Rajkumar Hajra

Indian Institute of Technology Indore | IITI · Discipline of Astronomy Astrophysics and Space Engineering

Geomagnetically induced current (GIC) measurements at the Mäntsälä, Finland (57.9° magnetic latitude) gas pipeline from 1999 through 2019 are analyzed. It is found that the GIC events with peak intensity > 10 $ > 10$ A are not individual peaks, but occur in clusters with duration from ∼5 to ∼38 hr when GIC values are almost continuously above ∼1.5...

Corotating interaction regions (CIRs) form in the interaction region between the solar-wind high-speed streams and slow streams, leading to compressed plasma and magnetic fields. Using solar-wind measurements upstream of Earth, we identified 290 CIRs encountered by Earth during January 2008 through December 2019 (Solar Cycle 24). The occurrence rat...

The near-Earth solar wind is in general super-Alfvénic and supermagnetosonic. Using all available near-Earth solar wind measurements between 1973 and 2020, we identified 30 intervals with sub-Alfvénic solar winds. The majority (83%) of the events occurred within interplanetary coronal mass ejection magnetic clouds (MCs)/driver gases. These MC sub-A...

The study of the properties and variations from planetary boundaries such as magnetosheaths and bow shocks is an important subject for magnetospheric dynamics and interaction with solar wind. The identification of these boundaries is important for those studies. Thus, the Haar wavelet decomposition technique is used to detect the planetary magnetos...

We present a statistical study of the intense geomagnetically induced currents (GICs) in the subauroral region, which can damage ground electronic systems. From the natural gas pipeline recordings taken near Mäntsälä, Finland (geographic: 60.6∘N, 25.2∘E), 605 GICs with peak intensity >10 A were registered from 1999 through 2019, ≈2 solar cycles. Du...

Seasonal features of geomagnetic activity and their solar-wind-interplanetary drivers are studied using more than five solar cycles of geomagnetic activity and solar wind observations. This study involves a total of 1296 geomagnetic storms of varying intensity identified using the Dst index from January 1963 to December 2019, a total of 75 863 subs...

Observations of the solar wind plasma and interplanetary magnetic field in the ecliptic plane by the Voyager 1 and 2 spacecraft are utilized to study the variation of the interplanetary shocks (with magnetosonic Mach number >1) encountered in the inner heliosphere, between ∼1 and ∼15 au from the Sun. The overwhelming majority (∼76%) of the shocks a...

Comets hold the key to the understanding of our Solar System, its formation and its evolution, and to the fundamental plasma processes at work both in it and beyond it. A comet nucleus emits gas as it is heated by the sunlight. The gas forms the coma, where it is ionised, becomes a plasma, and eventually interacts with the solar wind. Besides these...

Seasonal features of geomagnetic activity and their solar wind-interplanetary drivers are studied using more than 5 solar cycles of geomagnetic activity and solar wind observations. This study involves a total of 1239 geomagnetic storms of varying intensity identified using the Dst index from January 1963 to December 2019, a total of 75863 substorm...

The interplanetary and magnetospheric phenomena time-coincident with intense geomagnetically induced current (GIC) > 10 A and > 30 A events during 21 years (1999 through 2019) at the Mäntsälä, Finland (57.9° magnetic latitude) gas pipeline have been studied. Although forward shocks and substorms are predominant causes of intense GICs, some newly di...

In this erratum we rectify the parts of the paper that were not corrected before the publication of the paper. The conclusions of the paper are unchanged.

We study the long‐term variations of geomagnetic activity using more than five solar cycles of geomagnetic and solar wind observations. From the Dst index variation, 1523 geomagnetic storms were identified during January 1957 through December 2019, and 145 high‐intensity long‐duration continuous auroral electrojet (AE) activity (HILDCAA) events wer...

September 2017 was an extremely active space-weather period with multiple events leading to varying impacts on the Earth’s magnetosphere. The geoeffectiveness of a space-weather event largely depends on the magnetic reconnection between the southward interplanetary magnetic field and the day-side northward geomagnetic field. In this work, we estima...

Long-term variations in the relativistic (∼MeV) electrons in the Earth's radiation belt are explored to study seasonal features of the electrons. An L-shell dependence of the seasonal variations in the electrons is reported for the first time. A clear ∼6 month periodicity, representing one/two peaks per year, is identified for 1.5–6.0 MeV electron...

Solar Cycle 24, from December 2008 to December 2019, is recorded to be the weakest in magnitude in the space age (after 1957). A comparative study of this cycle with Solar Cycles 20 through 23 is presented. It is found that Solar Cycle 24 is not only the weakest in solar activity, but also in average solar wind parameters and solar wind–magnetosphe...

Three lower‐band (f < 0.5 fce) chorus riser elements detected in the dayside generation region were studied in detail using the Van Allen Probe data. Two subelements/wave packets within each riser were examined for their wave “frequency” constancy within seven consecutive wave cycles. The seven wave cycles contained the maximum amplitudes of the su...

After accompanying comet 67P/Churyumov-Gerasimenko on its journey around the Sun and observing the evolution of its induced magnetosphere throughout the comet’s life-cycle, the Rosetta operations concluded at the end of September 2016 with a controlled impact on the cometary nucleus. At that time, the comet was located more than 3.7 AU from the Sun...

Major geomagnetic storms are caused by unusually intense solar wind southward magnetic fields that impinge upon the Earth's magnetosphere (Dungey, 1961). How can we predict the occurrence of future interplanetary events? Do we currently know enough of the underlying physics and do we have sufficient observations of solar wind phenomena that will im...

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 numb...

Low frequency (LF) ~22 Hz to 200 Hz plasmaspheric hiss was studied using a year of Polar plasma wave data occurring during solar cycle minimum. The waves are found to be most intense in the noon and early dusk sectors. When only the most intense LF (ILF) hiss was examined, they are found to be substorm dependent and most prominent in the noon secto...

While Yi, Reid, Xue, Younger, Spargo, et al. (2017, http://doi:10.1002/2017JA024446) described the observational results showing solar wind high‐speed stream (HSS) impacts on the mesosphere over Antarctica, the specific physical mechanism behind them was not discussed. We discussed here how magnetospheric wave‐particle interactions and energetic ~2...

Geomagnetic storms are caused by solar wind southward magnetic fields that impinge upon the Earth’s magnetosphere (Dungey, 1961). How can we forecast the occurrence of these interplanetary events? We view this as the most important challenge in Space Weather. We discuss the case for magnetic clouds (MCs), interplanetary sheaths upstream of ICMEs, c...

Comets hold the key to the understanding of our solar system, its formation and its evolution, and to the fundamental plasma processes at work both in it and beyond it. A comet nucleus emits gas as it is heated by the sunlight. The gas forms the coma, where it is ionised, becomes a plasma and eventually interacts with the solar wind. Besides these...

Using in situ measurements from different instruments on board the Rosetta spacecraft, we investigate the properties of the newly discovered low-frequency oscillations, known as singing comet waves, that sometimes dominate the close plasma environment of comet 67P/Churyumov-Gerasimenko. These waves are thought to be generated by a modified ion-Weib...

Context. The Rosetta spacecraft made continuous measurements of the coma of comet 67P/Churyumov-Gerasimenko (67P) for more than two years. The plasma in the coma appeared very dynamic, and many factors control its variability. Aims. We wish to identify the effects of solar flares on the comet plasma and also their effect on the measurements by the...

Context. The Rosetta spacecraft made continuous measurements of the coma of comet 67P/ Churyumov-Gerasimenko (67P) for more than two years. The plasma in the coma appeared very dynamic, and many factors control its variability. Aims. We wish to identify the effects of solar flares on the comet plasma and also their effect on the measurements by the...

Intense ~300-Hz to 1.0-kHz plasmaspheric hiss was studied using Polar plasma wave data. It is found that the waves are coherent in all local time sectors with the wave coherency occurring in approximately three- to five-wave cycle packets. The plasmaspheric hiss in the dawn and local noon time sector are found to be substorm (AE*) and storm (SYM-H*...

Four interplanetary corotating interaction regions (CIRs) were identified during 2016 June – September by the Rosetta Plasma Consortium (RPC) monitoring in situ the plasma environment of the comet 67P/Churyumov-Gerasimenko (67P) at the heliocentric distances of ∼3–3.8 au. The CIRs, formed in the interface region between low- and high-speed solar wi...

Context. The Rosetta spacecraft provided us with a unique opportunity to study comet 67P/Churyumov–Gerasimenko (67P) from a close perspective and over a 2-yr time period. Comet 67P is a weakly active comet. It was therefore unexpected to find an active and dynamic ionosphere where the cometary ions were largely dominant over the solar wind ions, ev...

We present case studies of two interplanetary shock-induced supersubstorms (SSSs) with extremely high intensities (peak SML −4418 and −2668 nT) and long durations (∼1.7 and ∼3.1 hr). The events occurred on 2005 January 21 and 2010 April 5, respectively. It is shown that these SSSs have a different auroral evolution than a nominal Akasofu-type subst...

The Rosetta orbiter witnessed several hundred diamagnetic cavity crossings (unmagnetized regions) around comet 67P/Churyumov-Gerasimenko during its two year survey of the comet. The characteristics of the plasma environment inside these diamagnetic regions are studied using in situ measurements by the Rosetta Plasma Consortium instruments. While th...

We present Rosetta RPC case study from four events at various radial distance, phase angle and local time from autumn 2015, just after perihelion of comet 67P/Churyumov-Gerasimenko. Pulse like (high amplitude, up to minutes in time) signatures are seen with several RPC instruments in the plasma density (LAP, MIP), ion energy and flux (ICA) as well...

Solar-wind–geomagnetic activity coupling during high-intensity long-duration continuous AE (auroral electrojet) activities (HILDCAAs) is investigated in this work. The 1 min AE index and the interplanetary magnetic field (IMF) Bz component in the geocentric solar magnetospheric (GSM) coordinate system were used in this study. We have considered HIL...

The purpose of this study is to present a wavelet interactive filtering and reconstruction technique and apply this to the solar wind magnetic field components detected at the L1 Lagrange point ∼ 0.01 AU upstream of the Earth. These filtered interplanetary magnetic field (IMF) data are fed into a model to calculate a time series which we call AE∗....

An alternative scenario to the Ngwira et al. (2014, https://doi.org/10.1002/2013JA019661) high sheath densities is proposed for modeling the Carrington magnetic storm. Typical slow solar wind densities (~5 cm⁻³) and lower interplanetary magnetic cloud magnetic field intensities (~90 nT) can be used to explain the observed initial and main phase sto...

The variation of the relativistic “killer” electrons trapped in the Earth’s outer radiation belt is an extreme space weather phenomenon. We exemplify the processes by first studying intervals of high-speed solar wind streams (HSSs) in the declining phase of solar cycle 23. This is the portion of the solar cycle where the relativistic electron fluxe...

We present a detailed study of the cometary ionospheric response to a cometary brightness outburst using in situ measurements for the first time. The comet 67P/Churyumov-Gerasimenko (67P) at a heliocentric distance of 2.4 AU from the Sun, exhibited an outburst at ∼1000 UT on 19 February 2016, characterized by an increase in the coma surface brightn...

The purpose of this study is to present a wavelet interactive filtering and reconstruction technique and apply this to the solar wind magnetic field components detected at the L1 Lagrange point ~ 0.01 AU upstream of the Earth. This filtered interplanetary magnetic field (IMF) data is fed into a model to calculate a time series which we call AE*. Th...

Considering the magnetic reconnection and the viscous interaction as the fundamental mechanisms for transfer particles and energy into the magnetosphere, we study the dynamical characteristics of auroral electrojet (AE) index during high-intensity, long-duration continuous auroral activity (HILDCAA) events, using a long-term geomagnetic database (1...

We present a detailed study of the cometary ionospheric response to a cometary brightness outburst using in situ measurements for the first time. The comet 67P/Churyumov-Gerasimenko (67P) at a heliocentric distance of 2.4 AU from the Sun, exhibited an outburst at ~1000 UT on 19 February 2016, characterized by an increase in the coma surface brightn...

The impact of a high-speed solar wind stream (HSS) on the topside near-equatorial ionosphere (Arecibo: 28.17°N, L = 1.3) is investigated for the first time. Although the HSS did not lead to any significant geomagnetic storm activity, the ionosphere over Arecibo became hotter and expanded significantly in altitude as compared to a non-HSS interval....

The ESA’s comet chaser Rosetta has monitored the evolution of the ionized atmosphere of comet 67P/Churyumov-Gerasimenko (67P/CG) and its interaction with the solar wind, during more than two years. Around perihelion, while the cometary outgassing rate was highest, Rosetta crossed hundreds of unmagnetised regions, but did not seem to have crossed a...

Taking into account the primary mechanisms for transfer particles and energy into the magnetosphere, we have studied the dynamical characteristics of High-Intensity Long-Duration Continuous Auroral Activity (HILDCAA) events using a long-term geomagnetic database (1975–2012). The Recurrence Quantification Analysis method was applied on the auroral e...

The interplanetary and geomagnetic characteristics of High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events are studied using wavelet analysis technique. The Morlet wavelet transform was applied to the 1-minute interplanetary magnetic field (IMF) Bz component and the geomagnetic AE index during HILDCAA events. We have analyzed the AE...

A new scenario is presented for the cause of magnetospheric relativistic electron decreases (REDs) and potential effects in the atmosphere and on climate. High density solar wind heliospheric plasmasheet (HPS) events impinge onto the magnetosphere, compressing it along with remnant noon-sector outer-zone magnetospheric ~10-100 keV protons. The beta...

We study extremely intense substorms with SuperMAG AL (SML) peak intensities < -2500 nT (“supersubstorms”/SSSs) for the period from 1981 through 2012. The SSS events were often found to be isolated SML peaks and not statistical fluctuations of the indices. The SSSs occur during all phases of the solar cycle with the highest occurrence (3.8 year-1)...

We have begun a study of particularly intense substorms that occur during superstorms. We will relate the solar cycle dependences of events, whether they are externally or internally triggered, and their relationship to other factors such as magnetospheric preconditioning. If time permits, we will explore the details of the events and whether they...

High-intensity long-duration continuous AE activity (HILDCAA) events have been shown to be associated mostly with high-speed solar wind streams (HSSs) [Hajra et al., JGR, 118, 5626, 2013]. These geoeffective events, by definition [Tsurutani and Gonzalez, PSS, 35, 405, 1987], have peak AE intensities > 1,000 nT and continue for more than 2 days when...

The effects of high-energy particle precipitation on mesospheric and stratospheric ozone have been investigated during the last decades. However, while these effects have been widely discussed for the auroral region, little is known about the role of the high-energy particle precipitation on the stratospheric composition and thermal structure in th...

We analyze the energy budget of the ionosphere-thermosphere (IT) system during two High-Speed Streams (HSSs) on 22-31 January, 2007 (in the descending phase of solar cycle 23) and 25 April-2 May, 2011 (in the ascending phase of solar cycle 24) to understand typical features, similarities, and differences in magnetosphere-ionosphere-thermosphere (IT...

We present a geomagnetic quiet time (Dst > −50 nT) empirical model of ionospheric total electron content (TEC) for the northern equatorial ionization anomaly (EIA) crest over Calcutta, India. The model is based on the 1980–1990 TEC measurements from the geostationary Engineering Test Satellite-2 (ETS-2) at the Haringhata (University of Calcutta, In...

Electromagnetic ion (proton) cyclotron (EMIC) waves and whistler mode chorus are simultaneously detected in the Earth's dayside subsolar outer magnetosphere. The observations were made near the magnetic equator 3.1∘−1.5∘ MLAT (Magnetic LATitude) at 1300 MLT (Magnetic Local Time) from L = 9.9 to 7.0. It is hypothesized that the solar wind external p...

We present a comparative study of high-intensity long-duration continuous AE activity (HILDCAA) events, both isolated and those occurring in the "recovery phase" of geomagnetic storms induced by corotating interaction regions (CIRs). The aim of this study is to determine the difference, if any, in relativistic electron acceleration and magnetospher...

We examine particularly intense substorms (SML ≤–2500 nT), hereafter called "supersubstorms" or SSS events, to identify their nature and their magnetic storm dependences. It is found that these intense substorms are typically isolated events and are only loosely related to magnetic storms. SSS events can occur during super (Dst ≤–250 nT) and intens...