The effect of ammonia on the formation and growth of sulfuric acid nanoparticles was investigated experimentally. The nanoparticles were produced by negative corona discharge in NH₃/SO₂/H₂O/Air mixtures. The size distribution of the uncharged particles formed by homogenous nucleation was measured using a nano-DMA. In the absence of NH₃, the concentration and mean size of the formed particles increased as the concentrations of H₂O and SO₂ increased. With the help of mass spectrometric measurements using an ion mobility spectrometer/mass spectrometer (IMS/MS), increases in H₂O and SO₂ concentrations proved to lead to the formation of H₂SO₄. The enhancement of particle formation by the addition of NH₃ was observed, but the concentration of particles was only 1.2-2.2 times higher than that without NH₃. The mass spectra of negative ions showed that HSO₄¯(H₂SO₄)n ions significantly declined in the presence of NH₃, suggesting a reduction of free H₂SO₄ molecules. In addition, the HSO₄¯ ions associated with NH₃ molecules were not found in the mass spectra. These features may be explained by the rapid formation of ammonium bisulfate, which is unlikely to be negatively charged. In the growth of sulfuric acid nanoparticles, no notable effect of NH₃ was observed.

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After the Hyogoken-nanbu earthquake in 1995, it was reported that the propagation anomalies of the non-line-of sight 77.1 MHz FM radio waves broadcasted from Sendai were detected. It was then hypothesized that the propagation anomalies were due to ionospheric or atmospheric disturbances. Since then, over-horizon FM radio waves have been observed to clarify the hypothesis at many electromagnetic (EM) observatories. Some of them were observed on one propagation path or in a period less than one year. Therefore, it is highly desired to deal with some more propagation paths and more data during several years. In this paper, we describe the observation method and results for the non-line-of-sight FM radio of 77.1 MHz broadcasted from Sendai to Nobeyama, Yokosuka, Hitachi EM observatories. The observation period was for 3 years from January 2006 to December 2008. From the observation results, it was found that the received levels had seasonal variations in their fluctuations. The fluctuation levels in summer season were larger than those in winter. Comparing the received levels of the 77.1 MHz and the aerological atmospheric refractivity, it was also clarified that the received level fluctuations were mainly affected by the change of the aerological atmospheric refractivity. The cross correlation factors among received levels observed at the 3 sites depended on the propagation profiles. There were high correlations more than 0.6 between the received levels at Yokosuka and Hitachi, while there were low correlations less than 0.4 between the received levels at Yokosuka and Nobeyama. It was concluded that the non-line-of-sight 77.1 MHz FM radio waves were characterized by terrestrial propagations with atmospheric refractivity variations.

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There have been two different interests in the past as related to meteors and very low frequency (VLF) radiation in the atmosphere. The first deals with VLF pulses being produced by meteors entering the atmosphere, while the other deals with changes in the properties of the ionosphere due to meteors. To revisit these ideas, continuous measurements of VLF electromagnetic waves were performed simultaneously with optical imaging of meteors. The measurements were obtained during the Perseids, Orionids, and Leonids meteor showers during August, October, and November, 2007 and 2009. While unique VLF pulses could not be objectively associated with incoming meteors, the results indicate a distinct change in the background VLF atmospheric noise levels recorded on the nights of the meteor showers. We observed enhancements in the atmospheric noise parameter Vd, which is a useful quantitative measure of the impulsiveness of the noise, and is defined as the ratio (in decibels) of the root-mean-square amplitude to the average amplitude of the noise envelop, ranging from 2-2.5 dB (20-25% increase) relative to the normal levels. This enhancement in Vd is associated with decreased reception of VLF sferics at our station. These changes can be explained by either the attachment of ambient free electrons to the dust particles of meteoric origin, and/or the deposition of heavy ions with low mobility in the lower ionosphere. These ionospheric modifications cause more absorption, or inferior reflection conditions, for the background VLF noise sources, primarily produced by lightning.

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This paper was intended to find out any relation between anomalous line-of-sight propagations in the VHF band and occurrences of earthquakes near the VHF propagation path. The broadcasting waves from Tokyo tower were monitored continuously for 1155 days at Kiryu Gunma. Anomalous propagations were distinguished from the received data by using a statistical analysis. After the statistical thoughtful consideration, it was found out that earthquakes associated with anomalous propagations were characterized by (1) magnitude of earthquakes M≧4.5, (2) distance from epicenters L≦75km and (3) depth of hypocenters D≦50km.

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In this paper, we have studied the effect of earthquakes on Total Electron Content (TEC) data of the year 2007 at Agra (Geographic Lat. 27.2°N, Long. 78°E), India. The measurements of TEC are made by using a dual frequency GPS receiver system. We found 39 cases of earthquakes (M≥5.0) in the range of 2000 km from the observing station at Agra. It is observed that the TEC shows anomalous behavior in the form of enhancement and depletion 0–9 days prior to the occurrence of these earthquakes. We also study the simultaneous variation of foF₂ and TEC for the months of May and June, 2007. The foF₂ data exhibit enhanced anomaly on the same day of a large magnitude earthquake (M=6.0) in May, 2007 while for the same case of earthquake TEC shows anomaly before 02 days in the form of enhancement. The atmospheric oscillations and electric field generation during the earthquake preparation process may be the significant contributors of these anomalies in TEC and foF₂ data.

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Observation of VHF radio waves with high frequency resolution has been carried out at Tateyama, Japan. 48.25 MHz radio waves transmitted from Bangkok, Thailand, located in the distance of 4500 km from Tateyama were frequently received in 2001. These radio waves have a carrier of TV broadcast used in Thailand and vestigial side band whose bandwidth is 6 MHz. It is found that, simultaneously with the reception of the radio wave, maximum observed frequency (MOF) increased in spring, autumn, and winter. Since the electron density in the ionosphere was large in these seasons in 2001, the reception of the radio wave is obviously due to one-hop F₂ reflection. Simultaneous observations of both the reception of the radio wave and the enhancement of MOF have never been reported in the previous studies. Using ray tracing calculation, it is confirmed that this reception is due to the reflection from the ionosphere. The increase of the signal intensity corresponds to the crossing of the skip distance at Tateyama.

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