gurbax lakhina | Indian Institute of Geomagnetism (original) (raw)
Papers by gurbax lakhina
arXiv (Cornell University), Sep 29, 2022
Owing to the ever-present solar wind, our vast solar system is full of plasmas. The turbulent sol... more Owing to the ever-present solar wind, our vast solar system is full of plasmas. The turbulent solar wind, together with sporadic solar eruptions, introduces various space plasma processes and phenomena in the solar atmosphere all the way to the Earth's ionosphere and atmosphere and outward to interact with the interstellar media to form the heliopause and termination shock. Remarkable progress has been made in space plasma physics in the last 65 years, mainly due to sophisticated in-situ measurements of plasmas, plasma waves, neutral particles, energetic particles, and dust via space-borne satellite instrumentation. Additionally high technology ground-2 To appear in IEEE Transactions on Plasma Science
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.
![Research paper thumbnail of Erratum: “Existence domains of electrostatic solitary structures in the solar wind plasma” [Phys. Plasmas 23, 062902 (2016)]](https://attachments.academia-assets.com/106218044/thumbnails/1.jpg)
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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
Plasma
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...
Physica Scripta, 2020
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.
Physics of Plasmas, 2018
Electrostatic solitary waves (ESWs) have been observed in the Earth's magnetosphere, solar wind, ... more Electrostatic solitary waves (ESWs) have been observed in the Earth's magnetosphere, solar wind, lunar wake, and also in other planetary magnetospheres. The observed characteristics of the ESWs have been interpreted in terms of models based either on Bernstein-Green-Kruskal (BGK) modes/ phase space holes or ion-and electron-acoustic solitons. However, the space community has favored the models based on BGK modes/phase space holes. In this review, current understanding of the fluid models for ion-and electron-acoustic solitons and double layers in multi-component plasmas is presented. The relationship between the theoretical models and space observations of ESWs is emphasized. Two specific applications of ion-and electron-acoustic solitons to the occurrence of weak double layers and coherent electrostatic waves in the solar wind and the lunar wake are discussed by comparing the observations and theoretical predictions. It is concluded that models based on ion-and electron-acoustic solitons/double layers provide a plausible interpretation for the ESWs observed in space plasmas.
Solar Physics, 2015
We propose that the mechanism for the generation of weak double layers (WDLs) and low-frequency c... more We propose that the mechanism for the generation of weak double layers (WDLs) and low-frequency coherent electrostatic waves, observed by Wind in the solar wind at 1 AU, might be slow and fast ion-acoustic solitons and double layers. The solar wind plasma is modelled as a fluid of hot protons and hot α particles streaming with respect to protons, and suprathermal electrons having a κ-distribution. The fast ion-acoustic mode is similar to the ion-acoustic mode of a proton-electron plasma and can support only positive-potential solitons. The slow ion-acoustic mode is a new mode that occurs due to the presence of α particles. This mode can support both positive and negative solitons and double layers. The slow ion-acoustic mode can exist even when the relative streaming, U 0 , between α particles and protons is zero, provided that the α temperature, T i , is not exactly equal to four times the proton temperature, T p. An increase of the κ-index leads to an increase in the critical Mach number, maximum Mach number, and the maximum amplitude of both slow and fast ionacoustic solitons. The slow ion-acoustic double layer can explain the amplitudes and widths, but not the shapes, of the observed WDLs in the solar wind at 1 AU by Wind spacecraft. The Fourier transform of the slow ion-acoustic solitons/double layers would produce broadband low-frequency electrostatic waves having main peaks between 0.35 kHz to 1.6 kHz, with an electric field in the range of E = (0.01-0.7) mV m −1 , in excellent agreement with the observed low-frequency electrostatic wave activity in the solar wind at 1 AU.
Astrophysics and Space Science Library, 1998
![Research paper thumbnail of Response to “Comment on ‘Existence domains of slow and fast ion-acoustic solitons in two-ion space plasmas’” [Phys. Plasmas 23, 064701 (2016)]](https://attachments.academia-assets.com/103778077/thumbnails/1.jpg)
](Physics of Plasmas, 2016
Low frequency solitons and double layers in a magnetized plasma with two temperature electrons
Prompt penetration electric fields (PPEFs) and the consequential dayside ionospheric superfountai... more Prompt penetration electric fields (PPEFs) and the consequential dayside ionospheric superfountain (DIS) are reviewed. An example of O + uplift to ~840 km altitude at ~0940 local time (DMSP F15) during the superstorm of 30 October 2003 is illustrated. The SAMI-2 model is modified to incorporate intense superstorm electric fields. With an inclusion of a ~4 mV/m eastward electric field, SAMI-2* modeling results show many of the expected DIS effects.
Pramana, 2000
The nonlinear evolution of an electron acoustic wave is shown to obey the Davey-Stewartson I equa... more The nonlinear evolution of an electron acoustic wave is shown to obey the Davey-Stewartson I equation which admits so called dromion solutions. The importance of these two dimensional localized solutions for recent satellite observations of wave structures in the day side polar cap regions is discussed and the parameter regimes for their existence is delineated.
Journal of Geophysical Research: Space Physics, 2018
Intense~300-Hz to 1.0-kHz plasmaspheric hiss was studied using Polar plasma wave data. It is foun... more Intense~300-Hz to 1.0-kHz plasmaspheric hiss was studied using Polar plasma wave data. It is found that the waves are coherent in all local time sectors with the wave coherency occurring in approximately three-to five-wave cycle packets. The plasmaspheric hiss in the dawn and local noon time sector are found to be substorm (AE*) and storm (SYM-H*) dependent. The local noon sector is also solar wind pressure dependent. It is suggested that coherent chorus monochromatic subelements enter the plasmasphere (as previously suggested by ray tracing models) to explain these plasmaspheric hiss features. The presence of intense, coherent plasmaspheric hiss in the local dusk and local midnight time sectors is surprising and more difficult to explain. For the dusk sector waves, either local in situ plasmaspheric wave generation or propagation from the dayside plasmasphere is possible. There is little evidence to support substorm generation of the midnight sector plasmaspheric hiss found in this study. One possible explanation is propagation from the local noon sector. The combination of high wave intensity and coherency at all local times strengthens the suggestion that the electron slot is formed during substorm intervals instead of during geomagnetic quiet (by incoherent waves). Plasmaspheric hiss is found to propagate at all angles relative to the ambient magnetic field, θ kB. Circular, elliptical, and linear polarized plasmaspheric hiss have been detected. No obvious, strong relationship between the wave polarization and θ kB was found. This information of hiss properties should be useful in modeling wave-particle interactions within the plasmasphere. Plain Language Summary Plasmaspheric hiss is found to be coherent (at all local times). The coherency occurs in packets of~3 to 5 cycles. For the dawn and noon local time sectors, a scenario of substorm and solar wind pressure generation of outer zone chorus with further propagation into the plasmasphere is supported by the data analysis results. The predominant wave polarization of hiss is found to be elliptical, with some minor presence of circular and linear polarizations. This is in general agreement with theoretical expectations.The presence of intense, coherent plasmaspheric hiss strongly supports the new hypothesis that the electron slot is formed during substorms rather than geomagnetic quiet periods. The loss of relativistic E~1MeV electrons for the inner magnetosphere (L > 6) may be due to wave-particle interactions with coherent plasmaspheric hiss.
Encyclopedia of Solid Earth Geophysics, 2021
Nonlinear Processes in Geophysics, 2004
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 ...
2019 URSI Asia-Pacific Radio Science Conference (AP-RASC)
Weak double layers (WDLs) and coherent electrostatic waves in the range of frequencies above the ... more Weak double layers (WDLs) and coherent electrostatic waves in the range of frequencies above the proton plasma frequency, f pi , and smaller than or of the order of the electron plasma frequency, f pe , have been observed in the solar wind at 1 AU. A soliton model, which treats the solar wind plasma as a fluid of hot protons and hot particles streaming with respect to protons, and suprathermal electrons having a-distribution, is found to sustain slow and fast ion-acoustic solitons and double layers. The slow ion-acoustic mode is a new mode that occurs due to the presence of alpha particles. This mode can support both positive and negative solitons and double layers. The slow ion-acoustic mode can exist even when the relative streaming, U 0 , between alphas and protons is zero, provided alpha temperature, T i , is not exactly equal to 4 times the proton temperature, T p. An increase of the-index leads to an increase in the critical Mach number, maximum Mach number and the maximum amplitude of both slow and fast ion-acoustic solitons. The fast ion-acoustic mode can support only positive potential solitons. The predicted amplitudes and widths of slow ion-acoustic double layers are found to be in an excellent agreement with the observed amplitudes and widths of WDLs. The fast Fourier transform (FFT) of the ion-acoustic solitons/DLs would produce a broadband spectrum with a main peak between 0.35 kHz to 1.6 kHz, and E = (0.01-0.7) mV m 1 which are in excellent agreement with the observed electric fields (0.0054-0.54) mV m 1 associated with the low-frequency waves observed in the solar wind at 1 AU. It is proposed that WDLs and low-frequency coherent electrostatic waves, observed by Wind spacecraft in the solar wind at 1 AU [1], might be generated by the slow and fast ion-acoustic solitons and double layers.
arXiv (Cornell University), Sep 29, 2022
Owing to the ever-present solar wind, our vast solar system is full of plasmas. The turbulent sol... more Owing to the ever-present solar wind, our vast solar system is full of plasmas. The turbulent solar wind, together with sporadic solar eruptions, introduces various space plasma processes and phenomena in the solar atmosphere all the way to the Earth's ionosphere and atmosphere and outward to interact with the interstellar media to form the heliopause and termination shock. Remarkable progress has been made in space plasma physics in the last 65 years, mainly due to sophisticated in-situ measurements of plasmas, plasma waves, neutral particles, energetic particles, and dust via space-borne satellite instrumentation. Additionally high technology ground-2 To appear in IEEE Transactions on Plasma Science
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
Plasma
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...
Physica Scripta, 2020
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.
Physics of Plasmas, 2018
Electrostatic solitary waves (ESWs) have been observed in the Earth's magnetosphere, solar wind, ... more Electrostatic solitary waves (ESWs) have been observed in the Earth's magnetosphere, solar wind, lunar wake, and also in other planetary magnetospheres. The observed characteristics of the ESWs have been interpreted in terms of models based either on Bernstein-Green-Kruskal (BGK) modes/ phase space holes or ion-and electron-acoustic solitons. However, the space community has favored the models based on BGK modes/phase space holes. In this review, current understanding of the fluid models for ion-and electron-acoustic solitons and double layers in multi-component plasmas is presented. The relationship between the theoretical models and space observations of ESWs is emphasized. Two specific applications of ion-and electron-acoustic solitons to the occurrence of weak double layers and coherent electrostatic waves in the solar wind and the lunar wake are discussed by comparing the observations and theoretical predictions. It is concluded that models based on ion-and electron-acoustic solitons/double layers provide a plausible interpretation for the ESWs observed in space plasmas.
Solar Physics, 2015
We propose that the mechanism for the generation of weak double layers (WDLs) and low-frequency c... more We propose that the mechanism for the generation of weak double layers (WDLs) and low-frequency coherent electrostatic waves, observed by Wind in the solar wind at 1 AU, might be slow and fast ion-acoustic solitons and double layers. The solar wind plasma is modelled as a fluid of hot protons and hot α particles streaming with respect to protons, and suprathermal electrons having a κ-distribution. The fast ion-acoustic mode is similar to the ion-acoustic mode of a proton-electron plasma and can support only positive-potential solitons. The slow ion-acoustic mode is a new mode that occurs due to the presence of α particles. This mode can support both positive and negative solitons and double layers. The slow ion-acoustic mode can exist even when the relative streaming, U 0 , between α particles and protons is zero, provided that the α temperature, T i , is not exactly equal to four times the proton temperature, T p. An increase of the κ-index leads to an increase in the critical Mach number, maximum Mach number, and the maximum amplitude of both slow and fast ionacoustic solitons. The slow ion-acoustic double layer can explain the amplitudes and widths, but not the shapes, of the observed WDLs in the solar wind at 1 AU by Wind spacecraft. The Fourier transform of the slow ion-acoustic solitons/double layers would produce broadband low-frequency electrostatic waves having main peaks between 0.35 kHz to 1.6 kHz, with an electric field in the range of E = (0.01-0.7) mV m −1 , in excellent agreement with the observed low-frequency electrostatic wave activity in the solar wind at 1 AU.
Astrophysics and Space Science Library, 1998
Physics of Plasmas, 2016
Low frequency solitons and double layers in a magnetized plasma with two temperature electrons
Prompt penetration electric fields (PPEFs) and the consequential dayside ionospheric superfountai... more Prompt penetration electric fields (PPEFs) and the consequential dayside ionospheric superfountain (DIS) are reviewed. An example of O + uplift to ~840 km altitude at ~0940 local time (DMSP F15) during the superstorm of 30 October 2003 is illustrated. The SAMI-2 model is modified to incorporate intense superstorm electric fields. With an inclusion of a ~4 mV/m eastward electric field, SAMI-2* modeling results show many of the expected DIS effects.
Pramana, 2000
The nonlinear evolution of an electron acoustic wave is shown to obey the Davey-Stewartson I equa... more The nonlinear evolution of an electron acoustic wave is shown to obey the Davey-Stewartson I equation which admits so called dromion solutions. The importance of these two dimensional localized solutions for recent satellite observations of wave structures in the day side polar cap regions is discussed and the parameter regimes for their existence is delineated.
Journal of Geophysical Research: Space Physics, 2018
Intense~300-Hz to 1.0-kHz plasmaspheric hiss was studied using Polar plasma wave data. It is foun... more Intense~300-Hz to 1.0-kHz plasmaspheric hiss was studied using Polar plasma wave data. It is found that the waves are coherent in all local time sectors with the wave coherency occurring in approximately three-to five-wave cycle packets. The plasmaspheric hiss in the dawn and local noon time sector are found to be substorm (AE*) and storm (SYM-H*) dependent. The local noon sector is also solar wind pressure dependent. It is suggested that coherent chorus monochromatic subelements enter the plasmasphere (as previously suggested by ray tracing models) to explain these plasmaspheric hiss features. The presence of intense, coherent plasmaspheric hiss in the local dusk and local midnight time sectors is surprising and more difficult to explain. For the dusk sector waves, either local in situ plasmaspheric wave generation or propagation from the dayside plasmasphere is possible. There is little evidence to support substorm generation of the midnight sector plasmaspheric hiss found in this study. One possible explanation is propagation from the local noon sector. The combination of high wave intensity and coherency at all local times strengthens the suggestion that the electron slot is formed during substorm intervals instead of during geomagnetic quiet (by incoherent waves). Plasmaspheric hiss is found to propagate at all angles relative to the ambient magnetic field, θ kB. Circular, elliptical, and linear polarized plasmaspheric hiss have been detected. No obvious, strong relationship between the wave polarization and θ kB was found. This information of hiss properties should be useful in modeling wave-particle interactions within the plasmasphere. Plain Language Summary Plasmaspheric hiss is found to be coherent (at all local times). The coherency occurs in packets of~3 to 5 cycles. For the dawn and noon local time sectors, a scenario of substorm and solar wind pressure generation of outer zone chorus with further propagation into the plasmasphere is supported by the data analysis results. The predominant wave polarization of hiss is found to be elliptical, with some minor presence of circular and linear polarizations. This is in general agreement with theoretical expectations.The presence of intense, coherent plasmaspheric hiss strongly supports the new hypothesis that the electron slot is formed during substorms rather than geomagnetic quiet periods. The loss of relativistic E~1MeV electrons for the inner magnetosphere (L > 6) may be due to wave-particle interactions with coherent plasmaspheric hiss.
Encyclopedia of Solid Earth Geophysics, 2021
Nonlinear Processes in Geophysics, 2004
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 ...
2019 URSI Asia-Pacific Radio Science Conference (AP-RASC)
Weak double layers (WDLs) and coherent electrostatic waves in the range of frequencies above the ... more Weak double layers (WDLs) and coherent electrostatic waves in the range of frequencies above the proton plasma frequency, f pi , and smaller than or of the order of the electron plasma frequency, f pe , have been observed in the solar wind at 1 AU. A soliton model, which treats the solar wind plasma as a fluid of hot protons and hot particles streaming with respect to protons, and suprathermal electrons having a-distribution, is found to sustain slow and fast ion-acoustic solitons and double layers. The slow ion-acoustic mode is a new mode that occurs due to the presence of alpha particles. This mode can support both positive and negative solitons and double layers. The slow ion-acoustic mode can exist even when the relative streaming, U 0 , between alphas and protons is zero, provided alpha temperature, T i , is not exactly equal to 4 times the proton temperature, T p. An increase of the-index leads to an increase in the critical Mach number, maximum Mach number and the maximum amplitude of both slow and fast ion-acoustic solitons. The fast ion-acoustic mode can support only positive potential solitons. The predicted amplitudes and widths of slow ion-acoustic double layers are found to be in an excellent agreement with the observed amplitudes and widths of WDLs. The fast Fourier transform (FFT) of the ion-acoustic solitons/DLs would produce a broadband spectrum with a main peak between 0.35 kHz to 1.6 kHz, and E = (0.01-0.7) mV m 1 which are in excellent agreement with the observed electric fields (0.0054-0.54) mV m 1 associated with the low-frequency waves observed in the solar wind at 1 AU. It is proposed that WDLs and low-frequency coherent electrostatic waves, observed by Wind spacecraft in the solar wind at 1 AU [1], might be generated by the slow and fast ion-acoustic solitons and double layers.