Parker’s model in geodynamo

The eigenvalue problem for Parker’s dynamo model is considered. We study how the intensity of convection in the liquid core of the Earth affects the generation of the geomagnetic field with different directions of latitudinal field propagation. The scenarios of transition of the geomagnetic field from frequent to rare reversals are suggested.     

Magnetorotational instability in the Earth’s core

The anisotropy of the convection in the Earth’s core can act as a cause of its nonsolid rotation. In the case of differential rotation, the magneto-rotational instability (the Velikhov instability) can arise in the liquid core. It is shown that the development of the magneto-rotational instability of the hydromagnetic flows in the liquid core of the Earth can generate variations in the geomagnetic field observed on the Earth’s surface.     

Data assimilation in Parker’s dynamo model

Application of the extended Kalman filter in the data assimilation problem of the one-dimensional (1D) Parker dynamo model is considered for two extreme cases: (1) when the magnetic field observations are taken uniformly across the entire surface of the liquid core of the Earth and (2) when the observations are taken at one spatial point. The algorithm allows the model solution with arbitrary initial conditions to be modified based on observations. It is shown that the redundancy of the noised data can reduce the efficiency of the recovery of the solution. Considerations on the applicability of data assimilation for the case of a higher dimension and a solution’s convergence dependent on the density of the flow of information assimilated are suggested.     

The Global S$$_$$ Tide in Earth’s Nutation

Diurnal S\(_1\) tidal oscillations in the coupled atmosphere–ocean system induce small perturbations of Earth’s prograde annual nutation, but matching geophysical model estimates of this Sun-synchronous rotation signal with the observed effect in geodetic Very Long Baseline Interferometry (VLBI) data has thus far been elusive. The present study assesses the problem from a geophysical model perspective, using four modern-day atmospheric assimilation systems and a consistently forced barotropic ocean model that dissipates its energy excess in the global abyssal ocean through a parameterized tidal conversion scheme. The use of contemporary meteorological data does, however, not guarantee accurate nutation estimates per se; two of the probed datasets produce atmosphere–ocean-driven S\(_1\) terms that deviate by more than 30 \(\upmu \)as (microarcseconds) from the VLBI-observed harmonic of \(-16.2+i113.4\) \(\upmu \)as. Partial deficiencies of these models in the diurnal band are also borne out by a validation of the air pressure tide against barometric in situ estimates as well as comparisons of simulated sea surface elevations with a global network of S\(_1\) tide gauge determinations. Credence is lent to the global S\(_1\) tide derived from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and the operational model of the European Centre for Medium-Range Weather Forecasts (ECMWF). When averaged over a temporal range of 2004 to 2013, their nutation contributions are estimated to be \(-8.0+i106.0\) \(\upmu \)as (MERRA) and \(-9.4+i121.8\) \(\upmu \)as (ECMWF operational), thus being virtually equivalent with the VLBI estimate. This remarkably close agreement will likely aid forthcoming nutation theories in their unambiguous a priori account of Earth’s prograde annual celestial motion.     

Heat Transport Processes in the Earth’s Crust

The heat of the Earth derives from internal and external sources. A heat balance shows that most of the heat provided by external sources is re-emitted by long-wavelength heat radiation and that the dominant internal sources are original heat and heat generated by decay of unstable radioactive isotopes. Understanding of the thermal regime of the Earth requires appreciation of properties and mechanisms for heat generation, storage, and transport. Both experimental and indirect methods are available for inferring the corresponding rock properties. Heat conduction is the dominant transport process in the Earth’s crust, except for settings where appreciable fluid flow provides a mechanism for heat advection. For most crustal and mantle rocks, heat radiation becomes significant only at temperatures above 1200°C.

Ranges of AGW propagation in the Earth’s atmosphere

The propagation of atmospheric gravity waves (AGWs) is studied in the context of geometrical optics in the nonisothermal, viscous, and thermal-conductive atmosphere of Earth in the presence of wind shifts. Parametric diagrams are plotted, determining the regions of allowed frequencies and horizontal phase velocities of AGWs depending on the altitude. It is shown that a part of the spectrum of AGWs propagates in stationary air in an altitude range from the Earth’s surface through the ionospheric F1 layer. AGW from nearearth sources attenuate below 250 km, while waves generated at altitudes of about 300 km and higher do not reach the Earth’s surface because of the inner reflection from the thermosphere base. The pattern changes under strong thermospheric winds. AGW dissipation decreases with an adverse wind shift and, hence, a part of the wave spectrum penetrated from the lower atmosphere to the altitudes of F2 layer.     

Model of muon generation in the Earth’s atmosphere

The muon fluxes on the Earth’s surface and at depths of 7, 20, and 40 m of water equivalent are calculated based on a simple model of pion generation by primary particles with different energies. This generation model is based on the known concepts of multiple pion production. The model parameters are compared with the data obtained using accelerating machines.     

Inertial effects in the Earth’s crust and magnetosphere

A review of studies devoted to the problem of exciting magnetic signals in the crust associated with the formation of the major rupture in an earthquake source and with the propagation of seismic waves was given in [Sgrigna et al., 2004]. However, this review contains incorrect citations from original papers and several erroneous statements concerning inertial and inductive mechanisms of conversion of the energy of rock motion into magnetic field energy. These mistakes are analyzed in the present paper. The formal and physical similarity between seismomagnetic waves in the crust and Alfvén waves in the magnetosphere is used in the analysis. A comparative analysis of the inertial and inductive mechanisms of seismomagnetic field generation is performed. The Cherenkov criterion of Alfvén wave generation due to the ionospheric effect of acoustic waves from earthquakes and explosions is derived. Attention is also given to nonlinear phenomena (nonlinearity of a mechanomagnetic conversion in the crust and anharmonicity and self-focusing of Alfvén waves in the magnetosphere).     

Reflectionless acoustic gravity waves in the Earth’s atmosphere

The vertical wave propagation in an inhomogeneous compressible atmosphere is studied in the framework of a linear theory. Under specific conditions imposed on atmospheric parameters, solutions can be found in the form of travelling waves with variable amplitudes and wave numbers that do not reflect in the atmosphere in spite of its strong inhomogeneity. Model representations for the sound speed have been found, for which waves can propagate in the atmosphere without reflection. A wave energy flux retains these reflectionless profiles, which confirms that energy can be transferred to high altitudes. The number of these model representations is fairly large, which makes it possible to approximate real vertical distributions of the sound speed in the Earth??s atmosphere using piecewise reflectionless profiles. The Earth??s standard atmosphere is shown to be well approximated by four reflectionless profiles with weak jumps in the sound speed gradient. It has been established that the Earth??s standard atmosphere is almost completely transparent for the considered vertical acoustic waves in a wide range of frequencies, which is confirmed by observational data and conclusions derived using numerical solutions of original equations.     

Nitrogen storage and allocation in China’s forest ecosystems

Forests are important parts of terrestrial ecosystems and play a leading role in regional and global nitrogen(N) cycles.Detailed assessment of N storage and allocation in China's forests is critical to improve the accuracy of regional or global N estimates and to guide policy-makers in the formulation of scientific and effective N management measures. However, the fore stN storage at national scale remains unclear. Based on 4420 forest field-investigated data, we investigated the N storage allocation in China's forests, explored the spatial patterns and influence factors. The data included vegetation information on various organs(i.e., leaf, branch, stem, and root) and soil information at different depths(0-30 cm and 0-100 cm). The total N storage in China's forest ecosystems was 14.45±8.42 tN hm~(–2); 0.86±0.51 tN hm~(–2)(5.95%) in vegetation and 13.59±8.40 tN hm~(–2)(94.05%) in soil(0–100 cm). The storage and allocation of N varied significantly across various regions and forest types. For different ecological regions, N storage varied from 10.34 to 23.11 tN hm~(–2), and the allocation ratio of N storage between vegetation and soil(0–100 cm) varied from 0.03 to 0.16. For different forest types, the N storage varied from 12.87 to 18.32 tN hm~(–2), and the allocation ratio of N storage between vegetation and soil(0–100 cm) varied from 0.03 to 0.09. The spatial patterns relative to N storage and allocation in forests were different. Climate was the primary factor influencing the spatial variation in forestN storage, while soil texture was the main factor influencing the spatial variation in N allocation. These first estimates of N storage and allocation ratio in China's forests are keys for improving the fitting accuracy of regional N cycle models and provide a reference for regional management of forestN.     

Convection in anelastic models of the Earth’s liquid core

The effects of adiabatic cooling on the convection in the anelastic model of the liquid core of the Earth are considered. It is shown that even minor adiabatic cooling causes significant changes in the pattern of the convection, shifting the peak in the convection intensity to the inner part of the core. Just as in the Boussinesq model, both direct and inverse kinetic energy cascades are simultaneously present, and the direct cascade of entropy is observed.     

Detection of Antarctic oscillation signals in Earth’s oblateness variations

Variations of Earth’s oblateness (J ₂) reflect a large scale mass redistribution within the Earth system. The climate effect causing J ₂ interannual variations is still not clear, though previous studies indicated it may be related to EI Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). However, we have a new discovery of the significant Antarctic oscillation (AAO) signals in J ₂ interannual variations, especially on 4–6 year scales based on cross wavelet and wavelet coherence analysis with 95% confidence test during 1979–2012. The results additionally indicate that the close phase relationship between J ₂ and AAO (AAO leading J ₂ variations by 3 ± 2 months in phase) is far superior to that between J ₂ and ENSO/PDO on 4–6 year scales. In this work, we discuss, for the first time, a possible geophysical mechanism of AAO effecting J ₂ variations. The investigations are based on the definition of AAO and its spatial–temporal behavior influencing the large-scale mass movement. Finally, an approximate quantitative estimate of the AAO imprint on J ₂ with an emphasis on the atmospheric contribution is made.     

Regional instrumental series in reconstructions of global changes in the Earth’s climate

The possibility to apply long-term regional series to reconstruct the Earth’s global temperature in the past is considered. It is shown using symbolic analysis methods that significant (on the so-called order patterns) are relations of time series of St. Petersburg temperature with certain regional and global series. New sets of global temperature reconstructions, starting from the mid-18th century, are constructed on the basis of the previously proposed MSR and DPS methods.     

Low-frequency waves in the Earth’s magnetosheath: present status

The terrestrial magnetosheath contains a rich variety of low-frequency ( proton gyrofrequency) fluctuations. Kinetic and fluid-like processes at the bow shock, within the magnetosheath plasma, and at the magnetopause all provide sources of wave energy. The dominance of kinetic features such as temperature anisotropies, coupled with the high- conditions, complicates the wave dispersion and variety of instabilities to the point where mode identification is difficult. We review here the observed fluctuations and attempts to identify the dominant modes, along with the identification tools. Alfvén/ion-cyclotron and mirror modes are generated by T/T 1 temperature anisotropies and dominate when the plasma is low or high, respectively. Slow modes may also be present within a transition layer close to the subsolar magnetopause, although they are expected to suffer strong damping. All mode identifications are based on linearized theory in a homogeneous plasma and there are clear indications, in both the data and in numerical simulations, that nonlinearity and/or inhomogeneity modify even the most basic aspects of some modes. Additionally, the determination of the wave vector remains an outstanding observational issue which, perhaps, the Cluster mission will overcome.     

Three distinct types of hotspots in the Earth’s mantle

The origin of mantle hotspots is a controversial topic. Only seven (‘primary’) out of 49 hotspots meet criteria aimed at detecting a very deep origin (three in the Pacific, four in the Indo-Atlantic hemisphere). In each hemisphere these move slowly, whereas there has been up to 50 mm/a motion between the two hemispheres prior to 50 Ma ago. This correlates with latitudinal shifts in the Hawaiian and Reunion hotspots, and with a change in true polar wander. We propose that hotspots may come from distinct mantle boundary layers, and that the primary ones trace shifts in quadrupolar convection in the lower mantle.     

The Role of Water Vapour in Earth’s Energy Flows

Water vapour modulates energy flows in Earth's climate system through transfer of latent heat by evaporation and condensation and by modifying the flows of radiative energy both in the longwave and shortwave portions of the electromagnetic spectrum. This article summarizes the role of water vapour in Earth's energy flows with particular emphasis on (1) the powerful thermodynamic constraint of the Clausius Clapeyron equation, (2) dynamical controls on humidity above the boundary layer (or free-troposphere), (3) uncertainty in continuum absorption in the relatively transparent "window" regions of the radiative spectrum and (4) implications for changes in the atmospheric hydrological cycle.     

ZHANG Heng’s Seismometer and Longxi earthquake in AD 134

Introduction Houhan Shu?ZHANG Heng Biography written by FAN Ye(AD398?AD445,South-North Dynasties)described about the response of ZHANG Heng’s Seismometer to Longxi earthquake as follows.“On one occasion a dragon dropped a ball without an earthquake being felt.All the scholars in the capital blamed this effect happening without any feelings of the earthquake.Several days later,a messenger arrived reporting that an earthquake really had taken place at Longxi.There-upon people all a…