Intensive and transient energetic radiations associated with winter thunderstorm activities were detected around the west coast of Sea of Japan. We identified the source location of the transient energetic radiation, lasting for several minutes, through the observations of radiation, atmospheric electric field, and meteorological radar echoes. Our identification indicated that the transient energetic radiation was emitted from a downward hemispherical surface with regardless of lightning discharge, the bottom of which was about 300 m above sea level. This may occurs due to the generation of bremsstrahlung photons caused by electric fields inside the thunderstorm, because the energy of the observed radiation exceeds that of the radiation emitted from natural nuclides. In order to verify this speculation, we calculate the behavior of secondary cosmic ray electrons and photons in intensive electric fields by Monte Carlo technique. The photon flux largely increases just under the thundercloud if we assume that the electric field around the downward hemispherical surface is - 400 kV/m, and the photon energy spectrum shows a large increase in the energy region of several MeV. When the calculated energy spectrum emitted from the thunderstorm is consistent with the observed results, the large electric field around - 400 kV/m is required around the bottom of the thundercloud.
It is pointed out, that raindrop size distributions widely used to estimate theoretically the radio waves specific attenuation due to rain in the microwave range, inadequately represent the quantity of small raindrops. According to experimental data for some geographical regions (for example, Japan) the quantity of these raindrops is too large. This fact restricts the use of well known distributions in the terahertz range. So, taking into account small raindrops, the new distribution is proposed and the radio waves specific attenuation due to rain is estimated more precisely for mentioned and some other geographical regions.
There is an ionospheric potential between conductive solid-earth and ionosphere which reaches approximately 250 kV. The ionospheric potential is generated by the spherical shell capacitance of which is formed by positively charged ionosphere and negatively charged solid-earth. The capacitance is charged and discharged by the global thunderstorm activity and air-earth current in the fair weather, respectively. This large-scale electric circuit is termed a global electric circuit. Recently, it is pointed out that the variation of ionospheric potential is associated with global climate change, so that some of scientists started revisiting this traditional topic. In order to promote their resurvey, we show that a ground-based measurement of atmospheric electric field highly affected by atmospheric clouds, aerosols, and so on is still a useful tool to measure the variation of ionospheric potential through the simultaneous observations of ground-based atmospheric electric field, aerosols, and clouds on the R/V Hakuho Maru over the Pacific Ocean. In the period we obtained Carnegie curve, the observed AEF did not correlate to atmospheric aerosol concentration. The most plausible interpretation is that the observed variation of AEF reflected the variation of ionosphere potential.
Broadband radio interferometers have been developed to locate the sources of VHF/UHF radiation from lightning discharges in three spatial dimensions (3D) and time. In a previous work, a VHF broadband digital interferometer has been used to estimate the 3D lightning location from only one site. In order to study the accuracy of this algorithm, a cross check of one site 3D VHF broadband digital interferometer with Phased Array Radar (PAR) system will be introduced in this paper. In August 18, 2012, VHF pulses from lightning flashes have been recorded by VHF digital broadband interferometer LIB site located in Nara, Japan. On the same day the precipitation profile has been recorded using Phased Array RADAR (PAR) located in Osaka University. The 3D locations of four flashes are compared with the PAR horizontal and Range-Height Indicator RHI scan images. This comparison introduced a good correlation between 3D VHF broadband digital interferometer algorithm and the precipitation profiles recorded by PAR.
In recent years, it has been reported by many researchers that anomalies of the number of electrons in the ionosphere occur before earthquakes. Because the radio waves used for the global positioning system (GPS) propagate through the ionosphere, it is expected that the anomalies of the ionosphere causes fluctuations of the propagation path and propagation delay, and they result in positioning errors. Therefore, we attempt to predict earthquakes using the GPS positioning errors. In this paper, we discuss the relationship between the GPS positioning errors and earthquakes based on a statistical analysis using the data observed for more than one year.
We have been designing and developing Broadband Observation network for Lightning and Thunderstorm (BOLT) which locates radiation sources in 3D associated with lightning discharges. The BOLT consists of four or more LF receivers which detect electromagnetic (EM) waves in a wide frequency range from 5kHz to 500kHz. We have been operating the BOLT in Kansai, Japan, since Oct. 2012, for locating preliminary breakdowns (PB) followed by lightning discharges. We define PB from its pulse width and interpulse duration. In addition, we classified PB pulses into +PB and -PB, depending on initial polarity of PB pulses in the atmospheric electricity sign convention. In this paper, we identified 342 +PB pulses and 139 .PB pulses. We found that most of the -PB pulses occurred about 2.5 km higher than +PB. From a comparison of radar reflectivity factor it is found that most of the +PB and .PB pulses, respectively, occurred in the lower part or below the high reflectivity regions, and in the upper part or above the high reflectivity region. These results indicate that the difference of the polarity of PB pulses is determined by the polarity of charge region around locations of PB pulses.