Relativistic electron injections are one of the mechanisms of enhancements of relativistic (≥ 0.5 MeV) electrons in the Earth’s outer radiation belt. In this study, we present the statistical observation of 600 keV electron injections in the outer radiation belt using the Van Allen Probes data. Based on the different injection characteristics, 600 keV electron injections in the outer radiation belt are divided into “pulsed electron injections” and “non-pulsed electron injections”. The 600 keV electron injections are observed at over 4.5 < L < 6.4 under the geomagnetic conditions of 450 nT < AE < 1450 nT. L ~ 4.5 is an inward limit for 600 keV electron injections. Before the electron injections, the flux negative L shell gradient for ≤ 0.6 MeV electrons or the low electron fluxes in the injected region are observed. For 600 keV electron injections at different L shells, the source populations from the Earth’s plasma sheet are different. For 600 keV electron injections at higher L shells, the source populations are higher energy electrons (~ 200 keV at X ~ –9 RE), while the source populations for 600 keV electron injections at lower L shells are lower energy electrons (~ 80 keV at X ~ –9 RE). These results are important for our further understanding of electron injections and rapid enhancements of 600 keV electrons in the Earth’s outer radiation belt.
Widespread magmatism, metamorphic core complexes (MCCs), and significant lithospheric thinning occurred during the Mesozoic in the North China Craton (NCC). It has been suggested that the coeval exhumation of MCCs with uniform NW-SE shear senses and magmatism probably result from the decratonization event during the paleo-Pacific Plate retreat. Here we use 2-D finite element thermo-mechanical numerical models to investigate critical parameters controlling the formation of MCCs under far-field extensional stress. We observe three end-member deformation modes: MCC mode, symmetric-dome mode, and pure-shear mode. The MCC mode requires Moho temperature ≥ 700 °C and extensional strain rate ≥ 5×10-16 s-1, implying that the lithosphere had already been thinned when the MCC was formed in the Mesozoic. Combining with the widespread MCCs with the same NW-SE extension direction in the NCC, we suggest that MCCs are surface expressions of both large-scale extension and craton destruction and that rollback of the paleo-Pacific slab might be the common driving force.
The cause for substorm onset has not been understood. Chen CX (2016) proposed an entropy switch model, in which substorm onset is the result of the development of interchange instability. In this study, we try to find observation evidence for this model using Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. We examine two events, one with and the other without a streamer before substorm onset. In contrast to the stable magnetosphere, where the total magnetic field strength is a decreasing function and entropy is an increasing function of the down tail distance, in both events the total magnetic field strength and entropy are reversed before substorm onset. After onset, the total magnetic field strength, entropy, and other plasma quantities fluctuate. In addition, a statistical study is performed. Confined the events with THEMIS satellites location in the down tail region between 8~12 earth radius, and 3 hours before and after midnight, an occurrence rate of the total magnetic field strength reversal is found to be 69% and an occurrence rate of entropy reversal is found to be 77% of the total 205 events.
Recently, kilometer-scale Martian ionospheric irregularities have been measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission (Fowler et al., 2020). In this study, we carried out a simulation of kilometer-scale ionospheric irregularities at Mars. A uniform zonal neutral wind was adopted in this model, and the seeding source is the cosinusoidal perturbation of the plasma density. Results show that the vertical electric field shear could be induced when the plasma density perturbation occurred. The vertical electric field shear causes the velocity shear of the plasma between the topside and bottomside ionosphere. Then, the velocity shear of the plasma between the topside and bottomside ionosphere could produce smaller-scale (kilometer-scale) ionospheric irregularities than the previous simulation (Jiang et al., 2021). The kilometer-scale variations in the plasma density and magnetic field profiles (along the altitude) are comparable with observations.
This paper studies inter-annual variations of 6.5-Day Waves (6.5DWs) in 20110 km between 52°S52°N during March 2002January 2021 and their relations with equatorial stratospheric Quasi-Biennial Oscillation (QBO). 6.5DWs’ amplitudes in temperature are calculated based on SABER/TIMED observations. QBO zonal winds are obtained from ERA5 reanalysis dataset. QBO phases are derived from Empirical Orthogonal Functions (EOF) method. Wavelet analysis of 6.5DW variations demonstrates obvious spectral maximums around 2838 months in 32°52°N and 2630 months in 32°52°S. In the Northern Hemisphere, peak periods get longer poleward, while they remain unchanged with latitude in the Southern Hemisphere. Residual 6.5DWs’ amplitudes are calculated by removing composite amplitudes from 6.5DWs’ amplitudes. Comparisons between QBO and the monthly maximum residual 6.5DWs’ amplitudes (A_Mmax) show clear relations between QBO and 6.5DWs in both hemispheres, especially in the NH. When A_Mmax is large in the NH, mean QBO profile is easterly at all levels from 70 to 5 hPa. When it’s weak, mean QBO wind is weak westerly below 30 hPa. Linear Pearson correlation coefficients between QBO phases and A_Mmax show large positive values in 60110 km between 20°52°N in April and around 64 km at 24°S in February, and large negative values from 80 to 110 km between 20°N50°N in August and at 96106 km between 20°S44°S in February. These results indicate quantitative relations between QBO and 6.5DWs and provide credible evidences for further studies of QBO modulations on long-term variations of 6.5DWs.
The tropospheric impact of Arctic ozone loss events is still debatable. Using the ERA5 reanalysis and long-term integration by a climate-chemistry coupled model (CESM2-WACCM), the frequency of the Arctic ozone loss event and its tropospheric impacts are investigated in this study. On average, Arctic ozone loss events occur once in early spring every 14-15 years in both the ERA5 and the model. It is estimated from both ERA5 and modelling that roughly 40% of the strong polar vortex events in March are coupled with Arctic ozone loss and the remaining 60% are uncoupled. The composite difference between the two samples might be attributed to the pure impact of the Arctic ozone loss with the interference of strong polar vortices’ impact removed. Arctic ozone loss is accompanied by an increase in total ozone in midlatitudes with the maximum center in Central North Pacific. Comparing Arctic ozone loss events and pure strong polar vortex events uncoupled with ozone loss, the stratospheric NAM reverses earlier for the former. For the pure strong vortex events in early spring without Arctic ozone loss, the cold anomalies can extent from the stratosphere to the middle troposphere. The near surface warm anomalies are biased toward the continents during strong polar vortex events without ozone loss. In contrast, ozone loss in spring during the other 40% strong polar vortex events favors a concurrent and delayed warming of the near surface over the Arctic and its neighboring areas due to vertical redistribution of the solar radiation by the change in the ozone.
The Anninghe fault is a large left-lateral strike-slip fault in southwestern China. It has controlled the deposition and magmatic activities since the Proterozoic, and has frequent seismic activities. The Mianning-Xichang segment of the Anninghe fault is a seismic gap and has been locked with high stress. Many studies suggest that this segment has a great potential for large earthquakes (magnitude>7). We obtained three vertical profiles of the Anninghe fault (between Mianning and Xichang) based on inversion of P-wave first arrival times. The travel time data were picked from seismograms generated by Methane Gaseous Source and recorded by three linearly distributed across-fault dense arrays. The inversion results show that the P-wave velocity structures at depths of 0-2 km corresponds well with the local lithology. The Quaternary sediments have low seismic velocities, while the igneous rocks, metamorphic rocks and bedrocks have high seismic velocities. Then we further discuss the fault activities of the two fault branches of Anninghe fault in the study region based on the small earthquakes (magnitude between M_L 0.5 and M_L 2.5) detected by the Xichang array. The eastern fault branch is more active than the western branch, and the fault activities in the eastern branch are different on the northern and southern segments at the border of 〖28〗^° 〖21〗^' N. The obtained high-resolution models are essential for future earthquake rupture simulation and hazard assessment of the Anninghe fault zone. Future studies of velocity models at deeper depths may further explain the complex fault activities in the study region.
Planetary magnetosheaths are characterized by high plasma wave and turbulence activity. The Martian magnetosheath is no exception; both upstream and locally generated plasma waves have been observed in the region between its bow shock and magnetic boundary layer, its induced magnetosphere. This statistical study of wave activity in the Martian magnetosheath is based on 12 years (2005–2016) of observations made during Mars Express (MEX) crossings of the planet’s magnetosheath — in particular, data on electron density and temperature data collected by the electron spectrometer (ELS) of the plasma analyzer (ASPERA-3) experiment on board the MEX spacecraft. A kurtosis parameter has been calculated for these plasma parameters. This value indicates intermittent behavior in the data when it is higher than 3 (the value for a normal or Gaussian distribution). The variation of wave activity occurrence has been analyzed in relation to solar cycle, Martian orbit, and distance to the bow shock. Non-Gaussian properties are observed in the magnetosheath of Mars on all analyzed scales, especially in those near the proton gyrofrequency in the upstream region of the Martian magnetosphere. We also report that non-Gaussian behavior is most prominent at the smaller scales (higher frequencies). A significant influence of the solar cycle was also observed; the kurtosis parameter is higher during declining and solar maximum phases, when the presence of disturbed solar wind conditions, caused by large scale solar wind structures, increases. The kurtosis decreases with increasing distance from the bow shock, which indicates that the intermittence level is higher near the bow shock. In the electron temperature data the kurtosis is higher near the perihelion due to the higher incidence of EUV when the planet is closer to the Sun, which causes a more extended exosphere, and consequently increases the wave activity in the magnetosheath and its upstream region. The extended exosphere seems to play a lower effect in the electron density data.
Energetic neutral atoms (ENAs) are produced by the neutralization of energetic ions formed by shock-accelerated gradual solar energetic particle events (SEP). These high-energy ENAs (HENAs) can reach the Earth earlier than the associated SEPs and thus can provide information about the SEPs at the lower corona. The HENA properties observed at Earth depend on the properties of the coronal mass ejection (CME)-driven shocks that accelerate the SEPs. Using a model of HENA production in a shock-accelerated SEP event, we semi-quantitatively investigate the energy-time spectrum of HENAs depending on the width, propagation speed, and direction of the shock, as well as the density and ion abundances of the lower corona. Compared to the baseline model parameters, the cases with a wider shock width angle or a higher coronal density would increase the HENA flux observed at the Earth, while the case with an Earth-propagating shock shows a softened HENA spectrum. The comparison of expected HENA fluxes in different cases with a flight-proven ENA instrument suggests that solar HENAs can feasibly be monitored with current technologies, which could provide a lead time of 2−3 hours for SEPs at a few MeV. We propose that monitoring of solar HENAs could provide a new method to forecast shock-driven SEP events that are capable of significant space weather impacts on the near-Earth environment.
The space-borne fluxgate magnetometer (FGM) requires regular in-flight calibration to obtain its zero offset. Recently, Wang GQ and Pan ZH (2021a) developed a new method for the zero offset calibration based on the properties of Alfvén waves. They found that an optimal offset line (OOL) exists in the offset cube for a pure Alfvén wave and that the zero offset can be determined by the intersection of at least two nonparallel OOLs. Because no pure Alfvén waves exist in the interplanetary magnetic field, calculation of the zero offset relies on the selection of highly Alfvénic fluctuation events. Here, we propose an automatic procedure to find highly Alfvénic fluctuations in the solar wind and calculate the zero offset. This procedure includes three parts: (1) selecting potential Alfvénic fluctuation events, (2) obtaining the OOL, and (3) determining the zero offset. We tested our automatic procedure by applying it to the magnetic field data measured by the FGM onboard the Venus Express. The tests revealed that our automatic procedure was able to achieve results as good as those determined by the Davis–Smith method. One advantage of our procedure is that the selection criteria and the process for selecting the highly Alfvénic fluctuation events are simpler. Our automatic procedure could also be applied to find fluctuation events for the Davis–Smith method.
Atmospheric stellar occultation observation technology is an advanced space-based detection technology that can measure the vertical distribution of trace gas composition, temperature, and aerosol content in a planet’s atmosphere. In this study, an inversion algorithm of the onion-peeling method was constructed to invert the transmittance obtained from the forward mask. The method used a three-dimensional ray-tracing simulation to obtain the transmission path of the light in the Earth’s atmosphere. The relevant parameters were then combined in the high-resolution transmission molecular absorption (HITRAN) database, and line-by-line integration was performed to calculate the atmospheric transmittance. The transmittance value was then used as an input to calculate the vertical distribution of oxygen molecules when using the single-wavelength inversion of the onion-peeling method. Finally, the oxygen molecule content was compared with the value attained by the Mass Spectrometer and Incoherent Scatter Radar Extended (MSISE00) atmospheric model to determine the relative error of our model. The maximum error was found to be 0.3%, which is low enough to verify the reliability of our algorithm. Using Global-scale Observations of the Limb and Disk (GOLD) measured data to invert the oxygen number density, we calculated its relative deviation from the published result to further verify the algorithm. The inversion result was affected by factors such as prior data, the absorption spectral line type, the ellipticity of the Earth, and the accuracy of the orbit. Analysis of these error-influencing factors showed that the seasons and the Earth’s ellipticity affected the accuracy of the model only 0.001% and could therefore be ignored. However, latitude and solar activity had a greater impact on accuracy, on the order of 0.1%. The absorption line type affected the accuracy of the model by as much as 1%. All three of these factors therefore need to be considered during the inversion process.
One of the most important dynamic processes in the middle and upper atmosphere, gravity waves (GWs) play a key role in determining global atmospheric circulation. Gravity wave potential energy (GW Ep) is an important parameter that characterizes GW intensity, so it is critical to understand its global distribution. In this paper, a deep learning algorithm (DeepLab V3+) is used to estimate the stratospheric GW Ep. The deep learning model inputs are ERA5 reanalysis datasets and GMTED2010 terrain data. GW Ep averaged over 20−30 km from 60°S−60°N, calculated by COSMIC radio occultation (RO) data, is used as the measured value corresponding to the model output. The results show that (1) this method can effectively estimate the zonal trend of GW Ep. However, the errors between the estimated and measured value of Ep are larger in low-latitude regions than in mid-latitude regions, possibly due to the large number of convolution operations used in the deep learning model. Additionally, the measured Ep has errors associated with interpolation to the grid; this tends to be amplified in low-latitude regions because the GW Ep is larger and the RO data are relatively sparse, affecting the training accuracy. (2) The estimated Ep shows seasonal variations, which are stronger in the winter hemisphere and weaker in the summer hemisphere. (3) The effect of quasi-biennial oscillation (QBO) can be clearly observed in the monthly variation of estimated GW Ep, and its QBO amplitude may be less than that of the measured Ep.
A method for reconstructing crustal velocity structure using the optimization of stacking receiver function amplitude in the depth domain, named common conversion amplitude (CCA) inversion, is presented. The conversion amplitude in the depth domain, which represents the impedance change in the medium, is obtained by assigning the receiver function amplitude to the corresponding conversion position where the P-to-S conversion occurred. Utilizing the conversion amplitude variation with depth as an optimization objective, imposing reliable prior constraints on the structural model frame and velocity range, and adopting a stepwise search inversion technique, this method efficiently weakens the tendency of easily falling into the local extremum in conventional receiver function inversion. Synthetic tests show that the CCA inversion can reconstruct complex crustal velocity structures well and is especially suitable for revealing crustal evolution by estimating diverse velocity distributions. Its performance in reconstructing crustal structure is superior to that of the conventional receiver function imaging method.
The purpose of this study is to explore nonhydrological mass transfer in China contient. For this purpose, gravity recovery and climate experiment (GRACE) data were obtained to study the spatial distribution of time variant gravity signals in China contient. Then, from auxiliary hydrological data processed according to the current hydrological model, a new more comprehensive hydrological model of China contient was constructed. Finally, the time variant signals of this new hydrological model were removed from the time variant gravity field computed from GRACE data, thus obtaining a description of the nonhydrological mass transfer of China contient. The physical sources and mechanisms of the resulting mass transfer are then discussed. The improved, more realistic, hydrological model used here was created by selecting the hydrological components with the best correlations in existing hydrological models, by use of correlation calculation, analysis, and comparison. This improved model includes water in soils and deeper strata, in the vegetation canopy, in lakes, snow, and glaciers, and in other water components (mainly reservoir storage, swamps, and rivers). The spatial distribution of the transfer signals due to nonhydrological mass in China contient was obtained by subtracting the combined hydrological model from the GRACE time-variable gravity field. The results show that the nonhydrological signals in China contient collected in GRACE data were mainly positive signals, and were distributed in the Bohai Rim and the northern and eastern parts of the Tibetan Plateau. The above nonhydrological mass transfer signals have been studied further and are discussed. The results show that the nonhydrological mass migration signals in the Bohai Rim region originate primarily from sea level change and marine sediment accumulation. The mass accumulation from Indian plate collision in the Tibetan Plateau appears to be the main reason for the increase in the residual gravity field in that region.
On 21 May 2021 (UTC), an MW 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau. The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since the 2008 Wenchuan earthquake, and especially in proximity to the seismic gaps on the east Kunlun fault. Here we use satellite interferometric synthetic aperture radar data and subpixel offset observations along the range directions to characterize the coseismic deformation of the earthquake. Range offset displacements depict clear surface ruptures with a total length of ~170 km involving two possible activated fault segments in the earthquake. Coseismic modeling results indicate that the earthquake was dominated by left-lateral strike-slip motions of up to 7 m within the top 12 km of the crust. The well-resolved slip variations are characterized by five major slip patches along strike and 64% of shallow slip deficit, suggesting a young seismogenic structure. Spatial–temporal changes of the postseismic deformation are mapped from early 6-day and 24-day InSAR observations, and are well explained by time-dependent afterslip models. Analysis of Global Navigation Satellite System (GNSS) velocity profiles and strain rates suggests that the eastward extrusion of plateau is diffusely distributed across the east Bayan Har block, but exhibits significant lateral heterogeneities, as evidenced by magnetotelluric observations. The block-wide distributed deformation of the east Bayan Har block along with the significant co- and post-seismic stress loadings from the Madoi earthquake imply high seismic risks along regional faults, especially the Tuosuo Lake and Maqên–Maqu segments of the Kunlun fault that are known as seismic gaps.
The Mesozoic Yanshanian Movement affected the tectonic evolution of the North China Craton (NCC). It is proposed that Mesozoic cratonic destruction peaked ~125 Ma, possibly influenced by subduction of the western Pacific Plate beneath the Euro-Asian Plate in the Early Cretaceous. The southern Jinzhou area in the eastern block of the NCC preserves clues about the tectonic events and related geological resources. Studies of the regional stress field evolution from the Cretaceous to the Cenozoic can enhance our understanding of the tectonics and dynamics of the NCC. Borehole image logging technology was used to identify and collect attitudes of tensile fractures from 11 boreholes; these were subdivided into four groups according to dip direction, i.e., NNW-SSE, NWW-SEE, W-E and NE-SW. The development of these fractures was controlled primarily by the regional tectonic stress field; temperature, lithology, and depth contributed to some extent. In 136–125 Ma in the Early Cretaceous, the area was characterized by extension that was oriented NNW-SSE and NWW-SEE; from 125–101 Ma the extension was oriented W-E; after 101 Ma it was NE-SW. This counterclockwise trend has persisted to the present, probably related to oblique subduction of the Pacific Plate, and is characterized by ongoing extension that is nearly N-S-oriented and NEE-SWW-oriented compression.