Abstract.During the total solar eclipse observed in Europe on August 11, 1999, measurements were made of the amplitude and phase of four VLF transmitters in the frequency range 16-24 kHz. Five receiver sites wcrc set up, and significant variations in phase and amplitude are reported for 17 paths, more than any previously during an eclipse. Distances from transmitter to receiver ranged from 90 to 14,510 kin, although the majority were <2000 kin. Typically, positive amplitude changes were observed throughout the whole eclipse period on path lengths <2000 kin, while negative amplitude changes were observed on paths >10,000 kin. Negative phase changes were observed on most paths, independent of path length. Although there was significant variation from path to path, the typical changes observed were N3 dB and -
[1] A new, unique system has been developed for the automatic detection and analysis of whistlers. The Automatic Whistler Detector and Analyzer (AWDA) system has two purposes: (1) to automatically provide plasmaspheric electron densities extracted from whistlers and (2) to collect statistical data for the investigation of whistler generation and propagation. This paper presents the details of and the first results obtained by the automatic detector segment. The detector algorithm is based on image correlation where the target image is a preprocessed spectrogram of raw VLF signals and the pattern is a model whistler. The first AWDA system has been working in Tihany, Hungary (L = 1.8), and has collected 100,000 whistler traces per year. The overall detection efficiency using a parameter set optimized for purpose 2 is 90% for misdetection and 50-80% for false detection. The statistical analysis over the period February 2002 to February 2008 including 600,000 whistler traces shows high diurnal variations; whistler were mainly, but not only, detected when both the source and receiver regions were unlit. The seasonal occurrence is high during austral summer and low during austral winter. Comparison with Tarcsai et al. 's (1988) statistical study on Tihany whistlers shows differences in both diurnal and seasonal variations, but the latter study was made on 1388 manually identified whistlers only. The L value distributions of both data sets are similar. A global network of AWDA systems (AWDAnet) has been set up to overcome the time and space limitations of a single station; the network consists of 13 nodes, and another 6 are envisaged for the near future.
Abstract. Lightning Imaging Sensor (LIS) data have been analysed to ascertain the statistical pattern of lightning occurrence over southern Africa. The diurnal and seasonal variations are mapped in detail. The highest flash rates (107.2 km −2 y −1 ) occur close to the equator but maxima are also found over Madagascar (32.1 km −2 y −1 ) and South Africa (26.4 km −2 y −1 ). A feature of the statistics is a relatively steady contribution from over the ocean off the east coast of South Africa that appears to be associated with the Agulhas current.Lightning statistics are of intrinsic meteorological interest but they also relate to the occurrence of whistlers in the conjugate region. Whistler observations are made at Tihany, Hungary. Statistics reveal that the period of most frequent whistler occurrence does not correspond to the maximum in lightning activity in the conjugate region but is strongly influenced by ionospheric illumination and other factors. The whistler/flash ratio, R, shows remarkable variations during the year and has a peak that is narrowly confined to February and March.
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