A. Lubchich - Academia.edu (original) (raw)
Papers by A. Lubchich
Journal of Atmospheric and Solar-Terrestrial Physics, 2015
Behaviors of the integrated wave gain of electromagnetic ion cyclotron (EMIC) waves in the H + -H... more Behaviors of the integrated wave gain of electromagnetic ion cyclotron (EMIC) waves in the H + -He + plasma of the inner magnetosphere is investigated. The integrated wave gain is obtained by integration of a temporal local growth rate along a geomagnetic field line. The local growth rate is determined by the method of generalized on the case of a bi-ion plasma. The concentration of the cold plasma is obtained on a basis of an empirical model of the plasmasphere and trough by . The energetic proton flux in the equatorial inner magnetosphere is set by the empirical model of , which refers to the conditions of low geomagnetic activity. The coefficients of EMIC wave reflection from the conjugated ionosphere are calculated using the International Reference Ionosphere (IRI) model. It is shown that the integrated wave gain of the EMIC waves increases with L -shell increasing and peaks around 14-20 MLT. In the afternoon sector the integrated wave gain reaches maximum in the cold plasma of higher density. Here the EMIC waves with the frequency below the equatorial He + gyrofrequency will be generated. The main findings of our study are in agreement with the basic experimental results on the EMIC wave occurrence in the equatorial middle magnetosphere known from satellite observations.
Physics of Plasmas, 2000
A wave structure observed in the solar wind on 17 December 1990, is discussed, and it is found th... more A wave structure observed in the solar wind on 17 December 1990, is discussed, and it is found that this structure is associated with a slow-mode magnetosonic wave. The parameters of the wave such as the direction of the wave vector, the wave frequency and the decrement of attenuation, are estimated. It is shown that the peculiarities of the plasma motion in the wave may provide conditions corresponding to an effective adiabatic index less than unity. The variations of the proton density and temperature are analyzed. It proved that for the entire period of the wave structure passing the Earth, the value of the adiabatic index was less than unity, which agrees with the model by Pudovkin et al.
Physics of Fluids, 2004
Interaction of hydrodynamic waves with plane shock waves under the linear approximation is studie... more Interaction of hydrodynamic waves with plane shock waves under the linear approximation is studied. Two classical problems, namely, wave transformation and a rippling instability on a shock wave, are examined. Starting from 1945, these problems have been analyzed repeatedly. A number of enigmas have been revealed during more than half a century. We argue that some of them can be obviated by a revision of the existing approach to description of shock oscillations. These oscillations originate either due to incident perturbations or spontaneously (the latter case is relevant to the problem of shock stability) and are a first order of smallness. It is well known that the linear approximation enables solution of the problem on the unperturbed discontinuity surface, with the surface oscillations taken as a linearly independent mode. This mode signifies a transition from a local reference frame connected with the perturbed shock surface to a laboratory frame related to the unperturbed plane shock. It is traditionally supposed that two following kinematic effects are essential in this transition. One is a deformation of the surface, leading to small oscillations of the shock normal and shock tangent; the other is an additional velocity of the shock. We state that the conventional approach is incomplete and leads to certain methodical difficulties. In particular, within the conventional framework the shock oscillations do not satisfy the normal component of the Euler equation. Thus, this mode is not a partial solution of the hydrodynamic equations; therefore, it is not a linearly independent one. In order to avoid this difficulty and accomplish the description of the above transition, it is necessary to take into account the effect associated with noninertiality of the local reference frame. The transition into the noninertial frame corresponds to emergence of an inertial force field and additional pressure. The additional pressure is the field potential. It is of the first order of smallness and it influences the perturbed shock surface in the local frame, counterbalancing the effect of dynamic momentum flux oscillations. The physical ground of inertial force appearance is non-ideality of the medium inside the thin front of a real shock wave. The role of this additional effect in the interaction of a small amplitude wave with a plane shock is examined.
![Research paper thumbnail of Response to “Comment on ‘Interaction of small perturbations with shock waves’ ” [Phys. Fluids 21, 079101 (2009)]](https://attachments.academia-assets.com/52366768/thumbnails/1.jpg)
](Physics of Fluids, 2009
Electronic mail: lubchich@pgia.ru 1 A. Tumin, "Comment on 'Interaction of small perturbations wit... more Electronic mail: lubchich@pgia.ru 1 A. Tumin, "Comment on 'Interaction of small perturbations with shock waves'," Phys. Fluids 21, 079101 (2004). 2 A.A. Lubchich and M.I. Pudovkin, "Interaction of small perturbations with shock waves," Phys. Fluids 16, 4489 (2004). 3 J. Griffond, "Linear interaction analysis applied to a mixture of two perfect gases," Phys. Fluids 17, 086101 (2005).
Radiophysics and Quantum Electronics, 2008
ABSTRACT We analyze conditions for excitation of ULF waves in the ionospheric Alfvén resonator (I... more ABSTRACT We analyze conditions for excitation of ULF waves in the ionospheric Alfvén resonator (IAR), taking into account the altitude-inhomogeneous profile of the magnetospheric convection velocity. This profile is formed as a result of interaction of the convective flow with the neutral atmosphere at altitudes 90–150 km. ULF waves comprise oblique Alfvén waves, trapped into the IAR, and ionospheric drift waves, which are in resonance with them. These waves together form strongly anisotropic, closed current loops, whose scale along the magnetic field greatly exceeds their transverse scale, i.e., lz ≫ l⊥, and can be considered Alfvén vortices. Within the framework of the proposed model of the ionosphere, we study the instability threshold and the amplitude growth rate of the Alfvén vortices as functions of different parameters (wave vector k22A5, angle between the wave vector and the convection velocity, ratio of the Alfvén-wave and Pedersen conductivities, etc.). Some estimates are given in application to the observed small-scale field-aligned currents in the auroral ionosphere.
Geomagnetism and Aeronomy, 2008
ABSTRACT The effect of the interplanetary parameters on the latitudinal position of the substorm ... more ABSTRACT The effect of the interplanetary parameters on the latitudinal position of the substorm westward electrojet is studied in the work. The data from the IMAGE chain of magnetic stations and POLAR and WIND satellites for the period close to the solar activity minimum (1995–1996) and for the period of the solar activity maximum (2000) have been used for this purpose. It has been indicated that the electrojet poleward edge reaches, on average, higher latitudes at a higher solar wind velocity and at a larger (Bs) IMF southward component. It has been indicated that the average latitude of the westward electrojet center increases with increasing solar wind velocity and decreases with increasing IMF southward component, as a result of which the electrojet center is, specifically, not observed at high geomagnetic latitudes at large values of the IMF southward component.
Geomagn. …, 1994
... Res. Lett., 19, 609{612, 1992. Newell, PT, and C.-I. Meng, J. Geophys. ... Yahnin, A., MV Mal... more ... Res. Lett., 19, 609{612, 1992. Newell, PT, and C.-I. Meng, J. Geophys. ... Yahnin, A., MV Malkov, VA Sergeev, RJ Pelli-nen, OA Aulamo, S. Vennerstrom, E. Friis-Christensen, K. Lassen, C.Danielsen, JD Craven, C. Deehr, and LA Frank, J. Geophys. Res., 99, 4039{4051, 1994. ...
Space Science Reviews, 2006
Although the auroral substorm has been long regarded as a manifestation of the magnetospheric sub... more Although the auroral substorm has been long regarded as a manifestation of the magnetospheric substorm, a direct relation of active auroras to certain magnetospheric processes is still debatable. To investigate the relationship, we combine the data of the UV imager onboard the Polar satellite with plasma and magnetic field measurements by the Geotail spacecraft. The poleward edge of the auroral bulge, as determined from the images obtained at the LHBL passband, is found to be conjugated with the region where the oppositely directed fast plasma flows observed in the near-Earth plasma sheet during substorms are generated. We conclude that the auroras forming the bulge are due to the near-Earth reconnection process. This implies that the magnetic flux through the auroral bulge is equal to the flux dissipated in the magnetotail during the substorm. Comparison of the magnetic flux through the auroral bulge with the magnetic flux accumulated in the tail lobe during the growth phase shows that these parameters have the comparable values. This is a clear evidence of the loading-unloading scheme of substorm development. It is shown that the area of the auroral bulge developing during substorm is proportional to the total (magnetic plus plasma) pressure decrease in the magnetotail. These findings stress the importance of auroral bulge observations for monitoring of substorm intensity in terms of the magnetic flux and energy dissipation.
Journal of Atmospheric and Solar-Terrestrial Physics, 2011
ABSTRACT Different solar wind structures are observed: magnetic clouds (MC), recurrent streams (R... more ABSTRACT Different solar wind structures are observed: magnetic clouds (MC), recurrent streams (RS), and regions of their interaction with undisturbed solar wind (Sheath and CIR). Three of these structures, Sheath, CIR, MC, are the sources of geomagnetic storms. We have searched for distinctions in the development of substorm bulges occurring during geomagnetic storms connected with the MC, Sheath and CIR. Solar wind parameters were taken from the Wind spacecraft and the auroral bulge parameters were obtained from the Ultra Violet Imager onboard Polar spacecraft. We determined the dimensions of the auroral bulges, the poleward aurora propagation, and the onset latitude of auroral bulges. It is shown that auroral bulges “geometry” is different for the examined types of storms. In consequence, the ratio between longitudinal and latitudinal sizes is also different.
Journal of Atmospheric and Terrestrial Physics, 1996
E-region electron density variations were observed above Tromsø, Norway, by the EISCAT UHF radar ... more E-region electron density variations were observed above Tromsø, Norway, by the EISCAT UHF radar (69. 59°N, 19.23°E) in the morning hours on 17 December 1990. The density variations have been compared with the characteristics of the VLF emissions seen in the frequency range of 0.3-3 kHz observed in Sodankylä, Finland (67.51°N, 26.33°E) and in Lovozero (Russia), (67.97°N, 35.08°E). Two different types of precipitation relating to VLF waves were found. The first type is in the form of precipitation impulses having only a few seconds duration repeating at intervals of some tens to a hundred seconds. The electrons were primarily produced by substorms which had commenced in the midnight sector. The measured electron density profile suggests that the energy of the precipitating electrons is from below 20 to about 30 keV. Chorus emissions were simultaneously recorded showing properties which can be explained by the cyclotron instability in the magnetosphere. The second type of electron precipitation correlating with VLF waves has a duration of a few minutes. This precipitation is related to sudden impulses (SI) caused by a change in the solar wind pressure. The accompanying VLF waves had a frequency range from 1.5 to 2.5 kHz. The cyclotron instability together with the time depended magnetic field during the magnetospheric compression can explain the spectral and temporal characteristics of this kind of electron precipitation and VLF waves.
Annales Geophysicae, 2006
Data from Polar and Geotail spacecraft are combined to investigate the relationship between locat... more Data from Polar and Geotail spacecraft are combined to investigate the relationship between locations of active auroras and the magnetotail plasma sheet region where reversed fast plasma flows are generated during substorms. Using the magnetospheric magnetic field model, it is shown that at the beginning of the tailward fast flow the ionospheric footprint of the spacecraft measuring the flow tends to be located poleward of the auroral bulge. The spacecraft within the earthward flow is mapped equatorward of the poleward edge of the auroral bulge. We conclude that a source of the fast plasma flows is conjugated with the poleward edge of the auroral bulge. Analysis of the behavior of the plasma and the magnetic field in the vicinity of the source of the diverging flows allows us to conclude that the source region, interpreted as the magnetic reconnection site, coincides with the region of the cross-tail current reduction, and the tailward propagation of the region is associated with the tailward propagation of the current disruption front.
Annales Geophysicae, 2005
Characteristics of small amplitude plane waves within the medium separated by the plane discontin... more Characteristics of small amplitude plane waves within the medium separated by the plane discontinuity into two half spaces are analysed. The approximation of the ideal one-fluid magnetohydrodynamics (MHD) is used. The discontinuities with the nonzero mass flux across them are mainly examined. These are fast or slow shock waves and rotational discontinuities. The dispersion equation for MHD waves within each of half space is obtained in the reference frame connected with the discontinuity surface. The solution of this equation permits one to determine the wave vectors versus the parameter c p , which is the phase velocity of surface discontinuity oscillations. This value of c p is common for all MHD waves and determined by an incident wave or by spontaneous oscillations of the discontinuity surface. The main purpose of the study is a detailed analysis of the dispersion equation solution. This analysis let us draw the following conclusions. (I) For a given c p , ahead or behind a discontinuity at most, one diverging wave can transform to a surface wave damping when moving away from the discontinuity. The surface wave can be a fast one or, in rare cases, a slow, magnetoacoustic one. The entropy and Alfvén waves always remain in a usual homogeneous mode. (II) For certain values of c p and parameters of the discontinuity behind the front of the fast shock wave, there can be four slow magnetoacoustic waves, satisfying the dispersion equation, and none of the fast magnetoacoustic waves. In this case, one of the four slow magnetoacoustic waves is incident on the fast shock wave from the side of a compressed medium. It is shown that its existence does not contradict the conditions of the evolutionarity of MHD shock waves. The four slow magnetoacoustic waves, satisfying the dispersion equation, can also exist from either side of a slow shock wave or rotational discontinuity. (III) The expressions determining the polarisation of the MHD waves are derived in the reference frame connected with the discontinuity surface. This form of presentation is much more convenient in investigating the interaction of small perturbations with MHD discontinuities. It is shown that the perturbations of the velocity and magnetic field associated with the surface magnetoacoustic wave have Correspondence to: A. A. Lubchich (lubchich@pgi.kolasc.net.ru) the elliptic polarisation. Usually the planes of polarisation for the perturbations of the velocity and magnetic field are not coincident with each other.
Annales Geophysicae, 2006
Using the data from satellite CRRES and three geostationary LANL spacecraft, the propagation of a... more Using the data from satellite CRRES and three geostationary LANL spacecraft, the propagation of an electron cloud from midnight to the evening sector is investigated. An electron cloud was injected during a weak isolated substorm that developed on a quiet geomagnetic background. It is found that within the local time sector from 03:00 until at least 08:00 MLT, the propagation of electrons at perpendicular pitch-angles is well described by a simple model of drift in the dipole magnetic field. The flux levels in the field-aligned electrons increase simultaneously with the flux at perpendicular pitch angles, which is attributed to the pitch angle diffusion by the whistler mode. This pitch-angle diffusion leads to precipitation of electrons from a drifting cloud and an increase in the ionospheric electron density, simultaneously observed above Tromsø, Norway, by the EISCAT UHF radar in the morning sector (04:40-05:25 MLT). The precipitation develops as quasi-periodic pulses with a period of about 100 s. We discuss the models of pulsating precipitation due to the whistler cyclotron instability and show that our observations can be explained by such a model.
Annales Geophysicae, 2009
Using data from WIND spacecraft, we investigated the difference in substorm bulge development dur... more Using data from WIND spacecraft, we investigated the difference in substorm bulge development during different types of solar wind flow: solar wind recurrent streams (RS), corotating interaction regions (CIR), magnetic clouds (MC), and the region of interaction of magnetic clouds with undisturbed solar wind (Sheath). . All available auroral substorms observed by the Ultra Violet Imager onboard the Polar spacecraft during these periods were studied. It is shown that the largest latitudinal and longitudinal sizes of the auroral bulge expansions are during CIR and Sheath intervals. We found a difference in auroral bulge parameters for MC-and RS-associated substorms. In contrast to substorms associated with RS, the latitudinal size of the auroral bulge during MC is smaller, but longitudinal size is larger. As consequence, the ratio between longitudinal and latitudinal sizes for MC-associated substorms is also larger. We suggest that the latter feature is explained by different configuration of the near-Earth magnetotail during RS and MC.
Annales Geophysicae, 2014
ABSTRACT We examine the effectiveness of nonuniform, quasistatic, transverse electric fields that... more ABSTRACT We examine the effectiveness of nonuniform, quasistatic, transverse electric fields that are often observed in the auroral region in destabilization of inhomogeneous energy-density-driven (IEDD) waves. Specifically, the IEDD dispersion relation of Ganguli et al. (1985a, b) is evaluated for an electric field structure observed by the FAST satellite in the auroral ionosphere at 1000 km altitude. The background field-aligned current, plasma density and ion composition are derived from FAST observations. Other input parameters adopted in the calculations are varied in pertinent ranges. Unstable solutions are obtained that indicate a variety of frequencies and perpendicular wavelengths. These can manifest as a broadband spectrum of IEDD waves.
2 1 J J J + ≡ and the ratio 1 2 J J A = varied according to the equations ( ) [ J J 0 T 2 t sin 1... more 2 1 J J J + ≡ and the ratio 1 2 J J A = varied according to the equations ( ) [ J J 0 T 2 t sin 1 J J
Journal of Atmospheric and Terrestrial Physics, 1995
On 17 December 1990 a series magnetic impulsive events (MIEs) were observed at high latitudes nea... more On 17 December 1990 a series magnetic impulsive events (MIEs) were observed at high latitudes near local noon. EISCAT, situated some 5 hours of MLT away from the noon sector, detected simultaneous impulsive electron density enhancements at heights between 90 and 120 km. The MIEs at noon were also associated with riometer absorption spikes. The correlated EISCAT and riometer observations indicate that there was an elongated electron precipitation region some 3000 km wide stretching from local noon to morning. ]in close association with the impulsive electron precipitation, VLF emissions were observed by groundbased stations in the morning side. We interpret the large scale electron precipitation and VLF emissions as signatures of a global compression of the Earth's magnetosphere. This is confirmed by the specific type of magnetic variations simultaneously recorded at the worldwide network of magnetometers. We conclude that the small scale MIEs with their drifting ionospheric current vortex structures can (but do not necessarily have to) occur in conjunction with large scale Sis. Moreover, MIEs and Sis have a common origin: the interaction of solar wind inhomogeneities with the Earth's magnetosphere. They do, however, represent different effects of the same primary agent. © © 70 ° O © 65 © 0410 0420 O430 Time UT Norwegian and IMAGE networks
Journal of Atmospheric and Solar-Terrestrial Physics, 2015
Behaviors of the integrated wave gain of electromagnetic ion cyclotron (EMIC) waves in the H + -H... more Behaviors of the integrated wave gain of electromagnetic ion cyclotron (EMIC) waves in the H + -He + plasma of the inner magnetosphere is investigated. The integrated wave gain is obtained by integration of a temporal local growth rate along a geomagnetic field line. The local growth rate is determined by the method of generalized on the case of a bi-ion plasma. The concentration of the cold plasma is obtained on a basis of an empirical model of the plasmasphere and trough by . The energetic proton flux in the equatorial inner magnetosphere is set by the empirical model of , which refers to the conditions of low geomagnetic activity. The coefficients of EMIC wave reflection from the conjugated ionosphere are calculated using the International Reference Ionosphere (IRI) model. It is shown that the integrated wave gain of the EMIC waves increases with L -shell increasing and peaks around 14-20 MLT. In the afternoon sector the integrated wave gain reaches maximum in the cold plasma of higher density. Here the EMIC waves with the frequency below the equatorial He + gyrofrequency will be generated. The main findings of our study are in agreement with the basic experimental results on the EMIC wave occurrence in the equatorial middle magnetosphere known from satellite observations.
Physics of Plasmas, 2000
A wave structure observed in the solar wind on 17 December 1990, is discussed, and it is found th... more A wave structure observed in the solar wind on 17 December 1990, is discussed, and it is found that this structure is associated with a slow-mode magnetosonic wave. The parameters of the wave such as the direction of the wave vector, the wave frequency and the decrement of attenuation, are estimated. It is shown that the peculiarities of the plasma motion in the wave may provide conditions corresponding to an effective adiabatic index less than unity. The variations of the proton density and temperature are analyzed. It proved that for the entire period of the wave structure passing the Earth, the value of the adiabatic index was less than unity, which agrees with the model by Pudovkin et al.
Physics of Fluids, 2004
Interaction of hydrodynamic waves with plane shock waves under the linear approximation is studie... more Interaction of hydrodynamic waves with plane shock waves under the linear approximation is studied. Two classical problems, namely, wave transformation and a rippling instability on a shock wave, are examined. Starting from 1945, these problems have been analyzed repeatedly. A number of enigmas have been revealed during more than half a century. We argue that some of them can be obviated by a revision of the existing approach to description of shock oscillations. These oscillations originate either due to incident perturbations or spontaneously (the latter case is relevant to the problem of shock stability) and are a first order of smallness. It is well known that the linear approximation enables solution of the problem on the unperturbed discontinuity surface, with the surface oscillations taken as a linearly independent mode. This mode signifies a transition from a local reference frame connected with the perturbed shock surface to a laboratory frame related to the unperturbed plane shock. It is traditionally supposed that two following kinematic effects are essential in this transition. One is a deformation of the surface, leading to small oscillations of the shock normal and shock tangent; the other is an additional velocity of the shock. We state that the conventional approach is incomplete and leads to certain methodical difficulties. In particular, within the conventional framework the shock oscillations do not satisfy the normal component of the Euler equation. Thus, this mode is not a partial solution of the hydrodynamic equations; therefore, it is not a linearly independent one. In order to avoid this difficulty and accomplish the description of the above transition, it is necessary to take into account the effect associated with noninertiality of the local reference frame. The transition into the noninertial frame corresponds to emergence of an inertial force field and additional pressure. The additional pressure is the field potential. It is of the first order of smallness and it influences the perturbed shock surface in the local frame, counterbalancing the effect of dynamic momentum flux oscillations. The physical ground of inertial force appearance is non-ideality of the medium inside the thin front of a real shock wave. The role of this additional effect in the interaction of a small amplitude wave with a plane shock is examined.
Physics of Fluids, 2009
Electronic mail: lubchich@pgia.ru 1 A. Tumin, "Comment on 'Interaction of small perturbations wit... more Electronic mail: lubchich@pgia.ru 1 A. Tumin, "Comment on 'Interaction of small perturbations with shock waves'," Phys. Fluids 21, 079101 (2004). 2 A.A. Lubchich and M.I. Pudovkin, "Interaction of small perturbations with shock waves," Phys. Fluids 16, 4489 (2004). 3 J. Griffond, "Linear interaction analysis applied to a mixture of two perfect gases," Phys. Fluids 17, 086101 (2005).
Radiophysics and Quantum Electronics, 2008
ABSTRACT We analyze conditions for excitation of ULF waves in the ionospheric Alfvén resonator (I... more ABSTRACT We analyze conditions for excitation of ULF waves in the ionospheric Alfvén resonator (IAR), taking into account the altitude-inhomogeneous profile of the magnetospheric convection velocity. This profile is formed as a result of interaction of the convective flow with the neutral atmosphere at altitudes 90–150 km. ULF waves comprise oblique Alfvén waves, trapped into the IAR, and ionospheric drift waves, which are in resonance with them. These waves together form strongly anisotropic, closed current loops, whose scale along the magnetic field greatly exceeds their transverse scale, i.e., lz ≫ l⊥, and can be considered Alfvén vortices. Within the framework of the proposed model of the ionosphere, we study the instability threshold and the amplitude growth rate of the Alfvén vortices as functions of different parameters (wave vector k22A5, angle between the wave vector and the convection velocity, ratio of the Alfvén-wave and Pedersen conductivities, etc.). Some estimates are given in application to the observed small-scale field-aligned currents in the auroral ionosphere.
Geomagnetism and Aeronomy, 2008
ABSTRACT The effect of the interplanetary parameters on the latitudinal position of the substorm ... more ABSTRACT The effect of the interplanetary parameters on the latitudinal position of the substorm westward electrojet is studied in the work. The data from the IMAGE chain of magnetic stations and POLAR and WIND satellites for the period close to the solar activity minimum (1995–1996) and for the period of the solar activity maximum (2000) have been used for this purpose. It has been indicated that the electrojet poleward edge reaches, on average, higher latitudes at a higher solar wind velocity and at a larger (Bs) IMF southward component. It has been indicated that the average latitude of the westward electrojet center increases with increasing solar wind velocity and decreases with increasing IMF southward component, as a result of which the electrojet center is, specifically, not observed at high geomagnetic latitudes at large values of the IMF southward component.
Geomagn. …, 1994
... Res. Lett., 19, 609{612, 1992. Newell, PT, and C.-I. Meng, J. Geophys. ... Yahnin, A., MV Mal... more ... Res. Lett., 19, 609{612, 1992. Newell, PT, and C.-I. Meng, J. Geophys. ... Yahnin, A., MV Malkov, VA Sergeev, RJ Pelli-nen, OA Aulamo, S. Vennerstrom, E. Friis-Christensen, K. Lassen, C.Danielsen, JD Craven, C. Deehr, and LA Frank, J. Geophys. Res., 99, 4039{4051, 1994. ...
Space Science Reviews, 2006
Although the auroral substorm has been long regarded as a manifestation of the magnetospheric sub... more Although the auroral substorm has been long regarded as a manifestation of the magnetospheric substorm, a direct relation of active auroras to certain magnetospheric processes is still debatable. To investigate the relationship, we combine the data of the UV imager onboard the Polar satellite with plasma and magnetic field measurements by the Geotail spacecraft. The poleward edge of the auroral bulge, as determined from the images obtained at the LHBL passband, is found to be conjugated with the region where the oppositely directed fast plasma flows observed in the near-Earth plasma sheet during substorms are generated. We conclude that the auroras forming the bulge are due to the near-Earth reconnection process. This implies that the magnetic flux through the auroral bulge is equal to the flux dissipated in the magnetotail during the substorm. Comparison of the magnetic flux through the auroral bulge with the magnetic flux accumulated in the tail lobe during the growth phase shows that these parameters have the comparable values. This is a clear evidence of the loading-unloading scheme of substorm development. It is shown that the area of the auroral bulge developing during substorm is proportional to the total (magnetic plus plasma) pressure decrease in the magnetotail. These findings stress the importance of auroral bulge observations for monitoring of substorm intensity in terms of the magnetic flux and energy dissipation.
Journal of Atmospheric and Solar-Terrestrial Physics, 2011
ABSTRACT Different solar wind structures are observed: magnetic clouds (MC), recurrent streams (R... more ABSTRACT Different solar wind structures are observed: magnetic clouds (MC), recurrent streams (RS), and regions of their interaction with undisturbed solar wind (Sheath and CIR). Three of these structures, Sheath, CIR, MC, are the sources of geomagnetic storms. We have searched for distinctions in the development of substorm bulges occurring during geomagnetic storms connected with the MC, Sheath and CIR. Solar wind parameters were taken from the Wind spacecraft and the auroral bulge parameters were obtained from the Ultra Violet Imager onboard Polar spacecraft. We determined the dimensions of the auroral bulges, the poleward aurora propagation, and the onset latitude of auroral bulges. It is shown that auroral bulges “geometry” is different for the examined types of storms. In consequence, the ratio between longitudinal and latitudinal sizes is also different.
Journal of Atmospheric and Terrestrial Physics, 1996
E-region electron density variations were observed above Tromsø, Norway, by the EISCAT UHF radar ... more E-region electron density variations were observed above Tromsø, Norway, by the EISCAT UHF radar (69. 59°N, 19.23°E) in the morning hours on 17 December 1990. The density variations have been compared with the characteristics of the VLF emissions seen in the frequency range of 0.3-3 kHz observed in Sodankylä, Finland (67.51°N, 26.33°E) and in Lovozero (Russia), (67.97°N, 35.08°E). Two different types of precipitation relating to VLF waves were found. The first type is in the form of precipitation impulses having only a few seconds duration repeating at intervals of some tens to a hundred seconds. The electrons were primarily produced by substorms which had commenced in the midnight sector. The measured electron density profile suggests that the energy of the precipitating electrons is from below 20 to about 30 keV. Chorus emissions were simultaneously recorded showing properties which can be explained by the cyclotron instability in the magnetosphere. The second type of electron precipitation correlating with VLF waves has a duration of a few minutes. This precipitation is related to sudden impulses (SI) caused by a change in the solar wind pressure. The accompanying VLF waves had a frequency range from 1.5 to 2.5 kHz. The cyclotron instability together with the time depended magnetic field during the magnetospheric compression can explain the spectral and temporal characteristics of this kind of electron precipitation and VLF waves.
Annales Geophysicae, 2006
Data from Polar and Geotail spacecraft are combined to investigate the relationship between locat... more Data from Polar and Geotail spacecraft are combined to investigate the relationship between locations of active auroras and the magnetotail plasma sheet region where reversed fast plasma flows are generated during substorms. Using the magnetospheric magnetic field model, it is shown that at the beginning of the tailward fast flow the ionospheric footprint of the spacecraft measuring the flow tends to be located poleward of the auroral bulge. The spacecraft within the earthward flow is mapped equatorward of the poleward edge of the auroral bulge. We conclude that a source of the fast plasma flows is conjugated with the poleward edge of the auroral bulge. Analysis of the behavior of the plasma and the magnetic field in the vicinity of the source of the diverging flows allows us to conclude that the source region, interpreted as the magnetic reconnection site, coincides with the region of the cross-tail current reduction, and the tailward propagation of the region is associated with the tailward propagation of the current disruption front.
Annales Geophysicae, 2005
Characteristics of small amplitude plane waves within the medium separated by the plane discontin... more Characteristics of small amplitude plane waves within the medium separated by the plane discontinuity into two half spaces are analysed. The approximation of the ideal one-fluid magnetohydrodynamics (MHD) is used. The discontinuities with the nonzero mass flux across them are mainly examined. These are fast or slow shock waves and rotational discontinuities. The dispersion equation for MHD waves within each of half space is obtained in the reference frame connected with the discontinuity surface. The solution of this equation permits one to determine the wave vectors versus the parameter c p , which is the phase velocity of surface discontinuity oscillations. This value of c p is common for all MHD waves and determined by an incident wave or by spontaneous oscillations of the discontinuity surface. The main purpose of the study is a detailed analysis of the dispersion equation solution. This analysis let us draw the following conclusions. (I) For a given c p , ahead or behind a discontinuity at most, one diverging wave can transform to a surface wave damping when moving away from the discontinuity. The surface wave can be a fast one or, in rare cases, a slow, magnetoacoustic one. The entropy and Alfvén waves always remain in a usual homogeneous mode. (II) For certain values of c p and parameters of the discontinuity behind the front of the fast shock wave, there can be four slow magnetoacoustic waves, satisfying the dispersion equation, and none of the fast magnetoacoustic waves. In this case, one of the four slow magnetoacoustic waves is incident on the fast shock wave from the side of a compressed medium. It is shown that its existence does not contradict the conditions of the evolutionarity of MHD shock waves. The four slow magnetoacoustic waves, satisfying the dispersion equation, can also exist from either side of a slow shock wave or rotational discontinuity. (III) The expressions determining the polarisation of the MHD waves are derived in the reference frame connected with the discontinuity surface. This form of presentation is much more convenient in investigating the interaction of small perturbations with MHD discontinuities. It is shown that the perturbations of the velocity and magnetic field associated with the surface magnetoacoustic wave have Correspondence to: A. A. Lubchich (lubchich@pgi.kolasc.net.ru) the elliptic polarisation. Usually the planes of polarisation for the perturbations of the velocity and magnetic field are not coincident with each other.
Annales Geophysicae, 2006
Using the data from satellite CRRES and three geostationary LANL spacecraft, the propagation of a... more Using the data from satellite CRRES and three geostationary LANL spacecraft, the propagation of an electron cloud from midnight to the evening sector is investigated. An electron cloud was injected during a weak isolated substorm that developed on a quiet geomagnetic background. It is found that within the local time sector from 03:00 until at least 08:00 MLT, the propagation of electrons at perpendicular pitch-angles is well described by a simple model of drift in the dipole magnetic field. The flux levels in the field-aligned electrons increase simultaneously with the flux at perpendicular pitch angles, which is attributed to the pitch angle diffusion by the whistler mode. This pitch-angle diffusion leads to precipitation of electrons from a drifting cloud and an increase in the ionospheric electron density, simultaneously observed above Tromsø, Norway, by the EISCAT UHF radar in the morning sector (04:40-05:25 MLT). The precipitation develops as quasi-periodic pulses with a period of about 100 s. We discuss the models of pulsating precipitation due to the whistler cyclotron instability and show that our observations can be explained by such a model.
Annales Geophysicae, 2009
Using data from WIND spacecraft, we investigated the difference in substorm bulge development dur... more Using data from WIND spacecraft, we investigated the difference in substorm bulge development during different types of solar wind flow: solar wind recurrent streams (RS), corotating interaction regions (CIR), magnetic clouds (MC), and the region of interaction of magnetic clouds with undisturbed solar wind (Sheath). . All available auroral substorms observed by the Ultra Violet Imager onboard the Polar spacecraft during these periods were studied. It is shown that the largest latitudinal and longitudinal sizes of the auroral bulge expansions are during CIR and Sheath intervals. We found a difference in auroral bulge parameters for MC-and RS-associated substorms. In contrast to substorms associated with RS, the latitudinal size of the auroral bulge during MC is smaller, but longitudinal size is larger. As consequence, the ratio between longitudinal and latitudinal sizes for MC-associated substorms is also larger. We suggest that the latter feature is explained by different configuration of the near-Earth magnetotail during RS and MC.
Annales Geophysicae, 2014
ABSTRACT We examine the effectiveness of nonuniform, quasistatic, transverse electric fields that... more ABSTRACT We examine the effectiveness of nonuniform, quasistatic, transverse electric fields that are often observed in the auroral region in destabilization of inhomogeneous energy-density-driven (IEDD) waves. Specifically, the IEDD dispersion relation of Ganguli et al. (1985a, b) is evaluated for an electric field structure observed by the FAST satellite in the auroral ionosphere at 1000 km altitude. The background field-aligned current, plasma density and ion composition are derived from FAST observations. Other input parameters adopted in the calculations are varied in pertinent ranges. Unstable solutions are obtained that indicate a variety of frequencies and perpendicular wavelengths. These can manifest as a broadband spectrum of IEDD waves.
2 1 J J J + ≡ and the ratio 1 2 J J A = varied according to the equations ( ) [ J J 0 T 2 t sin 1... more 2 1 J J J + ≡ and the ratio 1 2 J J A = varied according to the equations ( ) [ J J 0 T 2 t sin 1 J J
Journal of Atmospheric and Terrestrial Physics, 1995
On 17 December 1990 a series magnetic impulsive events (MIEs) were observed at high latitudes nea... more On 17 December 1990 a series magnetic impulsive events (MIEs) were observed at high latitudes near local noon. EISCAT, situated some 5 hours of MLT away from the noon sector, detected simultaneous impulsive electron density enhancements at heights between 90 and 120 km. The MIEs at noon were also associated with riometer absorption spikes. The correlated EISCAT and riometer observations indicate that there was an elongated electron precipitation region some 3000 km wide stretching from local noon to morning. ]in close association with the impulsive electron precipitation, VLF emissions were observed by groundbased stations in the morning side. We interpret the large scale electron precipitation and VLF emissions as signatures of a global compression of the Earth's magnetosphere. This is confirmed by the specific type of magnetic variations simultaneously recorded at the worldwide network of magnetometers. We conclude that the small scale MIEs with their drifting ionospheric current vortex structures can (but do not necessarily have to) occur in conjunction with large scale Sis. Moreover, MIEs and Sis have a common origin: the interaction of solar wind inhomogeneities with the Earth's magnetosphere. They do, however, represent different effects of the same primary agent. © © 70 ° O © 65 © 0410 0420 O430 Time UT Norwegian and IMAGE networks