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The research on the movement law of surrounding rock under the condition of thick loose layer and thin bedrock mostly adopts theoretical research methods such as establishing a mechanical model and numerical calculation. It lacks research based on field dynamic measurement. The microseismic monitoring technology has been widely used in mine dynamic disaster monitoring and early warning in recent years. However, there are few studies on the failure law of surrounding rock under the condition of thick loose layer and thin bedrock based on microseismic monitoring technology. In view of the above problems, taking the 16001 working face of Zhaogu No. 1 Coal Mine of Coking Coal Energy Co., Ltd. as the engineering background, a high-precision microseismic monitoring system is established. The system is built by selecting the network arrangement mode of the borehole-roadway union. Based on the microseismic monitoring results, the dynamic failure law of surrounding rock in large mining height working face under the condition of thick loose layer and thin bedrock is studied. According to the accumulated released energy of surrounding rock, the energy density of the microseismic event is analyzed by adopting a nuclear density analysis method so as to achieve the purpose of studying the fracture development of the surrounding rock. The analysis results show that the maximum roof damage height is 87.8 m, and the maximum floor damage depth is 21.7 m. The maximum values all appear in the square stage of the working face, at which the roof water inrush risk is the highest. In the square stage, the roof-bearing rock beam is damaged, abnormal pressure occurs, and the damage degree of the roof, floor and advanced support is intensified. The results verify the existence of the stress breakdown effect. The sandy mudstone 48.3 m away from the roof of the working face is the key layer of the roof water barrier. The siltstone 67.7 m away from the roof is the breakdown control layer. The sandy mudstone 26.6 m away from the floor is the key layer of the floor water barrier. The results of microseismic monitoring and analysis are verified by bottom borehole peeping. The results show that the floor damage depth in the square area is more than 18 m, and the floor damage depth in other areas is 12-18 m. These results are consistent with the microseismic monitoring results.

A negative ionospheric storm occurred over the North American sector on 4 November 2021. By the integration of hemispheric power (HP), Ionospheric Connection Explorer (ICON), Global‐scale Observations of the Limb and Disk and global navigation satellite system total electron content (TEC) observations, a complete observation chain is obtained for the first time. At 07:11 UT, prominent energy was input into high latitudes. From 11:51 to 15:49 UT, strong southwestward neutral wind was observed by ICON over the south of North America, followed by significant ∑O/N2 depletion (60%) and temperature enhancement (∼300 K at ∼150 km). TEC depletion started at 12:00 UT in the northeastern North America and expanded to most of the United States. The TEC reduction showed the latitudinally tilted structure similar to that of ∑O/N2 depletion and temperature enhancement, which was shaped by the southwestward neutral wind. The thermosphere‐ionosphere‐electrodynamics general circulation model (TIEGCM) reproduced the observations qualitatively and was utilized to investigate the details of the negative storm generation and evolution processes. Strong equatorward wind and ∑O/N2 depletion reached the North America at midnight, much earlier than the TEC depletion, which began at sunrise. At 90°W, the time delay between TEC and ∑O/N2 depletions increased from ∼3.3 hr at 30°N to ∼11 hr at 60°N. Several factors contributed to the time delay including the time difference between midnight and sunrise, ∑O/N2 transport direction, westward wind and the variation of solar elevation angle with latitude. Plain Language Summary: During geomagnetic storms, the increase/decrease of ionospheric plasma density during geomagnetic storms relative to geomagnetic calm period is called positive/negative ionospheric storms. Due to the lack of observations of thermospheric properties, there are very few studies on negative storms over middle latitudes using direct neutral wind and temperature observations. This paper investigates the negative storm over the North American sector on 4 November 2021. A complete observation chain of the negative storm generating processes is presented by using hemispherical power index, neutral wind, neutral temperature and composition, and total electron content (TEC) measurements. Strong southward and westward neutral wind were observed by Ionospheric Connection Explorer satellite over middle and low latitudes. Global‐scale Observations of the Limb and Disk satellite also recorded prominent thermospheric composition changes and temperature enhancement. Subsequently, TEC depletion occurred was consistent with that of neutral temperature and composition variations. A numerical model is employed to uncover the details of the processes. Thermospheric composition changes occurred between 40° and 60°N firstly at 06:00 UT in the North America sector while TEC depletion appeared at 12:00 UT. There were four factors contributed to the time lag between TEC and composition changes including the time difference between midnight and sunrise, composition transport, westward wind and solar elevation angle. Key Points: During a negative storm, strong southwestward neutral winds and prominent ∑O/N2 depletion were observed by Ionospheric Connection Explorer and Global‐scale Observations of the Limb and Disk, respectivelyA complete observation chain of the negative ionospheric storm generation at middle latitudes is first established for the first timeThe time delay between TEC and ∑O/N2 depletions increased from 3.3 hr at 30°N to ∼11 hr at 60°N [ABSTRACT FROM AUTHOR]

Taking 1604 working face of Guhanshan Mine as the research background, by means of a high-precision micro-seismic monitoring system and numerical simulation, the dynamic failure characteristics of the surrounding rock and the danger of water inrush from the floor during the mining of the working face are studied. The results show that the asymmetrical energy release phenomenon occurs along the empty side and along the solid coal side of the bottom floor rock mass along the two sides of the working face. Among them, the bottom floor rock mass along the solid coal side has the largest damage scale with a depth of about 30 m. At a position of 12 m under the floor and 8 m in the inner staggered transportation lane, the energy density value of the surrounding rock is between 5-50 J/m2. Combined with the monitoring results of the surrounding rock deformation of the roadway, it is considered that the bottom pumping lane is located at this position and the mining disturbance is lower; the pumping roadway is located directly below the transport roadway or outside the transport roadway. The energy density of the surrounding rock release is greater than 100 J/m2, and the degree of disturbance is high. The numerical simulation results show that the bottom slot is located in the pressure relief area of the floor when the staggered groove is 8 m, which is located directly below the groove and is in the stress concentration area when the staggered groove is outside.

During geomagnetic storms, ionospheric storms can be driven by several mechanisms. Observations performed using ground- and space-based instruments were used to reveal the driver of the positive ionospheric storm over the South American sector during the 4 November 2021 geomagnetic storm. The positive storm appeared from 10:30 UT to 18:00 UT and covered the region from 40°S to 20°N. The maximum magnitudes of TEC (Total Electron Content) enhancement and relative TEC enhancement were about 20 TECU and 100%, respectively. Defense Meteorological Satellite Program (DMSP) also observed a significant electron density increase over South America and the eastern Pacific Ocean. In the meantime, about 50% ∑O/N2 enhancement was observed by the Global-scale Observations of the Limb and Disk (GOLD) satellite at low latitudes. Ionosonde observations (AS00Q and CAJ2M) registered an ~80 km uplift in F2 peak height (HmF2) and a prominent F2 peak electron density (NmF2) increase ~3 h after the uplift. A prominent enhancement in the cross-polar cap potential (CPCP) in the southern hemisphere was also observed by Super Dual Auroral Radar Network (SuperDARN) one hour earlier than the HmF2 uplift. Measurements of the Ionospheric Connection Explorer satellite (ICON) showed that the outward E×B drift was enhanced significantly and that the horizontal ion drift was poleward. According to the ICON ion drift observations, the HmF2 uplift was caused by an electric field rather than equatorward neutral wind. We propose that the enhanced eastward electric field dominated the positive ionospheric storm and that the thermospheric composition variation may have also contributed. [ABSTRACT FROM AUTHOR]

A thermospheric O and N2 column density ratio (∑O/N2) depletion with long‐duration (>16 hr) was observed by the Global‐scale Observations of the Limb and Disk at the Atlantic longitudes (75° ${}^{\circ}$W–20° ${}^{\circ}$W) and middle latitudes (20N–50° ${}^{\circ}$N) during the recovery phase of the 8 June 2019 geomagnetic storm. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations reproduced the ∑O/N2 depletion patterns with a similar magnitude, and indicated that the composition recovery at middle latitudes began several hours after the beginning of the recovery phase of the geomagnetic storm. The TIEGCM simulations enable quantitative analysis of the physical mechanisms driving the middle‐latitude composition changes during the storm recovery phase. This analysis indicates that vertical advection and molecular diffusion dominated the initial recovery of composition perturbations at middle latitudes. Horizontal advection was also a main driver in the initial recovery of composition, but its contribution decreased rapidly. In the late recovery phase, the composition recovery was mainly determined by horizontal advection. In comparison, vertical advection and molecular diffusion played a much less important role. Plain Language Summary: The column density ratio of atomic oxygen (O) to molecular nitrogen (N2) (∑O/N2) is an important indicator that reflects the response of thermospheric composition to geomagnetic disturbances. During the recovery phase of the geomagnetic storm on 8 June 2019, a long‐duration ∑O/N2 depletion was observed by geostationary orbit observations. This triggers some important questions. First, why the depletion persisted for such a long time? And, second, what are the physical mechanisms for the recovery of the depletion? Numerical simulations replicated the general morphology and evolution of the observed ∑O/N2 depletion. Diagnostic analysis of the simulations provides insight into the relative importance of horizontal advection, vertical advection and molecular diffusion in determining the recovery of middle latitude thermospheric composition perturbations. Model outputs show that these forcing terms have different effects on O and N2 perturbations at different times during the recovery phase of the geomagnetic storm. Key Points: A long‐duration ∑O/N2 depletion was observed by Global‐scale Observations of the Limb and Disk over the Atlantic Ocean during the recovery phase of a geomagnetic stormVertical advection and molecular diffusion dominated the initial recovery of the ∑O/N2 depletionIn the late recovery phase, the recovery of the perturbations was mainly determined by horizontal advection [ABSTRACT FROM AUTHOR]