Features of short-period variability of total electron content at high and middle latitudes

The study presents the results of comparative analysis of features of a short-period (with periods of internal gravity waves) variability of total electron content (TEC) in the ionosphere at middle (Novosibirsk) and high (Norilsk) latitudes over a long period of time (2003–2020). The period analyzed makes it possible to estimate not only diurnal and seasonal variations in the variability, but also its changes within the solar activity cycle. The level of TEC variability is shown to experience pronounced seasonal variations with maxima in winter months. The difference between the level of variability in winter and summer is about two times for Novosibirsk and up to seven times for Norilsk. The variability features a distinct diurnal variation; however, the diurnal dependence at the mid- and high-latitude stations differs significantly. At high latitudes, the level of variability in the winter period strictly depends on solar activity. For the mid-latitude station, there is no clear dependence of variability level on solar activity; in the years of solar maximum, on the contrary, a slight decrease in the variability is observed. In summer, the level of variability at both middle and high latitudes remains practically unchanged and does not depend on solar activity. The main features in the dynamics of variability are shown to be similar at stations located at other longitudes, except for the East American sector. The result obtained suggests that the short-period TEC variability at high latitudes is primarily related to changes in solar activity, but regular variations in the variability at midlatitudes are probably not associated with heliophysical activity. The observed increase in the level of short-period variability in the winter mid-latitude ionosphere is assumed to be related to an increase in wave activity in the stratosphere.

Features of short-period variability of total electron content at high and middle latitudes

The study presents the results of comparative analysis of features of a short-period (with periods of internal gravity waves) variability of total electron content (TEC) in the ionosphere at middle (Novosibirsk) and high (Norilsk) latitudes over a long period of time (2003–2020). The period analyzed makes it possible to estimate not only diurnal and seasonal variations in the variability, but also its changes within the solar activity cycle. The level of TEC variability is shown to experience pronounced seasonal variations with maxima in winter months. The difference between the level of variability in winter and summer is about two times for Novosibirsk and up to seven times for Norilsk. The variability features a distinct diurnal variation; however, the diurnal dependence at the mid- and high-latitude stations differs significantly. At high latitudes, the level of variability in the winter period strictly depends on solar activity. For the mid-latitude station, there is no clear dependence of variability level on solar activity; in the years of solar maximum, on the contrary, a slight decrease in the variability is observed. In summer, the level of variability at both middle and high latitudes remains practically unchanged and does not depend on solar activity. The main features in the dynamics of variability are shown to be similar at stations located at other longitudes, except for the East American sector. The result obtained suggests that the short-period TEC variability at high latitudes is primarily related to changes in solar activity, but regular variations in the variability at midlatitudes are probably not associated with heliophysical activity. The observed increase in the level of short-period variability in the winter mid-latitude ionosphere is assumed to be related to an increase in wave activity in the stratosphere.

Comparison of polar ionospheric behavior at Arctic and Antarctic regions for improved satellite-based positioning

In this paper, we investigate the hemispheric symmetric and asymmetric characteristics of ionospheric total electron content (TEC) and its dependency on the interplanetary magnetic field (IMF) in the northern and southern polar ionosphere. The changes in amplitude and phase scintillation are also probed through Global Ionospheric Scintillation and TEC monitoring (GISTM) systems recordings at North pole [Himadri station; Geographic 78°55′ N, 11°56′ E] and South pole [Maitri station; Geographic 70°46′ S 11°44′ E]. Observations show the range of %TEC variability being relatively more over Antarctic region (−40 % to 60 %) than Arctic region (−25 % to 25 %), corroborating the role of the dominant solar photoionization production process. Our analysis confirms that TEC variation at polar latitudes is a function of magnetosphere-ionosphere coupling, depending on interplanetary magnetic field (IMF) orientation and magnitude in the X ( B x Bx ), Y ( B y By ), and Z ( B z Bz ) plane. Visible enhancement in TEC is noticed in the northern polar latitude when B x < 0 Bx<0 , B y < − 6 nT By<-6\hspace{0.1667em}\text{nT} or B y > 6 nT By>6\hspace{0.1667em}\text{nT} and B z > 0 Bz>0 whereas the southern polar latitude perceives TEC enhancements with B x > 0 Bx>0 , − 6 nT < B y < 6 nT -6\hspace{0.1667em}\text{nT}<By<6\hspace{0.1667em}\text{nT} and B z < 0 Bz<0 . Further investigation reveals the intensity of phase scintillation being more pronounced than the amplitude scintillation during the disturbed geomagnetic conditions with excellent correlation with the temporal variation of TEC at both the stations. Corresponding variations in the parameters are studied in terms of particle precipitation, auroral oval expansion, Joule’s heating phenomena, and other ionospheric parameters. The studies are in line with efforts for improving ionospheric delay error and scintillation modeling and satellite-based positioning accuracies in polar latitudes.

Comparison of polar ionospheric behavior at Arctic and Antarctic regions for improved satellite-based positioning

In this paper, we investigate the hemispheric symmetric and asymmetric characteristics of ionospheric total electron content (TEC) and its dependency on the interplanetary magnetic field (IMF) in the northern and southern polar ionosphere. The changes in amplitude and phase scintillation are also probed through Global Ionospheric Scintillation and TEC monitoring (GISTM) systems recordings at North pole [Himadri station; Geographic 78°55′ N, 11°56′ E] and South pole [Maitri station; Geographic 70°46′ S 11°44′ E]. Observations show the range of %TEC variability being relatively more over Antarctic region (−40 % to 60 %) than Arctic region (−25 % to 25 %), corroborating the role of the dominant solar photoionization production process. Our analysis confirms that TEC variation at polar latitudes is a function of magnetosphere-ionosphere coupling, depending on interplanetary magnetic field (IMF) orientation and magnitude in the X ( B x Bx ), Y ( B y By ), and Z ( B z Bz ) plane. Visible enhancement in TEC is noticed in the northern polar latitude when B x < 0 Bx<0 , B y < − 6 nT By<-6\hspace{0.1667em}\text{nT} or B y > 6 nT By>6\hspace{0.1667em}\text{nT} and B z > 0 Bz>0 whereas the southern polar latitude perceives TEC enhancements with B x > 0 Bx>0 , − 6 nT < B y < 6 nT -6\hspace{0.1667em}\text{nT}<By<6\hspace{0.1667em}\text{nT} and B z < 0 Bz<0 . Further investigation reveals the intensity of phase scintillation being more pronounced than the amplitude scintillation during the disturbed geomagnetic conditions with excellent correlation with the temporal variation of TEC at both the stations. Corresponding variations in the parameters are studied in terms of particle precipitation, auroral oval expansion, Joule’s heating phenomena, and other ionospheric parameters. The studies are in line with efforts for improving ionospheric delay error and scintillation modeling and satellite-based positioning accuracies in polar latitudes.

Variability of GPS-derived Ionospheric TEC over Nigeria during a year of low solar activity

An investigation on the diurnal and seasonal variability of ionospheric Total Electron Content (TEC) over Nigeria is carried out in this study using Global Positioning System (GPS) observable. Nigeria coordinates fall within the trough of equatorial ionization anomaly region of African sector. The TEC data used were obtained from the ground-based GPS receiver stations of the Nigerian GNSS network of stations (NIGNET). The stations with their respective geomagnetic latitudes are Abuja (−1.64º), Yola (−1.32º), Zaria (−0.13º) and Kebbi (0.72º). The results of the diurnal analysis of the relative variability index (VD) revealed higher nighttime values than daytime values. The diurnal variation of VD also showed two conspicuous peaks: the post-midnight and the post-sunset. The diurnal-seasonal variation does not reveal any consistent pattern (no particular season leads the others throughout). On the average, considering all the seasons together maximum TEC variability occurred in Zaria (62%) and least in Yola (54%). Seasonally, maximum VD was recorded during March equinox and the least was recorded during December equinox.

Correlation between tropical-like cyclones in the Mediterranean Sea and the space weather

&lt;p&gt;The ionosphere is the dominant source of the errors in the Global Navigation Satellite Systems &amp;#160;(GNSS), which causes delays and degradation of the GNSS signal. These errors have an impact on many terrestrial and space applications that rely on GNSS. The key parameter for the study of the ionosphere is the Total Electron Content (TEC). In an effort to eliminate the impact of delayed GNSS signal caused by the ionospheric refraction on the accuracy of GNSS positioning and navigation, the researchers made significant advances and began other ionospheric research. This paper studies the variability of GNSS derived TEC values in the International quiet and disturbed days, but also in periods when three tropical-like cyclones in the Mediterranean developed. However, the term tropical-like cyclone distinguishes tropical cyclones developing outside the tropics (like in the Mediterranean Basin) from those developing inside the tropics. Mediterranean tropical cyclones, known as a Medicane, show no difference to other tropical cyclones and can be developed into a hurricane.&lt;/p&gt;&lt;p&gt;Hence, the variability of GNSS derived TEC values time series were analyzed during periods when three Medicanes happened in the fall of 2014, 2016, 2017. Data from eight GNSS stations of the European Permanent Network (EPN) were used and TEC calculations were performed using the VShell program. The results demonstrated that the TEC variability is reflected in daily variations within one month, for three different years of consideration. When the state of the ionosphere was disturbed by external influences, such as the space weather storms, the results demonstrated extreme changes in the number of electrons in the ionosphere. Variations of the TEC and parameter VTEC*sigma were analyzed in the weeks before and after three subtropical cyclones in the Mediterranean Sea, recorded in November 2014, November 2016 and November 2017. Special attention was given to the time series analysis of the variable VTEC*sigma for the GNSS stations located nearby the area where the Medicane developed and stations in regions away from the storm.&lt;/p&gt;&lt;p&gt;The results demonstrated higher VTEC values derived from GNSS stations in the area of the storm on the storm days, as well as the days before and after. Also, the results for the storm in November 2014 showed higher VTEC values compared to the other two tropical-like cyclones. The recorded events of space weather are in correlation with the days when three analyzed Medicanes developed. Therefore, it is difficult to distinguish whether the TEC variability was caused by the space weather storm or the Medicane.&lt;/p&gt;

Ionospheric total electron content of comet 67P/Churyumov-Gerasimenko

We study the evolution of a cometary ionosphere, using approximately two years of plasma measurements by the Mutual Impedance Probe on board the Rosetta spacecraft monitoring comet 67P/Churyumov-Gerasimenko (67P) during August 2014–September 2016. The in situ plasma density measurements are utilized to estimate the altitude-integrated electron number density or cometary ionospheric total electron content (TEC) of 67P based on the assumption of radially expanding plasma. The TEC is shown to increase with decreasing heliocentric distance (rh) of the comet, reaching a peak value of ~(133 ± 84) × 109 cm−2 averaged around perihelion (rh < 1.5 au). At large heliocentric distances (rh > 2.5 au), the TEC decreases by ~2 orders of magnitude. For the same heliocentric distance, TEC values are found to be significantly larger during the post-perihelion periods compared to the pre-perihelion TEC values. This “ionospheric hysteresis effect” is more prominent in the southern hemisphere of the comet and at large heliocentric distances. A significant hemispheric asymmetry is observed during perihelion with approximately two times larger TEC values in the northern hemisphere compared to the southern hemisphere. The asymmetry is reversed and stronger during post-perihelion (rh > 1.5 au) periods with approximately three times larger TEC values in the southern hemisphere compared to the northern hemisphere. Hemispheric asymmetry was less prominent during the pre-perihelion intervals. The correlation of the cometary TEC with the incident solar ionizing fluxes is maximum around and slightly after perihelion (1.5 au < rh < 2 au), while it significantly decreases at larger heliocentric distances (rh > 2.5 au) where the photo-ionization contribution to the TEC variability decreases. The results are discussed based on cometary ionospheric production and loss processes.