Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 33, 1457-1467, 2015
https://doi.org/10.5194/angeo-33-1457-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Regular paper
30 Nov 2015
Sub-ionospheric VLF signal anomaly due to geomagnetic storms: a statistical study
K. Tatsuta1, Y. Hobara1,2, S. Pal1,3, and M. Balikhin4 1Department of Communication Engineering and Informatics, The University of Electro-Communications, Tokyo, Japan
2Earth Environment Research Station, The University of Electro-Communications, Tokyo, Japan
3Indian Centre for Space Physics, Kolkata, India
4Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield, UK
Abstract. We investigate quantitatively the effect of geomagnetic storms on the sub-ionospheric VLF/LF (Very Low Frequency/Low Frequency) propagations for different latitudes based on 2-year nighttime data from Japanese VLF/LF observation network. Three statistical parameters such as average signal amplitude, variability of the signal amplitude, and nighttime fluctuation were calculated daily for 2 years for 16–21 independent VLF/LF transmitter–receiver propagation paths consisting of three transmitters and seven receiving stations. These propagation paths are suitable to simultaneously study high-latitude, low-mid-latitude and mid-latitude D/E-region ionospheric properties. We found that these three statistical parameters indicate significant anomalies exceeding at least 2 times of their standard deviation from the mean value during the geomagnetic storm time period in the high-latitude paths with an occurrence rate of anomaly between 40 and 50 % presumably due to the auroral energetic electron precipitation. The mid-latitude and low-mid-latitude paths have a smaller influence from the geomagnetic activity because of a lower occurrence rate of anomalies even during the geomagnetically active time period (from 20 to 30 %). The anomalies except geomagnetic storm periods may be caused by atmospheric and/or lithospheric origins. The statistical occurrence rates of ionospheric anomalies for different latitudinal paths during geomagnetic storm and non-storm time periods are basic and important information not only to identify the space weather effects toward the lower ionosphere depending on the latitudes but also to separate various external physical causes of lower ionospheric disturbances.

Citation: Tatsuta, K., Hobara, Y., Pal, S., and Balikhin, M.: Sub-ionospheric VLF signal anomaly due to geomagnetic storms: a statistical study, Ann. Geophys., 33, 1457-1467, https://doi.org/10.5194/angeo-33-1457-2015, 2015.
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We study the effect of geomagnetic storms on the sub-ionospheric VLF/LF propagations based on 2-year data from the network observations in Japan. Three statistical parameters such as average signal amplitude, variability of the signal amplitude, and nighttime fluctuation were calculated. These statistical parameters indicate significant anomalies during the geomagnetic storm in the high-latitude paths. While mid-latitude and low-mid latitude paths have smaller influence from the storm activity.
We study the effect of geomagnetic storms on the sub-ionospheric VLF/LF propagations based on...
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