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The Equatorial Electrojet (EEJ) is one of the important near‐earth space weather phenomena which exhibits significant diurnal, seasonal and solar activity variations. This paper investigates the EEJ variations at diurnal, seasonal and solar cycle time scales from the Indian sector and portrays a new empirical EEJ field model developed using the observations spanning over nearly two solar cycles. The Method of Naturally Orthogonal Components (MNOC), also known as Principal Component Analysis (PCA), was employed to extract the dominant patterns of principal diurnal, semi‐diurnal, and ter‐diurnal components contributing to the EEJ variation. The amplitudes of these diurnal, semi‐diurnal, and ter‐diurnal components in EEJ are found to vary significantly with the season and solar activity. The seasonal and solar activity dependencies of these principal components are modeled using suitable bimodal distribution functions. Finally, the empirical model for EEJ field was built by combining the principal components with their corresponding modeled amplitudes. This model accurately reproduces the diurnal, seasonal and solar activity variations of EEJ. The modeled monthly mean variations of EEJ field at ground exhibit excellent correlation of 0.96 with the observations with the root mean square error <5 nT. It also successfully captures the seasonal and solar activity variations of Counter Electrojet (CEJ). Finally, this model named "Indian Equatorial Electrojet (IEEJ) Model" is made publicly available for interested scientific users (https://iigm.res.in/system/files/IEEJ_model.html). Plain Language Summary: The equatorial electrojet (EEJ) is an intense current jet flowing in the upper atmosphere around 100 km. This is a unique phenomenon that occurs at only a few kilometers in height (e.g., 105–110 km) and with a horizontal (North‐South) width of a few hundred kilometers (e.g., ∼600 km) centered on the geomagnetic equator. This important geophysical phenomenon gives more insights into the equatorial ionospheric electrodynamical processes that have various impacts on satellite orbital dynamics, Global Positioning Systems and other satellite communication links, electrical power grids, etc. This study develops a new empirical model to predict the diurnal, seasonal, and solar activity variations in the intensity of this unique current system over the Indian longitude sector. Key Points: An empirical Equatorial Electrojet (EEJ) field model was developed using nearly two solar cycles of EEJ observations from the Indian sectorThe principal diurnal, semi‐diurnal, and ter‐diurnal components in the EEJ are modeled using suitable analytical functionsThis model can very accurately predict the diurnal, seasonal, and solar activity variations of monthly mean EEJ and CEJ fields at ground [ABSTRACT FROM AUTHOR]

Atmospheric electricity parameters (AEP) measurements from Antarctica predominantly feature either the potential gradient (PG) and/or air‐Earth current (AEC) density. We report for the first time simultaneous measurements of the bipolar ions concentration/conductivity, PG, and AEC density. AEP measurements were carried out at Maitri (70.8°S, 11.8°E) from December 2018 to November 2019. We formulated a few criteria, irrespective of the weather conditions, to select the electrically quiet days and some additional criteria based on the conductivity measurements to discern globally representative data (GRD) from such days. The measurements of the PG and AEC density over the Antarctic plateau demonstrated the diurnal curves similar to the Carnegie pattern, which represents the global thunderstorms and electrified shower clouds (ESCs) occurring on different continents and oceans, we regard the data having such trend as GRD. We found significant variability in the concentration of small bipolar ions/conductivity in the austral summer which in turn affects GRD. However, the concentration of bipolar ions is nearly consistent at ∼250 negative ions cm−3 and ∼300 positive ions cm−3 in winter and enhances the probability of GRD. Such differences can arise out of the prevalent planetary boundary layer processes in the two seasons. When the PG varied between ∼50 Vm−1 and ∼150 Vm−1 and the maximum range of conductivity variations was ∼0.2 × 10−14 ℧ m−1, the AEPs represented the signatures of the global thunderstorm and ESC activities. Plain Language Summary: Monitoring of the atmospheric electricity parameters is a simple technique to monitor global thunderstorm activity and electrified shower clouds. For this, the data need to be free from local disturbances. Obtaining such data in Antarctic Plateau was found to be successful. On the other hand, the coastal Antarctic stations, experience local or regional contributions in it. This paper attempts to provide some techniques to obtain globally representative data (GRD). This paper suggests that the diurnal variation of the concentration of bipolar small ions strongly impacts the GRD. Therefore a day free from the diurnal variation of the concentration of bipolar ions is essential to discern the global signals. The winter season appears to be a better season for this as the summer season experiences mild convection activity that causes local and regional electrical signals that contaminate the data. Key Points: Atmospheric electrical conductivity is the key parameter to discern globally representative data (GRD) over the Maitri, AntarcticaGRD is discernible on a day when conductivity is consistent, and such days are most common in local winterIn the austral summer, the planetary boundary layer (PBL) processes produce local electrical signals that interfere with the global signals [ABSTRACT FROM AUTHOR]

Pc1 geomagnetic pulsations, equivalent to electromagnetic ion cyclotron waves in the magnetosphere, display a specific amplitude modulation, though the region of the modulation remains an open issue. To classify whether the amplitude modulation has a magnetospheric or ionospheric origin, an isolated proton aurora (IPA), which is a proxy of Pc1 wave‐particle interactions, is compared with the associated Pc1 waves for a geomagnetic conjugate pair, Halley Research Base in Antarctica and Nain in Canada. The temporal variation of an IPA shows a higher correlation coefficient (0.88) with Pc1 waves in the same hemisphere than that in the opposite hemisphere. This conjugate observation reveals that the classic cyclotron resonance is insufficient to determine the amplitude modulation. We suggest that direct wave radiation from the ionospheric current by IPA should also contribute to the amplitude modulation. Plain Language Summary: The amplitude of electromagnetic ion cyclotron (EMIC) waves in the magnetosphere, which are observed as Pc1 waves on the ground, is an important parameter for characterizing the loss of energetic particles. The generation region of EMIC waves is well understood as being the magnetic equator, but the amplitude modulation region is not well‐established due to wide horizontal Pc1 wave propagation in ionospheric ducts. Here we compare the properties of Pc1 waves and isolated proton precipitation from an ideal geomagnetic conjugate observation at Halley Research Base in Antarctica and Nain in Canada. By visualizing the cyclotron resonance region in the magnetosphere as an isolated proton aurora (IPA), the ambiguity of the horizontal propagation effects of Pc1 waves in the ionosphere is ideally removed. The observed IPA in the northern hemisphere has remarkable similarities with Pc1 waves in the same northern hemisphere, but not the southern hemisphere, providing evidence that the temporal variations of wave amplitude can be characterized by an ionospheric current induced in the IPA, and cannot be described only by a classical cyclotron resonance mechanism at the magnetic equator. Therefore, this study suggests that an IPA ionospheric current contributes to temporal modulations of Pc1 waves on the ground. Key Points: Similarities and differences of magnetic conjugacy between Pc1 waves and isolated proton precipitation are reportedThe proton aurora shows a strong similarity with Pc1 waves in the same hemisphere, not characterized by classical cyclotron resonanceThis study suggests the importance of ionosphere for Pc1 waves by an ionospheric current modulation of an isolated proton aurora [ABSTRACT FROM AUTHOR]

In this paper, the variations of ionospheric irregularities have been studied using C/NOFS, ground-based GNSS and magnetometer measurements in Africa during the St. Patrick geomagnetic storm of March 17, 2013. The latitudinal distribution of irregularities was examined using GNSS-ROTI maps covering longitude 25°-45°E. Longitudinal characteristics were also investigated along with equatorial plasma bubbles (EPBs) and vertical drift velocity (Vz) from 12 to 21 March 2013. The results show postsunset irregularities from 12°S-27°N with the stronger ones confined within 1°S-7°S and 12°N-22°N in the prestorm period. The observed pre-reversal enhancement (PRE) with Vz varying from 22.51-59.47 m/s between 20.26 and 20.86 LT corresponded with the occurrence of EPBs. PRE greater than 40 m/s nevertheless, supported long lasting depletions. During the main phase, prompt penetration electric field enhanced the PRE thus, extended the latitudinal range of irregularities to 31°N. It also induced a long duration EPB along 15°E and several depletions over the Eastern sector. During the recovery phase, stormtime wind drove a conspicuous asymmetry in the morphology of the postsunset anomaly. This corresponded with the reduction in the latitudinal extent and strength of irregularities. Westward/eastward disturbance dynamo electric field inhibited/triggered irregularities in the postsunset/postmidnight period on 18 March over the Eastern sector. The difference in the drift accounted for the longitudinal variations of irregularities before the storm. During the main phase however, irregularities were present (reduced) over the Eastern (Atlantic/Western) sectors. This difference might have been related to the changes in the wind inferred from the anomaly shape. [ABSTRACT FROM AUTHOR]

The aim of the present study is to investigate the response of ionospheric total electron content (TEC), Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS) scintillations during 17 March 2015 St. Patrick's Day geomagnetic storm over Visakhapatnam, which is popularly known as Waltair (WALT) in the literature. GPS TEC observations obtained from five IGS stations (SGOC, IISC, HYDE, LCK4 and LHAZ) and WALT during the storm have been compared. The TEC derived from GPS, GLONASS constellations and CODE global ionosphere TEC map (GIM) over WALT has also been compared. Positive storm effect during the main phase of the storm and negative storm effect during the recovery phase of the storm were observed over the said stations. The variation of northern equatorial ionisation anomaly TEC (CODE GIM TEC maps) in response to the St. Patrick's Day storm over four Indian longitudes ( 75 ∘ E , 80 ∘ E , 85 ∘ E and 90 ∘ E ) has also been presented. Strong amplitude and phase scintillations were observed in the L-band signals of GPS and GLONASS constellations over WALT. Twelve satellite (Pseudo Random Noise) PRNs of GPS L1 and nine PRNs of each GLONASS L1 and L2-band signals were affected by strong amplitude and phase scintillation. The peak amplitude scintillation index (S4) obtained from the effected PRNs of GPS L1 signal and GLONASS L1-band signals over WALT range from 0.36 to 0.74 and 0.36 to 0.76, respectively. Strong fluctuations in rate of TEC index are noted over the said stations. This enhanced scintillation activity is mainly due to the main phase of the storm falls in the evening sector over the Indian region. [ABSTRACT FROM AUTHOR]