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Indian Institute of Geomagnetism (IIG)
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Recent Submissions
Understanding Quiet and Storm Time EMIC Waves - 2 Van Allen Probes Results
(2023) Remya, B.; Halford, A. J.; Sibeck, D. G.; Murphy, K. R.; Fok, M. -C.
Geomagnetic indices have been used as a proxy for studying electromagnetic ion cyclotron (EMIC) wave occurrences under di erent geomagnetic conditions. However, the drivers of EMIC waves are di erent during non-storm, storm time and during individual storm phases. Using 7 years of data from the twin Van Allen Probes, we demonstrate that the occurrence probability of EMIC waves are not well captured by a speci c
geomagnetic activity index alone, but is rather well manifested by considering individual storm phases. We show EMIC wave occurrence statistics during di erent storm phases (preonset, main and recovery) for geomagnetic activity indices Sym-H, AE, and Kp and
solar wind dynamic pressure Pdyn, illustrating that the occurrence rates vary signi cantly
during di erent storm phases even for a given geomagnetic index. We also utilize this
large database to show EMIC wave occurrence distribution, and how various wave and
plasma parameters behave under di erent geomagnetic conditions. EMIC waves occur
2.9 times more often during geomagnetic storms than during non-storm times. The
majority (72%) of storm time EMIC waves occur during the recovery phase due to long
recovering time, while the highest occurrence rates are in the pre-onset phase, followed by main and recovery phases. EMIC waves in the main phase have occurrence peaks in the dusk to pre-midnight sectors while recovery phase events spread to more MLT sectors
with peaks in the morning sector. Wave amplitudes are found to be evenly distributed
across di erent MLT sectors during all geomagnetic conditions.
Anisotropy of the near-field coseismic ionospheric perturbation amplitudes reflecting the source process: the 2023 February Turkey earthquakes
(2023) Bagiya, Mala S.; Heki, K.; Gahalaut, Vineet K.
The East Anatolian Fault in southern Turkey ruptured on 6 February 2023, causing a Mw 7.8
earthquake (EQ1), one of the largest strike-slip events recorded on land. ∼9 hr later, earthquake of Mw 7.7
(EQ2) occurred to the north of EQ1. We investigate here near-field coseismic ionospheric perturbations (CIP)
caused by acoustic waves (AWs) excited by coseismic vertical crustal movements. We find that observed CIP
periods were somewhat longer for EQ1 than EQ2. EQ1 also showed azimuthal dependence in CIP amplitudes
that cannot be explained by known factors such as geomagnetism and line-of-sight geometry. Numerical
experiments revealed that CIP by EQ1 can be well reproduced by assuming a suite of sources along the
fault that successively ruptured. Small but significant dependence of amplitudes and periods on azimuths
were caused by interference of AWs from multiple sources. We also found that CIP amplitudes of strike-slip
earthquakes tend to be lower than dip-slip earthquakes.
Interplanetary shocks between 0.3 and 1.0 au: Helios 1 and 2 Observations
(2023) Hajra, Rajkumar; Tsurutani, Bruce T.; Lakhina, G. S.; Lu, Quanming; Du, Aimin; Shan, Lican
The Helios 1 (H1) and Helios 2 (H2) spacecraft measured the solar winds at a distance between ∼0.3 and 1.0 au
from the Sun. With increasing heliocentric distance (rh), the plasma speed is found to increase at ∼34–40 km s−1
au−1 and the density exhibits a sharper fall (rh-
2) compared to the magnetic field magnitude (r - h
1.5) and the
temperature (rh-
0.8). Using all available solar wind plasma and magnetic field measurements, we identified 68 and
39 fast interplanetary shocks encountered by H1 and H2, respectively. The overwhelming majority (85%) of the
shocks are found to be driven by interplanetary coronal mass ejections (ICMEs). While the two spacecraft
encountered more than 73 solar wind high-speed streams (HSSs), only ∼22% had shocks at the boundaries of
corotating interaction regions (CIRs) formed by the HSSs. All of the ICME shocks were found to be fast forward
(FF) shocks; only four of the CIR shocks were fast reverse shocks. Among all ICME FF shocks (CIR FF shocks),
60% (75%) are quasi-perpendicular with shock normal angles (θBn) 45° relative to the upstream ambient
magnetic field, and 40% (25%) are quasi-parallel (θBn < 45°). No radial dependences were found in FF shock
normal angle and speed. The FF shock Mach number (Mms), magnetic field, and plasma compression ratios are
found to increase with increasing rh at the rates of 0.72, 0.89, and 0.98 au−1, respectively. On average, ICME FF
shocks are found to be considerably faster (∼20%) and stronger (with ∼28% higher Mms) than CIR FF shocks.
Kinetic Alfvén waves excited by multiple free energy sources in the magnetotail
(2023) Barik, K. C.; Singh, S. V.; Lakhina, G. S.
The generation of kinetic Alfvén waves (KAWs) is investigated through a three-component theoretical model
incorporating ion beam and velocity shear as the sources of free energy in a non-Maxwellian κ-distributed plasmas.
The model considers Maxwellian distributed background ions, drifting-Maxwellian beam ions, and κ-electrons as
its constituent species. It is found that the combination of either positive velocity shear with counter-streaming
beam ions or parallel streaming beam ions with negative velocity shear favors the excitation of KAWs. The effect
of the κ-parameter on the excitation of KAWs under the combined energy sources is explored. The effect of plasma
parameters such as number density, propagation angle, and temperature of plasma species on the real frequency
and the growth rate of KAWs are examined. For the plasma parameters pertinent to the magnetotail region of
Earth’s magnetosphere, the model is able to produce KAWs in the frequency range of ≈(5–67) mHz, which
matches well with the recent ‘Time History of Events and Macroscale Interactions during Substorms (THEMIS)’
observations in the near-Earth magnetotail region.
Electrostatic solitary waves in the Venusian ionosphere pervaded by the solar wind: a theoretical perspective
(2023) Rubia, R.; Singh, S. V.; Lakhina, G. S.; Devanandhan, S.; Dhanya, M. B.; Kamalam, T.
Electrostatic solitary waves (ESWs) in the Venusian ionosphere that are impinged by the solar wind are
investigated using a homogeneous, collisionless, and magnetized multicomponent plasma consisting of Venusian
H+ and O+ ions, Maxwellian Venusian electrons and streaming solar wind protons, and suprathermal electrons
following κ − distribution. The model supports the propagation of positive potential slow O+ and H+ ion-acoustic
solitons. The evolution and properties of the solitons occurring in two sectors, viz., dawn-dusk and noon-midnight
sector of the Venus ionosphere at an altitude of (200–2000) km, are studied. The theoretical model predicts positive
potential solitons with amplitude ∼(0.067–56) mV, width ∼(1.7–53.21) m, and velocity ∼(1.48–8.33) km s−1. The
bipolar soliton electric field has amplitude ∼(0.03–27.67) mV m−1 with time duration ∼(0.34–22) ms. These
bipolar electric field pulses when Fourier transformed to the frequency domain occur as a broadband electrostatic
noise, with frequency varying in the range of ∼9.78 Hz–8.77 kHz. Our results can explain the observed
electrostatic waves in the frequency range of 100 Hz–5.4 kHz in the Venus ionosphere by the Pioneer Venus
Orbiter mission. The model can also be relevant in explaining the recent observation of ESWs in the Venus
magnetosheath by the Solar Orbiter during its first gravity assist maneuver of Venus.
Equatorial plasma bubble association with lower atmospheric gravity waves – Further evidences
(2023) Ghodpage, R.N.; Taori, A.; Patil, M.K.; Gurav, O.B.; Patil, R.P.; Sripathi, S.
Space based radio wave communication and navigation has become need of the society. Atmospheric (thermospheric-ionospheric)
processes, such as Equatorial Plasma Bubbles (EPBs), affect the radio waves propagating through this region, causing heavy perturbations
on signals received at ground. This paper investigates the causative mechanism of EPB through the ground based remotely sensed
imaging observations of O (1S) 557.7 nm and O (1D) 630.0 nm emissions emanating from the upper mesosphere ( 100 km altitudes) and
thermosphere-ionosphere ( 250 km altitudes) over a low-latitude station, Kolhapur (16.8 N, 74.2 E, and dip lat. 10.6 N). Our investigation
revealed that the gravity waves evident in OI557.7 nm images exhibit a close association with the observed EPB structures. These
mesospheric gravity waves were found to travel from the South to North with horizontal wavelengths 35 and 56 km on 13–14 April
and 26–27 April 2015, respectively. The thermosphere-ionosphere measurements exhibited occurrence of the North–South aligned EPB
moving to the east with an inter depletion distance (IDD) equal to 44 km and 64 km. These results provide evidences on association
of the gravity waves with the EPB.
A mechanism for large-amplitude parallel electrostatic waves observed at the Magnetopause
(2023) Lakhina, G. S.; Singh, Satyavir; Sreeraj, Thekkeyil; Devanandhan, Selvaraj; Rubia, Rajith
Large-amplitude electrostatic waves propagating parallel to the background magnetic
field have been observed at the Earth’s magnetopause by the Magnetospheric Multiscale (MMS)
spacecraft. These waves are observed in the region where there is an intermixing of magnetosheath
and magnetospheric plasmas. The plasma in the intermixing region is modeled as a five-component
plasma consisting of three types of electrons, namely, two counterstreaming hot electron beams and
cold electrons, and two types of ions, namely, cold background protons and a hot proton beam.
Sagdeev pseudo-potential technique is used to study the parallel propagating nonlinear electrostatic
solitary structures. The model predicts four types of modes, namely, slow ion-acoustic mode, fast
ion-acoustic mode, slow electron-acoustic mode and fast electron-acoustic modes. Except the fast
ion-acoustic mode, all other modes support solitons. Whereas slow ion-acoustic solitons have positive
potentials, both slow and fast electron-acoustic solitons have negative potentials. For the case of
4% cold electron density, the slow ion-acoustic solitons have electric field (40–120) mV m1. The fast
Fourier transforms (FFT) of slow ion-acoustic solitons produce broadband frequency spectra having
peaks between 100 Hz to 1000 Hz. These theoretical predictions are in good agreement with
the observations. The slow and fast electron-acoustic solitons could be relevant in explaining the
low-intensity high (>1 kHz) frequency waves which are also observed at the same time.
Day-to-day quantification of changes in global lightning activity based on Schumann resonances
(2023) Bozóki, T.; Sátori, G.; Williams, E.; Guha, A.; Liu, Y.; Steinbach, P.; Leal, A.; Herein, M.; Atkinson, M.; Beggan, C. D.; DiGangi, E.; Koloskov, A.; Kulak, A.; LaPierre, J.; Milling, D. K.; Mlynarczyk, J.; Neska, A.; Potapov, A.; Raita, T.; Rawat, R.; Said, R.; Sinha, A. K.; Yampolski, Y.
The importance of lightning has long been recognized from the point of view of climate-related
phenomena. However, the detailed investigation of lightning on global scales is currently hindered by the
incomplete and spatially uneven detection efficiency of ground-based global lightning detection networks
and by the restricted spatio-temporal coverage of satellite observations. We are developing different methods
for investigating global lightning activity based on Schumann resonance (SR) measurements. SRs are
global electromagnetic resonances of the Earth-ionosphere cavity maintained by the vertical component of
lightning. Since charge separation in thunderstorms is gravity-driven, charge is typically separated vertically
in thunderclouds, so every lightning flash contributes to the measured SR field. This circumstance makes
SR measurements very suitable for climate-related investigations. In this study, 19 days of global lightning
activity in January 2019 are analyzed based on SR intensity records from 18 SR stations and the results are
compared with independent lightning observations provided by ground-based (WWLLN, GLD360, and
ENTLN) and satellite-based (GLM, LIS/OTD) global lightning detection. Daily average SR intensity records
from different stations exhibit strong similarity in the investigated time interval. The inferred intensity of global
lightning activity varies by a factor of 2–3 on the time scale of 3–5 days which we attribute to continental-scale
temperature changes related to cold air outbreaks from polar regions. While our results demonstrate that the SR
phenomenon is a powerful tool to investigate global lightning, it is also clear that currently available technology
limits the detailed quantitative evaluation of lightning activity on continental scales.
The possible cause of most intense geomagnetic superstorm of the 21st century on 20 November 2003
(2023) Raghav, Anil; Shaikh, Zubair; Vemareddy, P.; Bhaskar, Ankush; Dhamane, Omkar; Ghag, Kalpesh; Tari, Prathmesh; Dayanandan, Baiju; Suti, Badar Mohammed Al
An extreme geomagnetic storm has the potential to affect various technologies and activities
in space and on the ground, e.g., power grids, oil and gas industries, communications,
ground transportation, satellite infrastructure, global navigation satellite systems, aviation,
etc. Therefore, it is considered a major source of risk by various governmental agencies and
corporations at the international level. All notable space weather events (superstorms) are
caused by interplanetary coronal mass ejections (ICMEs). But not every ICME leads to an
extreme storm. Moreover, how does an extreme storm form? Or which explicit characteristic
of ICME actually is responsible for inducing a superstorm? Here, we re-investigate
the ICME characteristics that contribute to the most intense storm of the current century
that occurred on 20 November 2003. Interestingly, the studied ICME magnetic cloud shows
characteristics of extremely flattened (pancaked) structure i.e. quasi-planar magnetic structure
(PMS). The pancaked ICME shows less adiabatic expansion than usual in the compressed
direction, which leads to strong magnetic field strength, high plasma density, high
solar wind speed, high dynamic pressure, and a high eastward interplanetary electric field.
Here, we propose that the ICME that transformed into a quasi-PMS has the aforementioned
enhanced features with strong southward magnetic field component that contributes to efficiently
transferring plasma and energy into the Earth’s magnetosphere to cause the observed
superstorm.
Spatially heterogeneous lithospheric architecture of the Cambay rift basin and adjoining Aravalli-Delhi Fold Belt, western India – A synthesis of magnetotelluric results
(2023) Nagarjuna, Danda; Kumar, Amit; Pavankumar, G.; Rao, C.K.; Manglik, Ajay
The Cambay rift basin (CRB) evolution has been associated with separation of the Indian continent from the
African continent and subsequent interaction with the R´eunion mantle plume, which resulted in significant alternations
in the regional lithospheric structure of western India, more prominently in the CRB due to its
proximity to the plume track. In our continued effort to delineate the lithospheric structure of the CRB and
adjoining regions, we acquired magnetotelluric (MT) data at 31 sites along a profile across the CRB and analyzed
these. The 2D geoelectric model derived from this dataset reveals a collage of conductive and resistive formations.
The resistive blocks indicate the Archaean lithosphere on the west, the uplifted crust within the CRB, and
various structural units of the Precambrian Era on the east providing evidence for continuation of the Aravalli-
Delhi Fold Belt trend beneath the CRB into Saurashtra. The conductive anomalies beneath the CRB infer the
magmatic underplating associated with thermal influx derived from the upper mantle as a result of the R´eunion
plume interaction. Integration of previous geophysical and present results infers a spatially heterogeneous
lithosphere possibly representing an assemblage the Archaean and Proterozoic lithospheres beneath the CRB. The
Proterozoic lithosphere is more vulnerable to the impact of the R´eunion plume due to its weak nature in comparison
to the Archaean lithosphere. The Archaean lithosphere on the western side of CRB indicates initial stage
of rifting, whereas Proterozoic lithosphere infers second stage coeval with the Deccan volcanic eruption. The
heterogeneity in sedimentary thickness within the CRB spatially correlates with the contact of Archaean and
Proterozoic lithospheres, which might have played a role in the formation of the basin structure, and sediment
deposition.
Enhanced gravity wave activity in the mesosphere lower thermosphere region over Tirunelveli as a response to tropospheric convective event
(2023) Krishnapriya, K.; Sathishkumar, S.; Sridharan, S.
The recent upgrade of Medium-Frequency (MF) wind radar at Tirunelveli (8.7⁰N, 77.8⁰E) has improved the height and time resolution
of the wind measurements, which are utilized in the present study to examine high frequency (in periods 20–60 min) gravity waves
(GW) in the mesosphere and lower thermosphere (MLT) region. We observe, in addition to the dominant wave activity during equinox
months, dominant episodes of high-frequency GW activities in the meridional winds during the times 31 May–4 June and 25–27 June
2019. Using the perturbation ellipse method, we infer the direction of propagation of the GW and it is found to be in the north–south
plane. The GW activity in the MLT region exhibits anti-correlation with NOAA outgoing longwave radiation (OLR) and positive correlation
with rainfall rates indicating the latent heat release due to tropical convection as the possible source of the GW. Besides, the
presence of dynamical instability is inferred from the calculations using the radar wind and the spaceborne SABER (Sounding of Atmosphere
using Broadband Emission Radiometry) temperature data suggesting a possible causality of convectively generated GWs
dissipation.
Machine learning approach for detection of plasma depletions from TEC
(2023) Kapil, Chandan; Seemala, Gopi K.
Ionospheric delay is of concern for trans-ionospheric radio communication, especially for the navigation systems relying on these
satellite signals. Most of the ionospheric delays are estimated to a degree of first-order using dual frequency global navigation satellite
system (GNSS) receivers except during irregularities and equatorial plasma bubbles. The plasma bubbles are observed as a decrease or
reduction in total electron content (TEC) as a result of large-scale irregularities that are generated at the equatorial ionosphere. These
plasma bubbles can be detected from TEC values visually or by using mathematical algorithms. The mathematical algorithms may have
limitations based on assumptions made for the current dataset. Therefore, various machine learning (ML) techniques were tried by training
them with selected TEC depletions that are verified for accuracy. From this study, the Random Forest Method (RFM) has performed
well compared to other ML methods. The RFM is trained to use for the detection of TEC depletions from the Indian low-latitude region.
The training accuracy obtained is 97.6%, with a minimum classification error of 0.023%. The result obtained from the confusion matrix
ascertained that the proportion of positively classified cases that are truly positive that is the positive predictive value (PPV) is 96.8%.
These statistical results are validated after plotting the observed TEC depletion patch obtained from the ML method. There are cases in
which depletions detected by the ML method are appreciable over the mathematical algorithm. The ML technique once trained will not
have inherent limitations, as there are no assumptions or threshold values needed to set as required by most of the mathematical algorithms.
Thus, the results are encouraging and have scope for further improvement and advancement.
Performance of the CORDEX-SA regional climate models in simulating summer monsoon rainfall and future projections over East India
(2023) Barde, Vasundhara; Nageswararao, M. M.; Mohanty, U. C.; Panda, R. K.
—The Indian summer monsoon rainfall (ISMR, June–
September) is an important factor in agricultural planning and the
Indian economy. The ISMR over East India (EI: ChhattisgarhBihar-Jharkhand-Odisha) is particularly significant, and it can have
an impact on the country’s average ISMR. The current study
examined projected changes in ISMR over EI with two emission
scenarios, RCP4.5 and RCP8.5, for near (2017–2040) and far-future (2041–2070) projections using a set of ten CORDEX-SA
Regional Climate Model (RCMs). To begin, the performance of
raw and bias-corrected ISMR over EI outputs from ten CORDEXSA RCMs was compared to a high-resolution (0.25 9 0.25)
gridded rainfall analysis dataset from the India Meteorological
Department (IMD) over the hindcast period (1971–2005). Following that, bias-corrected results were used to calculate ISMR
projections over EI for the near and distant futures. Most RCMs,
according to the findings, can imitate the spatial pattern of ISMR
across EI but are restricted in their ability to capture actual magnitudes. Notably, RCM prediction skill increased greatly after
employing various bias-correction approaches, the quantile mapping (QQM) bias-correction technique outperformed other current
conventional bias correction methods, and the QQM technique was
employed for ISMR future projections using RCP4.5 and RCP8.5
emission scenarios. The analysis of ISMR projections over EI
reveals that there will be more deficit rainfall years in the short
term while more excess rainfall years in the far future.
Studies on the variability of mean winds in the mesosphere and lower thermosphere region (MLT) over Kolhapur (16.8oN, 74.2oE)
(2023) Naniwadekar, G.P.; Gurubaran, S.; Jadhav, A.P.; Ghodpage, R.N.; Patil, P.T.; Burud, D.S.
We present the study of mesospheric winds in the 78–98 km height range using observations by a partial
reflection radar station (MF–radar) situated at Kolhapur (16.8° N, 74.2° E), India. The sequential wind profiles over the
period of 2014–2019 obtained from this radar operated at 1.98 MHz are used for this study. To delineate the behaviour
of the winds in the mesosphere and lower thermosphere (MLT) region, we use wind data providing horizontal wind
velocities averaged for an hour. Details of the seasonal, annual, and inter-annual variations and also the climatology of
mean motion in zonal (East-West) and meridional (North-South) components in the MLT region over the
aforementioned period are presented. The zonal wind below 90 km has been observed with eastward flow for the period
of solstices and westward flow at equinoxes, showing strong semi-annual oscillations (SAO). While above 90 km,
annual oscillations (AO) are seen to be dominant. Annual oscillations (AO) are observed in the mean meridional wind,
with poleward motion during winter and equatorward motion during the remaining seasons. At higher altitudes (above
92 km), the poleward motion weakens and the equatorward wind flow becomes strong.
Nonlinear electrostatic structures and stopbands in a three-component magnetosheath plasma
(2023) Rufai, O.R.; Singh, S.V.; Lakhina, G.S.
Large amplitude parallel propagating electric field structures of nonlinear electron-acoustic waves are examined in an unmagnetized magnetosheath plasma. Based on the observations and simulations by Ergun et al. (2016), the plasma in the
magnetosheath side of the ion diffusion layer is modeled by a 3-component adiabatic fluid dynamic plasma consisting of
cold magnetospheric (MSP) electrons, magnetosheath electrons, and background ions. Using the Sagdeev pseudopotential
technique, for the plasma parameters recorded by the Magnetospheric Multiscale (MMS) mission in the magnetosheath side
of the ion diffusion region, existence regime of the nonlinear electrostatic solitary wave structures is obtained with the possibilities of stopbands (forbidden gap region). Stopbands or the forbidden gap region exists even when the drift velocity of
the cold electron beam is zero. The forbidden gap region becomes wider and the Mach numbers of the regions supporting
solitary structures become larger by an increase in the drift velocity of the cold electron beam. The results are in agreement
with the magnetosheath electrostatic waves having amplitudes of 100s mV/m and frequencies up to 3.2 kHz observed by the
MMS.
The global representativeness of fair-weather atmospheric electricity parameters from the coastal station Maitri, Antarctica
(2023) Jeeva, K.; Sinha, A. K.; Seemala, Gopi K.; Pawar, S. D.; Guha, A.; Kamra, A. K.; Williams, E. R.; Ravichandran, M.
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.
Extreme space weather events of solar cycle 24: X-class solar flares and their impact on the low-latitude D-region ionosphere
(2023) Venkatesham, K.; Maurya, Ajeet K.; Singh, Rajesh; Dwivedi, Suneet
X-class solar flares, which occurred in the daytime from 2008 to 2016 during solar cycle 24, were studied for their influence on the lower ionosphere over the low-equatorial Indian region. To understand the D-region behaviour during flare events, we used the very low fre-quency (VLF) navigational transmitter NWC (19.8 kHz) signal recorded at Pryagraj, Uttar Pradesh, India. A total of seven parameters were estimated: (i) the mag-nitude of X-ray flux, (ii) VLF signal rising amplitude perturbation (SRAP), (iii) X-ray flux and NWC signal start time difference (STD), (iv) peak time difference (PTD), (v) Wait’s ionospheric parameters h′ (reference height), (vi) β (sharpness factor) and (vii) D-region electron density difference (EDD) to determine the overall effect of solar flares on the D-region. The re-sults suggest that three parameters (X-ray flux, SRAP and h′) show a decreasing trend through the linear fit line, two parameters (β and EDD) show an increasing trend, while the remaining two parameters show a mixed trend (decrease during low activity and increase during high activity). Further, the trend line during the diurnal variation shows an increasing trend for X-ray flux, PTD and h′, and a decreasing trend for SRAP, STD, β and EDD. Deviation in the case of individual events may indicate the dependence of these parame-ters on the seasons as well. The present study will pro-vide the base for more robust analysis and modelling work in the future to understand the complexity of ion-ospheric change during flare events, and to develop a predictive model for space weather mitigation.
The drift history of the Dharwar Craton and India from 2.37 Ga to 1.01 Ga with refinements for an initial Rodinia configuration
(2023) Miller, Scott R.; Meert, Joseph G.; Pivarunas, Anthony F.; Sinha, Anup K.; Pandit, Manoj K.; Mueller, Paul A.; Kamenov, George D.
Coupled paleomagnetic and geochronologic data derived from mafic dykes provide valuable records of
continental movement. To reconstruct the Proterozoic paleogeographic history of Peninsular India, we
report paleomagnetic directions and U-Pb zircon ages from twenty-nine mafic dykes in the Eastern
Dharwar Craton near Hyderabad. Paleomagnetic analysis yielded clusters of directional data that correspond
to dyke swarms at 2.37 Ga, 2.22 Ga, 2.08 Ga, 1.89–1.86 Ga, 1.79 Ga, and a previously undated dual
polarity magnetization. We report new positive baked contact tests for the 2.08 Ga swarm and the 1.89–
1.86 Ga swarm(s), and a new inverse baked contact test for the 2.08 Ga swarm. Our results promote the
2.08 Ga Dharwar Craton paleomagnetic pole (43.1 N, 184.5 E; A95 = 4.3 ) to a reliability score of R = 7
and suggest a position for the Dharwar Craton at 1.79 Ga based on a virtual geomagnetic pole (VGP) at
33.0 N, 347.5 E (a95 = 16.9 , k = 221, N = 2). The new VGP for the Dharwar Craton provides support
for the union of the Dharwar, Singhbhum, and Bastar Cratons in the Southern India Block by at least
1.79 Ga. Combined new and published northeast-southwest moderate-steep dual polarity directions
from Dharwar Craton dykes define a new paleomagnetic pole at 20.6 N, 233.1 E (A95 = 9.2 , N = 18;
R = 5). Two dykes from this group yielded 1.05–1.01 Ga 207Pb/206Pb zircon ages and this range is taken
as the age of the new paleomagnetic pole. A comparison of the previously published poles with our
new 1.05–1.01 Ga pole shows India shifting from equatorial to higher (southerly) latitudes from 1.08
Ga to 1.01 Ga as a component of Rodinia.
Observation of Alfvén waves in an ICME-HSS interaction region
(2023) Dhamane, Omkar; Raghav, Anil; Shaikh, Zubair; Panchal, Utsav; Ghag, Kalpesh; Tari, Prathmesh; Choraghe, Komal; Bhaskar, Ankush; Telloni, Daniele; Mishra, Wageesh
The Alfvén wave (AW) is the most common fluctuation present within the solar wind emitted from the Sun. Whether or not AWs can originate after the collision of an Interplanetary
Coronal Mass Ejection (ICME) and a High-Speed Stream (HSS) remains an open question.
To find an answer to this question, we have investigated an ICME-HSS interaction event
observed on 21st October 1999 at 1 AU by the WIND spacecraft. We have used the Walén
test to identify AWs and estimated the Elsässer variables to find its characteristics. We explicitly find dominant sunward AWs within the ICME, whereas the trailing HSS has strong
anti-sunward AWs. We suggest that the ICME-HSS interaction deforms the Magnetic Cloud
(MC) of the ICME, resulting in the generation of AWs inside the MC. Additionally, the existence of reconnection within the ICME’s early stage could also contribute to the origin of
AWs within it.
Simultaneous electric, magnetic and ULF anomalies associated with moderate earthquakes in Kumaun Himalaya
(2023) Bulusu, Jayashree; Arora, Kusumita; Singh, Shubham; Edara, Anusha
Variations in electric and magnetic (EM) felds were examined at two sites: Dhanachuli
near the Main Boundary Thrust (MBT) and Patiyasar near the Main Central Thrust (MCT)
in Kumaun Himalaya, India. Anomalous EM signatures are defned based on medium-term
data recordings. The patterns of anomalous EM signatures are then linked to the occurrence of moderate earthquakes (3.5≤M≤5.0), enhanced along the MCT. The vertical
component of the magnetic feld is due to microtremors prior to the earthquakes; electric
felds also show positive anomalies. Surface waves due to microtemors associated with the
earthquakes is refected in the polarization ratios of geomagnetic data in the Pc4 range
(0.01 Hz), a few days prior to each earthquake. In the case of one earthquake, during which
suitable data could be retrieved, we observe a frequency change in ULF (Pc1 range) in
addition to the enhancement of the Pc4, prior to the event.
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