Abstract
The characteristics of anomalous radio propagation in the frequency 1 - 30 MHz before and after the 2011 Tohoku-Oki earthquake are firstly revealed by using oblique ionograms for the pass from Wakkanai to Kokubunji which is closest to the epicenter. An oblique ionogram with a wavy-shape-trace was observed at 06:30 UTC on 11 March 2011 after the 2011 Tohoku-Oki earthquake. The velocity of northward-propagating disturbance caused this wavy-shape-trace is estimated to be 130 m/s. This wave-shape-trace shows very clear signature appearing in the oblique ionograms as the characteristic of strong ionospheric disturbances triggered by the earthquake. An oblique ionogram with a steep slopy-shape-trace was observed at 04:45 UTC on 11 March 2011 one hour before the 2011 Tohoku-Oki earthquake. This slopy-shape-trace is investigated as the signatures of preseismic ionospheric anomaly. This anomalous oblique ionogram with a slopy-shape-trace is examined with the slope ratio of virtual height to sweep-frequency, and the difference between monthly median foF2 and hourly value foF2 at Wakkanai and Kokubunji. These features appearing in oblique ionograms suggest that it is useful for studying the signatures of preseismic ionospheric anomaly.
Highlights
An oblique ionogram with a wavy-shape-trace was observed at 06:30 UTC on 11 March 2011 after the 2011 Tohoku-Oki earthquake
The velocity of northward-propagating disturbance caused this wavy-shape-trace is estimated to be 130 m/s. This wave-shape-trace shows very clear signature appearing in the oblique ionograms as the characteristic of strong ionospheric disturbances triggered by the earthquake
This paper focuses on the trace shape and trace distortions around the maximum observable frequency in the oblique ionogram trace which shows a signature of the anomalous radio propagation
Summary
Tohoku-Oki earthquake (M9.0) occurring at 0546:18 UTC on 11 March 2011 in Japan have been analyzed by the high-resolution GPS total electron content (TEC) observation of GPS receiver network, GEONET [1] [2] [3] [4], the ionograms of four ionosonde stations in Japan [5] [6], and the SuperDARN Hokkaido HF radar [7] [8]. Ionospheric disturbances were detected at 06:00 UTC at four ionosonde stations in Japan and an irregular distorted echo trace was observed at Kokubunji closest to the epicenter and 400 km away [5] [6]. The oblique ionospheric sounding data, namely oblique ionograms have not been previously examined for studying the characteristics of anomalous radio propagation associated with the super strong earthquake. In this paper the characteristics of anomalous radio propagation in the frequency 1 - 30 MHz before and after the 2011 Tohoku-Oki earthquake are investigated by oblique ionograms obtained for the pass of relatively medium distance 1068 km between Wakkanai and Kokubunji which is closest to the epicenter. This paper focuses on the trace shape and trace distortions around the maximum observable frequency in the oblique ionogram trace which shows a signature of the anomalous radio propagation. The characteristics appearing in oblique ionograms before and after the 2011 Tohoku-Oki earthquake are shown and discussed in three types of oblique ionogram traces
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
