The extensive information on global lightning activity gathered by the space-based Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) finds endless applications in many research areas. When these satellites pass the South Atlantic Anomaly (SAA) centered near the lower east coast of South America, precipitating cosmic particles cause numerous false lightning detections. This induces an application of increasingly aggressive filtering, resulting in higher rejection rates of true flashes along with the radiation noise. Differences in the exposure to SAA and filtering procedures result in notable differences between OTD and LIS lightning distributions in this region. We draw readers' attention to these differences, and show that such filtering procedures may result in a systematic loss of information important for Schumann resonance and Transient Luminous Events. We also suggest that the high lightning activity in the SAA region indicated by LIS, may be a manifestation of a link between the cosmic and Earth weather, and possibly a yet unexplored feedback mechanism between lightning discharges and the cosmic particle precipitation.
After the Hyogoken-nanbu earthquake in 1995, Kushida et al. reported that they had detected propagation anomalies of the non-line-of-sight FM radio wave of 77.1MHz broadcasted from Sendai. They hypothesized that the propagation anomalies were due to the ionospheric disturbances which might be affectted by the earthquake. Then, non-line-of-sight FM radio waves have been observed to clarify the hypothesis at many electromagnetic observatories. We also started observation of non-line-of-sight FM radio waves with a dual frequency method from 1996. Now, more than 140 tuners have been operated at our twelve observatories in Japan. Our previous observation results suggested that propagation anomalies might be affected by meteorological conditions rather than by the ionospheric disturbances. It is highly required to investigate the propagation characteristics of non-line-of-sight FM radio waves and the meteorological data near propagation paths. So we have been observing non-line-of-sight FM radio waves at Kajigamori electromagnetic observatory in order to clarify correlation between the aerological atmospheric refractivity and the propagation characteristics of FM radio waves. The observed FM radio wave frequencies were 88.0MHz from Oita and 83.2MHz from Miyazaki. The observation period was for 3 years from January 2006 to December 2008. It was found from our observational results that the received levels of non-line-of-sight FM radio waves had seasonal variations in their fluctuations. The fluctuation levels in summer season were larger than those in winter. They were strongly correlated with the aerological atmospheric refractivity.
During the total solar eclipse in India on July 22, 2009, we measured the amplitude of the fixed frequency VLF transmitter signals (f =19.8 kHz, NWC, Australia) at Agra (Geographic Lat. 27.2°N, Long. 78°NE), using a SoftPAL (Software based phase and amplitude logger) receiver. It was the longest total solar eclipse in the 21st century seen in India ever since 18 August, 1968. We analysed the VLF data for a period of fifteen days (±7 days from the date of the event) and found that the amplitude of the signal decreased on 22 July in the time sector of 2 hrs between 0530 and 0730 hours LT with the maximum depletion during the period of total solar eclipse. The result is interpreted in terms of depletion of electron density in the D region of the ionosphere caused by the solar eclipse.
Though there have been several papers suggesting the important role of atmospheric gravity waves (AGWs) in the generation mechanism of seismo-ionospheric perturbations, no reports have appeared on the statistical study of the AGW effect. Based on the data over nine years and for many propagation paths in and around Japan, this paper presents the first statistical result on the role of AGW in seismo-ionospheric effects. The conclusion by means of superimposed epoch analysis is that the AGW modulation (fluctuation) is rather enhanced about 10 days only for shallow (depth ‹ 40km) earthquakes, but its significance level is just close to the conventional 2σ (σ : standard deviation) level. So that, we can conceive that the AGW channel is the most dominant hypothesis for seismo- ionospheric perturbations, but an alternative channel such as chemical (+ electric field) channel is also operative either simultaneously for an EQ or may be dominant for a small number of earthquakes.