Systematic behavior of semiempirical global ionospheric models in quiet geomagnetic conditions (original) (raw)
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Ionospheric total electron content: Spatial patterns of variability
Journal of Geophysical Research: Space Physics
The distinctive spatial patterns of the ionosphere's total electron content (TEC) response to solar, seasonal, diurnal, and geomagnetic influences are determined across the globe using a new statistical model constructed from 2-hourly TEC observations from 1998 to 2015. The model combines representations of the physical solar EUV photon and geomagnetic activity drivers with solar-modulated sinusoidal parameterizations of four seasonal cycles and solar-modulated and seasonally modulated parameterizations of three diurnal cycles. The average absolute residual of the data-model differences is 2.1 total electron content unit, 1 TECU = 10 16 el m À2 (TECU) (9%) and the root-mean-square error is 3.5 TECU (15%). Solar and geomagnetic variability, the semiannual oscillation and the diurnal and semidiurnal oscillations all impact TEC most at low magnetic latitudes where TEC itself maximizes, with differing degrees of longitudinal inhomogeneity. In contrast, the annual oscillation manifests primarily in the Southern Hemisphere with maximum amplitude over midlatitude South America, extending to higher southern latitudes in the vicinity of the Weddell Sea. Nighttime TEC levels in the vicinity of the Weddell Sea exceed daytime levels every year in Southern Hemisphere summer as a consequence of the modulation of the diurnal oscillations by the seasonal oscillations. The anomaly, which is present at all phases of the solar cycle, commences sooner and ends later under solar minimum conditions. The model minus data residuals maximize at tropical magnetic latitudes in four geographical regions similar to the ionosphere pattern generated by lower atmospheric meteorology. Enhanced residuals at northern midlatitudes during winter are consistent with an influence of atmospheric gravity waves.
Journal of the Nigerian Society of Physical Sciences
This paper compares the quiet time variation of the Total Electron Content (TEC) over four stations located at high and mid latitudes in the northern and southern hemispheres of the African-European longitudes. Five years Global Positioning System (GPS) data, from 2002 to 2006, representing the periods of high to low solar activities were used for the study. Generally, the maximum diurnal values of TEC are observed between 10:00 – 14:00 LT in all the stations during the periods investigated. The minimum values of TEC are observed during the pre-sunrise hours for the two mid latitude stations and around the pre-midnight/post-midnight for the high latitude stations. The maximum values of TEC, however vary with season, latitude and solar activity in all the stations. The values decrease with increase in latitudes and decrease in solar activity. The values range between 10 – 32 and 11 – 50 TECU respectively, for high and mid latitudes for all the years considered. Seasonally, the highes...
Radio Science, 1997
In this study, Total Electron Content (TEC) observations acquired by a GNSS receiver installed at Sonmiani (Geog. Coord. 25.19 • N, 66.74 • E, Geomag. Coord. 17.62 • N, 141.5 • E) are being reported for the first time. The data utilized is hourly instantaneous TEC values during 10 International Quiet Days (IQDs) per month from Jul-14 to Jun-15, totaling 120 observation days for monitoring nominal TEC. The findings confirm the semi-annual trend of TEC over Sonmiani, which lies at the northern crest of Equatorial Ionization Anomaly (EIA) region. The TEC measurements are then compared with NeQuick-2 and International Reference Ionosphere (IRI-2012) models. It was found that the TEC values derived from NeQuick-2 are in better agreement with GNSS measurements than those from IRI-2012. The TEC measurements also show seasonal variation which is largest during Equinox months. The TEC value in Dec solstice is higher than the Jun solstice, which confirms that the seasonal anomaly is playing a major role in this
Journal of applied science and environmental management, 2024
Ionospheric modelling is a major approach to predicting the behavior of the ionosphere particularly in regions where Global Positioning Systems (GPS) are not readily available. Hence, the objective of this paper is to measure and compare Total Electron Content (TEC) for Assessment of Ionospheric Models during April 7, 2000 Geomagnetic Storms. Measured Total Electron Content (TEC) from experimental records (April 5-9, 2000) were compared with those predicted by the improved versions of the International Reference Ionosphere (IRI-2012 and IRI-Plas2015) and the NeQuick models. The mean values of TEC in five days of the months were plotted against the hours of the same day and the root mean square error of the models which shows their deviations from the GPS data were used to observe the diurnal variations in TEC and the performances of the ionospheric models respectively. The data obtained confirmed that TEC has their highest values during the midnight period and lowest values during the sunset period at the Australian stations and we also confirmed that European stations had their highest TEC values during the daytime and their lowest values during the night time. We affirmed that the North American station in USA had its highest TEC values during the night time and lowest values during day time. The Asian station had its highest TEC values during the day time and lowest values during the midnight period. However, NeQuick, IRIPlas2015, and NeQ-IRI produced better estimate of TEC than the IRI-2001 and IRI-2001COR at all locations during the phases of the geomagnetic storm.
The use of the Global Positioning System (GPS) phase and group-delay measurements by a receiver at the for ionospheric studies has been described. These observations show that any new GPS measurements of ionospheric Total Electron Content (TEC) can be a valuable tool for global, regional and local monitoring of the regular and disturbed ionospheric structure and electrodynamics in time domain less than a few minutes. In addition, the data set allowed the comparison between the experimental data and values derived from ionospheric models.
Journal of Geophysical Research: Space Physics, 2018
A new method for probing the spatial and temporal features of the topside ionosphere is presented. The Vary-Chap model given by linear functions was used to estimate the scale height and its gradient. Based on the global coverage of the Radio-Occultation (RO) data, Spherical Harmonic functions were applied to detect some spatial features of the estimated topside, such as an anti-correlation between the scale height and its gradient in the geomagnetic Equator. In addition, a Fourier time-dependent method was applied in ten consecutive years to both estimate and predict the temporal evolution of the topside. As a result, the temporal variation of the peak height showed high correlation with the scale height and the electron density peak showed high correlation with the Global Electron Content and a strong anti-correlation with the gradient of the scale height. This suggests that the equatorial topside was mainly controlled by the ExB equatorial vertical drift, that increases the scale height and the peak height, and the diffusion of the electrons along the geomagnetic lines, that reduces the gradient of the scale height at the equatorial region and increases the electron density peak in the low-latitudes. Also, a one-year prediction with a reasonable margin of errors showed that the proposed model is a powerful tool for predicting features of the topside ionosphere, which may have special interesting for the development of climatological models.
Evaluation of ionospheric models for Central and South Americas
Advances in Space Research, 2019
This work shows a 20-month statistical evaluation of different Total Electron Content (TEC) estimators for the Central and South America regions. The TEC provided by the International GNSS Service (IGS) in the area covered around the monitoring GNSS stations are used as reference values, and they are compared to TEC estimates from the physics-based (Sheffield University Plasmasphere Ionosphere Model-PIM) and the empirical (Neustrelitz TEC Model-Global-NTCM-GL) models. The mean TEC values show strong dependence on both solar activity and seasonal variation. A clear response was noticed for a period close to 27 days due to the mean solar rotation, as seen in the solar flux measurements. Consistently, the mean TEC values present an annual variation with maxima during December solstices for southern stations with geographic latitudes greater than 25 S. Semi-annual dependence has been observed in TEC for the sector between AE25 of geographical latitude but with modulations caused by fluctuation in the solar radiation. We observed a high correlation between solar radio flux F10.7 and NTCM-GL outputs. The fast increases in F10.7 index have caused significant differences between IGS data and NTCM-GL results mainly for equatorial and low latitudes. For the initial months of the evaluated period (January-April, 2016), the errors of the physics-based model were considerably larger, mainly near the equatorial ionization anomaly. The discrepancies observed in SUPIM results are mainly due to inputs of solar EUV flux. The EUVAC model has underestimated EUV flux between January and April, 2016, when the solar activity was moderated and Solar2000 model has overestimated such flux during low solar cycle period between May and August, 2017. In relation to IGS data, the two assessed models presented smaller differences during the June solstice season of 2016.
1988
Total ionospheric electron contents (TEC) were measured by global positioning system (GPS) dual-frequency receivers developed by the Jet Propulsion Laboratory (JPL). The measurements included P-code (precise ranging code) and carrier phase data for six GPS satellites during multiple 5-hour observing sessions. A set of these GPS TEC measurements were mapped from the GPS lines of sight to the line of sight of a Faraday beacon satellite by statistically fitting the TEC data to a simple model of the ionosphere. The mapped GPS TEC values were compared with the Faraday rotation measurements. Because GPS transmitter offsets are different for each satellite and because some GPS receiver offsets were uncalibrated, the sums of the satellite and receiver offsets were estimated simultaneously with the TEC in a least squares procedure. The accuracy of this estimation procedure is evaluated, indicating that the error of the GPS-determined line of sight TEC can be at or below 1×1016 el/m2. Consequ...