Analysis of the enhanced negative correlation between electron density and electron temperature related to earthquakes

Abstract. Ionospheric perturbations in plasma parameters have been observed before large earthquakes, but the correlation between different parameters has been less studied in previous research. The present study is focused on the relationship between electron density (Ne) and temperature (Te) observed by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite during local nighttime, in which a positive correlation has been revealed near the equator and a weak correlation at mid- and low latitudes over both hemispheres. Based on this normal background analysis, the negative correlation with the lowest percent in all Ne and Te points is studied before and after large earthquakes at mid- and low latitudes. The multiparameter observations exhibited typical synchronous disturbances before the Chile M8.8 earthquake in 2010 and the Pu'er M6.4 in 2007, and Te varied inversely with Ne over the epicentral areas. Moreover, statistical analysis has been done by selecting the orbits at a distance of 1000 km and ±7 days before and after the global earthquakes. Enhanced negative correlation coefficients lower than −0.5 between Ne and Te are found in 42% of points to be connected with earthquakes. The correlation median values at different seismic levels show a clear decrease with earthquakes larger than 7. Finally, the electric-field-coupling model is discussed; furthermore, a digital simulation has been carried out by SAMI2 (Sami2 is Another Model of the Ionosphere), which illustrates that the external electric field in the ionosphere can strengthen the negative correlation in Ne and Te at a lower latitude relative to the disturbed source due to the effects of the geomagnetic field. Although seismic activity is not the only source to cause the inverse Ne–Te variations, the present results demonstrate one possibly useful tool in seismo-electromagnetic anomaly differentiation, and a comprehensive analysis with multiple parameters helps to further understand the seismo–ionospheric coupling mechanism. \keywords{Ionosphere (plasma temperature and density)}

[1]  M. Parrot,et al.  Variations of electron density and temperature in ionosphere based on the DEMETER ISL data , 2010 .

[2]  Xuhui Shen,et al.  Ionospheric perturbations of electron density before the Wenchuan Earthquake , 2010 .

[3]  S. Fukao,et al.  Longitudinal variations of the topside ionosphere at low latitudes: Satellite measurements and mathematical modelings , 1996 .

[4]  J. Qian,et al.  The characteristics of quasistatic electric field perturbations observed by DEMETER satellite before large earthquakes , 2014 .

[5]  Xuhui Shen,et al.  Analysis of ionospheric plasma perturbations before Wenchuan earthquake , 2009 .

[6]  M. Hayakawa,et al.  A perturbation of DC electric field caused by light ion adhesion to aerosols during the growth in seismic-related atmospheric radioactivity , 2007 .

[7]  Wang Wei,et al.  Electron density perturbation before Chile M8.8 earthquake , 2011 .

[8]  Ondrej Santolik,et al.  Decrease of intensity of ELF/VLF waves observed in the upper ionosphere close to earthquakes: A statistical study , 2009 .

[9]  D. Sharma,et al.  Ionospheric electron and ion temperatures response to seismic activity , 2013 .

[10]  Jann‐Yenq Liu,et al.  Longitudinal structure of the equatorial ionosphere: Time evolution of the four-peaked EIA structure , 2007 .

[11]  Jiadong Qian,et al.  Response of the ionospheric electron density to different types of seismic events , 2011 .

[12]  Glenn Joyce,et al.  Sami2 is Another Model of the Ionosphere (SAMI2): A new low-latitude ionosphere model , 2000 .

[13]  Christine Amory-Mazaudier,et al.  Midlatitude ionospheric plasma temperature climatology and empirical model based on Saint Santin incoherent scatter radar data from 1966 to 1987 , 2004 .

[14]  A. K. Gwal,et al.  Ionospheric variations observed by the DEMETER satellite in the mid-latitude region during strong earthquakes , 2007 .

[15]  Xuhui Shen,et al.  ULF/ELF ionospheric electric field and plasma perturbations related to Chile earthquakes , 2011 .

[16]  S. Watanabe,et al.  Correlation between electron density and temperature in the topside ionosphere , 2011 .

[17]  Cheng-Ling Kuo,et al.  Ionosphere plasma bubbles and density variations induced by pre‐earthquake rock currents and associated surface charges , 2011 .

[18]  Masashi Kamogawa,et al.  Reduction of electron temperature in low‐latitude ionosphere at 600 km before and after large earthquakes , 2008 .

[19]  Biqiang Zhao,et al.  Longitudinal variations of electron temperature and total ion density in the sunset equatorial topside ionosphere , 2008 .

[20]  Xuemin Zhang,et al.  Ground-based and satellite DC-ULF electric field anomalies around Wenchuan M8.0 earthquake , 2012 .

[21]  Michel Parrot,et al.  Statistical analysis of automatically detected ion density variations recorded by DEMETER and their relation to seismic activity , 2012 .

[22]  M. Parrot,et al.  Ionospheric density variations recorded before the 2010 Mw 8.8 earthquake in Chile , 2011 .

[23]  Jean-Pierre Lebreton,et al.  Examples of unusual ionospheric observations made by the DEMETER satellite over seismic regions , 2006 .

[24]  Shigeto Watanabe,et al.  Season, local time, and longitude variations of electron temperature at the height of ∼600 km in the low latitude region , 1996 .

[25]  Marie-Anne Clair,et al.  The Demeter microsatellite and ground segment , 2006 .

[26]  M. Parrot,et al.  Attenuation of electromagnetic waves at the frequency ~1.7 kHz in the upper ionosphere observed by the DEMETER satellite in the vicinity of earthquakes , 2012 .

[27]  Shoichiro Fukao,et al.  A plasma temperature anomaly in the equatorial topside ionosphere , 1997 .

[28]  R. Heelis,et al.  Longitudinal and seasonal variations in nighttime plasma temperatures in the equatorial topside ionosphere during solar maximum , 1999 .

[29]  M. Hayakawa,et al.  Penetration characteristics of electromagnetic emissions from an underground seismic source into the atmosphere, ionosphere, and magnetosphere , 1995 .

[30]  M. Parrot,et al.  "Real time analysis" of the ion density measured by the satellite DEMETER in relation with the seismic activity , 2012 .

[31]  Xuhui Shen,et al.  Phenomena of electrostatic perturbations before strong earthquakes (2005–2010) observed on DEMETER , 2012 .

[32]  G. Fang,et al.  An Analysis of Ionospheric Variations Before the Wenchuan Earthquake with DEMETER Data , 2009 .

[33]  M. Parrot,et al.  Daytime longitudinal structures of electron density and temperature in the topside ionosphere observed by the Hinotori and DEMETER satellites , 2011 .

[34]  William J. Burke,et al.  The 27-day variations of plasma densities and temperatures in the topside ionosphere , 2003 .

[35]  Biqiang Zhao,et al.  Yearly variations of global plasma densities in the topside ionosphere at middle and low latitudes , 2007 .

[36]  Sergey Pulinets,et al.  Physical mechanism of the vertical electric field generation over active tectonic faults , 2009 .

[37]  S. Choudhary,et al.  Ionospheric anomalies associated with the Haiti earthquake of 12 January 2010 observed by DEMETER satellite , 2012 .

[38]  Xuhui Shen,et al.  IONOSPHERIC PERTURBATIONS ASSOCIATED WITH THE M8.6 SUMATRA EARTHQUAKE ON 28 MARCH 2005 , 2010 .

[39]  P.-L. Blelly,et al.  The ISL Langmuir probe experiment processing onboard DEMETER: Scientific objectives, description and first results , 2006 .

[40]  J. Lebreton,et al.  Validation of electron density and temperature observed by DEMETER , 2013 .

[41]  T. Fang,et al.  Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT‐3/COSMIC: Three‐dimensional electron density structures , 2007 .

[42]  Sergey Pulinets,et al.  Ionospheric Precursors of Earthquakes; Recent Advances in Theory and Practical Applications , 2004 .

[43]  Lu Li,et al.  Statistical backgrounds of topside-ionospheric electron density and temperature and their variations during geomagnetic activity , 2011 .