Vertical TEC over seismically active region during low solar activity

z abstract Using data of Japanese dense array of GPS receivers (GEONET) we analyzed variations of total electron content (TEC) over Japan during a period of low solar and geomagnetic activity in April-September 2008. During that time, five large earthquakes with magnitude M46.8 occurred around the Japanese Islands. We calculated vertical TEC with time resolution of 1 h and we compared the TEC over Japan with TEC over southwestern USA. In order to detect abnormal signals, we processed daily TEC based on median and quartile of preceding 15 days. Knowing that the decisive role in the ionosphere state is performed by space weather effects, we compared the estimated TEC values with time series of the Bz component of the interplanetary magnetic field (IMF), UV solar radiation, index of geomagnetic activity Dst and planetary index Kp. We have found that though the analyzed time period falls on the minimum of solar activity, the observed positive anomalies in the regional TEC correspond to fluctuations of IMF Bz and to the following increase in Kp and Dst indices. Other case of � 25% TEC increase in the duration of four days (DOY: 140-143) is, most likely, caused by increase in the solar UV radiation and coincides with growth of the global TEC. Other positive or negative abnormal TEC variations coincide with fluctuations of the global mean TEC or are of large spatial scale, i.e. much larger than the earthquake preparation zone. Therefore, it is rather difficult to find correlation between the observed anomalies and the five large earthquakes. Our results do not disprove the possibility of precursory phenomena but show the difficulties in identifying earthquake precursors in the ionosphere TEC on the background of TEC changes produced by space weather effects, even during solar minimum.

[1]  Andrzej Krankowski,et al.  Precursory phenomena observed in the total electron content measurements before great Hokkaido earthquake of September 25, 2003 (M = 8.3) , 2007 .

[2]  Sergey Pulinets,et al.  Seismic activity as a source of the ionospheric variability , 1998 .

[3]  B. Morena,et al.  Quasi-periodic fluctuations in ionospheric absorption in relation to planetary activity in the stratosphere , 1991 .

[4]  Toshitaka Tsuda,et al.  Global dayside ionospheric uplift and enhancement associated with interplanetary electric fields , 2004 .

[5]  Y. J. Chuo,et al.  Variations of ionospheric total electron content during the Chi‐Chi Earthquake , 2001 .

[6]  M. Parrot,et al.  Correlation between GEOS VLF emissions and earthquakes , 1985 .

[7]  Sergey Pulinets,et al.  Correlation analysis technique revealing ionospheric precursors of earthquakes , 2004 .

[8]  Chien-Hung Lin,et al.  Seismoionospheric GPS total electron content anomalies observed before the 12 May 2008 Mw7.9 Wenchuan earthquake , 2009 .

[9]  M. Gokhberg,et al.  Experimental measurement of electromagnetic emissions possibly related to earthquakes in Japan , 1982 .

[10]  James L. Garrison,et al.  Investigation of ionospheric electron content variations before earthquakes in southern California, 2003–2004 , 2007 .

[11]  Sergey Pulinets,et al.  Main phenomenological features of ionospheric precursors of strong earthquakes , 2003 .

[12]  Yi-Ben Tsai,et al.  Seismo‐ionospheric signatures prior to M≥6.0 Taiwan earthquakes , 2000 .

[13]  E. Afraimovich,et al.  Dynamics of total electron content distribution during strong geomagnetic storms , 2007 .

[14]  Sergey Pulinets,et al.  Quasielectrostatic Model of Atmosphere-Thermosphere-Ionosphere Coupling , 2000 .

[15]  E. Astafyeva,et al.  Effects of strong IMF B z southward events on the equatorial and mid-latitude ionosphere , 2009 .

[16]  J. Bernard Minster,et al.  GPS detection of ionospheric perturbations following the January 17, 1994, Northridge Earthquake , 1995 .

[17]  S. Pulinets.  Natural radioactivity, earthquakes, and the ionosphere , 2007 .

[18]  S. Pulinets,et al.  Ionospheric precursors of earthquakes , 2004 .

[19]  J. Laštovička.  Lower ionosphere response to external forcing: A brief review , 2009 .

[20]  L. Lanzerotti.  Solar Terrestrial Physics , 2003 .

[21]  M. Hayakawa,et al.  Results of subionospheric radio LF monitoring prior to the Tokachi (M=8, Hokkaido, 25 September 2003) earthquake , 2004 .

[22]  A. Coster,et al.  Unexpected connections between the stratosphere and ionosphere , 2010 .

[23]  E. Afraimovich,et al.  TEC anomalies—Local TEC changes prior to earthquakes or TEC response to solar and geomagnetic activity changes? , 2008 .

[24]  E. Afraimovich,et al.  Variations of the total electron content in the ionosphere from GPS data recorded during the Hector Mine earthquake of October 16, 1999, California , 2004 .

[25]  S. Shalimov.  Ionospheric Irregularities Initiated by Planetary Waves , 2001 .

[26]  Y. J. Chuo,et al.  A statistical investigation of preearthquake ionospheric anomaly , 2006 .

[27]  I. P. Dobrovolsky,et al.  Estimation of the size of earthquake preparation zones , 1979 .

[28]  D. Pfeffermann,et al.  Small area estimation , 2011 .

[29]  I. V. Zhivetiev,et al.  Global electron content: a new conception to track solar activity , 2008 .

[30]  E. L. Afraimovich,et al.  The shock-acoustic waves generated by earthquakes , 2001 .

[31]  H. Rishbeth.  Ionoquakes: Earthquake precursors in the ionosphere? , 2006 .

[32]  M. Hayakawa,et al.  VLF monitorig of atmosphere-ionosphere boundary as a tool to study planetary waves evolution and seismic influence , 2001 .

[33]  Yi-Ben Tsai,et al.  Pre-earthquake ionospheric anomalies registered by continuous GPS TEC measurements , 2004 .

[34]  早川 正士,et al.  Electromagnetic phenomena related to earthquake prediction , 1994 .

[35]  J. Liu,et al.  Empirical models of Total Electron Content based on functional fitting over Taiwan during geomagnetic quiet condition , 2009 .