Indian Journal of Radio & Space Physics Vol 42, February 2013, pp 18-26 Ionospheric electron and ion temperatures response to seismic activity D K Sharma 1,$,* , A Bardhan 1 & Jagdish Rai 2 1 Department of Physics, Manav Rachna College of Engineering, Faridabad 121 001, Haryana, India 2 Department of Physics, Indian Institute Technology, Roorkee 247 667, Utranchal, India $ E-mail: dksharma.mrce@mrei.ac.in, dksphdes@rediffmail.com Received 6 July 2012; revised 31 December 2012; accepted 2 January 2013 A connection between earthquake and ionosphere has been proposed in the last few decades. A number of hypotheses have been suggested as the earthquake precursory to reduce the hazard of life and property but could not succeed. In the present study, effort has been made to correlate the ionospheric temperature anomalies to seismic activities. The ionospheric electron and ion temperatures were measured with the help of Retarding Potential Analyzer (RPA) payload aboard the Indian SROSS-C2 satellite. The data is used for the period 1995-1998 in the altitude range 430-630 km over the Indian region. The details of seismic events during this period were downloaded from the United State Geological Survey (USGS) website. The normal day ion and electron temperatures have been compared to the temperatures recorded during the seismic event. It has been observed that there is significant enhancement in the electron and ion temperatures. The electron temperature was enhanced by 1.2 - 1.5 times compared to the average normal day electron temperature. However, the ion temperature was 1.1 - 1.3 times over the average normal day ion temperature. The satellite data was analysed for corresponding seismic event duration in such way that the other possible effects are eliminated. Keywords: Ionosphere electron temperature, Ionosphere ion temperatures, F2 region, Seismic activity PACS Nos: 94.20.dj; 91.30.pc 1 Introduction A large number of earthquakes occur every year in different regions and approximately 100-120 of them have a magnitude of ≥5. These events are extremely hazardous for the inhabitants. The ionospheric anomalies associated with seismic activity appearing few days to few hours prior to the event have been studied in detail based on variety of measurements and theoretical analyses 1-11 . Several papers report the satellite recordings of ionospheric disturbances possibly associated with earthquakes. The ground-based measurements of signatures associated with the seismic and non- seismic phenomenon are distinguishable to high accuracy. However, based on space-born measurements, distinguishing the non-seismic and seismic induced atmospheric and ionospheric anomalies remains a challenging task. This situation has been discussed in several recent papers 12-16 paying attention to different criteria of data selection. However, the main problem is that these studies were not statistical in a grid sense due to multi-parametric dependence of expected events on natural conditions and principal impossibility to separate time and space variations from one satellite observations. What is needed is the data set either continuous in space at a fixed time or in contract continuous in time at a fixed place to use the conventional statistical methods. In addition to the ambiguity of observational conclusions, the underlying coupling mechanism of lithosphere-atmosphere-ionosphere system is also unclear 16 . On the other hand, knowledge of the seismicity and underlying processes should be improved by using the satellite methods as it happened with climate and weather study when the proper satellite information became available. To prove the direct relationship between quasi-static electric field and plasma density anomalies and seismic activity is a difficult, but actual task of the modern ionosphere physics. An anomalous increase of 3-7 mV m -1 in the vertical component of the quasi- static electric field has been first observed onboard INTERCOSMOS-BULGARIA-1300 satellite in the near-equatorial ionosphere over the earthquake region ~15 min before an earthquake with magnitude of 4.8 by Chmyrev et al. 17 A reliable correlation between the global distribution of seismic activity and ion density variations in the ionosphere has been proposed by Hayakawa et al. 18 Possible generation of the seismically related electric field in the atmosphere and