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D0.3-0042 mode conversion processes of terrestrial hectometric radiation observed by PWS onboard the Akebono satellite
Summaryof Abstracts
1793
D0.3-0035 USE OF COORDINATED OBSERVATIONS OF AURORA¢STRUCTURE OF ENERGETIC PARTICLE DROPOUT AND MAGNETIC DATA FOR THE DIAGNOSTICS OF MAGNETOSPHERIC SUBSTORMS L. I. Vagina, 1 V. A. Sergeev 1 and A. G. Yahnin 2
1Institute of Physics, University of St. Petersburg, 198904 Russia 2Polar Geophysical Institute, Apatity, Russia ABSTRACT A series of meridional and longitudinal particle flux distributions is investigted. These distributions have been measured by low-altitude polar-orbiting spacecraft in the region of the substorm current wedge (SCW) and above the region of of the development of aurorae before and shortly after substorm onset. A very intense flux of energetic particles was observed in the region of the aurora after onset of the substorm. The aurora projects to the dipolarization region in the inner magnetosphere.
D0.3-0036 STUDIES ON THE IONOSPHERIC DIVERGENT HALL CURRENT A. Yoshikawa and K. Yumoto
Dept. Earth and Planetary Sciences, Kyushu University, Japan ABSTRACT A comprehensive study of the electromagnetic coupling of MHD waves through the magnetosphere, ionosphere, atmosphere and solid Earth has been performed. The most important view of this study is the "divergent Hall current (DHC)' which closes the field-aligned current in the homogeneous ionosphere. It is well known that when a shear Alfvdn wave is incident on the ionosphere, the 90 ° rotation of the wave magnetic field across the ionosphere is caused by the one-step mode conversion of the Hall effect. On the other hand, the DHC is an ionosphereic current driven by the resultant rotational electric field that is produced as a result of multi-step mode conversion between divergent and rotational electric fields due to the Hall effect. In past studies the rotational electric field had been neglected in the low-frequency and horizontally localized limits of the oscillations. However, when the horizontal scale is beyond ,-~ 1000 km and of period higher than 50 s, the ionospheric currents are dominated by the DCH. The DCH is shown to be a primary source of physical phenomena arising from the multi-step mode conversion. Various aspects of the DCH are analyzed adn its physical background is elucidated.
D0.3-0042 MODE CONVERSION PROCESSES OF TERRESTRIAL HECTOMETRIC RADIATION OBSERVED BY PWS ONBOARD THE A K E B O N O SATELLITE M. Iizima and H. Oya
Dept. Astronomy and Geophysics, Tohoku University, Aramaki, Aoba, Sendai 980-77, Japan ABSTRACT Since the initial studies on mode conversion processes from electrostatic plasma waves into electromagnetic waves, the mode conversion process has been considered to be one of the main processes to produce non-thermal electromagnetic waves in space plasma. The PWS (Plasma Wave and Sounder experiment) onboard the EXOS-D (Akebono) satellite has provided plenty of data that show clear evidences of the mode conversion process in the equatorial plasmasphere region as well as the top side polar ionosphere and also evidences for Terrestrial Hectometric Radiation (THR). THR's of discrete multi-banded nature has been observed on many polar orbits. For a slab model of the fieldaligned irregularity in the auroral region, numerical calculations have been carried out to seek a possible mechanism
1794
R. Potteletteand R. A. Treumann
of multi-banded emissions in the THR spectra. The results show that the conversion of the electrostatic plasma waves to the escaping electromagnetic waves takes place with periodicity in frequency when the wave lengths are matched with the condition to form standing waves in a given slab. These finite slab effects can be the orogin of the discrete multi-band structure in the THR spectra.
D0.3-0046CHARACTERISTCSOFELFEMISSIONSOBSERVEDBYFREJAAROUNDLOCALPROTON GYRO-FRQUENCY O. Santollk I and M. Parrot 2
1Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic 2LPCE/CNRS, Orleans, France ABSTRACT Using multicomponent measurements of electric and magnetic fields in the the ELF range, we investigate the propagation and polarization characteristics of several types of electromagnetic emissions around the proton gyro-frequency fH+. The data of the low-orbiting Freja satellite are examined in the auroral and sub-auroral regions as well as inside the plasmasphere. We also present a statistical study of the electromagnetic emissions which have a lower frequency limitation in a wide band below fn+. They occur outside the plasmasphere, mainly at auroral latitudes. The maximum wave power is observed before local noon, and no events have been detected during local night. The analysis shows nearly circular and right-handed polarization and downward nearly field-aligned propagation. The origin of these emissions could be possibly explained by the tunneling of the dwon-going auroral hiss below the two-ion cutoff frequency.
D0.3-0050 THE PRECIPITATION OF ENERGETIC ELECTONS INTO THE EARTH'S ATMOSPHERE IN 1994: INTERPLANETARY AND GEOMAGNETIC CONDITIONS V. S. Makhmutov, G. A. Bazilevskaya, A. A. Lazarj, V. A. Shurshakov, Yu. A. Ivanov and Ts. Dachev
1 Lebedev Physical Institute, Russian Academy of Sciences, Moscow 2Institute of Biomedical Problems, Moscow 3Space Physics Department, Bulgarian Academy of Sciences, Sofia, Bulgaria ABSTRACT The precipitation of energetic electrons into the Earth's atmosphere during 1994 was observedduring periods when strong enhancements of energetic electrons appeared at geostationary orbit detected by GOES-7. We present characteristics of some electron precipitation events (EPEs) derived from balloon measurements in the polar region (at Murmansk, 68.95 N, 33.05 E). The results obtained in the stratosphere are compared with measurements on board the Mir station, GOES-7, and other spacecraft in order to find a relation between the properties of the EPEs and the geomagnetic and interplanetary conditions.
1793
D0.3-0035 USE OF COORDINATED OBSERVATIONS OF AURORA¢STRUCTURE OF ENERGETIC PARTICLE DROPOUT AND MAGNETIC DATA FOR THE DIAGNOSTICS OF MAGNETOSPHERIC SUBSTORMS L. I. Vagina, 1 V. A. Sergeev 1 and A. G. Yahnin 2
1Institute of Physics, University of St. Petersburg, 198904 Russia 2Polar Geophysical Institute, Apatity, Russia ABSTRACT A series of meridional and longitudinal particle flux distributions is investigted. These distributions have been measured by low-altitude polar-orbiting spacecraft in the region of the substorm current wedge (SCW) and above the region of of the development of aurorae before and shortly after substorm onset. A very intense flux of energetic particles was observed in the region of the aurora after onset of the substorm. The aurora projects to the dipolarization region in the inner magnetosphere.
D0.3-0036 STUDIES ON THE IONOSPHERIC DIVERGENT HALL CURRENT A. Yoshikawa and K. Yumoto
Dept. Earth and Planetary Sciences, Kyushu University, Japan ABSTRACT A comprehensive study of the electromagnetic coupling of MHD waves through the magnetosphere, ionosphere, atmosphere and solid Earth has been performed. The most important view of this study is the "divergent Hall current (DHC)' which closes the field-aligned current in the homogeneous ionosphere. It is well known that when a shear Alfvdn wave is incident on the ionosphere, the 90 ° rotation of the wave magnetic field across the ionosphere is caused by the one-step mode conversion of the Hall effect. On the other hand, the DHC is an ionosphereic current driven by the resultant rotational electric field that is produced as a result of multi-step mode conversion between divergent and rotational electric fields due to the Hall effect. In past studies the rotational electric field had been neglected in the low-frequency and horizontally localized limits of the oscillations. However, when the horizontal scale is beyond ,-~ 1000 km and of period higher than 50 s, the ionospheric currents are dominated by the DCH. The DCH is shown to be a primary source of physical phenomena arising from the multi-step mode conversion. Various aspects of the DCH are analyzed adn its physical background is elucidated.
D0.3-0042 MODE CONVERSION PROCESSES OF TERRESTRIAL HECTOMETRIC RADIATION OBSERVED BY PWS ONBOARD THE A K E B O N O SATELLITE M. Iizima and H. Oya
Dept. Astronomy and Geophysics, Tohoku University, Aramaki, Aoba, Sendai 980-77, Japan ABSTRACT Since the initial studies on mode conversion processes from electrostatic plasma waves into electromagnetic waves, the mode conversion process has been considered to be one of the main processes to produce non-thermal electromagnetic waves in space plasma. The PWS (Plasma Wave and Sounder experiment) onboard the EXOS-D (Akebono) satellite has provided plenty of data that show clear evidences of the mode conversion process in the equatorial plasmasphere region as well as the top side polar ionosphere and also evidences for Terrestrial Hectometric Radiation (THR). THR's of discrete multi-banded nature has been observed on many polar orbits. For a slab model of the fieldaligned irregularity in the auroral region, numerical calculations have been carried out to seek a possible mechanism
1794
R. Potteletteand R. A. Treumann
of multi-banded emissions in the THR spectra. The results show that the conversion of the electrostatic plasma waves to the escaping electromagnetic waves takes place with periodicity in frequency when the wave lengths are matched with the condition to form standing waves in a given slab. These finite slab effects can be the orogin of the discrete multi-band structure in the THR spectra.
D0.3-0046CHARACTERISTCSOFELFEMISSIONSOBSERVEDBYFREJAAROUNDLOCALPROTON GYRO-FRQUENCY O. Santollk I and M. Parrot 2
1Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic 2LPCE/CNRS, Orleans, France ABSTRACT Using multicomponent measurements of electric and magnetic fields in the the ELF range, we investigate the propagation and polarization characteristics of several types of electromagnetic emissions around the proton gyro-frequency fH+. The data of the low-orbiting Freja satellite are examined in the auroral and sub-auroral regions as well as inside the plasmasphere. We also present a statistical study of the electromagnetic emissions which have a lower frequency limitation in a wide band below fn+. They occur outside the plasmasphere, mainly at auroral latitudes. The maximum wave power is observed before local noon, and no events have been detected during local night. The analysis shows nearly circular and right-handed polarization and downward nearly field-aligned propagation. The origin of these emissions could be possibly explained by the tunneling of the dwon-going auroral hiss below the two-ion cutoff frequency.
D0.3-0050 THE PRECIPITATION OF ENERGETIC ELECTONS INTO THE EARTH'S ATMOSPHERE IN 1994: INTERPLANETARY AND GEOMAGNETIC CONDITIONS V. S. Makhmutov, G. A. Bazilevskaya, A. A. Lazarj, V. A. Shurshakov, Yu. A. Ivanov and Ts. Dachev
1 Lebedev Physical Institute, Russian Academy of Sciences, Moscow 2Institute of Biomedical Problems, Moscow 3Space Physics Department, Bulgarian Academy of Sciences, Sofia, Bulgaria ABSTRACT The precipitation of energetic electrons into the Earth's atmosphere during 1994 was observedduring periods when strong enhancements of energetic electrons appeared at geostationary orbit detected by GOES-7. We present characteristics of some electron precipitation events (EPEs) derived from balloon measurements in the polar region (at Murmansk, 68.95 N, 33.05 E). The results obtained in the stratosphere are compared with measurements on board the Mir station, GOES-7, and other spacecraft in order to find a relation between the properties of the EPEs and the geomagnetic and interplanetary conditions.