16:00 〜 16:15
[MIS04-13] Daily variation of NmF2 before Large Earthquakes
キーワード：地震、電離圏擾乱、ダイナモ電場
Many reports which have been published so far concern the case study as well as the statistical study. The reports have shown that ionosphere (TEC/ NmF2) is modified about 7-10 days before some (not all) large earthquakes. All papers, without exception, have tried to find the deviation of NmF2 /TEC of one or two days from the monthly average data or the quartile. However, this approach to study earthquake precursor needs to be avoided. We need to study the continuous daily variation of NmF2/TEC before large earthquakes, by taking space weather condition into account.
Our past study suggests that the driving force to modify the ionosphere is dynamo electric field in the ionosphere. The behavior of NmF2 is explained by the intensified east ward (west ward) dynamo electric field during daytime (night time): Depending on the intensity of the electric field, NmF2 increases or decreases both day and night. As the eastward electric field increases, NmF2 first increases because the recombination of the electrons with neutral density reduces. The stronger electric field lifts the ionosphere height to much higher altitude, and as a result, NmF2 reduces.
The magnetic flux tube which is filled or partly filled by the plasma lift -up due to the daytime eastward electric field. The plasma which partly fills the magnetic tube flows down along the magnetic field line both day and nighttime. At night this effect is intensified due to the downward plasma drift caused by the westward electric field. As a result, NmF2 at high latitude shows clear night time NmF2 increase. The intensification of the electric field can be produced by the large dynamo electric potential over the epicenter. The plasma irregularities in the dynamo regions in the height region 0f 100 km, causing the reduced conductivity. The reduced conductivity is a result of plasma irregularities generated by the breaking of acoustic gravity waves.
References
Oyama, K. I, C. H. Chen, L. Barkov, D. Minakshi, K. Ryu, J. Y. Liu, and H. Liu, Precursor effect of March 11 2011 off the coast of Tohoku earthquake on high and low latitude ionospheres and its possible disturbing mechanism, Advances Space Res., 63, 2623-2637, 2019, https://doi.org/10.1016/j.asr.2018.12.042
Oyama, K.- I., and M. Devi, Study of Anomalous behavior of ionosphere prior to large earth quakes - Present and Future, Space Res. Today, 2020 August Issue, No 208, 36- 43, 2020
Devi, M., A. K. Barbara, , S. Patgiri, A. Depueva, K.-I. Oyama, V. Depuev, and Y. Ruzhin, Perturbation Features Imprinted on Ionosphere by Successive Clusters of Strong Earthquakes: Role of Atmospheric Coupling Dynamics, December 2019,Geomagnetism and Aeronomy 59(8):955-970, DOI: 10.1134/S0016793219080036
Devi, M., Devi, A .K Barbara, K. -I. Oyama, A. Medhi, S. Patgiri, S. Das, M. Saikia, A. Depueva and V. Depuev, Earthquake time tropospheric wind flow pattern: a supplement to the upper atmospheric preludes during strong Tohoku earthquake event of March 2011, International Journal of Electronics and Applied Research (IJEAR) vol. 7, issue 1, June 2020 Online (http://eses.net.in/online_journal.html) ISSN 2395-0064
Our past study suggests that the driving force to modify the ionosphere is dynamo electric field in the ionosphere. The behavior of NmF2 is explained by the intensified east ward (west ward) dynamo electric field during daytime (night time): Depending on the intensity of the electric field, NmF2 increases or decreases both day and night. As the eastward electric field increases, NmF2 first increases because the recombination of the electrons with neutral density reduces. The stronger electric field lifts the ionosphere height to much higher altitude, and as a result, NmF2 reduces.
The magnetic flux tube which is filled or partly filled by the plasma lift -up due to the daytime eastward electric field. The plasma which partly fills the magnetic tube flows down along the magnetic field line both day and nighttime. At night this effect is intensified due to the downward plasma drift caused by the westward electric field. As a result, NmF2 at high latitude shows clear night time NmF2 increase. The intensification of the electric field can be produced by the large dynamo electric potential over the epicenter. The plasma irregularities in the dynamo regions in the height region 0f 100 km, causing the reduced conductivity. The reduced conductivity is a result of plasma irregularities generated by the breaking of acoustic gravity waves.
References
Oyama, K. I, C. H. Chen, L. Barkov, D. Minakshi, K. Ryu, J. Y. Liu, and H. Liu, Precursor effect of March 11 2011 off the coast of Tohoku earthquake on high and low latitude ionospheres and its possible disturbing mechanism, Advances Space Res., 63, 2623-2637, 2019, https://doi.org/10.1016/j.asr.2018.12.042
Oyama, K.- I., and M. Devi, Study of Anomalous behavior of ionosphere prior to large earth quakes - Present and Future, Space Res. Today, 2020 August Issue, No 208, 36- 43, 2020
Devi, M., A. K. Barbara, , S. Patgiri, A. Depueva, K.-I. Oyama, V. Depuev, and Y. Ruzhin, Perturbation Features Imprinted on Ionosphere by Successive Clusters of Strong Earthquakes: Role of Atmospheric Coupling Dynamics, December 2019,Geomagnetism and Aeronomy 59(8):955-970, DOI: 10.1134/S0016793219080036
Devi, M., Devi, A .K Barbara, K. -I. Oyama, A. Medhi, S. Patgiri, S. Das, M. Saikia, A. Depueva and V. Depuev, Earthquake time tropospheric wind flow pattern: a supplement to the upper atmospheric preludes during strong Tohoku earthquake event of March 2011, International Journal of Electronics and Applied Research (IJEAR) vol. 7, issue 1, June 2020 Online (http://eses.net.in/online_journal.html) ISSN 2395-0064