Tetsuo Miyake

Investigation of electron density profile in the lower ionosphere by SRP-4 rocket experiment

The SRP-4 rocket was launched at 12:07 LT on 18 March 2002. The objective of this rocket experiment is the investigation of the electron density profile in the high-latitude D-region of the ionosphere at noon. The Low frequency and Medium frequency band radio Receiver (LMR) and the DC Probe System (DPS) were installed on-board the rocket to estimate the D-region electron density. The LMR measured the intensities of radio waves received from ground-based stations operating at 257 kHz, 660 kHz and 820 kHz, respectively. The DPS measured the electron current and the positive ion current using the biased electrodes. The electron density profile at altitudes below 90 km was estimated from the measured absorption of these radio waves. It was found that the electron density began to increase at the altitude of 52 km and was larger than that estimated by the International Reference Ionosphere model at altitudes from 74 km to 89 km.

Study of VLF band electromagnetic waves in the Antarctica observed by polar patrol balloons

The two large scientific balloons (PPB: polar patrol balloons) were launched on January 13th, 2003 at Syowa Station in Antarctica. The balloons reached the altitude of 33 km, and observed various data for about two weeks. We developed the wideband electromagnetic wave receiver onboard PPB and observed ELF/VLF waves in Antarctica. VLF band waves observed in Antarctica are frequently modulated in frequency. Among these frequency modulations, the modulations of about 20 sec are considered to have relations with the compressional Alfven waves. By taking cross correlations between data observed by two balloons, we can identify the direction from which VLF waves propagate as well as the source region where these waves are excited. We compared one event observed by both balloons on January 17th, and found the time when the strong VLF wave observed by the 8th PPB was 3 seconds earlier than that observed by the 10th PPB. This result indicates that this VLF wave propagates with the velocity of about 67 km/s. The projection of this velocity on the equator plane is about 1800 km/s, which is almost the same order as the estimated velocity of the compressional Alfven waves in this region.

Measurement of characteristics of MF radio wave propagation in the ionosphere by the S-310-33 rocket experiment

The electron density in the lower ionosphere is very interesting because it affects the MF radio wave propagation. In order to investigate the electron density profile in the lower ionosphere, we load the S-310-33 rocket with the medium frequency receiver (MFR), and the S-310-33 rocket experiment was carried out. The MFR observed the radio wave intensities at 238 kHz and 873 kHz in the lower ionosphere. The electron density in the lower ionosphere is estimated by the MF absorption method. The MF absorption method is developed to estimate the electron density by comparing the observed wave intensity with that calculated with the full wave method. In the profile of the radio wave intensities observed by the MFR the radio wave is suddenly absorbed at an altitude of from 88.5 km to 89.5 km. The electron density is estimated to increase suddenly at this altitude.