Description: Warm Deep Water intrusion over the Antarctic continental shelves threatens the Antarctic ice-sheet stability by enhancing the basal melting of ice shelves. In East Antarctica, the Antarctic Slope Current (ASC), along with the Antarctic Slope Front (ASF), acts as a potential vorticity barrier to prevent the warm modified Circumpolar Deep Water (mCDW) from ventilating the cold and fresh shelf. However, mCDW onshore transport is still observed within certain shelf regions, such as submarine troughs running perpendicular to the continental shelf. This study focuses on the dynamic mechanisms governing mCDW intrusion within a submarine trough over the fresh shelf regions, East Antarctica. Based on an idealized eddy-resolving coupled ocean-ice shelf model, two high resolution process-oriented numerical experiments are conducted to reveal the mechanisms responsible for the mCDW onshore transport. Three dynamic mechanisms governing cross-slope mCDW intrusion are identified: 1) the bottom pressure torque, 2) the topography beta spiral, and 3) the topography Rossby waves. These three mechanisms simultaneously govern the mCDW intrusion together. The bottom pressure torque plays a leading role in driving the time-mean onshore flow whose vertical structure is determined by the topography beta spiral, while the topography Rossby waves contribute to the high-frequency oscillations in the onshore volume and heat transport. The simulated spatial distribution and seasonality of mCDW intrusion qualitatively coincide with the observed mCDW intrusion over fresh shelf regions, East Antarctica. Both the topography beta spiral and the ASC play an important role in governing the seasonality of mCDW intrusion.

Description: The rapid convergence of PPP-RTK depends on the ionospheric correction including the accuracy and prior information. However, the traditional grid-based ionospheric model often uses fixed ionospheric prior information without taking into account the spatiotemporal diversity of the ionosphere, thus weakening the performance of PPP-RTK and limiting its application scenarios. In this study, a self-validation grid-based ionospheric model is proposed to improve the performance of PPP-RTK. A grid-based slant ionospheric model adapted to multi-scale networks is developed first with the careful consideration of receiver DCBs. Additionally, the ionosphere residuals obtained by self-validation of each reference station are assigned to the regional area based on distance and time, providing more reasonable ionospheric prior information for PPP-RTK. Then, PPP-RTK can achieve fast convergence with more reasonable ionospheric prior information. Experiments conducted under different ionospheric conditions demonstrate that the modified model significantly improves both the positioning accuracy and convergence time of PPP-RTK. During the ionosphere calm period, the average convergence time is reduced from 15.4s to 4.1s and the positioning accuracy is improved by 29.96% compared with the traditional grid model. Furthermore, during the ionosphere active period, the positioning accuracy is improved from (0.08, 0.10, 0.39) m to (0.05, 0.04, 0.12) m, with the improvement of 37.50%, 60.00%, 69.23% in the east, north and up directions, respectively.

Description: Earth’s climate experienced a major reorganization across the mid-Pleistocene transition (MPT) from 1.25 to 0.6 million years ago (Ma), when the dominant climate periodicity transitioned from 41-thousand years (kyr) to around 100-kyr. The MPT occurred without a concomitant shift in the orbital forcing rhythm, so it is related to internal climate dynamics rather than external astronomical forcing. Here, we investigate Asian climate dynamics associated with two extreme glacial loess coarsening events at the onset and middle of the MPT by combining new and existing grain size and magnetic susceptibility records from the Chinese Loess Plateau (CLP) spanning the last 1.6 Ma. We find that the two extreme glacial events were marked by a combination of intensified and expanded Asian aridity, winter monsoon strengthening, and distinct coarsening of loess layers L15 and L9-1 across the CLP. These two glacial intensifications coincided with notable Northern Hemisphere glacial ice sheet expansion at 1.25 and 0.9 Ma when the 100-kyr initiated and intensified. By integrating observations, land-sea correlations, and model simulations, we propose that these anomalously dry and windy Asian glacials were probably driven by an amplified terrestrial climate response to the coincident Northern Hemisphere ice sheet expansion. The shift from a 41-kyr to 100-kyr orbital periodicity across the MPT also occurred in our monsoon records, which reflect Northern Hemisphere ice sheet control on orbital-scale Asian climate variability, not just on extreme glacial Asian climate events at 1.25 and 0.9 Ma. Our study supports a close relationship between Asia-interior and global climate changes.

Description: The late Pliocene warm period, approximately 3.0 to 3.3 million years ago, is the most recent geological warm period in the Earth’s history. We used PlioMIP simulations together with proxy evidence to investigate the westerlies and paleomonsoon variation in the late Pliocene warm period. Compared to the pre-industrial period, the simulated westerlies generally shifted poleward with a dipole pattern, and were closely related to the change of the tropospheric meridional temperature gradient as a result of thermal structure adjustment. Convincing geological evidences from the North Pacific deep-sea sites supported the major features of the simulated North Pacific westerlies. The simulated global land monsoon system enhanced in terms of area and monsoon precipitation, mainly over northern Africa, Asia, and northern Australia, and was roughly consistent with the reconstructions. The anomalous inland water vapor transportation together with the variation of vertical moisture advection and evaporation, explains most of the global land monsoon changes. The poleward shift of the westerlies and global land monsoon systems corresponded to the poleward shift of the mean meridional circulation. The sea surface temperatures and sea ice contributed to the model spread of the westerly anomalies and global land monsoon. The poleward shift and intensified Asian monsoon, and/or an overall intensified global land monsoon in the late Pliocene warm period is hypothesized to contribute to the lowering of atmospheric CO〈sub〉2〈/sub〉 concentration and the subsequent onset of the sustained major Northern Hemisphere glaciation, through the impact on and feedback from the terrestrial carbon cycle process.

Description: Ice crystals play a crucial role in cloud optical properties and precipitation formation, as their shape affects their radiative properties, diffusional growth rate, fall speed, and collision efficiency. While the habit of ice crystals is determined by the ambient environment (i.e., temperature and humidity) in which they grow, it is also shaped by microphysical processes such as riming and aggregation. However, existing single-label classification algorithms face limitations when it comes to assigning multiple labels to a single ice crystal (i.e., a rimed column) or classifying the various components of an aggregated ice crystal.To overcome these limitations, this study introduces a novel multi-label classification system that considers both basic habits and physical processes leading to the observed ice crystal shapes. An object detection algorithm is presented that classifies each component of an aggregated ice crystal individually (including both basic habits and physical processes). The algorithm was trained on 18’000 ice crystal images and tested on 2300 ice crystal images captured by a holographic imager during the NASCENT campaign in Ny-Alesund, Svalbard. The algorithm offers a classification of both basic habits and microphysical processes with an accuracy of 86.5% and 81.4% respectively. The study results provide a deeper understanding of ice crystal shapes, which can improve precipitation and radiation estimates, and further contribute to advances in weather forecasting and climate research. Additionally, the algorithm's performance has shown a better generalization ability to predict ice crystal habits in new datasets compared to traditional deep learning algorithms.

Description: The central body of the Sanjiang lateral collision zone is located in western Yunnan, China, in the southeast margin of the Tibetan Plateau. The long evolutionary history resulted in numerous changes in crustal thickness, and complex deep tectonics in the study area, which also makes it an important metallogenic belt in China. With the seismic data recorded by a temporary array (SJ-Array) and permanent stations (Nov. 2018 ~ Dec. 2020), we build a high-precision earthquake catalog using a workflow of deep learning-based phase automatic picking, correlation, and location. We automatically detect and locate more than six times as many microseismic events as in the regular catalog, and the minimum magnitude of completeness MC was reduced from ML1.1 to ML0.1. Our high-precision earthquake catalog clearly reveals the characteristics of faults, and also provides more abundant effective records for S-wave splitting analysis. Using the S-wave splitting analysis technique and microseismic events, we obtain the spatial variation characteristics of upper crustal anisotropy of the Sanjiang lateral collision zone, with finer distribution and accuracy. In the interested area, it is shown that the dominant polarization of the fast S wave is NNW. In addition, the study area can be divided into three subzones from the west to the east according to the various mean polarizations. Our study demonstrates the local tectonic differences in the Sanjiang lateral collision zone and indicates that the crustal structure may be strongly controlled by the fault and block boundary strike.

Description: Low earth orbit (LEO) satellites have a natural advantage in sensing geocenter motion due to their low altitude. However, the complicated low-altitude space environment poses notable challenges for LEO orbit modeling, which can eventually impact the quality of derived geocenter motion. In this study, we focus on the LEO-based geocenter estimation. The geocenter motion is directly estimated in the LEO dynamic POD without incorporating ground GNSS observations. We use dynamic models instead of onboard accelerometer measurements for the non-gravitational forces in order to investigate the impact of orbit modeling on the geocenter estimation. Three year (2019-2021) onboard GNSS observations from seven LEO satellites in different orbits are processed. Our results indicate a strong correlation between LEO solar radiation pressure (SRP) modeling and estimated geocenter motion. The imperfections of a priori box-wing model can result in severe distortions of geocenter estimates, especially for the Z components. But by introducing a SRP scale factor, most orbital artifacts signal in the geocenter coordinates can be eliminated, and the time resolution of SRP scale factor have a negligible influence on the geocenter estimates. Furthermore, we compare our result with the solution based on the accelerometer measurements, and observed a good consistency in the annual signal characteristic of both solutions. We also evaluate the contribution of multiple LEO combination to the geocenter estimation. The combination of multiple LEO can significantly reduce the corelation between geocenter coordinates and orbit dynamic parameters, thereby improving the reliability of the derived geocenter motion.

Description: The continuing retreat of sea ice affects the Arctic mesoscale eddies, and its future evolution will strongly influence air-sea-ice interactions. However, knowledge of eddy activity is limited to sparse observations and coarse resolution models. How future eddies and their effects will evolve remains uncertain. Here, we apply the global unstructured model FESOM2 for 143 years of 4.5 km-Arctic simulations up to 2100 and 1 km-Arctic simulations for 5 years from 2010; 2090 to reveal the interactions between eddies, winds, sea ice and the energy budget of eddy kinetic energy (EKE) in a high resolution view. We demonstrate a significant increase in future Arctic EKE from 0-200 m, which is stronger in summer when sea ice melts. The future abundance of EKE can be explained by an increase in winter eddy generation and a decrease in summer eddy dissipation. This also leads to an enhancement of the horizontal velocity field, thus filling the Arctic Ocean with eddies in the future.

Description: In terms of inferring the terrestrial water storage (TWS) changes, the Global Navigation Satellite System (GNSS) and Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) observations have complementary advantages in spatio-temporal resolution, spatial coverage and spectrum sensitivity. We present a joint inversion strategy to infer TWS changes by simultaneously inverting GNSS vertical displacements and GRACE/GFO mass concentration (mascon) solutions in the Yangtze River Basin of China, for the period of January 2011 to December 2020. The GRACE/GFO-derived empirical covariance function is used as the regularization constraint matrix, and no external constraint information has been introduced to the joint inversion model. The performance of the joint inversion strategy is validated through the closed-loop simulation and external hydrological and meteorological data. The closed‐loop simulation study shows that the joint inversion results have higher accuracy and reliability than those of GNSS- or GRACE/GFO-only estimates and present more spatial detail than the traditional Laplacian matrix-based joint solutions. The estimated results of measured data demonstrate that the spatio-temporal distribution of TWS changes derived from GNSS and GRACE/GFO are generally in good agreement, but evident differences in the local scope can be observed due to the respective features of the two technologies. The joint inversion results can fully utilize the complementary advantages of GNSS and GRACE/GFO observations, which presents better agreements with hydrological and meteorological data compared to the GNSS- and GRACE/GFO-only estimates. Additionally, the joint solutions-based scale factors can be well used for signal attenuation and leakage correction of GRACE/GFO results.

Description: Ultra-low frequency (ULF) waves are known to radially diffuse hundreds-keV to few-MeV electrons in the magnetosphere, as the range of drift frequencies of such electrons overlaps with the frequencies of the waves, leading to resonant interactions. The theoretical framework for this process is described by analytic expressions of the resonant interactions between electrons and toroidal and poloidal ULF wave modes in a background magnetic field. However, most expressions of the radial diffusion rates are derived only for equatorially mirroring electrons, and are based on estimates of the power of ULF waves that are obtained either from spacecraft close to the equatorial plane or from the ground. We present recent statistical observations based on THEMIS and Arase multi-year in-situ observations, showing that the wave power in magnetic fluctuations is significantly enhanced away from the magnetic equator, consistent with models simulating the natural modes of oscillation of magnetospheric field lines. We present 3D particle simulation results, which show different effects of these waves on electrons of different pitch angles, as electrons mirroring at higher magnetic latitudes will experience considerably higher ULF wave fluctuations than equatorial electrons. We discuss implications of these observations for the estimation of radial diffusion rates and highlight the need for incorporating pitch-angle-dependent radial diffusion coefficients in global models of the radiation belts.