We report observations of co-existing rising and falling tone emissions of Electromagnetic Ion Cy... 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.
Abstract. An analysis of low order mode coupling equations is used to describe the nonlinear beha... 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 be... 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...
Propagation characteristics of electrostatic electron and ion cyclotron waves, ion- and electron-... 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.
Bulletin of the Astronomical Society of India, 2007
Solar cycle-23 witnessed many successive intense X-ray solar flares and coronal mass ejections (C... 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.
2019 URSI Asia-Pacific Radio Science Conference (AP-RASC), 2019
A generation mechanism of the Kinetic Alfvén Waves (KAWs) by the ion beam and velocity shear will... 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 ...
We report observations of co-existing rising and falling tone emissions of Electromagnetic Ion Cy... 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.
Abstract. An analysis of low order mode coupling equations is used to describe the nonlinear beha... 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 be... 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...
Propagation characteristics of electrostatic electron and ion cyclotron waves, ion- and electron-... 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.
Bulletin of the Astronomical Society of India, 2007
Solar cycle-23 witnessed many successive intense X-ray solar flares and coronal mass ejections (C... 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.
2019 URSI Asia-Pacific Radio Science Conference (AP-RASC), 2019
A generation mechanism of the Kinetic Alfvén Waves (KAWs) by the ion beam and velocity shear will... 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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