F2 Layer Peak Electron Density Research Articles

Long term relationships of electron density with solar activity

Greenhouse gases such as carbon dioxide and methane that are causing climate change may cause long term trends in the thermosphere and ionosphere. The paper aims to contribute to explore long term effects in the ionosphere focusing on the impact of solar activity changes. Peak electron density data derived from vertical sounding measurements covering 65 years at the ionosonde stations Juliusruh (JR055), Boulder (BC840) and Kokubunji (TO536), have been utilized to estimate the long-term behavior of daytime ionospheric F2 layer ionization in relation to the solar 10.7 cm radio flux index F10.7. In parallel, Global Navigation Satellite System (GNSS) based vertical total electron content (TEC) data over the ionosonde stations in combination with the peak electron density data have been used to derive the equivalent slab thickness τ for estimating long-term behavior in the time period 1996-2022. A new approach has been developed for deriving production and loss term proxies for studying long-term ionization effects from F2 layer peak electron density and TEC data. The derived coefficients allow estimating the long-term variation of atomic oxygen and molecular nitrogen concentrations including their ratio during winter months. The noon-time slab thickness values over Juliusruh correlate well with the decrease of F10.7 and the F2 layer peak height and enable estimating the neutral gas temperature. The equivalent slab thickness decreases by about 20 km per decade in the period 1996-2022, indicating a thermospheric cooling by about 100 K per decade for Juliusruh. Whereas the oxygen concentration decreases, the loss term, considered as a proxy for molecular components of the neutral gas, in particular N2, increases with the long-term solar activity variation. Considering 11 years averages of the production and loss terms under wintertime conditions, the long-term study reveals for the O/N2 ratio a percentage decrease of 5% per decade and for F10.7 about 3.1% per decade in a linear approach referred to the year 1970. Linear models of 11 years averaged NmF2 and foF2 from corresponding F10.7 show a very close correlation with the temporal variation of F10.7 until about 1990. The root mean square errors are in the order of 1.0 -1.3 ‧1010m-3 for NmF2 and 0.03-0.05 MHz for foF2. After 1990 the linear models clearly deviate from F10.7 at all selected ionosonde stations indicating a non-local effect.

Statistical Study of the Ionospheric Slab Thickness at Beijing Midlatitude Station

The ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2) is known as the ionospheric equivalent slab thickness (EST, also known as τ), and it is a crucial indicator of the ionosphere. Using TEC and NmF2 data from the years 2010 to 2017, this work conducts a comprehensive statistical analysis of the ionospheric slab thickness in Beijing, which is in the midlatitude of East Asia. The outcomes show that the τ have different diurnal variations at different seasons for high/low-solar-activity years. On the whole, daytime τ significantly greater than nighttime τ in summer, and it is the opposite for the τ in winter regardless of the solar cycle, whereas the τ during equinox shows different morphology for high/low-solar-activity years. Specifically, daytime τ is larger than nighttime τ during equinox in years of high-solar activity, while the opposite situation applies for the τ during equinox in years of low-solar activity. Moreover, the pre-sunrise and post-sunset peaks are most pronounced during winter for low-solar-activity years. In summer, there is a great increase in τ during the morning hours when compared with other seasons. Furthermore, the τ decreases with the solar activity during nighttime, whereas it seems there is no correlation between daytime τ and solar activity. This paper explained the primary diurnal variations in τ across different seasons during high-/low-solar-activity years by analyzing relative fluctuations of TEC and NmF2 throughout the corresponding period. In addition, based on the disturbance index (DI), which is calculated by instantaneous τ and its corresponding median, this paper found that the storm-time τ might increase when compared with its median value during the daytime, while it may both increase and decrease during the nighttime, especially around dawn and dusk hours. To further analyze the physical mechanism, an example on 2 October 2013 is also presented. The results indicate that the positive disturbance of τ during the main phase of a geomagnetic storm might be caused by the prompt penetration electric field and neutral wind during the storm, and the τ increases during the early recovery phase might be due to the disturbance dynamo electric field as well as the neutral wind during the storm. Moreover, there is a negative disturbance of τ in the recovery phase during the most disturbed sunrise hours, and it might be due to the electric field reversal, neutral wind or other factors during this period. This paper notes the differences of τ in midlatitude between different longitudinal sectors from the related climatology and storm-time behavior, as it would be helpful to improve the current understanding of τ at midlatitudes in East Asia.

Singular spectrum analysis and modeling of the temporal variations of the global ionospheric F2-layer peak electron density retrieved from COSMIC radio occultation measurements

The singular spectrum analysis (SSA) is a relatively new method for decomposing time series into separable and interpretable series (i.e., trend, periodic, and irregular components). Here, the ionospheric variability in the peak electron density (NmF2) observations provided by FORMOSAT-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation measurements during 2009–2019, which completely covers solar-cycle 24, was examined using the nonparametric method (SSA). This study identified different temporal patterns inherent in the COSMIC data, which can be employed to reconstruct/model noise-free time series. Based on a proper choice of SSA parameters, it was observed that SSA can be employed to extract various components of these datasets. Additionally, the results showed that the slowly varying component (trend) was largely influenced by solar activity and closely followed the behavior of the sunspot cycle. The SSA method demonstrated seasonal patterns (the semiannual component). Based on the patterns, the reconstructed series for each of the selected components were separately modeled with a corresponding fit function using the 10.7 cm solar proxy, which prior be smoothed by Spline fitting. It was observed that the polynomial function efficiently modeled the trend component with R2 = 0.95, while the harmonic function adequately represented the semiannual component with R2 = 0.97. To validate the proposed model, the data were estimated for the time interval from January 2020 to August 2022, which represented the ascending phase of the ongoing solar-cycle 25. The results revealed that the modeled data correlated with the observed COSMIC-2 data with a high correlation coefficient (0.95). These findings indicate that the underlying model can effectively describe the behavior of the electron density during the investigated period, and the SSA method is particularly powerful for analyzing nonstationary time series and capable of identifying sub-time series (trends along with seasonal periodic components).

Nightside 135.6 nm emission enhancements of mid/low latitudes during geomagnetic storms as observed by the ionosphere PhotoMeter (IPM) on the Chinese meteorological satellite FY-3D

IPM has detected nightside 135.6 nm emission enhancements over a wide latitude range, from the sub-auroral latitudes to the equatorial regions during geomagnetic storms. Our work, presented in this paper, uses the data of IPM to understand these 135.6 nm emission enhancements during of geomagnetic storms and studies the variations of total electron content (TEC) and the F2 layer peak electron density (NmF2) in the region of enhanced emissions. Middle and low latitude emission enhancements are presented during several medium storms in 2018. The variations of both the integrated electron content (IEC) derived from the nighttime OI 135.6 nm emission by IPM and TEC from the International GNSS Service (IGS) relative to the daily mean of magnetically quiet days of per each latitude bin (30°≦geographic latitude < 40°, 15°≦geographic latitude < 30°, 0°≦geographic latitude < 15°, −15°≦geographic latitude < 0°, −30°≦geographic latitude < -15°, −40°≦geographic latitude < -30°) are investigated and show that on magnetically storm day, IEC by IPM always increases, while TEC from IGC may increase or decrease. Even if both increase, the increase of IEC is greater than that of TEC. From the comparison of IEC and TEC during magnetic storms, it can be seen that the enhancement of the nighttime 135.6 nm emissions is not entirely due to the ionospheric change. The time of IEC enhancements at each latitude bin is in good agreement, which mainly corresponds to the main phase time of the geomagnetic storm event and lasts until the recovery phase. The available ground-based ionosonde stations provide the values of NmF2 which match the 135.6 nm emissions measured by IPM in space and time. The variations of NmF2 squared can characterize the variations of the OI 135.6 nm emissions caused by O+ ions and electrons radiative recombination. The study results show that the OI 135.6 nm emission enhancements caused by O+ ions and electrons radiative recombination (where NmF2 squared increases) are obviously a contribution to the measured 135.6 nm emission enhancements by IPM. The contribution accounts for at least one of all contributions to the measured 135.6 nm emission enhancements by IPM. However, where the NmF2 squared provided by ionosonde decrease or change little (where the OI 135.6 nm emissions cause by O+ ions and electrons radiative recombination also decrease or change little), the emission enhancements measured by IPM at storm-time appear to come from the contributions of other mechanisms, such as energetic neutral atoms precipitation, or the mutual neutralization emission (O+ + O-→2O + hʋ (135.6 nm)) which also occupies a certain proportion in 135.6 nm airglow emission at night.

Comparative study of the polar region ionospheric NmF2 and IRI-2016 models

The propagation of radio waves can be significantly affected by the ionosphere, which have a serious impact on broadcasting, communication, positioning and navigation. The International Reference Ionosphere (IRI) provides multiple ionospheric parameters for given location, time and date. In order to study the applicability of the IRI-2016 model in polar ionosphere, long-term observations from the dynasonde at Tromso (TRO), EISCAT Svalbard Radar (ESR) at Longyearbyen (LYB) and digisonde DPS-4 at Zhongshan (ZHS) were used to analyze the prediction accuracy of IRI model, with the help of mathematical statistics, correlation coefficients and time series. The data of F2 layer peak electron density (NmF2) are sorted as monthly medians of NmF2 for each hours, months, and solar activities. The results show that there is a good correlation between IRI prediction and observations during solar minimum years, with the correlation coefficients larger than 0.8 except winter at Longyearbyen, better than that during solar maximum years. The correlation decreases as latitude increases. It is the best at Tromso, and better at Zhongshan than at Longyearbyen. This suggests that the IRI-2016 model is mostly applicable at the auroral latitude station Tromso. But the IRI-2016 model has poor applicability at the cusp latitude station, both Zhongshan and Longyearbyen.

Climatology of TEC Longitudinal Difference in Middle Latitudes of East Asia

In this paper, a statistical analysis of the diurnal, seasonal and solar cycle variation in the TEC longitudinal difference in midlatitudes of East Asia is presented using CODE GIMs data in 2015–2019. Moreover, the empirical neutral wind model HWM-14 and geomagnetic field model IGRF-2020 were employed to analyze the influence of geomagnetic configuration-neutral wind mechanism on the TEC longitudinal difference, and the F2 layer peak electron density (NmF2) data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) were also used to study the role of local electron density in the TEC longitudinal difference. For the high solar activity year, the results show that east-west TEC longitudinal difference index Re/w is negative in the noon and positive at evening-night. Moreover, the longitudinal difference of daytime TEC is most evident in summer, less in autumn and least in spring and winter, while the nighttime difference is most obvious in equinox, followed by summer and winter during nighttime. The model simulation shows that the TEC longitude difference around noon is mainly caused by the zonal wind-declination mechanism, and a 4-h time delay seems to be an optimal result for the vertical drift velocity to cause the longitudinal TEC difference during pre-noon hours. At night, the uplifting electron flux, which is a product of local electron density and vertical drift velocity, shows a good correlation with Re/w, indicating that the local electron density is also an important factor affecting the TEC longitudinal difference during the nighttime. Moreover, there was about a 3-h time delay between the TEC longitudinal variations and the uplifting electron flux at night. For the low solar activity years, the western TEC is greater than eastern TEC during most of the year except in the summer nighttime. The TEC diurnal variation in the east and west suggested that the nighttime Re/w should be related to other physical process, such as the midlatitude summer nighttime anomaly (MSNA) in the east and the ionospheric nighttime enhancement (INE). The current study provides evidence for the longitudinal difference of NmF2 in East Asian midlatitudes and geomagnetic configuration-neutral wind mechanism proposed in previous studies and finds some new features which need further studying to improve our current understanding of ionospheric longitudinal difference in the low solar activity years. The results provide new insight into TEC longitudinal variations at midlatitudes, and they can contribute to understanding the ionosphere-thermosphere coupling system.

Statistical Study of the Ionospheric Slab Thickness at Yakutsk High-Latitude Station

The ionospheric equivalent slab thickness (EST, also named τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. This paper presents a comprehensive statistical study of the ionospheric slab thickness at Yakutsk, located at the high latitude of East Asia, using the GPS-TEC and ionosonde NmF2 data for the years 2010–2017. The results show that the τ has different diurnal and seasonal variations in high- and low-solar-activity years, and the τ is greatest in the winter, followed by the equinox, and it is smallest in the summer in both high- and low-solar-activity years, except during the noontime of low-solar-activity years. Specifically, the τ in inter of high-solar-activity year shows an approximate single peak pattern with the peak around noon, while it displays a double-peak pattern with the pre-sunrise and sunset peaks in winter of the low-solar-activity years. Moreover, the τ in the summer and equinox have smaller diurnal variations, and there are peaks with different magnitudes during the sunrise and post-sunset periods. The mainly diurnal variation of τ in different seasons of high- and low-solar-activity years can be explained within the framework of relative variation of TEC and NmF2 during the corresponding period. By defining the disturbance index (DI), which can visually assess the relationship between instantaneous values and the median, we found that the geomagnetic storm would enhance the τ at Yakutsk. An example on 7 June 2013 is also presented to analyze the physical mechanism. It should be due to the intense particle precipitation and expanded plasma convection electric field during the storm at high-latitude Yakutsk station. The results would improve the current understanding of climatological and storm-time behavior of τ at high latitudes in East Asia.

Pattern of F2-layer peak electron density across African Ionosonde locations and response to solar activity

The diurnal, longitudinal, and latitudinal characteristics of the F2-layer peak electron density (NmF2) at six African stations comprising mid- and equatorial latitudes was investigated. The study covers years of low- (F10.7 = 82.2sfu) and high- (198.6sfu) solar activities. The results revealed that the NmF2 noontime-bite-out was prevalent only in the equatorial latitude. There is latitudinal (geographic) influence on the NmF2 pre-noon and post-noon peak magnitudes at the equatorial locations irrespective of solar activity. The pattern of the NmF2 amplitude during some selected specific time showed that the noontime-12LT, sunset-18LT and midnight-00LT observations are latitudinally inclined, whereas that of the sunrise-06LT is longitudinally-based for both conditions of solar events. Generally, there is a semi-annual asymmetry in the NmF2 monthly pattern with peaks in the equinoctial months. This asymmetry is significant at equatorial latitudes at daytime (06LT/12LT) and nighttime (18LT/00LT) but absent at nighttime of mid-latitudes. The asymmetry feature at the equatorial stations finds its explanation in the ionization anomaly being triggered by the fountain effect mechanism. The NmF2/F10.7 pair correlation (r) presents highest value at 06LT at all equatorial stations for both conditions of solar activity. Generally, r is higher during LSA than during HSA, and finds its explanation in the rate of ionized neutral species and ionospheric electrodynamics. The equatorial noontime bite-out amplitude (bite-outamp) is highest in equinoxes and is latitudinally inclined. We obtained a higher bite-out intensity at the equatorial stations during the HSA than the LSA period by a factor of ≈ 41 %. The importance of thermospheric neutral winds in the large-scale distribution of plasmas was emphasized.

Quiet-time seasonal behaviour of the ionosphere measured by the Ionosphere PhotoMeter (IPM) on the Chinese meteorological satellite FY-3D compared with the IRI2016 model predictions

In this paper, we examine the climatology structure of the mid-night ionosphere at approximately two o’clock local time of a low-solar-activity year and discrepancies between Ionosphere PhotoMeter (IPM) observations and IRI (International Reference Ionosphere) model-2016 predictions using (1) a global structure for the F2 layer peak electron density (NmF2) for four seasons, (2) the mean NmF2 values at different latitudes by month, and (3) the monthly distribution of the global average of NmF2. The data is collected by the IPM, a far-ultraviolet nadir- viewing photometer that has been aboard the second-generation, polar-orbiting Chinese meteorological satellite Feng-Yun 3D (FY-3D) since its launch on November 25th, 2017 and has provided excellent opportunities for many scientific investigations of the ionosphere. We collected night glow data under low geomagnetic activity (KP ≤ 4) during 2018, and the data obtained five days before and after a full-moon night were removed to prevent the influence of stray light. Before analysing the climatology of the ionosphere and comparing the results with those obtained from IRI2016, the accuracy of NmF2 measured by IPM was evaluated by comparison with data from ground-based ionosondes. A statistical comparative analysis of NmF2 measured by IPM and ionosonde indicated a difference of 20% at middle latitudes and 28% at low latitudes. The global behaviour of NmF2 measured by IPM and IRI for four seasons shows that the IRI model generally captures the morphology of the latitudinal structure and hemispheric asymmetry in NmF2 observed by IPM. A comparison between IPM-measured NmF2 and IRI-predicted NmF2 indicates that the former is systematically lower than the latter. The difference in the measurements and predictions can be as large as 300%.

Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location

The ionospheric equivalent slab thickness (τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. In this paper, a comprehensive statistical analysis of the diurnal, seasonal, solar, and magnetic activity variations in the τ at Guam (144.86°E, 13.62°N, 5.54°N dip lat), which is located near the magnetic equator, is presented using the GPS-TEC and ionosonde NmF2 data during the years 2012–2017. It is found that, for geomagnetically quiet days, the τ reaches its maximum value in the noontime, and the peak value in winter and at the equinox are larger than that in summer. Moreover, there is a post-sunset peak observed in the winter and equinox, and the τ during the post-midnight period is smallest in equinox. The mainly diurnal and seasonal variation of τ can be explained within the framework of relative variation of TEC and NmF2 during different seasonal local time. The dependence of τ on the solar activity shows positive correlation during the daytime, and the opposite situation applies for the nighttime. Specifically, the disturbance index (DI), which can visually assess the relationship between instantaneous τ values and the median, is introduced in the paper to quantitatively describe the overall pattern of the geomagnetic storm effect on the τ variation. The results show that the geomagnetic storm seems to have positive effect on the τ during most of the storm-time period at Guam. An example, on the 1 June 2013, is also presented to analyze the physical mechanism. During the positive storms, the penetration electric field, along with storm time equator-ward neutral wind, tends to increase upward drift and uplift F region, causing the large increase in TEC, accompanied by a relatively small increase in NmF2. On the other hand, an enhanced equatorward wind tends to push more plasma, at low latitudes, into the topside ionosphere in the equatorial region, resulting in the TEC not undergoing severe depletion, as with NmF2, during the negative storms. The results would complement the analysis of τ behavior during quiet and disturbed conditions at equatorial latitudes in East Asia.

Persistent perturbations of ionosphere at diminution of solar and geomagnetic activity during 21–24 solar cycles

Moderate ionospheric disturbances combined with storm signatures are characterized by the positive ionospheric index (WU), the negative index (WL), and the range (WE = WU – WL). We assign weights to these indices as a function of the magnitude of the W-index, the observation latitude of the critical frequency of the F2 layer, foF2 (the F2 layer peak electron density, NmF2) or total electron content (TEC). It is shown that moderate ionospheric irregularities (W = ±2) occur more than 20% of the time, while ionospheric storms (W = ±3 and ± 4) are observed in about 5% of Global Ionosphere Maps (GIM-TEC) observations for the period 1994–2020. The response of WU, WL and WE indices are provided for the intense storm on 14–15 December 2006 measured by solar wind and interplanetary magnetic field parameters, and geomagnetic Kp, ap, aa and Dst-indices. Sustained perturbations in WU, WL and WE indices are observed with GIM-TEC observations from 1994 to 2020 in contrast to the geomagnetic Kp-index depletion. The sustained perturbations are also observed with foF2-based 3-h local ionospheric indices WUf, WLf, and WEf at Moscow, Slough-Chilton and Canberra from 1945 to 2020, despite the trends of decreasing in solar activity, Kp, ap, aa and Dst-indices, and GIM-TEC-based ionospheric storms. These persistent irregularities appear to be due to moderate-level ionospheric perturbations, a fact that did not receive sufficient attention within the research community so far.

An aided Abel inversion technique assisted by artificial neural network-based background ionospheric model for near real-time correction of FORMOSAT-7/COSMIC-2 data

The assumption of spherical uniformity while the retrieval of electron density profiles from the Global Navigation Satellite Systems-Radio Occultation (GNSS-RO) observations is often violated and introduces significant errors in the retrieved electron density profile data. This paper presents an improved Abel-inversion technique by incorporating the horizontal gradients in the ionosphere, which are routinely derived from the Artificial Neural Network (ANN) based background NmF2 (peak electron density of F2-layer) model (ANNC2) assimilated with near real-time Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (FORMOSAT-7/COSMIC-2) NmF2 data. The ANNC2-aided Abel inversion is then implemented for more accurate retrieval of electron density profiles from COSMIC-2 in real-time. It is found that the ANNC2-aided inversion has improved the electron density values around the F2-region and below, which yields a clear separation between two anomaly crests. Further, the ANNC2-aided Abel inversion had significantly reduced the artificial plasma caves beneath the equatorial ionization anomaly crests. Furthermore, COSMIC-2 NmF2 observations obtained from both classical and the ANNC2-aided Abel inversion are compared with the ground-based Digisonde data and found that the ANNC2-aided inversion gives the better results. This study provides some new insights on the aided Abel inversion technique assisted by ANN models for the real-time correction of Abel retrieved electron density profiles.

The three-dimensional ionospheric electron density imaging in Japan using the approximate Kalman filter algorithm

The three-dimensional ionospheric electron density (Ne) over Japan is retrieved by assimilating the ground-based total electron content (TEC) datasets into the International Reference Ionosphere (IRI) background model. To reduce the computational burdens encountered in the full Kalman filter (KF) algorithm, the simplified KF (SKF), a time-independent data assimilation scheme with no recursion, is adopted. The spatial resolution is 1°, 1°, and 30 km in latitude, longitude, and altitude, and the temporal resolution is 1 h. Regarding the quite geomagnetic condition, seasonal variations in the ionosphere were investigated firstly. The results show that the reconstructed Ne could well capture the seasonal ionospheric characteristics and semiannual anomaly. Subsequently, NmF2 (F2 layer peak electron density) values during April 3–9, 2013 (high solar activity) and 2018 (low solar activity) were reproduced and simulated by the SKF and IRI model, respectively. In contrast with the ionosonde data, the results indicated the reconstructed NmF2 was apt to capture the underlying trends of diurnal and annual variations more accurately. For the efficiency under the disturbed geomagnetic condition, we took a great geomagnetic storm that happened on August 26, 2018 as an example. The reproduced results also provided better imaging for Ne distributions by analyzing the vertical slices and profiles provided by SKF and IRI. It is suggested that the SKF algorithm is promising for ionospheric researches and practical applications in Japan.

Global Comparison of F2-Layer Peak Parameters Estimated by IRI-2016 With Ionospheric Radio Occultation Data During Solar Minimum

The F2-layer peak parameters of the International Reference Ionosphere (IRI) model are critical to its subsequent applications because of the vital role of the peak parameters in determining other IRI model outputs. Therefore, we analyzed the statistical deviation and ionospheric climatology of NmF2/hmF2 between the most current version of the IRI model, namely IRI-2016, and ionospheric radio occultation (IRO) data, including Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) and FengYun-3C (FY3C), during the recent solar minimum in 2017-2019. The International Union of Radio Science (URSI) model for F2-layer peak electron density (NmF2) and the Bilitza-Sheikh-Eyfrig (BSE), Altadill-Magdaleno-Torta-Blanch (AMTB), and SHUbin (SHU) models for maximum ionization height (hmF2) in IRI-2016 are compared with the IRO dataset. A statistical analysis shows a systematic offset of less than 10% in NmF2 between IRI-2016 URSI and IRO data, and the SHU option for hmF2 shows a better fit to IRO data than BSE and AMTB. A climatology comparison shows that NmF2 estimated by IRI-2016 URSI is consistent with that of the IRO dataset in terms of the general trend in the typical ionospheric characteristics; except for some discrepancies in the marine area, the IRO data may provide a feasible reference for IRI estimation in marine regions. The hmF2 options of BSE/AMTB/SHU show hemispheric asymmetry like the IRO dataset. Moreover, hmF2 of BSE/AMTB and IRO/SHU show some discrepancies in fine structures, such as the day-night reversal phenomenon.

Investigation of the ionosphere over Antarctica under quiet space weather conditions: results of vertical sounding of the ionosphere September 14–24, 2020

We present observational results of variations in the ionospheric parameters hmF2 and NmF2 over the Ukrainian Antarctic station “Akademik Vernadsky” for magnetically quiet conditions. The results of comparative analysis of observational data and the International Reference Ionosphere-2016 model predictions are presented. The main objective of this study is to investigate the temporal variations of two key ionospheric parameters – the F2 layer peak height and electron density – during very quiet space weather conditions using data of vertical sounding of the ionosphere obtained over the Ukrainian Antarctic station “Akademik Vernadsky” and comparison the observation results with model values. Methods: The temporal variations of the F2 layer peak height and electron density were calculated from ionograms obtained with ionosonde installed at the Ukrainian Antarctic station “Akademik Vernadsky” with subsequent electron density profile inversion. Diurnal variations of hmF2 and NmF2 were calculated using a set of sub-models of the IRI-2016 model for comparison with results of observational studies. Results: We found that for the Antarctic region option of IRI-2016 model for the F2 layer peak height SHU-2015 provides a better fit for hmF2 through the investigated period compare to the AMTB-2013 model predictions. Electron density models (URSI, CCIR) generally well reproduce the observed variations of NmF2 during periods of absence non-standard manifestations of space weather, which are possible for quiet conditions too. Hypotheses regarding the possible reasons for experimental and model differences in variations of NmF2 are discussed. The analysis of effect of geomagnetic storm on September 24, 2020 on NmF2 variations was carried out. Conclusions: The obtained results demonstrate peculiarities of the state of the ionosphere-plasmasphere system over Antarctica under very quiet space weather conditions and provide evaluation of predictive capabilities of modern international reference ionosphere models. New knowledge about the features of electron density variations in the ionosphere for magnetically quiet conditions over the Antarctic region has practical value for specialists which are engaged in the study of the near-Earth space environment, in particular, at high latitudes, and also work on correction of global ionospheric models. Keywords: electron density, F2 layer peak height, ionosonde, quiet space weather, models of the ionosphere, downward plasma flux

Longitudinal and Interhemispheric Ionospheric Response to 2009 and 2013 SSW Events in the African‐European and Indian‐East Asian Sectors

AbstractThe ionospheric response to two sudden stratospheric warming (SSW) events that occurred during low (2009) and moderate solar activity (2013) around 10°E (±10°) African‐European and 95°E (±10°) Indian‐East Asian sectors is investigated. The total electron content (TEC) obtained from a meridional chain of stations in the two sectors are used to understand the interlongitudinal and interhemispheric response to these SSW events. Significant depletion of daytime TEC was observed after the onset of 2009 SSW around the equatorial ionization anomaly (EIA) crest followed by an increase during the decaying phase of SSW. The formation of an early peak in the daytime TEC and semidiurnal variation in the response of TEC in the form of morning enhancement and afternoon depletion was observed at low latitudes. The morning enhancement is prominent at northern low latitudes while afternoon depletion is more at southern low latitudes. The conspicuous TEC perturbations characterized by semidiurnal variation in mid‐January of 2013 override the sudden increase in solar activity after the onset of the SSW. SSW impacted semidiurnal perturbations in F2 layer peak electron density (NmF2) and height (hmF2) noticed at Cocos Island, the southern hemisphere low latitude station. Longitudinal and interhemispheric differences in the magnitude and evolution of TEC perturbations were noticed. The longitudinal differences in SSW modulation of TEC might be attributed to the differential impact of the nonmigrating tides and differences in the geomagnetic field elements between the two sectors. The meridional wind in the mesosphere and lower thermosphere region contribute to the TEC enhancement.

Observation of thermosphere and ionosphere using the ionosphere PhotoMeter (IPM) on the Chinese meteorological satellite FY-3D

The Ionosphere PhotoMeter (IPM) is a far ultraviolet nadir-viewing photometer that flew aboard the second-generation, polar-orbiting Chinese meteorological satellite Feng-Yun 3D (FY-3D), which was launched on November 25th, 2017. By observing far ultraviolet night-time OI 135.6 nm emissions, which are produced by the recombination of O+ ions and electrons, the F2 layer peak electron density (NmF2) can be deduced. During daytime IPM was designed to measure the OI 135.6 nm and N2 Lyman-Birge-Hopfield (LBH) band emissions, which would be used to infer the O/N2 ratio, a key diagnostic of neutral dynamics in the daytime. The paper shows the measurement results from IPM taken during its initial months of Operation. A quantitative comparison showing NmF2 from IPM and ground-based ionosondes is presented, and the correlation value R between the ground-based ionosondes and the satellite NmF2 is 0.91. The global O/N2 ratio distribution during geomagnetic storm on 25 through 30 August is presented and illustrated, which could show the latitudes of the ionospheric positive/negative storm in different longitude ranges. The O/N2 ratio significantly decreases during the main and recovery phase of the storm as expected. The correlation value R between the O/N2 ratio retrieved from IPM data and the ionospheric electron density provided by ground-based ionosondes during storms in August 2018 is about 0.78.

The day-glow data application of FY-3D IPM in monitoring O/N2

The Ionosphere Photometer (IPM) is a far ultraviolet nadir-viewing photometer that flew aboard the second-generation, polar-orbiting Chinese meteorological satellite FY-3D, which was launched on November 25th, 2017. The F2 layer peak electron density (NmF2) and O/N2 the column density ratio can be deduced by far ultraviolet measurements of night-time OI 135.6 nm emissions, which are produced by the recombination of O+ ions and electrons, and the day-time OI 135.6 nm and N2LBH wavelength emissions produced by the photoelectron impact excitation of atomic oxygen O and molecular nitrogen N2. Analysis of the IPM data indicated the stray light at 135.6 nm wavelength is under deducted. Based on comparison with the emissive intensity calculation of AURIC model, the day-time data was conducted to make a revision of stray light. The reliable factor (1.13) of stray light subtraction was obtained by fitting the median values of the observed data points per each latitude bin to the model data. According to the O/N2 error estimation from the estimated factor of the stray light, when the factor does not change by more than 0.03, the error of O/N2 ratio from the factor will not exceed 20%. The O/N2 changes retrieved from revised IPM data during storms in April and August 2018 are well correlated with Dst indices. The research results show that the IPM data could provide a good monitoring of O/N2 changes during magnetic storms.

Ionosphere over Ukrainian Antarctic Akademik Vernadsky station under minima of solar and magnetic activities, and daily insolation: case study for June 2019

We present ionospheric observational results obtained over Ukrainian Antarctic Akademik Vernadsky station. Ionospheric parameters (peak electron density and height, electron density and electron and ion temperatures in the topside) during the period near the local winter solstice in the Southern Hemisphere (June 28—29, 2019) are considered. The main objective is to show distinctive features of variations in ionospheric parameters during a prolonged period with very low solar and magnetic activities, and minimal daily insolation. Methods. F2 layer peak electron density and height were calculated from ionogramsobtained with ionosonde installed at the station with subsequent profile inversion. Defense Meteorological Satellite Program (DMSP) and Swarm data acquired over the station are used as well. Diurnal variations of electron density, and electron and ion temperatures at the altitude of the satellites’ orbits were calculated using a set of sub-models of the International Reference Ionosphere-2016 (IRI-2016) model. Results. We found a very good agreement between the observed and model variations of F2 layer peak electron density. Significant (by ~2 times) nighttime enhancement of electron density was observed on June 29. Electrondensity models show the similar increase of the density at the same time interval but this enhancement is much more smoothed comparing with the observations. Peak height values obtained using ionosonde are very close to ones calculated with the IRI-2016 sub-models. Satellite data are in a good consistency with the IRI model predictions, especially for electron density obtained by Swarm satellite. Conclusions. Multi-instrumental observations revealed a number of unique features of the ionosphere over Antarctic Peninsula under minima of solar and magnetic activities, and daily insolation.

GITM‐Data Comparisons of the Depletion and Enhancement During the 2017 Solar Eclipse

AbstractThe total solar eclipse of 21 August 2017 was simulated with the Global Ionosphere‐Thermosphere Model (GITM), and the results were compared with the total electron content (TEC) measurements provided by the Global Navigation Satellite System, as well as F2 layer peak electron density (NmF2) derived from six ionosondes. TEC decreased over North America by ~54.3% in the model and ~57.6% in measurements, and NmF2 decreased by ~20–50% in the model and ~40–60% in the measurements. GITM predicted a posteclipse enhancement of ~10% in TEC and NmF2, consistent with observations which suggested an increase of ~10–25% in TEC and ~10–40% in NmF2. GITM showed that the divergence of horizontal winds drove the increase in Oxygen after the eclipse allowing an increase in the ionization rate. The slower charge exchange due to both the decreased ion temperature and N2 density allowed an increase of O+ density in the F region also.