Observational signatures of unusual outgoing longwave radiation (OLR) and atmospheric gravity waves (AGW) as precursory effects of May 2015 Nepal earthquakes

Abnormal Gravity Wave Activity in the Stratosphere Prior to the 2016 Kumamoto Earthquakes

“…The period of perturbation and its spatial extent are quite similar in both the stratosphere and lower ionosphere. Because of the output rate of 1 hr in the stratospheric analysis, we cannot estimate the frequency (or period) of excited AGWs with periods less than 2 hr, even though Hayakawa et al (2018), Rozhnoi et al (2013), and Chakraborty et al (2018) have suggested the importance of AGW range by showing the enhancement in the fluctuation spectral density in VLF data in the range from 10 min to a few hours when we observe VLF ionospheric perturbations before an EQ. There is an additional paper we have to cite.…”

“…Unfortunately, the source of generation of those gravity waves on the near Earth's surface is poorly understood. As we have referred in section 1, Chakraborty et al (2018) have reported the preseismic signatures of OLR and ionospheric perturbations, but the quantitative connection between the two still remains quite unclear. Their study reveals only the coexistence of thermal anomaly and ionospheric AGWs before a major EQ.…”

A martingale-based temporal analysis of pre-earthquake anomalies at Jiuzhaigou, China, in the period of 2009-2018

“…Other methods involving analysis of thermal properties and statistical analysis of standard deviation have been proposed to find anomalies in the OLR data before earthquake [6], [18]. Chakraborty et al studied the effects of seismic events on OLR in the M7.3 Nepal earthquake that occurred on May 12, 2015, and a previous large earthquake in on Apri25, 2015 [19]. They used the method of Eddy field calculation mean to find the anomaly and the relation with the tectonic plate boundary.…”

“…Xiong et al utilized a data mining technique based on wavelet transform to analyse the anomalies of longwave emission radiation (OLR) data; they propose that there is a certain correlation between the abnormal information found and earthquakes [20]. The OLR, from several decades, provides a significant pattern of transient anomalies preceding earthquakes [6], [7], [19], [21]- [23]. The OLR anomaly corresponds to a large area of ground coverage and coincides with the main epicentral zone [6], and primary was used to research Earth radiative budget and climate.…”

“…After the abnormal signal is extracted, it needs to be further analysed. Generally, the occurrence of an earthquake has a preparation process may start 1-30 days ago [19], [25]. To validate their result and to find out those characteristics of OLR in other aspects, we apply some statistical studies based on the data of Jiuzhaigou, China, 2009-2018 in this study, and we were more focus on the Ms6.5 earthquake at Aug 8th, 2017 to conduct the time series analysis.…”