the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Characteristics and mechanisms of near-surface atmospheric electric field negative anomalies preceding the 5 September, 2022, Ms6.8 Luding earthquake, China
Lixin Wu
Xiao Wang
Yuan Qi
Jingchen Lu
Wenfei Mao
Abstract. A Ms6.8 strike-slip earthquake (EQ) occurred in Luding, Sichuan province, China, on 5 September, 2022, causing great losses to the surrounding Ganzi Prefecture and Ya’an City. In this research, the near-surface atmospheric electric field (AEF), recorded at four discretely distributed sites 15d before the Luding EQ, were analyzed and discriminated by using multi-source auxiliary data including precipitation, cloud base height and low cloud cover, and nine possible seismic AEF anomalies at four sites were obtained preliminarily. Accordingly, surface microwave brightness temperature (MBT), which is very sensitive to the surface dielectrics and closely related to the air ionization, together with surface soil moisture, lithology, and 3D-simulated crustal stress field, was jointly analyzed for confirming the seismic relations of the obtained negative AEF anomalies. The geophysical environment for crustal high-stress concentration, positive charge carriers transfer and surface accumulation was demonstrated to exist and satisfy the conditions of generating locally the negative AEF anomalies. Furthermore, to deal with the spatial disparities in sites and regions with potential atmospheric ionization, the data of near-surface wind field was employed to scrutinize the reliability of the AEF anomalies by comprehensively considering the spatial relationships among surface charges accumulation areas, wind direction and speed, as well as the AEF site. Finally, four negative AEF anomalies were deemed to be closely related to the Luding EQ, and the remaining five anomalies were ruled out. The mechanism of negative AEF anomalies before the Luding EQ were believed to be: positive charge carriers were generated from the underground high stress concentration areas, and then transferred to and accumulated on the ground surface and to ionize the surface air, thus disturbing the aground AEF. This study offers an approach to identify and analyze the seismic AEF anomalies, and is also helpful to study the pre-shocking coupling process between coversphere and atmosphere.
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Lixin Wu et al.
Status: open (until 24 Oct 2023)
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CC1: 'Comment on egusphere-2023-1761', J. Liu, 06 Sep 2023
reply
The authors analyzed AEF data before Luding earthquake, and further confirmed the anomalies with surface P-hole aggregation. I think the data analysis can support the conclusion of this manuscript. I just have some minor comments as follows.
- For the criteria of FW-AEF, the last one is “no long period of negative AEF anomalies”. Why? What is the time range of this period?
- The time in Figure 3 is local time or universal time? Usually, the time of satellite data is universal time. Is there the jet-lagged between the AEF and MBT?
Citation: https://doi.org/10.5194/egusphere-2023-1761-CC1 -
CC2: 'Reply on CC1', Xiao Wang, 06 Sep 2023
reply
Thank you very much for your valuable comments on our manuscript, and our responses are listed below.
Question 1:For the criteria of FW-AEF, the last one is “no long period of negative AEF anomalies”. Why? What is the time range of this period?
Answer：
Firstly, except for excluding the effects of precipitation and low clouds, other factors being able to affect AEF, such as changes in aerosol concentration due to human activities, cannot be judged clearly due to data limitation. Secondly, and most critically, previous studies have proved that FW-AEF is usually positive, and the current acceptable theory also holds that this is the case. Obtaining a more realistic AEF curve as the FW-AEF background of GEC is crucial for the identification and extraction of AEF anomalies. So, the time periods with negative values from the curve of AEF need to be excluded in advance, so as to characterize the changes of AEF in the natural state only.This time period is chosen as one day in that FW-AEF shows one-day periodic changes, which are affected by temperature, humidity and sunshine.
Question 2:
The time in Figure 3 is local time or universal time? Usually, the time of satellite data is universal time. Is there the jet-lagged between the AEF and MBT?
Answer：
The time of all data used in this paper has been adjusted to be local time, including the AEF data itself. The MBT data recorded originally in UTC has also been converted to local time based on the satellite transit time. However, due to the different data accessibility, it is inevitable that there is a small difference in time between multiple sources of data, but we chose the data with the closest time to suppress this inconsistency.All above will be amended and noted in the final submitted version.
Citation: https://doi.org/10.5194/egusphere-2023-1761-CC2
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RC1: 'Comment on egusphere-2023-1761', Anonymous Referee #1, 02 Oct 2023
reply
On 5 September 2022, an Ms6.8 earthquake struck Luding, China, causing extensive damage. This study analyzed near-surface atmospheric electric field (AEF) data collected 15 days before the earthquake, along with various other data sources. The authors identified nine possible AEF anomalies related to the earthquake. They confirmed four of these anomalies to be closely linked to the earthquake, while ruling out the other five. The mechanism behind these anomalies involves the transfer of positive charge carriers from underground high-stress areas to the surface, ionizing the air and disrupting the atmospheric electric field. This research is interesting and provides insights into identifying seismic AEF anomalies and understanding the pre-earthquake processes between the Earth's crust and the atmosphere.
My opinion is that the work must be published after some points are clarified.
Figure 2. It is not clear if the figure represents a typical day of FW-AEF or a daily mean curve.
Lines 172-175. Among magnetic indices, only Dst is used. However, some penetrating field currents can appear in middle latitudes on occasion of some auroral activity. It would be more conservative to consider also AE index: when it is lower than 100, it is practice to neglect the presence of that kind of currents. Could you please check if AE is lower than 100 in the period of interest?
Figure 3. It shows at its top panel the daily mean values of Dst and SSN. However, this value for Dst is not appropriate and cannot well characterize the level of magnetic activity. It would be more appropriate its hourly value.
Figure 3. How did you define the 0 value of AEF?
Minor correction
Line 344. Please change “were” with “was”.
Citation: https://doi.org/10.5194/egusphere-2023-1761-RC1
Lixin Wu et al.
Lixin Wu et al.
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