Preearthquake anomalous ionospheric signatures observed at low‐mid latitude Indian station, Delhi, during the year 2015 to early 2016: Preliminary results

Abstract

We have analyzed five major earthquake events measuring greater than 6 on Richter scale (M > 6) that occurred during the year 2015 to early 2016, affecting Indian region ionosphere, using F2 layer critical parameters (foF2, hmF2) obtained using Digisonde from a low‐mid latitude Indian station, Delhi (28.6°N, 77.2°E, 19.2°N geomagnetic latitude, 42.4°N dip). Normal day‐to‐day variability occurring in ionosphere is segregated by calculating F2 layer critical frequency and peak height variations (ΔfoF2, ΔhmF2) from the normal quiet time behavior apart from computing interquartile range. We find that the ionospheric F2 region across Delhi by and large shows some significant perturbations 3–4 days prior to these earthquake events, resulting in a large peak electron density variation of ~200%. These observed perturbations indicate towards a possibility of seismo‐ionospheric coupling as the solar and geomagnetic indices were normally quiet and stable during the period of these events. It was also observed that the precursory effect of earthquake was predominantly seen even outside the earthquake preparation zone, as given by Dobrovolsky et al. (1979). The thermosphere neutral composition (O/N2) as observed by Global Ultraviolet Imager, across Delhi, during these earthquake events does not show any marked variation. Further, the effect of earthquake events on ionospheric peak electron density is compared to the lower atmosphere meteorological phenomenon of 2015 sudden stratospheric warming event.

Ionospheric Response to Sudden Stratospheric Warming Events Across Longitudes During Solar Cycle 24

“…It is noteworthy here that these magnitudes of ionospheric variation as observed during SSW events are comparable to that observed during geomagnetic storms from “above,” making these SSW contributions from “below” to be significant enough from an ionospheric perspective. These results of similar ionospheric perturbations from meteorological and solar‐driven phenomena further validate the result reported by Gupta and Upadhayaya (2017a, 2017b) in their study for Asian region. Further, in our analysis of SSW events between 2009 and 2019, the maximum ionospheric variation (ΔVTEC max ), as observed from the four longitudinal chains, showed comparable to even larger variations during minor SSW events, for example, in Chain 1, the minor warming events of 2015 and 2016, respectively, showed a maximum variation of 83.4% and 61.7%, whereas a maximum variation of 61.9% was observed for the major event of 2019 (not shown here).…”

Land – Atmosphere – Meteorological coupling associated with the 2015 Gorkha (M 7.8) and Dolakha (M 7.3) Nepal earthquakes

“…The temporal information for anomalous Figure 12. The OLR (outgoing longwave radiation) and IOND (ionospheric disturbances) observed by many (Maurya et al, 2016;Gupta and Upadhayaya, 2017;Chakraborty et al, 2018). It is clearly observed Figure 10.…”

“…MWBT: microwave brightness temperature; SAT: surface air temperature; SM: soil moisture; SLHF: surface latent heat flux; CO: carbon monoxide; OLR represents outgoing longwave radiation variations (Chakraborty et al, 2018). IOND indicates ionospheric disturbances (Maurya et al, 2016, Gupta andUpadhayaya 2017).…”

STUDI FREKUENSI KRITIS (foF2) PADA LAPISAN IONOSFER YANG BERHUBUNGAN DENGAN KEJADIAN GEMPA BUMI DI SEGMEN MENTAWAI TAHUN 2010-2015

“…Oleh karena itu penelitian ini bertujuan untuk melihat prekusor gempa bumi melalui analisa anomali foF2 pada lapisan ionosfer sebelum kejadian gempa bumi di wilayah Mentawai Sumatra Barat selama kurun waktu 2005-2015. Penelitan tentang anomali foF2 yang berhubungan dengan gempa bumi telah berhasil di beberapa tempat [11,12,13]. Pada penelitian ini stasiun ionosonda Kototabang, Kabupaten Agam, Sumatera Barat digunakan untuk mengamati foF2 pada lapisan F yang berhubungan dengan kejadian gempa bumi pada segmen Mentawai, zona Subduksi Sumatra selama tahun 2005-2015.…”