Investigation on variations of apparent stress in the region in and around the rupture volume preceding the occurrence of the 2021 Alaska MW8.2 earthquake

On July 29, 2021, a large earthquake of MW8.2 occurred south of the Alaska Peninsula. To investigate the spatial-temporal changes of crustal stress in the earthquake-stricken area before this event, we selected 159 earthquakes of 4.7 ≤ MW ≤ 6.9 that occurred in the epicentral region and its surroundings between January 1980 and June 2021 to study the temporal variation and spatial distribution of their apparent stress. In addition, we analyzed the correlation between seismic activities and Earth’s rotation and explored the seismogenic process of this earthquake. The crustal stress rose from January 2008 to December 2016. This period was followed by a sub-instability stage from January 2017 until the occurrence of the MW8.2 earthquake. The average rate of apparent stress change in the first five years of the stress increase period was roughly 2.3 times that in the last four years. The lateral distribution of the apparent stress shows that the areas with apparent stress greater than 1.0 MPa exhibited an expanding trend during the seismogenic process. The maximum apparent stress was located at the earthquake epicenter during the last four years. The distribution of the apparent stress in the E-W vertical cross section revealed that an apparent stress gap formed around the hypocenter during the first five years of the stress increase period, surrounded by areas of relatively high apparent stress. After the Alaska earthquake, most parts of this gap were filled in by aftershocks. The seismic activities during the sub-instability stage exhibited a significant correlation with Earth’s rotation.

Secular Effect of Geomagnetic Field and Gravitational Waves on Earth’s Satellite Orbits

In this work we study the perturbation and the change in the orbital elements due to the earth’s magnetic field and the gravitational waves. The acceleration components are derived in the radial, transverse to it and normal to the orbital plane. The equation for the rates of variation of the elements is formed and solved to find the secular variation in the element for polar and equatorial satellites.

Rotation of the Earth as a Triaxial Rigid Body

The Earth is taken as a triaxial rigid body, which rotates freely in the Euclidian space. The starting equations are the Euler dynamic equations, with A smaller than B and B smaller than C. The Euler equations are solved, and the numerical results are provided. In the calculations, the following parameters are used: (C-B)/A=0.003 273 53; (B-A)/C=0.000 021 96; (C-A)/B=0.003 295 49, and the mean angular velocity of the Earth's rotation, ω =0.000 072 921 15 rad/s. Calculations show that, besides the self-rotation of the Earth and the free Euler procession of its rotation, there exists the free nutation: the nutation angle, or the angle between the Earth's momentary rotation axis and the mean axis that periodically change with time. The free nutation is investigated.

Effect of Altitude, Right Ascension of Ascending Node and Inclination on Lifetime of Circular Lunar Orbits

The lifetime of a lunar satellite orbit is constrained by the non-spherical nature of the Moon’s gravity field. The orbital lifetime of lunar orbits depends significantly on the initial conditions of the orbit. Right ascension of ascending node (Ω) is one of the important orbital parameter affecting the orbital lifetime. In the present work we have analyzed the effect of Ω on the variation of lifetime with altitude for circular lunar orbits. It is found that at a particular initial altitude, a small increase in the altitude results in substantial increase in the orbital lifetime due to effect of the long periodic terms of Earth’s gravity on eccentricity and this transition altitude is different for different Ω. Further, it is observed that the variation of transition altitude with Ω follows a definite, but different trend for orbits with different inclinations. The transition altitude for polar orbits is found to be higher without the effect of Sun and Earth gravity. Variation of transition altitude with orbital inclination is also analyzed. Lifetimes of high altitude circular lunar orbits are analyzed and it is observed that at high altitudes lifetime decreases with altitude.

Remarks about External Forces Acting on Earth’s Rotation Axis

It is well known that a variation in the direction of Earth’s rotation axis is a real astronomical phenomenon, named nutation. It is interesting if a variation of this axis can take place only in intensity, in the simplest theoretical case of only two rigid body dynamics. This paper presents two positions of the Moon during its monthly orbit, where a sudden variation of Earth’s rotation axis in intensity can take place. The duration of this phenomenon is limited in time, maybe an instant or a day, and then a vortex can appear.

Earth: Review Article

Every year on 22 April, we have celebrated Earth Day and the beautiful planet we call home. Earth Day, established in 1970, has been used to highlight our planet’s environmental challenges and raise awareness of the importance of protecting our world for future generations [1]. To provide the protection of our planet, we should explain Earth’s environmental challenges to the best of our knowledge in frames of contemporary Geophysics. This paper gives a short overview of the developed Hypersphere World-Universe Model (WUM) and pay particular attention to the principal role of Dark Matter (DM) in the Earth’s life. In this manuscript, we discuss different aspects of the Earth: a condition of Young Earth before the Beginning of life on It;Internal Structure;“The 660-km Boundary” that we named Geomagma;Random Variations of Earth’s Rotational Speed on a daily basis;Origin of Moon;Expanding Earth;Internal Heating;Faint Young Sun paradox;Geocorona and Planetary Coronas;High-Energy Atmospheric Physics. WUM proposed principally different ways to solve the problems of Internal Heating, Origin of the Moon, and Faint Young Sun paradox based on DM core of the Earth. The Model revealed the fact that the Sun Activity causes the Geomagma Activity and, as a consequence, Random Variations of Earth’s Rotational Speed by the varying Sun’s magnetic field.

GPS天线相位中心校正对低轨卫星精密定轨的影响研究

执行各种低轨卫星任务的官方在公布定轨结果的同时并没有公布星载接收机的天线相位中心校正(PCV)信息,而PCV误差是星载GNSS精密定轨必须考虑的主要误差源之一。以GRACE卫星任务为例研究PCV误差对低轨卫星精密定轨的影响,利用GPS观测数据直接估计与相位误差有关的天线相位偏差(PCO)和PCV参数,然后利用K波段测距系统和卫星激光测距仪数据进行定轨评定。

JASON-2天线相位中心变化估计及1cm精密轨道确定

利用JASON-2卫星1a的实测星载GPS数据,基于非差简化动力学定轨残差,建立JASON-2接收机天线相位中心变化(PCV)模型。采用一个轨道重复周期的独立数据,分析JASON-2的PCV对定轨残差和定轨精度的影响。引入所得PCV确定JASON-2的1a的最终精密轨道,通过残差分析、重叠弧段对比以及与JPL外部精密轨道比较等方式对轨道精度进行评价,结果表明,所得PCV能够提升JASON-2卫星精密轨道精度且结果比较稳定,可以实现3DRMS接近2.5cm、径向RMS约1.0cm的定轨精度。

Low-latitude hydroclimate changes related to paleomagnetic variations during the Holocene in coastal southern China

The variations in precipitation have displayed a complex pattern in different regions since the mid-to-late-Holocene.Cloud formation processes may have a significant impact on precipitation,especially during the tropical marine processes and summer monsoon which convey abundant water vapor to coastal southern China and inland areas.Here,we use two 7500 year sedimentary records from the Pearl River Delta and the closed Maar Lake,respectively,in coastal southern China to reconstruct the mid-to-late-Holocene humidity variability and explore its possible relationship with cloud cover modulated by the Earth’s magnetic fields(EMF).Our proxy records document an apparent increase in wetness in coastal southern China between 3.0 and 1.8 kyr BP.This apparent increase in humidity appears to be consistent with the lower virtual axial dipole moments and,in turn,with a lower EMF.This correlation suggests that the EMF might have been superimposed on the weakened monsoon to regulate the mid-to-late-Holocene hydroclimate in coastal southern China through the medium of galactic cosmic rays,aerosols,and cloud cover.However,further investigations are needed to verify this interaction.

Dramatic variations in the Earth's main magnetic field during the 20th century

Analysis of the International Geomagnetic Reference Field (IGRF) 1900-2000 showsthat the Earth’s main magnetic field has changed dramatically during the 20th century: its dipole moment has decreased by 6.5% since 1900, the strengths of its quadrupole and octupole have increased by 95% and 74%, respectively, four major planetary-scale magnetic anomalies on the Earth’s surface have enhanced by 21%-56%, and the magnetic center has shifted 200 km towards the Pacific Ocean. These time-variation features are similar to the behavior before a geomagnetic polarity reversal.

Design and analysis of the Macao Science Satellite-1's laser retro-reflector array

The origin and spatial-temporal variation of the Earth’s magnetic field(EMF)is one of the important scientific problems that has long been unsolved.The Macao Science Satellite-1(MSS-1)under construction is China’s first high-precision EMF measurement satellite.To satisfy the highly precise requirements of the MSS-1 orbit measurement,a light,high-precision,four-prism laser retroreflector array was designed.It weighs approximately 285 g,its effective reflection area is greater than 1.77 cm^(2),and its size is 100×100×41 mm.The laser retro-reflector array has excellent performance,and it can achieve a ranging precision at the subcentimeter level for satellite laser ranging.It will be developed and installed on the MSS-1 as a power-free load for high-precision orbit measurement and accurate orbit calibration.The MSS-1 is planned to be brought into the International Laser Ranging Service observations.More than 31satellite laser ranging stations in the International Laser Ranging Service around the world will be able to measure the MSS-1 with long arcs,which will support the scientific mission of high-precision EMF exploration.

Numerical simulation of the sensor output on Macao Science Satellite-1

Macao Science Satellite-1(MSS-1)will be launched at the early of 2023 into a near-circular orbit.The mission is designed to measure the Earth’s geomagnetic field with unpreceded accuracy through a new perspective.The most important component installed on the satellite,to ensure high accuracy,is the deployable boom(Optical Bench).A Vector Field Magnetometer(VFM),an Advanced Stellar Compass(ASC),and a Couple Dark State Magnetometers(CDSM)are deployed on the deployable boom.In order to maximize the mission’s scientific output,a numerical simulator on MSS-1’s deployable boom was required to evaluate the adaptability of all devices on the deployable boom and assist the satellite’s data pre-processing.This paper first briefly describes the synthesis of the Earth’s total magnetic field and then describes the method simulating the output of scalar and vector magnetometers.Finally,the calibration method is applied to the synthetic magnetometer data to analyze the possible noise/error of the relevant instruments.Our results show that the simulator can imitate the disturbance of different noise sources or errors in the measuring system,and is especially useful for the satellite’s data processing group.

A Japanese Record of an Annular Solar Eclipse and Variation of the Earth's Rotation

Although the Japanese records of central or near central solar eclipses (i.e. the total, annular and total-annular eclipses) are not very old, so long as their documents definitely recording the observational place, date and phenomenon of the eclipse or the parameters can be defined through some textual researches even if

Variation of the earth's rotation derived from timing records of solar eclipse in ancient China

In the study of variation of the earth’s rotation based on the records of some ancientastronomical events, the timing records of ancient astronomical events and phenomena, suchas solar and lunar eclises and lunar occultation, are important components of the data.The reliable records, especially those from the countries and regions with advanced an-cient astronomy and timing technology, contain valuable information on the variation

Geophysical and Chemical Evidence in the Depletion of Ozone

The depletion of ozone is due to not only some chemical reaction, but also some physical changes, such as Solar Proton Events with solar flare, violent vortex of air currents with the changes of the earth’s rotation caused by earth’s deformation and so on We found that the tidal force by the sun makes the earth’s oblateness large on the 0° Latitude and small on the 23 5°Latitude The tidal force by the moon and nine planets can make this effect strong This is a basic reason for the creation of ozone hole and El Nino \;As shown from calculation,the earth tide by the sun makes the earth′s deformation and rotation change periodically.When the situation of the sun moves from 23.5°N to 23.5°S,the length of a day will change±0.00027s.When the earth moves from aphelion to perihelion,the length of a day will increase 0.00007s.The earth tide by the moon can increase or decrease this effect periodically.They are the reasons of the earth′s rotation decelerating from 30 July to 16 November and the ozone hole over the south Pole sky expanding with El Nino.The SSW unified stress field of the earth is the tectonic evidence of the orbital effect of the earth′s rotation and deformation.The moon′s declination and obliquity of the ecliptic determine the direction of the principal compressive stress field. Scientists discover chlorion layer in atmosphere while they studied freon.Chlorion can fly in to atmosphere from continent and ocean in many ways.The photolyte of freon is only one way of them,such as electrolysis and photolysis of sodium chloride and hydrogen chloride.The differential rotation of the earth’s layers mix ozone with chlorion and create a ozone hole over the Qinghai Tibet plateau sky.The depletion of ozone and El Nino are the results of the differential rotation.

New Long-Term Climate Oscillations

The astronomical theory of climate change is based on the solution of differential equations describing Earth’s orbital and rotational motions. The equations are used to calculate the change in insolation over the Earth’s surface. As a result of the author’s solution of the orbital problem, the periods and amplitudes of Earth-orbit variations and their evolution have been refined. Unlike previous studies, the equations of Earth’s rotational motion are solved completely. The Earth’s rotational axis precesses relative to a direction different from the direction of the orbit’s axial precession, and oscillates with periods of half a month, half a year and 18.6 years. Also, its oscillations occur with irregular periods of several tens of thousands of years and more. All these motions lead to oscillations of the obliquity in the range of 14.7° to 32.1°, which prove to be 7 - 8 times larger than obtained by a previous theory. In the same proportion, the Earth’s insolation oscillations increase in amplitude, with insolation extremes occurring in other epochs than those in the previous theory. The amplitudes and the onset times of the extremes correlate with known paleoclimate changes. Thirteen insolation periods of paleoclimate variation over an interval of 200 thousand years are identified. From the insolation evolution calculated over a time interval of 1 million years, 6 climate gradations from very cold to very warm are identified.

Variational solution about over-determined geodetic boundary value problem and its related theories

A new solving method for Laplace equation with over-determined geodetic boundary conditions is pro- posed in the paper, with the help of minimizing some kinds of quadratic functional in calculus of variation. At first, the so-called variational solution for over-determined geodetic boundary value problem is defined in terms of principles in calculus of variation. Then theoretical properties related with the solution are derived, especially for its existence, uniqueness and optimal approximation. And then the computational method of the solution is discussed, and its expression is exhibited under the case that all boundaries are spheres. Finally an arithmetic example about EGM96 gravity field model is given, and the computational results show that the proposed method can efficiently raise accuracy to deal with gravity data. In all, the variational solution of over-determined geodetic boundary value problem can not only fit to deal with many kinds of gravity data in a united form, but also has strict mathematical basements.

Improved-GRACE卫星重力轨道参数优化研究

基于改进的半解析法,利用激光干涉系统星间速度误差、GPS接收机轨道位置误差和轨道速度误差以及加速度计非保守力误差影响累计大地水准面的联合误差模型,开展了我国Improved-GRACE卫星重力测量计划轨道参数的优化选取论证。模拟结果表明:1)在300阶处,基于350km轨道高度估计累计大地水准面的精度为3.993×10-1m,基于300km和250km轨道高度估计精度分别提高了8.770倍和77.145倍,基于400km和450km轨道高度估计精度分别降低了8.718倍和75.307倍;2)基于50km星间距离估计累计大地水准面的精度为3.993×10-1m,基于110km和220km星间距离估计精度分别降低了1.259倍和1.395倍;3)我国将来首颗Improved-GRACE重力卫星的平均轨道高度和平均星间距离设计为350km与50km较优。

利用计算机断层成像方法由观测图像重建等离子体层全球密度分布--投影数据不完备问题

在用计算机断层成像方法由EUV观测图像重建等离子体层全球密度分布时,地球的遮挡和有限角度都会导致投影数据不完备,从而无法精确重建出等离子体层的密度分布.本文针对该问题,提出一种基于图像总变差极小化的代数迭代算法.通过重建等离子体层投影数据缺失最为严重的中心子午面,证明该算法能够显著提高重建图像的质量.并且在IMAGE卫星仅能达到90°的有限投影角度下,此算法重建图像的相关系数可达0.760,而代数迭代算法的相关系数仅为0.696.

低轨回归轨道卫星轨迹漂移特性分析与控制

针对低轨回归轨道卫星,建立了星下点轨迹漂移的数学模型,研究了星下点轨迹保持控制的问题。首先,分析了回归轨道星下点轨迹的约束条件,给出了星下点轨迹漂移与卫星轨道根数偏差之间的关系。在此基础上,将星下点轨迹保持控制问题转化为基于平均轨道根数的相对轨道控制问题,其中参考卫星是虚拟的,仅受到地球引力影响,利用高斯摄动方程建立了包含J2摄动和大气阻力摄动的相对运动方程,基于Lyapunov理论设计了星下点轨迹保持的相对平均轨道根数反馈控制律。仿真结果表明,所设计的星下点轨迹控制律能有效地实现星下点轨迹保持的要求。