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The equatorial post-sunset ionospheric irregularities induce rapid fluctuations in the phase and amplitude of global navigation satellite system (GNSS) signals which may lead to the loss of lock and can potentially degrade the position accuracy. This study presents a new analysis of L-band scintillation from a low latitude station at Guntur (Geographic 16.44°N, 80.62°E, dip 22.18°), India, for the period of 18 months from August 2021 to January 2023. The observations are categorized either in the medium Earth-orbiting (MEO) or geosynchronous orbiting (GSO) satellites (GSO is considered as a set of the geostationary and inclined geosynchronous satellites) for L1, L2, and L5 signals. The results show a higher occurrence of moderate (0.5 < S4 ≤ 0.8) and strong (S4 > 0.8) scintillations on different signals from the MEO compared to the GSO satellites. Statistically, the average of peak S4 values provides a higher confidence in the severity of scintillations on a given night, which is found to be in-line with the scintillation occurrences. The percentage occurrence of scintillation-affected satellites is found to be higher on L1 compared to other signals, wherein a contrasting higher percentage of affected satellites over GSO than MEO is observed. While a clear demarcation between the L2/L5 signals and L1 is found over the MEO, in the case of GSO, the CCDF over L5 is found to match mostly with the L1 signal. This could possibly originate from the space diversity gain effect known to impact the closely spaced geostationary satellite links. Another major difference of higher slopes and less scatter of S4 values corresponding to L1 versus L2/L5 from the GSO satellite is found compared to mostly non-linear highly scattered relations from the MEO. The distribution of the percentage of scintillation-affected satellites on L1 shows a close match between MEO and GSO in a total number of minutes up to ~60%. However, such a number of minutes corresponding to higher than 60% is found to be larger for GSO. Thus, the results indicate the possibility of homogeneous spatial patterns in a scintillation distribution over a low latitude site, which could originate from the closely spaced GSO links and highlight the role of the number of available satellites with the geometry of the links, being the deciding factors. This helps the ionospheric community to develop inter-GNSS (MEO and GSO) operability models for achieving highly accurate positioning solutions during adverse ionospheric weather conditions. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a very important energy conversion process that plays a vital role in solar wind-magnetosphere coupling. This study presents a unique analysis of the coordinated observations from MMS, Cluster and THEMIS spacecraft during a geomagnetic storm on 31 December 2015. The analyses are aimed to understand the intricacies of the short-scale processes during 4 different short (20 min) encounters and a long duration (8 h) traversal of all the satellites covering the main and the recovery phase of the storm. The main results show that at the reconnection sites in the magnetotail, the FAC density is majorly contributed by the electrons moving anti-parallel to the magnetic field. Significantly, the FACs estimated from the Curlometer method and plasma (or local) method agree well and authenticate the interpretations. The majority of the electron population is found to shift towards the mid (0.2–2 keV) and high-energy (2–30 keV) range during the reconnection, wherein higher (∼one order more) ion and electron energy flux is observed under the effect of the intense storm compared to non-storm cases. The Hall electric field is found to be the major contributor to the total electric field during magnetic reconnection whereas, we observe the growing significance of the pressure divergence term during later phases of the storm. Longer duration (8-hour) continuous observations from the unique alignment of the four spacecrafts show a dominance of magnetic (plasma) properties over plasma (magnetic) properties in the magnetotail (magnetopause). The magnetotail (magnetopause) is found to be highly dynamic with higher (lower) levels of the electric and magnetic field, ion and electron temperature, and simultaneous lower (higher) levels of plasma density, energy flux, and FACs. The drastic enhancements of the plasma and field parameters happen in the sun-earth plane and during different crossings at the magnetopause and magnetotail. The simultaneous observations from magnetopause and magnetotail during a moderate geomagnetic storm indicate further needful coordinated investigations on the nature of reconnections on the day and night side and variations during the intense category of storms. [ABSTRACT FROM AUTHOR]

Four supersubstorms of the solar cycle 24 are analyzed to investigate the global variations in the H‐component and geomagnetically induced currents (GICs). The response to the storm sudden commencement (SSC) of the 2012 and 2017 events is observed differently over different latitude bands. Initially, the latitude band of 0°–45° shows a step‐like preliminary positive impulse (PPI), 45°–65° shows a Gaussian‐kind of PPI and 65°–90° shows a preliminary reverse impulse, followed by a main impulse all over. The H‐component variations during the supersubstorm periods show a strong north‐south asymmetry over the high latitudes which is attributed to the seasonal dependence of the growth and decay of ionospheric currents respectively in the summer and winter hemispheres. The co‐latitude band of ∼55°–65° shows a complete reversal of phase (i.e., global positive peak) of the H‐component compared to the maximum depression observed from the close‐by latitude bands and peak depressions in the SYM‐H, SML, and AE indices. The low latitude variations exhibit a dominant local time‐dependent control of the perturbation electric fields over the short and long terms during the geomagnetic events. The D‐component variations reflect complex ionospheric contributions during the SSC and the main phase with more asymmetries and variability. The GIC threat represented by the dB/dt peaks during the supersubstorms shows the highest magnitude (∼900 nT/min) in the latitude band of 60°–75° with a secondary peak over the dip equatorial regions. Further, some scattered and prominent peaks over the mid and high latitudes outside the supersubstorm periods are also observed. Plain Language Summary: Supersubstorms are the extreme class of geomagnetic substorms associated with an intense short‐duration solar energy input in the magnetosphere‐ionosphere system. Such supersubstorms are known to cause severe threats to the technical and electrical systems in polar region and near‐Earth space. Recently completed solar cycle exhibited only four 4 supersubstorms during May 2011, March 2012 and September 2017 which have been also associated with geomagnetic storm. This study utilizes geomagnetic signatures observed from magnetometer stations spread over the globe. Some interesting patterns are found which include a latitude‐specific response during the first shock and later during the main phase. A reversal in polarity of the geomagnetic perturbation during the supersubstorms is highly striking observation, which is commonly observed from a mid‐to‐high latitude band during these events. Further, each latitude band is found to show a dependency on the local time. An effort is made to classify the contribution from disturbed ionospheric current from a sum of the total disturbance current. This study also provides intriguing results on the geomagnetically induced currentss during these extreme events, which is necessary with respect to understand the cause‐effect relationship of the space weather disturbances and the associated hazards that the earth and the human civilization may face. Key Points: Three distinct latitude‐specific signatures are established in response to the sudden impulseIntriguing mid‐to‐high latitude positive reversals during minimum depressions in the SML index and H‐component variations elsewhereLarge amplification of dB/dt depicting unusually large geomagnetically induced currents during and outside the supersubstorm occurrences [ABSTRACT FROM AUTHOR]

A novel GNU radio-based software-defined radio receiver using universal serial radio peripheral (USRP) front end and Yagi antenna is developed to record meteor echoes in passive mode using FM broadcast. Pilot observations are made for four days in August–September 2020 to record FM signals at 103.2, 104, and 107.5 MHz with a varying sample rate of 8 and 200 kHz. The in-phase and quadrature signals are processed to obtain the amplitude and phase of the received signals for identification of the meteor echoes. A new algorithm is developed to automatically detect the echoes using a normalized amplitude threshold and a minimum temporal separation between two echoes. Overdense meteor echoes with a plateau-like amplitude response are found using a ratio test and remaining echoes are rejected. Thus, the system can detect almost all types of meteor echoes reported earlier. Notably, signatures of fragmentation and background wind are also observed in the form of different phase patterns. Histogram of the meteor counts shows a peak for shorter durations indicating larger populations of the smaller size of meteoroids. The log–log plot of the meteor duration versus count is found to exhibit a characteristic transition of the slope. An empirical estimate of the height of the echoes is obtained. The echoes show micrometeoroid populations, which may depend upon the transmitting–receiving setup and the geometry. Hence, an inexpensive, low-power, portable, passive and automated meteor detection system is demonstrated, which can be highly useful for understanding the meteor phenomena and estimation of atmospheric parameters. [ABSTRACT FROM AUTHOR]