DSpace at IIGThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.http://http://library.iigm.res.in:8080/jspui2023-05-22T14:39:00Z2023-05-22T14:39:00ZTsallis’ Analysis of the Horizontal Component of the Earth’s Magnetic Field over India during 2002Jayapal, R.Anilkumar, C. P.Unnikrishnan, K.Venugopal, Chanduhttp://library.iigm.res.in:8080/xmlui/handle/123456789/17122023-02-21T10:37:06Z2022-01-01T00:00:00ZTitle: Tsallis’ Analysis of the Horizontal Component of the Earth’s Magnetic Field over India during 2002
Authors: Jayapal, R.; Anilkumar, C. P.; Unnikrishnan, K.; Venugopal, Chandu
Abstract: A widely used measure of entropy to quantify uncertainity in an open system is the Boltzmann-Gibbs (B-G) entropy. It, however, cannot describe non-equilibrium systems with large variability and multi-fractality. A generalisation of the B -G entropy is the Tsallis’ entropy. The values of the horizontal components of the Earth’s magnetic field, observed at various stations in India in 2002 were used. During the years 2000 –2002, solar cycle 23 reached its maximum. Data from Ettaiyapuram (ETT, latitude = 9010’ N, longitude =78001’ E, geomagnetic latitude =0.130N), Visakhapatnam (VIS,17041’ N, 83019’ E,8.170N), Hyderabad (HYD,17025’ N, 78033’ E, 8.170N), Alibag (ABG, 18037’ N, 72052’ E, 10.020N) and Tirunelveli (TVI, 8042’ N,77048’ E,0.320S) were used. Using these values as inputs, we demonstrate that Tsallis’ entropy can be used to detect minor differences in the horizontal components of the geomagnetic field observed between different pairs of stations. The method is a very simple and elegant one to detect minor variations between pairs of similar signals.2022-01-01T00:00:00ZTheory of ion holes in plasmas with flat-topped electron distributionsAravindakshan, HarikrishnanVasko, Ivan Y.Kakad, AmarKakad, BharatiWang, Rachelhttp://library.iigm.res.in:8080/xmlui/handle/123456789/17112023-02-21T10:22:25Z2023-01-01T00:00:00ZTitle: Theory of ion holes in plasmas with flat-topped electron distributions
Authors: Aravindakshan, Harikrishnan; Vasko, Ivan Y.; Kakad, Amar; Kakad, Bharati; Wang, Rachel
Abstract: Coherent bipolar electric field structures with negative unipolar potentials are widely observed in space plasmas. These bipolar structures are often found to be ion Bernstein Greene Kruskal (BGK) modes or ion holes. Most theoretical models of ion holes assume them to be stationary with respect to the background plasma that follows either Maxwellian or kappa-type distribution. In this paper, we present a new theoretical model of ion holes where the structures are non-stationary, and electrons follow flat-topped distribution. We use the classical BGK approach to derive the inequality separating allowed and forbidden simultaneous values of amplitude and spatial width of ion holes. The model reveals that the parametric space for the existence of ion holes decreases with their speed. We applied the developed model to the largest available dataset of ion holes obtained from the magnetospheric multiscale spacecraft observations in the Earth's bow shock region.2023-01-01T00:00:00ZThe Structure and Microstructure of Rising-Tone Chorus With Frequencies Crossing at f ∼ 0.5 fceChen, RuiTsurutani, Bruce T.Gao, XinliangLu, QuanmingChen, HuayueLakhina, Gurbax S.Hajra, Rajkumarhttp://library.iigm.res.in:8080/xmlui/handle/123456789/17102023-02-21T09:47:55Z2022-01-01T00:00:00ZTitle: The Structure and Microstructure of Rising-Tone Chorus With Frequencies Crossing at f ∼ 0.5 fce
Authors: Chen, Rui; Tsurutani, Bruce T.; Gao, Xinliang; Lu, Quanming; Chen, Huayue; Lakhina, Gurbax S.; Hajra, Rajkumar
Abstract: Intense, midnight-to-dawn sector, near-equatorial, chorus rising tones which cross frequencies of_0.5_ce have been analyzed to determine their structures and possible substructures. Upper 𝐴𝐴band (𝐴𝐴 ≥ 0.5𝑓𝑓ce ) chorus and “𝐴𝐴gap” (𝐴𝐴 ∼ 0.5𝑓𝑓ce ) chorus are examined in detail for the first time. It is found that upper band chorus and gap chorus are composed of the same structure as lower 𝐴𝐴 band (𝐴𝐴 ≤ 0.5𝑓𝑓ce ) chorus: they are composed of short-duration subelements, which are monochromati𝐴𝐴c with 𝐴𝐴 ≤ 1% . These findings have strong implications for the chorus element generation mechanism. Following Kennel and Petschek (1966, https://doi.org/10.1029/JZ071i001p00001) the overall chorus riser is most likely generated by anisot𝐴𝐴ropic (𝐴𝐴⟂∕𝑇𝑇‖ > 1) ∼10–100 keV substorm-injected electrons. Assuming cyclotron resonance, the upper band chorus is generated by the low energy portion of the electron spectrum. The often-present gap at _0.5_ce is related to Landau/cyclotron damping. This however is not the end of the story. There is another type of two-frequency chorus (called Type 2) for which the lower band is not well connected to the upper band. A Type 2 chorus reported previously by Fu et al. (2014, https://doi.org/10.1002/2014JA020364) has also been studied in detail. Both the lower band and upper band are composed of subelements which are monochromatic. Such a similar fine structure for the different type of chorus may imply a similar generation mechanism, for which the difference between them is just the energy range of resonant energetic electrons. One mechanism discussed here, generation by phase bunched electrons, will be tested in the near future.
Plain Language Summary Understanding chorus structure and microstructure is essential toward understanding the wave generation mechanisms and wave-particle interaction consequences. In this paper we show that upper 𝐴𝐴band (𝐴𝐴 ≥ 0.5𝑓𝑓ce ) chorus and gap ch𝐴𝐴orus (𝐴𝐴 ∼ 0.5𝑓𝑓ce ) are composed of substructures (subelements) which are monochromati𝐴𝐴c with 𝐴𝐴 ≤ 1% . These are the same features of lower 𝐴𝐴band (𝐴𝐴 ≤ 0.5𝑓𝑓ce ) chorus. The Kennel-Petschek theory therefore needs to be enlarged such that phase-bunching of ∼10–100 keV substorm injected anisotropic electrons occur, which then “lase” to yield the monochromatic wave subelements. Coherent and monochromatic chorus can explain the rapid burstiness of ionospheric microburst X-ray structures. There is another type of upper band chorus, called Type 2 upper band chorus, where the lower band chorus elements are not clearly connected to the upper band chorus. A Type 2 chorus reported previously by Fu et al. (2014, https://doi.org/10.1002/2014JA020364) has been examined in this paper. The apparently unrelated upper band has been found to be composed of subelements which are monochromatic in nature. Thus the different type of chorus may be excited by a similar generation mechanism, for which the difference between them is only the energy interval of the resonant energetic electrons.2022-01-01T00:00:00ZA case of anomalous electric field perturbations in the equatorial ionosphere during post-sunset hours: InsightsKumar, A.Chakrabarty, D.Fejer, B. G.Reeves, G. D.Rout, D.Sripathi, S.Seemala, G. K.Sunda, S.Yadav, A. K.http://library.iigm.res.in:8080/xmlui/handle/123456789/17092023-02-21T09:21:15Z2023-01-01T00:00:00ZTitle: A case of anomalous electric field perturbations in the equatorial ionosphere during post-sunset hours: Insights
Authors: Kumar, A.; Chakrabarty, D.; Fejer, B. G.; Reeves, G. D.; Rout, D.; Sripathi, S.; Seemala, G. K.; Sunda, S.; Yadav, A. K.
Abstract: During a weak geomagnetic storm (Ap = 15) on 24 December 2014, the penetration electric field perturbations over the Indian dip equatorial sector are found to be anomalous on a number of occasions during post-sunset hours. The event is anomalous as the magnitude and polarity of penetration electric fields do not obey the existing paradigm. The penetration electric field perturbations are investigated using the vertical drifts derived from the CADI (Canadian Advanced Digital Ionosonde) measurements at Tirunelveli (8.7° N, 77.7° E, dip angle: 1.7°). During this event, we observed post-sunset vertical drift of ∼42 ms−1 not only at 1810 LT but also ∼36 ms−1 at ∼2100 LT which is anomalous. Interestingly, the dawn-dusk component of interplanetary electric field (IEFy) is relatively less ( < 2 mV/m) at ∼2100 LT compared to the interval 1930-2030 LT (IEFy ∼3 mV/m). Despite that, the vertical drift observed over Tirunelveli is very close to zero or nominally upward during 1930-2030 LT. In addition, the downward drift just after 2130 LT on this night is found to be exceptionally large ( ∼-60 ms−1). By combining vertical total electron content over the Indian sector with the OI 630.0 nm airglow intensity from Mt. Abu, chain of magnetometer and Los Alamos National Laboratory (LANL) geosynchronous satellite particle measurements, it is suggested that the anomalous penetration electric field perturbations on this night arise from the effects of IMF By and substorm.
Plain Language Summary Variation in the zonal electric field in the equatorial ionosphere during post-sunset hours is important to understand the plasma distribution over low latitudes and also generation of plasma irregularities. The changes in the ionospheric conditions over low/equatorial latitudes have implications for communication and navigational applications. Therefore, if ionospheric electric field over equatorial ionosphere behaves anomalously during space weather events, it will be difficult to model the low latitude ionosphere for scientific understanding and practical applications. In this investigation, we show that the less studied Y-component of interplanetary magnetic field and substorm can significantly modulate the ionospheric electric field giving rise to anomalous response2023-01-01T00:00:00Z