5:15 PM - 6:45 PM
[PEM12-P14] Comparison between the measurement by a sounding rocket and model calculation of the current density in the sporadic E layer
Keywords:sounding rocket, sporadic E layer, current density
The sporadic E layer is a region of high electron density that occurs suddenly and locally in the ionospheric E region, and is known to reflect radio waves in the VHF band (30 to 300 MHz). When the direction of the horizontal wind in the neutral atmosphere varies with altitude and has a shear structure along the vertical direction, ions above and below converge to the middle of the shear and form a sporadic E layer, since their motion is affected by the earth's magnetic field (Wind Shear theory). The sporadic E layer appears at an altitude of about 100 km, where the means of direct observation is limited to sounding rockets. Due to the limited opportunities for direct observation, physical process of the generation and extinction of the sporadic E layer remains unknown. It is meaningful to derive the altitude distribution of the electric current density from the magnetic field measured by sounding rockets for the advanced understanding of the sporadic E layer.
The sounding rocket S-310-38 was launched from Uchinoura Space Center (USC) in Kagoshima Prefecture on February 6, 2008 and reached an altitude of 160 km. The sporadic E layer was confirmed by imaging observation with a Magnesium Ion Imager (MII) and the electron density observation with an Impedance probe onboard the rocket. The rocket was equipped with a Digital Fluxgate magnetometer (DFG), that measures three orthogonal components of the magnetic field (one is along the rocket’s axis and the others are in the plane around the spin axis) at a sampling frequency of 200 Hz. In order to subtract the modeled magnetic field and obtain the fluctuation component, it is necessary to determine the attitude of the rocket. It was planned to determine the attitude of the rocket by a star imager, but because the observation was in an area with too much sunlight, the information on the star positions could not be obtained and the attitude of the rocket could not be determined. The attitude of the rocket was estimated by assuming that the roll axis direction of the rocket moved on a circle by the precession motion.
In this study, we analyzed the fluctuation component of the magnetic field measured during the flight, and derived the density of the electric current flowing inside and outside the sporadic E layer. On the other hand, we calculated the electric current by the general Ohm's law equation expressing the electromagnetic relationship in the ionosphere. In the equation, the electrical conductivity was given by measured electron density, estimated ion composition ratio and neutral particle density. The composition ratio of the main ions (NO+, O2+, O+) was given by the IRI model, and the number density of the main neutral particles (N2, O2, O) was given by the NRLMSIS model. The electric field and the neutral wind velocity were given by the GAIA model, because they were not measured by the sounding rocket. We compared the current density calculated from the spatial variation of the observed magnetic field data with that calculated from the general Ohm's law. Furthermore, we discussed how the ionosphere is heated by converting the kinetic energy of ions and electrons into Joule thermal energy. We will discuss the prospects for our future project, the sounding rocket S-310-46, which is scheduled to be launched in July of this year for the comprehensive observation of the sporadic E layer.
The sounding rocket S-310-38 was launched from Uchinoura Space Center (USC) in Kagoshima Prefecture on February 6, 2008 and reached an altitude of 160 km. The sporadic E layer was confirmed by imaging observation with a Magnesium Ion Imager (MII) and the electron density observation with an Impedance probe onboard the rocket. The rocket was equipped with a Digital Fluxgate magnetometer (DFG), that measures three orthogonal components of the magnetic field (one is along the rocket’s axis and the others are in the plane around the spin axis) at a sampling frequency of 200 Hz. In order to subtract the modeled magnetic field and obtain the fluctuation component, it is necessary to determine the attitude of the rocket. It was planned to determine the attitude of the rocket by a star imager, but because the observation was in an area with too much sunlight, the information on the star positions could not be obtained and the attitude of the rocket could not be determined. The attitude of the rocket was estimated by assuming that the roll axis direction of the rocket moved on a circle by the precession motion.
In this study, we analyzed the fluctuation component of the magnetic field measured during the flight, and derived the density of the electric current flowing inside and outside the sporadic E layer. On the other hand, we calculated the electric current by the general Ohm's law equation expressing the electromagnetic relationship in the ionosphere. In the equation, the electrical conductivity was given by measured electron density, estimated ion composition ratio and neutral particle density. The composition ratio of the main ions (NO+, O2+, O+) was given by the IRI model, and the number density of the main neutral particles (N2, O2, O) was given by the NRLMSIS model. The electric field and the neutral wind velocity were given by the GAIA model, because they were not measured by the sounding rocket. We compared the current density calculated from the spatial variation of the observed magnetic field data with that calculated from the general Ohm's law. Furthermore, we discussed how the ionosphere is heated by converting the kinetic energy of ions and electrons into Joule thermal energy. We will discuss the prospects for our future project, the sounding rocket S-310-46, which is scheduled to be launched in July of this year for the comprehensive observation of the sporadic E layer.