auroral zones, cusps and polar caps. In the nightside auroral oval and in the cusp/cleft sectors the phase scintillation was observed in both hemispheres at about the same times and was correlated with geomagnetic activity. The scintillation level was very similar in approximately conjugate locations in Qiqiktarjuaq (75.4 • N; 23.4 • E CGM lat. and lon.
The paper presents a method for computing the ionospheric total electron content (TEC) using the combination of the phase and code measurements at the frequencies f1 and f2 of the global positioning system, and applies it to study the TEC variations and disturbances during the magnetic storm in March 2015 using GPS continuous data in the Southeast Asia region. The computation results show that the TEC values calculated by using the combination of phase and code measurements are less dispersed than the ones by using only the pseudo ranges. The magnetic storm whose the main phase was on the 17th March 2015, with the minimum value of the SYM/H index of-223 nT is the biggest during the 24th solar cycle. In the main phase, the crests of the equatorial ionization anomaly (EIA) expanded poleward with large increases of TEC amplitudes, that provides evidence of the penetration of the magnetospheric eastward electric field into the ionosphere and of the enhancement of the plasma fountain effect associated with the upward plasma drifts. In the first day of the recovery phase, due to the effect of the ionospheric disturbance dynamo, the amplitude of northern crest decreased an amount of about 25% with respect to an undisturbed day, and this crest moved equatorward a distance of about 11 o , meanwhile the southern crest disappeared completely. In the main phase the ionospheric disturbances (scintillations) developed weakly, meanwhile in the first day of the recovery phase, they were inhibited nearly completely. During the storm time, in some days with low magnetic activity (Ap<~50 nT), the ionospheric disturbances in the local night-time were quite strong. The strong disturbance regions with ROTI > 0.5 concentrated near the crests of the EIA. The latitudinal-temporal TEC disturbance maps in these nights have been established. The morphology of these maps shows that the TEC disturbances are due to the medium-scale travelling ionospheric disturbances (MSTID) generated by acoustic-gravity waves in the northern crest region of the EIA after sunset moving equatorward with the velocity of about 210 m/s.
2010
Arrays of GPS Ionospheric Scintillation and TEC Monitors (GISTMs) are used in a comparative scintillation study focusing on quasi-conjugate pairs of GPS receivers in the Arctic and Antarctic. Intense GPS phase scintillation and rapid variations in ionospheric total electron content (TEC) that can result in cycle slips were observed at high latitudes with dual-frequency GPS receivers during the first significant geomagnetic storm of solar cycle 24 on 5-7 April 2010. The impact of a bipolar magnetic cloud of north-south (NS) type embedded in high speed solar wind from a coronal hole caused a geomagnetic storm with maximum 3-hourly Kp = 8and hourly ring current Dst = −73 nT. The interhemispheric comparison of phase scintillation reveals similarities but also asymmetries of the ionospheric response in the northern and southern auroral zones, cusps and polar caps. In the nightside auroral oval and in the cusp/cleft sectors the phase scintillation was observed in both hemispheres at about the same times and was correlated with geomagnetic activity. The scintillation level was very similar in approximately conjugate locations in Qiqiktarjuaq (75.4 • N; 23.4 • E CGM lat. and lon.
The occurrence of the mid-latitude ionospheric trough in GPS-TEC measurements
Advances in Space Research, 2009
Simultaneous GPS observations from about 150 stations of European Permanent Network (EPN) have been used for studying dynamics of latitudinal profiles and structure of mid-latitude ionospheric trough (MIT). For the analyses, the TEC maps over Europe were created with high spatial and temporal resolution. The latitudinal profiles were produced from TEC maps with one-hour interval for geographic latitude range from 35N to 75N. The structure of latitudinal profiles relates to the occurrence of the ionospheric trough. The location of the trough depends on season, local time, and both geophysical and geomagnetic conditions. The trough structure in GPS-TEC demonstrates a smooth shape. The trough occurrence as a distinguished structure is more distinct during winter. The relation of TEC in the trough minimum to the equator and polar walls amounted to a factor of 2-4. The diurnal, seasonal as well as storm-time dynamics of the latitudinal profiles and the trough-like structure during different geomagnetic conditions are also presented. Day by day snapshots demonstrate great variability of TEC profiles and MIT, essential changes of the ionosphere structure took place during a storm. Similarly to the F2 region trough, the position of the TEC trough shifts towards lower latitudes during disturbances. In the storm-time, the TEC trough was recognized during daytime at latitudes lower than 70N. This paper presents the statistics describing the dynamics of the trough location.