ALBERT

Description: Seismological studies generally suggest that the Earth’s inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth. Previous body-wave studies of the inner core have relied on ray tracing or waveform modeling using one-dimensional (1D) models. Here we present non-linear tomographic inversions of the inner core anisotropy using three-dimensional (3D) ray tracing, spline parameterization, and a large collection of PKP differential travel times. We adapt a pseudo-bending ray tracing (PBR) method in spherical coordinates for seismic rays that traverse the inner core (PKP(DF) phase). The method iteratively perturbs each discontinuity point and continuous segment of the ray through 3D earth structure so that its travel time is minimum. The 3D anisotropic structure of the inner core is approximated to the first order as 3D heterogeneous (but isotropic) structure for a given ray. The data are corrected using a scaled mantle tomographic model. The inner core anisotropy model obtained has the following major features. (1) The model has strong hemispherical and depth variation. The isotropic velocity in the topmost inner core is greater in quasi-eastern hemisphere (QEH) (40–160°E) than in quasi-western hemisphere (QWH) (other longitudes). The anisotropy is weak in QEH to the depth of 600–700 km below the inner core boundary (ICB), while in QWH, the anisotropy increases at much shallower depth (about 100–200 km below the ICB) to about 3–4%, then remains at about 2–4% throughout the rest of the inner core. (2) The anisotropy form changes abruptly (over a depth range of about 150 km) at the radius of about 600 km, slightly less than half of the inner core radius, forming a distinct inner inner core (IIC). The velocity in the IIC has maximums at equatorial and polar directions and minimum at an angle of about 40° from the equatorial plane. The velocity in the outer inner core (OIC), however, changes little for ray directions 0–40° from the equatorial plane. (3) Despite large variation of the anisotropy, the isotropic velocity (Voigt average) throughout the inner core is nearly uniform. The results suggest that the OIC is likely composed of the same type of iron crystals with uniform chemistry, but the IIC may be composed of a different type of crystal alignment, a different iron phase, or a different chemical composition. Our tests on model parameterization, mantle correction, and linear and non-linear inversion suggest the main features of our model are very robust. However, fine scale structures are likely to differ, particularly in the major transition zones, e.g., in the topmost QWH (isotropy to anisotropy), between OIC and IIC (change in the form of anisotropy), and between QEH and QWH in OIC (difference in anisotropy strength). Searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful.

Description: Arctic warming is affecting snow cover and soil hydrology, with consequences for carbon sequestration in tundra ecosystems. The scarcity of observations in the Arctic has limited our understanding of the impact of covarying environmental drivers on the carbon balance of tundra ecosystems. In this study, we address some of these uncertainties through a novel record of 119 site-years of summer data from eddy covariance towers representing dominant tundra vegetation types located on continuous permafrost in the Arctic. Here we found that earlier snowmelt was associated with more tundra net CO2 sequestration and higher gross primary productivity (GPP) only in June and July, but with lower net carbon sequestration and lower GPP in August. Although higher evapotranspiration (ET) can result in soil drying with the progression of the summer, we did not find significantly lower soil moisture with earlier snowmelt, nor evidence that water stress affected GPP in the late growing season. Our results suggest that the expected increased CO2 sequestration arising from Arctic warming and the associated increase in growing season length may not materialize if tundra ecosystems are not able to continue sequestering CO2 later in the season.

Description: This study presents observational findings of air-sea turbulent heat flux anomalies during the onset of the South China Sea summer monsoon (SCSSM) in 2021 and explains the mechanism for high-resolution heat flux variations. Turbulent heat flux anomalies are not uniform throughout the basin but indicate a significant regional disparity in the South China Sea (SCS), which also experiences evident year-to-year variability. Using buoy- and cruise-based air-sea measurements, high-temporal (hourly) anomalies in the latent heat flux during the SCSSM burst are unexpectedly determined by sea-air humidity differences under near-neutral marine atmospheric boundary layer (MABL) stability conditions, with secondary wind effects. However, latent heat anomalies are mainly induced by wind speed under mixed unstable and near-neutral MABL conditions. The sensible heat flux is much weaker, with its anomalies dominated by sea-air temperature differences regardless of the boundary layer condition. The observational results are used to examine the discrepancies in turbulent heat fluxes and associated air-sea variables in reanalysis products. The comparisons indicate that latent and sensible heat fluxes in the reanalysis are overestimated by approximately 52 Wm〈sup〉-2〈/sup〉 and 3 Wm〈sup〉-2〈/sup〉, respectively. These overestimations are mainly induced by higher sea-air humidity/temperature estimates. The relative humidity is underestimated by approximately 6.4% in two high-resolution reanalysis products. The higher SST (near-surface specific humidity) and lower air temperature (specific air humidity) eventually lead to higher estimates of sea-air humidity/temperature (2.2 g·kg〈sup〉-1〈/sup〉/0.6 °C), which are the dominant factors controlling the variations in the air-sea turbulent heat fluxes.

Description: On May 22, 2021, an Mw7.4 earthquake occurred in Maduo, Qinghai, China. The epicenter was located at 34.59 degrees north latitude and 98.34 degrees east longitude. This paper uses ASF HyP3 and MintPy software to conduct time-series InSAR analysis by using the Sentinel-1 SAR images from 2018 to 2023, and then to study the temporal and spatial distribution of regional crustal deformation and the distribution of the seismic fault ruptures. The time-series InSAR analysis are taken in three groups: Pre-earthquake period from January 2018 to May 2021, Earthquake onset period from April 2021 to June 2021, and Post-earthquake period From June 2021 to January 2023. The LOS(Light of Sight) velocity results of the time series INSAR analysis in the three groups and three dimension velocity of GPS stations in this area are fused to obtain regional tectonic strain rates, co-seismic fault slips, and post-seismic displacements. The results show that crustal deformation before the earthquake is small, the range of the coseismic surface rupture of the Maduo earthquake overlaps with the abnormal area of the regional strain field obtained, and the post-seismic viscoelastic deformation is strongly correlated with Maduo earthquake fault.

Description: As the third pole of the earth, the Qinghai-Tibet Plateau plays an important role in the formation and evolution of climate. To clarify the impact of road engineering, hydropower development projects and mineral development projects on the ecological security barrier system of the Qinghai-Tibet Plateau is the basis and premise of strengthening the ecological environment protection of the Qinghai-Tibet Plateau. The impacts of major construction projects on the Qinghai-Tibet Plateau on water conservation, soil and water conservation, carbon sequestration, climate change, and biodiversity were studied. The research results will provide scientific support for the optimization of the ecological security barrier system and functional areas of the Qinghai-Tibet Plateau, and are of great significance for promoting the sustainable development of the ecological environment of the Qinghai-Tibet Plateau.

Description: Radiative forcing by aerosol-cloud interaction (ACI) remains the largest uncertainty in climate projection based on the IPCC AR6 report in 2021. Many Earth system models tend to overestimate aerosol effective radiative forcing (ERF〈sub〉aer〈/sub〉) mainly because of the overly strong ACI forcing, including Department of Energy’s Energy Exascale Earth System Model (E3SM). In the effort to developing E3SM v3, we incorporated a new cloud microphysics scheme - the Predicted Particles Properties (P3) and the improved the deep convective wet removal treatments, aiming at providing better simulations of clouds, radiation, and ACI. We find that comparing with the original Morrison-Gettelman (MG2) scheme, the P3 improves shortwave cloud radiative forcing by over 1 W m〈sup〉-2〈/sup〉 and reduces ERF〈sub〉aer〈/sub〉 by 0.17 W m〈sup〉-2〈/sup〉 in global mean. By improving aerosol wet removal treatments for deep convection (e.g., cloud-borne aerosol detrainment, aerosol secondary activation, and cloud-borne aerosol removal), we effectively decrease the overestimation of aerosol burden and lifetime, and reduce the positive biases in aerosol optical depth and aerosol mass concentration. The resultant direct and indirect forcing components of ERF〈sub〉aer〈/sub〉 are significantly decreased. With some further turning in the minimal cloud droplet number concentrations (Nc), the autoconversion Nc exponent, and the subgrid factor for ice nucleation in cirrus clouds, we can achieve an aerosol forcing of about -0.9 W m〈sup〉-2〈/sup〉 which is well within the reference range by IPCC AR6 report. Such effort addresses the outstanding issue of E3SM - unreasonably strong ERF〈sub〉aer〈/sub〉, which would help reproduce the global temperature trend since the industrial revolution.

Description: In this paper, a point target analysis method is developed for measuring the slant range from SAR satellite to the ground corner reflector. By using the pre-measured coordinate of the corner reflector and the precise orbit of SAR satellite, the theoretical slant range can be calculated, and the residual of the corrected slant range measurement by point target analysis is then obtained. For repeated SAR images over corner reflectors, the time series of the residual of measured slant ranges can be formed and used to detect displacements of corner reflectors. This method has been used to analyze five corner reflectors in Shanghai by using tens of Sentinel-1A SAR images. All the five corner reflectors are in same shape and size, which is triangular trihedral with inner-leg of 1.2 meter. Two of the five corner reflectors are located on stable ground, and three of them are located on Shanghai Yangtze River Bridge. The results show that the average standard deviation of the residual is about 0.15m, and it is affected by the nearby scattering environment of the individual corner reflector. The vibration of the bridge leads to larger standard deviations of the residuals. In addition, re-setup experiments of the two ground corner reflectors are conducted, they are raised up by 0.10m intentionally, which can be detected successfully through analysis of the residual time series. This method can be used to monitor large displacement of ground movements, such as landslides and movements of mining dams, by using high resolution SAR images.

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: The multi-methods were used to analyze the factors affecting the change of water and sediment, and the contribution rate of human activities and climate change to the impact of water and sediment using the data of water and sediment and remote sensing images from five hydrological stations in the upper reaches of the Yellow River from 1964 to 2019. Both runoff and sediment load in the upper reaches of the mainstem Yellow River showed a decreasing trend, with a small decrease in runoff and a significant decrease in sand transport in the last decade. The multi-year average sand transport at Guide, Xunhua and Xiaochuan stations greatly reduced. The runoff of the upper Yellow River changed significantly since 1986, and the sediment load were mostly changed significantly in 1969, 1986 and 2004, which coincide with the operation time of the large cascade reservoirs. Moreover, there is a cyclical pattern of runoff and sediment load in the upper reaches of the Yellow River, with 8a, 16a, 22a and 36a cycles in runoff and 4-8a, 18-21a, 27a and 35-39a cycles in sediment load. The construction of cascade reservoirs had an impact on the peak flood pattern, which reduced the annual runoff by 36% in the five years before and after the construction of Longyangxia Reservoir and Lijiaxia Reservoir. In general, water and sediment in the upper reaches of the Yellow River were affected by cascade reservoir construction, conversion of farmland to grassland and climate change.