Investigation of Subauroral Ionosphere under Disturbed Geomagnetic Conditions during the High Solar Activity Year 2012 at Maitri, Antarcitica

This study mainly focuses on the prediction of the variability of the vertical total electron content (VTEC) and validation of the new versions of the International Reference Ionosphere (IRI 2016), IRI extended to the plasmasphere (IRI‐Plas 2017), and NeQuick 2 models over the equatorial anomaly region during 2013–2018. The Global Positioning System (GPS)‐derived VTEC data inferred from the South American equatorial region during the relatively high (2013–2014), descending (2015–2016), and low (2017–2018) solar activity years have been considered as measurements to validate the models. The modeled (IRI 2016, IRI‐Plas 2017, and NeQuick 2) VTEC values are generally larger than the GPS‐derived VTEC values, with the highest overestimation being illustrated by the IRI‐Plas 2017 model. Small underestimations are also observed in employing the IRI 2016 and NeQuick 2 models, especially when the solar activity increases. The highest root‐mean‐square Deviations (RMSDs) reaching up to 10 TEC units (TECU) is observed in some hours while using the IRI‐Plas 2017 model during the high solar activity years. RMSDs less than 5 TECU are also observed on most of the hours while utilizing the model during all solar activity years. However, RMSD values less than 2 TECU (while using the NeQuick 2 model) and less than 1 TECU (while using the IRI 2016 model) are seen on most of the hours during 2013–2018. This shows that the performance of the IRI 2016 and NeQuick 2 is better than the IRI‐Plas 2017 with the IRI 2016 model consistently revealing the best in all solar activity years.

The magnitude and inter-hemispheric asymmetry of equatorial ionization anomaly-based on CHAMP and GRACE observations

The height of the peak electron density (hmF2) and the critical frequency of the F2 layer (foF2) are very important in the research of ionospheric electrodynamics and high frequency (HF) wireless communication. In the article, we validated the hmF2/foF2 model values of the latest version of the International Reference Ionosphere (IRI-2016) with observations from three ionosonde stations which belong to low, middle, and high latitudes (i.e., Sanya, Beijing and Mohe) over China during a high solar activity year (2014, F10.7 = 145.9 sfu) and a low solar activity year (2016, F10.7 = 88.7 sfu). Among them, foF2 model values can be obtained through the International Radio Consulting Committee (CCIR) model or the International Union of Radio Science (URSI) model, both of which have the “F-peak storm model” on or ‘off’ options; hmF2 model values can be obtained through Bilitza-Sheikh-Eyfrig (BSE-1979), Altadill-Magdaleno-Torta-Blanch (AMTB-2013), or SHUbin (SHU-2015) model. The IRI-2016 hmF2/foF2 model values were evaluated by root mean square (RMS) values and mean absolute relative error (MARE). The results show that for the foF2 parameter, the performance of IRI-2016 can be improved by choosing “F-peak storm model” on option in geomagnetic-disturbed days. Whether in high or low solar activity years, for foF2, the IRI-2016 options of CCIR have better prediction ability than IRI-2016 options of URSI in low and high latitudes over China, and the IRI-2016 options of URSI have better prediction ability than IRI-2016 options of URSI in middle latitudes. For hmF2, the IRI-2016 option of SHU-2015 has better prediction ability than the IRI-2016 options of AMTB-2013 and BSE-1949 in high latitudes over China, the IRI-2016 options of SHU-2015 and BSE-1979 have better prediction ability than IRI-2016 options of AMTB-2013 in mid and low latitudes over China.

Evaluation of ionospheric and solar proxy indices for IRI-Plas 2017 model over the East African equatorial region during solar cycle 24

In this paper, we propose a novel Total Electron Content (TEC) map prediction model, named ED‐AttConvLSTM, using a Convolutional Long Short‐Term Memory (ConvLSTM) network and attention mechanism based on encoder‐decoder structure. The inclusion of the attention mechanism enhances the efficient utilization of spatiotemporal features extracted by the ConvLSTM, emphasizing the significance of crucial spatiotemporal features in the prediction process and, as a result, leading to an enhancement in predictive performance. We conducted experiments in East Asia (10°N–45°N, 90°E−130°E). The ED‐AttConvLSTM was trained and evaluated using the International GNSS Service TEC maps over a period of six years from 2013 to 2015 (high solar activity years) and 2017 to 2019 (low solar activity years). We compared our ED‐AttConvLSTM with IRI‐2016, COPG, LSTM, GRU, ED‐ConvLSTM and ED‐ConvGRU. The results indicate that our model surpasses the comparison models in forecasting both high and low solar activity years, across most months and UT moments in a day. Moreover, our model exhibits notably superior prediction performance during the most severe phases of a magnetic storm when compared to the comparison models. Subsequently, we then also discuss how the prediction performance of our model is affected by latitude. Finally, we discuss the diminishing performance of our model in multi‐day predictions, demonstrating that its reliability for forecasts ranging from one to 4 days in advance. Beyond the fifth day, there is a pronounced decline in the model's performance.

In recent years, transformer has been widely used in natural language processing (NLP) and computer vision (CV). Comparatively, forecasting image time sequences using transformer has received less attention. In this paper, we propose the conv-attentional image time sequence transformer (CAiTST), a transformer-based image time sequences prediction model equipped with convolutional networks and an attentional mechanism. Specifically, we employ CAiTST to forecast the International GNSS Service (IGS) global total electron content (TEC) maps. The IGS TEC maps from 2005 to 2017 (except 2014) are divided into the training dataset (90% of total) and validation dataset (10% of total), and TEC maps in 2014 (high solar activity year) and 2018 (low solar activity year) are used to test the performance of CAiTST. The input of CAiTST is presented as one day’s 12 TEC maps (time resolution is 2 h), and the output is the next day’s 12 TEC maps. We compare the results of CAiTST with those of the 1-day Center for Orbit Determination in Europe (CODE) prediction model. The root mean square errors (RMSEs) from CAiTST with respect to the IGS TEC maps are 4.29 and 1.41 TECU in 2014 and 2018, respectively, while the RMSEs of the 1-day CODE prediction model are 4.71 and 1.57 TECU. The results illustrate CAiTST performs better than the 1-day CODE prediction model both in high and low solar activity years. The CAiTST model has less accuracy in the equatorial ionization anomaly (EIA) region but can roughly predict the features and locations of EIA. Additionally, due to the input only including past TEC maps, CAiTST performs poorly during magnetic storms. Our study shows that the transformer model and its unique attention mechanism are very suitable for images of a time sequence forecast, such as the prediction of ionospheric TEC map sequences.

A comprehensive analysis on the ionospheric planetary wave activity is undertaken using 8 years of ionosonde data at Trivandrum (8.5°N, 77°E), a dip equatorial station. The study reveals that the dominant planetary wave is of 16‐day type and its strength is maximum in winter solstice/autumnal equinox and minimum in summer solstice in high solar activity conditions. In low solar activity years planetary wave activity strength is more or less comparable in vernal equinox, autumnal equinox, and winter solstice, while it is observed to be least in summer solstice. Further, the planetary wave activity shows direct correlation with solar activity for the different seasons. Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite observations of off‐equatorial E‐region zonal winds confirm the fact that they are strong westward in high solar activity years compared to low solar activity years. The strong westward winds aid the upward propagation of westward propagating planetary waves in high solar activity years. Planetary waves reaching the off‐equatorial E‐region modulate the equatorial F‐region via the coupling along the magnetic field lines. The role of planetary waves in modulating the pre‐reversal enhancement, equatorial spread F duration, and its spread range on a day‐to‐day basis is brought out quantitatively for both high and low solar activity conditions. The study emphasizes the importance of ionospheric planetary wave studies for the prediction of equatorial spread F characteristics.

Present Paper describes analysis of GPS-data recorded at low latitude station Hyderabad (Geographic latitude 17 $$^\circ $$ , 25′ N, longitude 78 $$^\circ $$ , 33′ E), India to study the effect of magnetic activity on ionospheric TEC. The total electron content (TEC) data were considered for the ionosphere during five most quiet and most disturbed days for each month of the solar minimum year 2009 and the high solar activity year 2013. The results show that GPS-TEC is found to be more during disturbed days than that during quiet days with a maximum difference during the equinox season. In addition, the difference in TEC during quiet and disturbed days is found to be higher for solar maximum than that for solar minimum year. Moreover the GPS-TEC variations depend on the season with the maximum in equinox season and minimum in summer and winter season. Generally daytime TEC is found to be larger than that in the nighttime which is maximized around the local noontime hour but the peak formation delayed for the solar minimum year. The EIA development process during the solar minimum is quite slow and occurs in late afternoon as compared to that during the high solar activity year. In addition, this delay is larger for summer and winter season than that for equinox months. The formation of post sunset anomaly in the post-sunset sector (1900–2300 LT) is prominent during high solar activity year 2013 whereas same is insignificant for solar minimum year 2009. The post-sunset anomaly could be attributed to pre-reversal enhancement (PRE) of zonal electric field.

Evaluation of long-term variability of ionospheric total electron content from IRI-2016 model over the Indian sub-continent with a latitudinal chain of dual-frequency geodetic GPS observations during 2002 to 2019

Vibrationally excited molecular nitrogen plays an important role in the F region ionosphere. It increases the loss rate of the dominant ion O+ and reduces the electron concentration in the F region of the ionosphere. In this paper, we use a theoretical numerical ionospheric model to study the effect of on the ionosphere during four time periods, each including both geomagnetically quiet and storm disturbed periods, with considering and without considering the role of in the numerical ionospheric model. The four periods simulated are (1) May 14–20, 1997; (2) May 1–10, 1998; (3) June 11–15, 1990 and (4) April 6–10, 2000. By Comparing the simulated results with the observational ones, it is shown that has a significant effect on the ionosphere during high solar activity years. While for the low solar activity years, the role played by is very limited, much less than that in high solar activity years. It is also shown that for the high solar activity years, when constructing an ionospheric physical model, one must take into account not only for geomagnetically disturbed period but also for quiet period. Moreover, it is found that the effect of on the ionospheric electron density distribution depends on the vibrational temperature Tv adopted. When taking the value of Tn as Tv(where Tn is the background neutral temperature) the simulated result, compared with the observation one, is not as good as that when Tv is calculated by the steady state analytical solution. Moreover, our simulation results show that, for high solar activity years, the effect of on the distribution of ionospheric electron concentration is to reduce the electron density for the altitudes above 150km, while its effect on the electron density below 150km is very small. The F2 layer peak height hmF2 is not affected very much by .

Strengths of the equatorial electrojets are derived at Indian and American sectors employing the same procedure as in Part I, for high solar activity years. On examining the morphological features of the strengths at this activity including the counter electrojet events, a comparative study is made with these results and those obtained for low solar activity years. It is noticed that the strengths in the American sector are uniformly larger during high solar activity when compared with low activity years. Similar increase at high over low is within the theoretically derived ratio at the Indian sector. Probable reasons for this enhanced ratio at American sector are discussed.Morning counter electrojet events are found to be larger in number in both the sectors during high solar activity years. However, afternoon counter electrojet phenomenon is confined to low solar activity years and is more prominent in the Indian sector. The simultaneous occurrence of counter electrojet intervals at both the sectors in the two phases of solar activity show that the morning simultaneous events are more during high and afternoon events more in low solar activity years. Lunar influence appears to exist in the occurrence of morning counter electrojet which maximises at the lunar ages 05 and 17 at both phases of solar activity.

The occurrence rate of the equatorial plasma bubble (EPB) with season, solar activity, and geomagnetic conditions are investigated using long‐term data sets of Malaysia Real‐Time Kinematics Network (MyRTKnet) from 2008 to 2013. The rate of TEC (total electron content) change index (ROTI) in 5 min was derived from MyRTKnet data to detect the EPB with scale sizes around tens of kilometers. Then, the daily east‐west cross sections of 2‐D ROTI maps were used to examine the EPB features over 100°E–119°E longitudes. The EPBs tend to occur successively in one night along the observational coverage of MyRTKnet during equinoxes in high solar activity years. The perturbations in a form of wavelike structures along the observed longitudes might be responsible for the development of successive EPBs due to high growth rate of the Rayleigh‐Taylor instability (RTI) process. On the contrary, the occurrence of successive EPBs is infrequent and the occurrence day of EPB remains active during equinoctial months in low solar activity years. The small growth rate of the RTI process during low solar activity years might require a strong seed perturbation to generate the EPB structure. The occurrence probability of the EPB was found to be similar during quiet and disturbed geomagnetic conditions. The results imply that the strong perturbations play an important role in the development of the EPB in low solar activity years. Nonetheless, the high growth rate of the RTI could cause the successive occurrence of the EPB in high solar activity years.

Strengths of the equatorial electrojets are derived at Indian and American sectors employing the same procedure as in Part I, for high solar activity years. On examining the morphological features of the strengths at this activity including the counter electrojet events, a comparative study is made with these results and those obtained for low solar activity years. It is noticed that the strengths in the American sector are uniformly larger during high solar activity when compared with low activity years. Similar increase at high over low is within the theoretically derived ratio at the Indian sector. Probable reasons for this enhanced ratio at American sector are discussed.Morning counter electrojet events are found to be larger in number in both the sectors during high solar activity years. However, afternoon counter electrojet phenomenon is confined to low solar activity years and is more prominent in the Indian sector. The simultaneous occurrence of counter electrojet intervals at both the sectors in the two phases of solar activity show that the morning simultaneous events are more during high and afternoon events more in low solar activity years. Lunar influence appears to exist in the occurrence of morning counter electrojet which maximises at the lunar ages 05 and 17 at both phases of solar activity.

Comparison of the observed topside ionospheric and plasmaspheric electron content derived from the COSMIC podTEC measurements with the IRI_Plas model results

Forecasting ionospheric TEC using least squares support vector machine and moth-flame optimization methods in China