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: 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: 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: For the purpose of orbit validation, currently, many low Earth orbit (LEO) satellites of Earth observation missions are equipped with laser retro-reflectors. These Satellites Laser Ranging (SLR) observations exhibit a great potential to improve the accuracy of the SLR-based terrestrial reference frame, which is only realized by spherical geodetic satellites at present. How to weigh the SLR observations collected by different LEO satellites is always a troublesome issue when processing these observations. The purpose of this study is to optimize the integration of multi-LEO satellite SLR solutions by adjusting the weights of the observations using the Helmert Variance component estimation (VCE). The SLR observations of seven LEO satellites from three typical LEO missions: GRACE-Follow-On, Swarm, and Sentinel-3, are processed. The results indicate that the coordinate accuracy of SLR stations is significantly improved by 21% after applying VCE, while the improvement for Earth pole coordinates can reach 34%. We find that classifying the observations by satellite-station pair in the VCE processing outperforms the satellite-specific or station-specific observations classification. We also investigate the impact of range bias parameterization on the VCE performance. In addition, considering a steep rise in the computational time when using VCE, we evaluate the feasibility of a simplified VCE method in SLR observation processing. The result indicates that the simplified VCE solution can present the same performance as the traditional VCE solution, but the computational efficiency is significantly improved by thirty times.

Description: The multiple scale atmospheric or oceanic prediction has been a challenging issue due to different dynamical and thermodynamic processes involved and the uncertainty inherent in highly nonlinear and stochastic forcing, such as the prediction of Asian summer monsoon (ASM) precipitation. The seamless prediction was proposed to address this issue. The idea behind this approach is that temporal averaging reduces the spread of the prediction ensemble but retains the approximate first moment, which effectively increases the signal-to-noise ratio of the prediction. In this study, the superiority of the seamless prediction was assessed for the ASM precipitation at timescales from days to weeks. The hindcasts from the European Center for Medium-Range Weather Forecasts in the Subseasonal to Seasonal ensemble dataset were used for the detailed assessment. Results show significant advantages by the seamless approach in evaluating the ASM precipitation prediction on timescales ranging from two days to three weeks. Furthermore, the source of the average window predictability was analyzed for two lead times with significantly superior prediction accuracy: lead times of 4d4d and 3w3w. For 4d4d, the Madden–Julian Oscillation is dominant, while the role of the El Niño–Southern Oscillation phase becomes substantial for 3w3w. These results offer a detailed analysis for the prediction of ASM precipitation within a framework of seamless prediction, benefiting further interpretation of seamless prediction of ASM precipitation.

Description: For a generation or more, the mass spectrometry that developed at the frontier of molecular biology was worlds apart from isotope ratio mass spectrometry, a label-free approach done on optimized gas-source magnetic sector instruments. Recent studies show that electrospray-ionization Orbitraps and other mass spectrometers widely used in the life sciences can be fine-tuned for high-precision isotope ratio analysis. Since isotope patterns form everywhere in nature based on well-understood principles, intramolecular isotope measurements allow unique insights into a fascinating range of research topics. This Perspective introduces a wider readership to current topics in stable isotope research with the aim of discussing how soft-ionization mass spectrometry coupled with ultrahigh mass resolution can enable long-envisioned progress. We highlight novel prospects of observing isotopes in intact polar compounds and speculate on future directions of this adventure into the overlapping realms of biology, chemistry, and geology.

Description: The PPP-RTK system, which combines the advantages of precise point positioning (PPP) and real-time kinematic (RTK), is capable to provide a centimeter-level real-time positioning service for an unlimited number of users. Traditionally, the extended Kalman filter (EKF) is the conventional method for parameter estimation in the existing PPP-RTK system. Recently, an alternative method known as factor graph optimization (FGO), which fully leverages the time correlation among historical measurements, has the potential to further improve the accuracy and robustness of PPP-RTK solutions. In this contribution, the factor graph optimization-based PPP-RTK framework is developed, where the raw pseudorange and phase observations, the constructed time-differenced carrier-phase measurement, and precise atmospheric corrections are employed to construct a variety of factors in a real-time sliding -window for parameter optimal estimation. The continuously tracked ambiguities (often longer than window size) are estimated as a constant variable while the ambiguity resolution is conducted independently between epochs. The effectiveness of the proposed method is evaluated by several vehicular tests in an urban environment. Results indicate that the FGO-based PPP-RTK presents much more robust positioning solutions with accuracy improvements of 44% to 67% compared to the EKF-based solution. Besides, the contribution of the FGO method to ambiguity resolution is fully investigated and the results demonstrated that the proposed method could significantly improve the performance of ambiguity resolution by reducing the ambiguity search space and increasing the ratio and availability.

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: Red river fault (RRF) is a deep large active fault in the SE margin of the Tibetan Plateau. It is also the southwest boundary of the Sichuan-Yunnan block (SYB). SYB is a 2nd-order tectonic block, having been compressed by two 1st-order tectonic blocks, i.e. the Tibetan plateau block and the South China block. Several faults, such as Lijiang-Xiaojinhe fault (LXF) and Xiaojiang fault (XJF), intersect with RRF, which frequently results in occurrence of strong earthquakes in the intersection area. The structure and deformation have been influeneced by the confliction between the Indian plate and the Eurasian plate, as well as the obstruction of the South China block. In order to investigate the seismic anisotropy and the deformation pattern around the RRF, this study displays the S wave azimuthal anisotropy by the ambient noise data in the crust, also reveals seismic anisotropy by the S wave splitting of body waves. With this chance, this study will comprehensively coalesce multiple seismic data to analyze the S wave anisotropy in the the crust and the upper mantle. We will discuss the deformation pattern and possible material flow in the lithosphere or in the upper mantle. The deep tectionics and the motion pattern beneath the RRF will provide with key seismic constraints on the deep metallogeny, the deep seismogenic zone and the dynamic mechanisms [supported by NSFC Project 41730212 and National Key R&D Project of China 2017YFC1500304].

Description: Two preliminary gravity disturbance grids are derived from airborne gravity data collected by the National Geodetic Survey, USA as part of the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project. The data set does not include releases after 2020. Nominal altitude and spatial resolution of GRAV-D surveys are ~6.3 km and ~20 km, respectively. Actual flight altitude varies from ~ 5 km to ~11 km resulting in heterogeneous spatial resolution of the gravity signal from block to block, and within each block. The airborne data used in this study includes all collected flight lines as of December 2022 covering the US territory and the US-Canada Great Lakes region with extension of about 100 km into Canada and Mexico along land borders. The least-squares collocation is chosen for the 3-D interpolation to derive the two grids at a constant height of 6000 m and on the reference ellipsoid, respectively. The two grids are assessed by the Poisson downward continuation for consistence between the two grids; comparisons are made with ultra-high degree Global Gravitational Models (EGM2008, EIGEN6C-4, XGeoidRefA, and XGM2019e), and a regional geoid model is computed by including the terrestrial gravity data. An airborne-only geoid model is determined and evaluated using GPS-Levelling data over the US and satellite altimetry data over the Great Lakes region. The two new gravity grids are expected to contribute to geodetic, geophysical and geological applications, especially development of the North-American and Pacific Geopotential Datum of 2022 (NAPGD2022).