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We report observations of co-existing rising and falling tone emissions of Electromagnetic Ion Cyclotron (EMIC) waves by THEMIS E spacecraft. The investigation of these fine structures of the EMIC waves is essential from the point of view... more
We report observations of co-existing rising and falling tone emissions of Electromagnetic Ion Cyclotron (EMIC) waves by THEMIS E spacecraft. The investigation of these fine structures of the EMIC waves is essential from the point of view of understanding the connection between the proton holes and the proton hills in velocity phase-space. The wave packets of rising and falling tones are tracked by Poynting vector analysis, where we observe that the rising tones are propagating northward and the falling tones are propagating southward. The nonlinear wave growth theory supports our observations. We propose a model where the proton velocity distribution function evolves through the formation of proton holes on the negative side of the distribution function and mirrored resonant protons forming proton hills on the positive side of the distribution function, allowing us to observe the co-existing rising and falling tone EMIC waves.
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Abstract. An analysis of low order mode coupling equations is used to describe the nonlinear behavior of the Rayleigh-Taylor (RT) instability in the equatorial ionosphere. The nonlinear evolution of RT instability leads to the development... more
Abstract. An analysis of low order mode coupling equations is used to describe the nonlinear behavior of the Rayleigh-Taylor (RT) instability in the equatorial ionosphere. The nonlinear evolution of RT instability leads to the development of shear flow. It is found that there is an interplay between the nonlinearity and the shear flow which compete with each other and saturate the RT mode, both in the collisionless and collisional regime. However, the nonlinearly saturated state, normally known as vortices or bubbles, may not be stable. Under certain condition these bubbles are shown to be unstable to short scale secondary instabilities that are driven by the large gradients which develop within these structures. Some understanding of the role of collisional nonlinearity in the shear flow generations is also discussed. 1
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... more
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 elect...
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Propagation characteristics of electrostatic electron and ion cyclotron waves, ion- and electron- acoustic waves in a four-component magnetized plasma comprising of protons, doubly charged Helium ions, beam electrons and superthermal... more
Propagation characteristics of electrostatic electron and ion cyclotron waves, ion- and electron- acoustic waves in a four-component magnetized plasma comprising of protons, doubly charged Helium ions, beam electrons and superthermal electrons following a kappa distribution are presented. The model supports 12 plasma modes: two electron cyclotron (modes 1 and 12), two electron acoustic (modes 2 and 11), two fast ion acoustic (modes 3 and 10), two slow ion acoustic (modes 4 and 9), two proton cyclotron (modes 5 and 8) and two Helium cyclotron (modes 6 and 7). At parallel propagation, with increase in electron beam speed, mode 11 first merges with slow ion acoustic mode 4 and then with fast ion acoustic mode 3 and drives them unstable. For oblique propagation and without the electron streaming, coupling of various plasma modes occurs and it weakens with increase in the angle of propagation. Further, for oblique propagation with finite electron beam velocity, merging as well as coupling of various plasma modes are observed. Growth rates as well as wave numbers of the excited slow and fast ion acoustic modes are much smaller in magnetized plasma than in an unmagnetized one. The results are relevant to observations of electrostatic waves in the lunar wake.
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Solar cycle-23 witnessed many successive intense X-ray solar flares and coronal mass ejections (CME) during the peak activity period, as well as in the descending phase of the cycle. Some of these emissions had large solar energetic... more
Solar cycle-23 witnessed many successive intense X-ray solar flares and coronal mass ejections (CME) during the peak activity period, as well as in the descending phase of the cycle. Some of these emissions had large solar energetic particle events associated with them. When such solar ejecta impact the Earth’s magnetosphere, they cause large scale disturbances in the geomagnetic field known as geomagnetic storms. Large variability in the occurrence characteristics of geomagnetic storms is controlled ultimately by the solar activity. Thus the changes in the interplanetary conditions are distinctly seen in the low latitude geomagnetic records as each storm event differs from the other. Several intense storm events of solar cycle-23 are analyzed for assessing the role of interplanetary magnetic field components By (east-west) and Bz (north-south) in controlling the generation and development of various types of storms.
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A generation mechanism of the Kinetic Alfvén Waves (KAWs) by the ion beam and velocity shear will be discussed. For this, a three component plasma model consisting of cold background ions, hot electrons and hot ion beams is considered.... more
A generation mechanism of the Kinetic Alfvén Waves (KAWs) by the ion beam and velocity shear will be discussed. For this, a three component plasma model consisting of cold background ions, hot electrons and hot ion beams is considered. The model is very general in the sense that all the three species have drifting Maxwellian distribution, non-uniform streaming and velocity shear and can be applied to magnetospheric regions where velocity shear is present. The effect of ion beam alone and the combined effect of the ion beam as well as the velocity shear in exciting the KAWs will be discussed. It is found that the ion beam alone can excite these KAWs. However, in the presence of ion beam along the ambient magnetic field and negative velocity shear or antiparallel ion beam and positive shear, the wave growth is much larger as compared to ion beam case alone. Also, the anti-parallel ion beam and positive shear can excite the KAWs with significantly higher growth rate as compared to the ...
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Occurrence of electrostatic solitary waves (ESWs) is ubiquitous in space plasmas, e.g., solar wind, Lunar wake and the planetary magnetospheres. Several theoretical models have been proposed to interpret the observed characteristics of... more
Occurrence of electrostatic solitary waves (ESWs) is ubiquitous in space plasmas, e.g., solar wind, Lunar wake and the planetary magnetospheres. Several theoretical models have been proposed to interpret the observed characteristics of the ESWs. These models can broadly be put into two main categories, namely, Bernstein–Green–Kruskal (BGK) modes/phase space holes models, and ion- and electron- acoustic solitons models. There has been a tendency in the space community to favor the models based on BGK modes/phase space holes. Only recently, the potential of soliton models to explain the characteristics of ESWs is being realized. The idea of this review is to present current understanding of the ion- and electron-acoustic solitons and double layers models in multi-component space plasmas. In these models, all the plasma species are considered fluids except the energetic electron component, which is governed by either a kappa distribution or a Maxwellian distribution. Further, these mod...
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Low-frequency instabilities excited by energetic oxygen ions are investigated. The model consists of Maxwellian distributions for electrons and protons and Dory Guest Harris loss-cone distribution for oxygen ions. The electrons and... more
Low-frequency instabilities excited by energetic oxygen ions are investigated. The model consists of Maxwellian distributions for electrons and protons and Dory Guest Harris loss-cone distribution for oxygen ions. The electrons and protons are treated as magnetized and oxygen ions as unmagnetized. The response of the electrons is fully electromagnetic and that of the protons and oxygen ions is electrostatic. A
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A detailed numerical simulation of the nonlinear state of the RayleighTaylor instability has been carried out. There are three distinct phases of evolution where it is governed by the (i) linear effects, (ii) effects arising from the... more
A detailed numerical simulation of the nonlinear state of the RayleighTaylor instability has been carried out. There are three distinct phases of evolution where it is governed by the (i) linear effects, (ii) effects arising from the conventional nonlinear terms and (iii) subtle nonlinear ...
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A detailed numerical simulation of the nonlinear state of the RayleighTaylor instability has been carried out. There are three distinct phases of evolution where it is governed by the (i) linear effects, (ii) effects arising from the... more
A detailed numerical simulation of the nonlinear state of the RayleighTaylor instability has been carried out. There are three distinct phases of evolution where it is governed by the (i) linear effects, (ii) effects arising from the conventional nonlinear terms and (iii) subtle nonlinear ...
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Ultra low-frequency (ULF) electromagnetic waves, in the frequency range of ~1 mHz to 3 Hz, have been observed in the polar cusp and other regions of the Earth's magnetosphere by several spacecrafts, e.g., Geotail, Polar and CLUSTER.... more
Ultra low-frequency (ULF) electromagnetic waves, in the frequency range of ~1 mHz to 3 Hz, have been observed in the polar cusp and other regions of the Earth's magnetosphere by several spacecrafts, e.g., Geotail, Polar and CLUSTER. There are strong indications that these waves are generated locally by the energetic ion beams injected during magnetic reconnection taking place at the magnetopause. Ion beams observed in the polar cusp, plasma sheet boundary layer (PSBL), and on the auroral zone field lines are expected to have spatial gradients in their drift velocity. A generation mechanism for the ULF waves is proposed in terms of kinetic Alfvén wave instability driven by velocity shear of the ion beams. The noise due to velocity shear driven Alfvén modes is electromagnetic in nature, and also has a finite parallel electric field component.
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<p>Low frequency (LF) ~22 Hz to 200 Hz plasmaspheric hiss was studied using a year of... more
<p>Low frequency (LF) ~22 Hz to 200 Hz plasmaspheric hiss was studied using a year of Polar<br>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 sector. The noon sector ILF waves were also determined to be independent of solar wind ram pressure. The ILF hiss intensity is independent of magnetic latitude. ILF hiss is found to be highly coherent in nature. ILF hiss propagates at all angles relative to<br>the ambient magnetic field. Circular, elliptical, and linear/highly elliptically polarized hiss have been detected, with elliptical polarization the dominant characteristic. A case of linear polarized ILF hiss that occurred deep in the plasmasphere during geomagnetic quiet was noted. The waveforms and polarizations of ILF hiss are similar to those of intense high frequency hiss. We propose the hypothesis that ~10–100 keV substorm injected electrons gradient drift to dayside minimum B pockets close to the magnetopause to generate LF chorus. The closeness of this chorus to low altitude entry points into the plasmasphere will minimize wave damping and allow intense noon‐sector ILF hiss. The coherency of ILF hiss leads the authors to predict energetic electron precipitation into the midlatitude ionosphere and the electron slot formation during substorms. Several means of testing the above hypotheses are discussed.<br> <br>References<br>[1] Tsurutani, B.T., S.A. Park, B.J. Falkowski, J. Bortnik, G.S. Lakhina, A. Sen, J.S. Pickett, R. Hajra, M. Parrot, and P. Henri (2020), Low frequency (f < 200 Hz) Polar plasmasheric hiss: Coherent and intense, J. Geophys. Res. Spa. Phys., in press. </p>
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ABSTRACT There has been a lack of understanding why mirror modes are present in planetary magnetosheaths, at comets, and in the heliosheath. Linear theory indicates that the ion cyclotron instability should dominate over the mirror mode... more
ABSTRACT There has been a lack of understanding why mirror modes are present in planetary magnetosheaths, at comets, and in the heliosheath. Linear theory indicates that the ion cyclotron instability should dominate over the mirror mode instability in electron-proton plasma. In this paper, we take a new approach. We examine the role of plasma electron temperature anisotropy on the ion cyclotron and mirror mode instabilities. It will be shown that an inclusion of anisotropic electrons with T⊥ e/T∥ e ≥ 1.2 reduces the ion cyclotron growth rate substantially and increases the mirror mode growth rate. The minimum plasma beta for mirror instability dominance (over the ion cyclotron instability) is βp = 0.5.
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During intense magnetic storms, prompt penetration electric fields (PPEFs) through <b>E</b>×<b>B</b> forces near the magnetic equator uplift the dayside ionosphere. This effect has been called the “dayside... more
During intense magnetic storms, prompt penetration electric fields (PPEFs) through <b>E</b>×<b>B</b> forces near the magnetic equator uplift the dayside ionosphere. This effect has been called the “dayside superfountain effect”. Ion-neutral drag forces between the upward moving O+(oxygen ions) and oxygen neutrals will elevate the oxygen atoms to higher altitudes. This paper gives a linear calculation indicating how serious the effect may be during an 1859-type (Carrington) superstorm. It is concluded that the oxygen neutral densities produced at low-Earth-orbiting (LEO) satellite altitudes may be sufficiently high to present severe satellite drag. It is estimated that with a prompt penetrating electric field of ~ 20 mV/m turned on for 20 min, the O atoms and O+ ions are uplifted to 850 km where they produce about 40 times more satellite drag per unit mass than normal. Stronger electric fields will presumably lead to greater uplifte...
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Preliminary results from an investigation of the helicon instability in a plasma composed of protons, electrons and singly charged oxygen ions, are presented. The velocity distribution function for each plasma component is modeled by a... more
Preliminary results from an investigation of the helicon instability in a plasma composed of protons, electrons and singly charged oxygen ions, are presented. The velocity distribution function for each plasma component is modeled by a bi-Lorentzian distribution, which allows each particle species to possess a power law tail of arbitrary spectral index. This permits us to model accurately the shape of the power law tails observed on particle species in the plasma sheet region, where the helicon mode is believed to play an important role. The presence of a hard power law tail on the oxygen component is found to dramatically enhance the maximum growth rate of the instability when the oxygen ions possess a small T||>T⊥ anisotropy. Above a certain value of T||/T⊥, however, this behavior is reversed. The growth rate decreases as the spectral index of the protons is decreased. The relevance of these effects to the central plasma sheet region is briefly discussed. .
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ABSTRACT Fine structure and polarization of the chorus waves in the Dayside Outer Zone (DOZ) portion of the Earth magnetosphere are studied using GEOTAIL plasma wave and magnetic field data. Dayside chorus is noted to be composed of ~ 0.1... more
ABSTRACT Fine structure and polarization of the chorus waves in the Dayside Outer Zone (DOZ) portion of the Earth magnetosphere are studied using GEOTAIL plasma wave and magnetic field data. Dayside chorus is noted to be composed of ~ 0.1 to 0.5 s rising tone emissions called elements. Chorus rising-tone elements are composed of coherent subelements or packets with durations of ~ 0.005 to 0.01 s. The peak amplitudes within a packet can be ~0.2 nT or greater. The subelement or packet amplitudes are at least an order of magnitude larger than previously-estimated chorus amplitudes obtained by power spectral measurements. Chorus waves are detected propagating both almost along the ambient magnetic field, Bo, and at oblique angles near the Gendrin angle. It is experimentally found that chorus is circularly polarized (to first order) independent of the direction of propagation relative to Bo. We demonstrate that this is what one would expect theoretically. There will be important consequences for wave-particle interactions which we will explore in our talk.
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Large amplitude low-frequency electromagnetic waves, electric bipolar pulses (electron holes), and electromagnetic electron cyclotron waves have been observed in the polar cap/cusp boundary layer by Polar. It is proposed that nonlinear... more
Large amplitude low-frequency electromagnetic waves, electric bipolar pulses (electron holes), and electromagnetic electron cyclotron waves have been observed in the polar cap/cusp boundary layer by Polar. It is proposed that nonlinear low-frequency waves, consisting of Alfvén and/or proton cyclotron waves, can drive high-frequency electrostatic modes which saturate by trapping electrons, thereby leading to the generation of electron holes. The free