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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.