First results of Low-latitude Ionospheric Irregularities measured by NavIC and GPS near the Anomaly Crest and the Magnetic Equator (original) (raw)
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Annals of Geophysics
Ionospheric irregularities degrade the performance of radio technological system by producing fluctuations in amplitude and phase of signal passing through them, a phenomenon which is known as scintillation. This study presents diurnal and seasonal variations of ionospheric irregularities during ascending phase of solar activity from 2009 to 2014 by using the amplitude scintillation index S4 computed from a dual frequency GPS receiver installed at the low-latitude station of Varanasi (Lat. 25.31° N, Long. 82.97° E). Scintillation occurrences are found to be higher during nighttime hours (1930-0130 LT), and characterized by an equinoctial maximum throughout the years 2009-2014, except for the peculiar solar minimum year 2009. Gravity wave seed perturbation from lower atmosphere and pre-reversal enhancement (PRE) in zonal electric field have been considered to explain the observed seasonal occurrences, which have been also compared with previous results obtained from observations and model. Influence of solar activity on scintillation occurrence has also been studied, and it was found that there is linear dependence between the solar activity and scintillation occurrence, which is seasonally variable.
INDIAN JOURNAL OF …, 2006
Scintillation of VHF (250 MHz) signals from FLEETSAT (73 o E) was recorded at the equatorial anomaly crest location, Rajkot, in India during 1991-93. The irregularity parameters: S 4 index, and fade rate and spectral parameters: spectral slope and upper roll off frequency, f u are derived and their variation with time of night and with solar activity studied. S 4 index and fade rate increase with solar activity. The spectral slope does not show any systematic dependence on solar activity but f u increases with solar activity. These results, when interpreted in terms of Fresnel size, indicate a shifting of irregularity spectrum towards longer scales in low solar activity period. The temporal variation of these parameters, after the irregularity generation phase, also indicate preponderence of large (kilometer) scale irregularities around midnight-post-midnight period, consistent with earlier simultaneous radar and scintillation observations at Jicamarca. The solar activity dependence of S 4 index is interpreted as due to the variation of background F-region plasma density variations. The results suggest that when strong scattering causes strong scintillations, f u is not representative of the Fresnel scale.
Journal of Physics: Conference Series, 2017
The present investigation is dedicated to the evaluation of GPS performance under disturbed geomagnetic conditions at the equatorial region. When GPS signals encounter the ionospheric irregularities of different size developed during high geomagnetic or solar activity, they undergo rapid changes in their phase and amplitude, known as scintillations. We have studied the occurrence characteristics of scintillation events during geomagnetic storms of different intensity at the crest of equatorial anomaly station Bhopal (23.2N, 77.6E). To accomplish this study we have used two data sets: Disturbed Storm Time (Dst) index and Amplitude Scintillation (S4) index. The geomagnetic storm activity is characterized by the Dst index and the evaluation of GPS performance during disturbed geomagnetic condition is realized through S4 index. We have selected thirty one geomagnetic storms that occurred during the year 2004 and 2005. We then classified these geomagnetic storms and scintillation events into weak, moderate and intense and weak, moderate and strong according to Dst index and S4 index respectively. During all the storm events we observed a good number of scintillation events. We then performed the correlation analysis between the Dst index and S4 index, to find out the impact of storm intensity on the occurrence of scintillation events.
Study of Low-latitude Ionospheric Scintillation using NavIC
2021
Equatorial ionospheric irregularities have been studied in the past and have produced interesting insights about ionospheric physics and processes. Here, we present the initial results of a long term study of ionosphere near the Equatorial Ionization Anomaly (EIA) using the Navigation with the Indian Constellation (NavIC). We have characterized the ionospheric irregularities in terms of the power spectral density at different dynamical frequencies. The formalism is similar to as suggested by [1-3] using the phase screen modelling of the ionosphere. The observations of the C/N o (dB-Hz) variation have been taken by utilizing the L5 (1176.45 MHz) signal of NavIC over Indore located near the northern crest of EIA. We show some initial results as a proof of concept study from a single day (December 4, 2017) scintillation observations. This is a first of its kind study in this region with NavIC. From the power spectral density analysis, we have demonstrated that NavIC is capable of detecting such irregularities over long periods over this region and has implications in forecasting such events in the future.
The present paper reports the occurrence of ionospheric scintillation (S4 > 0.2) measured using GPS receiver (GISTM) at Surat, (21.160N, 72.780E) located near the northern crest of equatorial anomaly in India. The results are presented for data collected during di�erent levels of solar activity from Jan-2009 to Dec-2011. These long time observations phenomenon, which covers low to moderate solar activity period, have shown features such as, diurnal, monthly, seasonal, magnetic activity and solar cycle variation in scintillation occurrence. It was observed that the diurnal variation of the amplitude scintillation predominately occurred after sunset time (18:00 to 06:00 LT). Our observation shows that the duration of scintillation occurrence is found to be maximum during moderate solar activity and least during low solar activity. The seasonal variation shows that the occurrence of scintillation is observed to be maximum for equinox months, less in winter months and least in summer...
Study of GPS Ionospheric Scintillations Over Equatorial Anomaly Station Bhopal
International Journal of Earth Sciences
The paper deals with the statistical analysis of GPS L-band scintillations at the equatorial anomaly station Bhopal (geographic coordinates: 23.2ºN, 77.6ºE; geomagnetic coordinates 14.29° N, 151.12°E) for the descending low solar activity period. During the period of observation (January 2005 to December 2006), the variation of scintillations with local time, season and magnetic activity are reported. The occurrence of scintillation is found to be maximum in equinox months and minimum in summer months. We got different levels of scintillation in some months, but found that the weak scintillation ((0.2<S 4 ≤0.4) is dominating throughout the period. The suppression or enhancement of pre-midnight scintillations during magnetic disturbed and quiet periods is found to be a seasonal and local time dependent factor. Pre-midnight and post midnight occurrence of scintillation is also reported in the paper. Pre-midnight scintillation was found to be maximum in equinox whereas it is minimum in winter months. Importance of the work lies in the evaluation of ionospheric irregularities at equatorial latitudes during the descending low solar activity period.
2021
The ionosphere is a complex and highly variable physical system with the F-layer, which occupies at the highest altitude, contains the greatest concentration of free electrons. Under the extreme circumstance of the ionosphere such as in the periods of high solar activity or magnetic storms or simply in the equinoctial months each year, this layer is very often disturbed. During the disturbances, the small-scale irregularities develop and disperse microwave radio signals, and thus generate rapid fluctuations in the amplitude and phase of satellite signals. This phenomenon causes the ionosphere to be scintillated and is called ionospheric scintillation. The impacts of scintillation cannot be mitigated by the multi-frequency technique that is very effective when dealing with ionospheric delay. Consequently, ionospheric scintillation is one of the most significant threats for space geodetic techniques, especially for stations operating in the polar regions or areas near the equator. To ...
In the present study, we have used 250 MHz radio signal radiated by geostationary satellite UFO-02 to study the occurrence characteristics of very high frequency scintillations associated with ionospheric irregularities during recent extreme low solar activity period from 2008 to 2010 at low latitude Indian station Varanasi (Geomag. latitude = 14°55 0 N, long. = 154°E, Dip angle = 37.3°, Sub-ionospheric dip = 34°). The impact of this recent extreme low solar activity period on ionosphere is investigated. It is observed that the scintillation occurrence is low having maximum percentage occurrence during pre-midnight periods. With increasing interest in understanding the behavior of ionospheric irregularities, an effort has been made to examine also the influence of solar and magnetic activity over the occurrence of scintillations. During the extreme low solar activity years the scintillation occurrences do not vary linearly with the sunspot number. The inhibition and generation of irregularities during enhanced magnetic activity period are explained by considering changes in the electric field. The spectral analysis provide spectral index for irregularities which varied between-1.5 and-8 and characteristic length of irregularities varied between 400 and 1200 m which confirms that 250 MHz scintillations observed over Varanasi were associated with intermediate scale irregularities.
2012 Abstracts IEEE International Conference on Plasma Science, 2012
The paper deals with the statistical analysis of GPS L-band scintillations at the equatorial anomaly station Bhopal (geographic coordinates: 23.2ºN, 77.6ºE; geomagnetic coordinates 14.29° N, 151.12°E) for the descending low solar activity period. During the period of observation (January 2005 to December 2006), the variation of scintillations with local time, season and magnetic activity are reported. The occurrence of scintillation is found to be maximum in equinox months and minimum in summer months. We got different levels of scintillation in some months, but found that the weak scintillation ((0.2<S 4 ≤0.4) is dominating throughout the period. The suppression or enhancement of pre-midnight scintillations during magnetic disturbed and quiet periods is found to be a seasonal and local time dependent factor. Pre-midnight and post midnight occurrence of scintillation is also reported in the paper. Pre-midnight scintillation was found to be maximum in equinox whereas it is minimum in winter months. Importance of the work lies in the evaluation of ionospheric irregularities at equatorial latitudes during the descending low solar activity period.
Journal of Earth System Science, 2011
In recent years, measurements of total electron content (TEC) have gained importance with increasing demand for the GPS-based navigation applications in trans-ionospheric communications. To study the variation in ionospheric TEC, we used the data obtained from GPS Ionospheric Scintillation and TEC monitoring (GISTM) system which is in operation at SVNIT, Surat, India (21.16 • N, 72.78 • E) located at the northern crest of equatorial anomaly region. The data collected (for the low sunspot activity period from August 2008-December 2009) were used to study the diurnal, monthly, seasonal semi-annual and annual variations of TEC at Surat. It was observed that the diurnal variation at the region reaches its maximum value between 13:00 and 16:00 IST. The monthly average diurnal variations showed that the TEC maximizes during the equinox months followed by the winter months, and are lowest during the summer months. The ionospheric range delay to TEC for the primary GPS signal is 0.162 m per TECU.