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SummaryTime-varying gravity fields play a crucial role in understanding and analyzing geodynamic processes, particularly the migration of matter across the Earth's surface. However, the current limitations in spatiotemporal resolution hinder their accurate representation. In this context, the use of a giant constellation of low-orbit satellites holds great potential for accurately recovering time-varying gravity fields with high spatiotemporal resolution. Based on the orbital parameters of 5199 satellites in 123 different orbital planes in the first phase configuration of the Starlink constellation and the orbital parameters of the Bender constellation in the next generation gravity mission, we conducted a closed-loop simulation to analyze the recovery ability of time-varying gravity field in 9 days using the short-arc integral method. The errors of aliasing AOHIS signal (Atmosphere, Ocean, Hydrology, Ice, and Solid Earth), ocean tide models, orbit positions, inter-satellite range rates, and accelerometer observations were considered in the numerical simulation. Compared with the Bender constellation, the Starlink-like constellation can effectively decrease the aliasing errors in the spatial- and frequency-domain when the observation noise is not considered. The Starlink-like constellation can also effectively improve the reliability of low-degree coefficients (below degree 15) of retrieved time-varying gravity field models and present higher time resolution (within 9 days) for the full degree spherical harmonic solutions than the Bender constellation when the observation noise is considered. The aliasing effect on the low-degree part of the Bender constellation can be significantly decreased by combining the Starlink-like and Bender constellations, and the accuracy of the recovered time-varying gravity field within degree 30 can be improved by about 0.5 ∼ 1 order of magnitude. Our results can provide a technical reference for the design of future gravity satellite mission.

Efficient implementation of equivalent medium parameterization in finite-difference seismic wave simulation methods

Geophysical Journal International - Thu, 08/15/2024 - 00:00

SummaryGrid point discretization of the model has a significant impact on the accuracy of finite-difference seismic waveform simulations. Discretizing the discontinuous velocity model using local point medium parameters can lead to artifact diffraction caused by the stair-step representation and inaccuracies in calculated waveforms due to interface errors, particularly evident when employing coarse grids. To accurately represent model interfaces and reduce interface errors in finite-difference calculations, various equivalent medium parametrization methods have been developed in recent years. Most of these methods require volume-integrated averaging calculations of the medium parameter values within grid cells. The simplest way to achieve this volume averaging is to apply numerical integration averaging to all grid cells. However, this approach demands considerable computational time. To address this computational challenge, we propose employing a set of auxiliary grids to identify which grid cells intersected by the welded interface and perform volume averaging only on these specific cells, thereby reducing unnecessary computational overhead. Additionally, we present a three-dimensional tilted transversely isotropic equivalent medium parameterization method, which effectively suppresses interface errors and artefact diffraction under the application of coarse grids. We also provide an approach for computing the normal direction of the interface, which is essential for the tilted transversely isotropic equivalent medium parameterization. Numerical tests validate the accuracy of the tilted transversely isotropic equivalent medium parameterization method and demonstrate the practicality of the implementation proposed in this paper for complex models.

Combining evolutionary computation with machine learning technique for improved short-term prediction of UT1-UTC and length-of-day

Earth,Planets and Space - Thu, 08/15/2024 - 00:00

Over the years, prediction techniques for the highly variable angular velocity of the Earth represented by Earth's rotation (UT1-UTC) and length-of-day (LOD) have been continuously improved. This is because ma...

What to know about the MyShake app, California's earthquake warning system

Phys.org: Earth science - Wed, 08/14/2024 - 20:08

With the unpredictable and destructive nature of earthquakes, a few extra seconds of notice can make all the difference in the world.

Marine heat waves in the Baltic Sea: Researchers investigate causes and effects

Phys.org: Earth science - Wed, 08/14/2024 - 19:22

Marine heat waves—periods in which the upper water layers in the sea temporarily become exceptionally warm—are occurring with increasing frequency worldwide. Recent studies by the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) have now confirmed this trend also for the Baltic Sea. The first study is published in the journal Climate Dynamics.

Geochemistry study links ancient anorthosites to early Earth's hot subduction

Phys.org: Earth science - Wed, 08/14/2024 - 19:22

A team of researchers has made strides in understanding the formation of massif-type anorthosites, enigmatic rocks that only formed during the middle part of Earth's history. These plagioclase-rich igneous rock formations, which can cover areas as large as 42,000 square kilometers and host titanium ore deposits, have puzzled scientists for decades due to conflicting theories about their origins.

Tropical Atlantic mixing rewrites climate pattern rules

Phys.org: Earth science - Wed, 08/14/2024 - 19:13

The churning of the upper ocean in the tropics of the Atlantic Ocean plays a crucial role in shaping long-term climate patterns across the world, a new study has found.

Deep reinforcement learning-based attitude control for spacecraft using control moment gyros

Recent articles in Advances in Space Research - Wed, 08/14/2024 - 19:10

Publication date: Available online 7 August 2024

Source: Advances in Space Research

Author(s): Snyoll Oghim, Junwoo Park, Hyochoong Bang, Henzeh Leeghim

Analysis of the background signal in Tianwen-1 MINPA

Recent articles in Advances in Space Research - Wed, 08/14/2024 - 19:10

Publication date: Available online 7 August 2024

Source: Advances in Space Research

Author(s): Ziyang Wang, Bin Miao, Yuming Wang, Chenglong Shen, Linggao Kong, Wenya Li, Binbin Tang, Jijie Ma, Fuhao Qiao, Limin Wang, Aibing Zhang, Lei Li