Algorithm grwat for Automated Hydrograph Separation by B.I. Kudelin’s Method: Problems and Perspectives

Water Resources - An algorithm for automated graph-analytical separation of hydrograph, underlying grwat software package is described in detail and analyzed. This system is designed for separation...     

Dynamic variation and the fast acceleration of particles in Earth’s radiation belt

We have quantitatively investigated the radiation belt’s dynamic variations of 1.5-6.0 MeV electrons during 54 CME (coronal mass ejection)-driven storms from 1993 to 2003 and 26 CIR (corotating interaction region)-driven recurrent storms in 1995 by utilizing case and statistical studies based on the data from the SAMPEX satellite. It is found that the boundaries determined by fitting an exponential to the flux as a function of L shell obtained in this study agree with the observed outer and inner boundaries of the outer radiation belt. Furthermore, we have constructed the Radiation Belt Content (RBC) index by integrating the number density of electrons between those inner and outer boundaries. According to the ratio of the maximum RBC index during the recovery phase to the pre-storm average RBC index, we conclude that CME-driven storms produce more relativistic electrons than CIR-driven storms in the entire outer radiation belt, although the relativistic electron fluxes during CIR-related storms are much higher than those during CME-related storms at geosynchronous orbit. The physical radiation belt model STEERB is based on the three-dimensional Fokker-Planck equation and includes the physical processes of local wave-particle interactions, radial diffusion, and adiabatic transport. Due to the limitation of numerical schemes, formal radiation belt models do not include the cross diffusion term of local wave-particle interactions. The numerical experiments of STEERB have shown that the energetic electron fluxes can be overestimated by a factor of 5 or even several orders (depending on the pitch angle) if the cross diffusion term is ignored. This implies that the cross diffusion term is indispensable for the evaluation of radiation belt electron fluxes. Formal radiation belt models often adopt dipole magnetic field; the time varying Hilmer-Voigt geomagnetic field was adopted by the STEERB model, which self-consistently included the adiabatic transport process. The test simulations clearly indicate that the adiabatic process can significantly affect the evolution of radiation belt electrons. The interactions between interplanetary shocks and magnetosphere can excite ULF waves in the inner magnetosphere; the excited polodial mode ULF wave can cause the fast acceleration of "killer electrons". The acceleration mechanism of energetic electrons by poloidal and toroidal mode ULF wave is different at different L shells. The acceleration of energetic electrons by the toroidal mode ULF waves becomes important in the region with a larger L shell (the outer magnetosphere); in smaller L shell regions (the inner magnetosphere), the poloidal mode ULF becomes responsible for the acceleration of energetic electrons.     

Estimates of Current Helicity and Tilt of Solar Active Regions and Joy’s Law

Geomagnetism and Aeronomy - The tilt angle, current helicity and twist of solar magnetic fields can be observed in solar active regions. We carried out estimates of these parameters by two ways....     

A tentative model for the explanation of Båth law using the order parameter of seismicity in natural time

Using the order parameter of seismicity defined in natural time, we suggest a simple model for the explanation of Båth law, according to which a mainshock differs in magnitude from its largest aftershock by approximately 1.2 regardless of the mainshock magnitude. In addition, the validity of Båth law is studied in the Global Centroid Moment Tensor catalogue by using two different aftershock definitions. It is found that the mean of this difference, when considering all the pairs mainshock-largest aftershock, does not markedly differ from 1.2 and the corresponding distributions do not depend on the mainshock’s magnitude threshold in a statistically significant manner. Finally, the analysis of the cumulative distribution functions provides evidence in favour of the proposed model.     

Zhang Heng’s Seismoscope(3):Disappearance & Scientific Value

The ancient idea of Heavenly Punishment confused natural phenomena with social issues,which resulted in Zhang Heng’s tragedy in his later years and seismoscope. The instrument might have been lost in the end of the Eastern Han Dynasty. A series of extremely serious chaotic social events caused by war took place,such as a fire in Luoyang,forging coins by destroying copper wares,relocation of the capital,sharp population decrease,and the destruction of the Ling Observatory. Zhang’s scientific thought and successful practice had played an important role in ideological enlightenments at the primary stage of modern seismology at the end of the nineteenth century. There is a glorious course of"innovation—inheritance—re-innovation"of scientific and technical development from the inception Zhang Heng’s seismoscope to the modern seismograph invented by Milne,et al.     

Donald V. Helmberger’s art and science of waveforms

I arrived at the Caltech Seismo Lab early in May 1972.The faculty and graduate students had the run of an old mansion(Donnelly Lab)that was slightly tattered ar...     

SH Wave Number Green’s Function for a Layered,Elastic Half-Space. Part I: Theory and Dynamic Canyon Response by the Discrete Wave Number Boundary Element Method

We present a closed-form frequency-wave number (ω – k) Green’s function for a layered, elastic half-space under SH wave propagation. It is shown that for every (ω – k) pair, the fundamental solution exhibits two distinctive features: (1) the original layered system can be reduced to a system composed by the uppermost superficial layer over an equivalent half-space; (2) the fundamental solution can be partitioned into three different fundamental solutions, each one carrying out a different physical interpretation, i.e., an equivalent half-space, source image impact, and dispersive wave effect, respectively. Such an interpretation allows the proper use of analytical and numerical integration schemes, and ensures the correct assessment of Cauchy principal value integrals. Our method is based upon a stiffness-matrix scheme, and as a first approach we assume that observation points and the impulsive SH line-source are spatially located within the uppermost superficial layer. We use a discrete wave number boundary element strategy to test the benefits of our fundamental solution. We benchmark our results against reported solutions for an infinitely long circular canyon subjected to oblique incident SH waves within a homogeneous half-space. Our results show an almost exact agreement with previous studies. We further shed light on the impact of horizontal strata by examining the dynamic response of the circular canyon to oblique incident SH waves under different layered half-space configurations and incident angles. Our results show that modifications in the layering structure manifest by larger peak ground responses, and stronger spatial variability due to interactions of the canyon geometry with trapped Love waves in combination with impedance contrast effects.     

Three Decades of Seismic Activity at Mt. Vesuvius: 1972–2000

We analyse the seismic catalogue of the local earthquakes which occurred at Somma-Vesuvius volcano in the past three decades (1972–2000). The seismicity in this period can be described as composed of a background level, characterised by a low and rather uniform rate of energy release and by sporadic periods of increased seismic activity. Such relatively intense seismicity periods are characterised by energy rates and magnitudes progressively increasing in the critical periods. The analysis of the b value in the whole period evidences a well-defined pattern, with values of b progressively decreasing, from about 1.8 at the beginning of the considered period, to about 1.0 at present. This steady variation indicates an increasing dynamics in the volcanic system. Within this general trend it is possible to identify a substructure in the time sequence of the seismic events, formed by the alternating episodes of quiescence and activity. The analysis of the source moment tensor of the largest earthquakes shows that the processes at the seismic source are generally not consistent with simple double-couples, but that they are compatible with isotropic components, mostly indicating volumetric expansion. These components are shown to be statistically significant for most of the analysed events. Such focal mechanisms can be interpreted as the effect of explosion phenomena, possibly related to volatile exsolution from the crystallising magma. The availability of a reduced amount of high quality data necessary for the inversion of the source moment tensor, the still limited period of systematic observation of Vesuvius micro-earthquakes and, above all, the absence of eruptive events during such interval of time, cannot obviously permit the outlining of any formal premonitory signal. Nevertheless, the analysis reported in this paper indicates a progressively evolving dynamics, characterised by a generally increasing trend in the seismic activity in the volcanic system and by a significant volumetric component of recent major events, thus posing serious concern for a future evolution towards eruptive activity.     

Aerosol Forcing: Rapporteur’s Report and Summary

This paper summarizes the discussions held during the session dedicated to Aerosol forcing at the Workshop Observing and Modelling Earth’s Energy Flows. The session Aerosol forcing was convened by P. Ingmann and J. Heintzenberg and included 10 presentations given by R. Kahn, D. Winker, U. Baltensperger, J. Haywood, S. Schwartz, J. Heintzenberg, H. Le Treut, U. Lohmann, R. Wood, and E. Philipona. The presentations given ranged from overviews of current observational capabilities to analyses of aerosol–cloud interactions in observations and models of varying complexity. This paper is organized around a few key points, summarizing the major points of agreement, disagreement, and discussion that the presentations gave rise to. The focus is largely on the uncertainties that remain with regard to aerosol forcing, particularly related to aerosol-cloud interactions and indirect aerosol effects on climate.     

Forecasting aftershock activity: 1. Adaptive estimates based on the Omori and Gutenberg–Richter laws

The method for forecasting the intensity of the aftershock processes after strong earthquakes in different magnitude intervals is considered. The method is based on the joint use of the time model of the aftershock process and the Gutenberg–Richter law. The time model serves for estimating the intensity of the aftershock flow with a magnitude larger than or equal to the magnitude of completeness. The Gutenberg–Richter law is used for magnitude scaling. The suggested approach implements successive refinement of the parameters of both components of the method, which is the main novelty distinguishing it from the previous ones. This approach, to a significant extent, takes into account the variations in the parameters of the frequency–magnitude distribution, which often show themselves by the decreasing fraction of stronger aftershocks with time. Testing the method on eight aftershock sequences in the regions with different patterns of seismicity demonstrates the high probability of successful forecasts. The suggested technique can be employed in seismological monitoring centers for forecasting the aftershock activity of a strong earthquake based on the results of operational processing.     

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.     

Tunguska phenomenon: Discharge processes near the earth’s surface

An investigation of the Tunguska cosmic body’s epicenter showed that both dried trees and those that survived the catastrophe are marked with characteristic deteriorations. For the trees that survived near the epicenter (the distance is <4 km), cracks of up to 7 m in length are found on their stems. All the vegetation near the explosion epicenter has traces of uniform scorch that covered the trees even on the land parts isolated by water. On the background of this uniform scorch, a notable feature is carbonization that touched the tree tops and the earth-directed ends of broken branches. All tops of both living and dried trees in the central zone are burned and dead. Carbonization of tops and branch ends was observed up to a distance of 10–15 km from the epicenter; i.e., charge processes took place over an area of more than 500 km² in size. Carbonized branch ends have a characteristic “bird’s nail” shape, which has no analogs on the Earth. Similar deterioration is typical for the crater shape that obtains an anode during arc discharge combustion. It is supposed that the duration of these charge processes could be ≥1 min.     

Methods for reconstructing harmonic functions from the magnetic field ΔT and V.N. Strakhov’s function ΔS: A review

We give an overview of the methods designed for reconstructing close-to-harmonic functions from the magnetic field ΔT. The formula of Yu.P. Tafeev is refined. It is shown that this refined formula directly leads to the relation derived by V.M. Gordin and his colleagues that allows isolating the harmonic component in the function ΔT. V.N. Strakhov’s linearized representation of the function ΔT is immediately derived from the main approximate Tafeev formula for Q ΔT. The experience of using Strakhov’s ΔS function in the interpretation of the magnetic anomaly ΔT generated by the Krivoi Rog structure is described. It is noted that the problem of reconstructing the corresponding harmonic functions from the data of magnetic and gravity surveys has much in common. The specific features of measuring the magnetic field H and magnetic induction B in the material media are considered, and the physical interpretation of these fields is presented.     

Coronal Holes as Tracers of the Sun’s Global Magnetic Field in Cycles 21–23 of Solar Activity

The dependences of the number and parameters of non-polar coronal holes (CHs) on characteristics of the Sun’s global magnetic field (GMF) are investigated in cycles 21–23 of solar activity (1976–2012) based on data from the CH catalog of the Mountain Astronomical Station of the Main (Pulkovo) Astronomical Observatory of the Russian Academy of Sciences. The influence of variations in the GMF structural arrangement on the CH number and parameters is considered. It is shown that the more stable and steadystate the GMF topology is in the cycle, the higher are the GMF values. The majority of CHs form over periods of stable GMF structure. With a growth in the rate of structural GMF changes, the CH number and the values of all CH parameters decrease. The correlation between the area, extension in latitude and longitude, and magnetic flux of CHs and the intensity of both the calculated coronal field and the observed large-scale photospheric magnetic field is higher in cycles with larger magnetic-field values and with a more stable GMF structure. Non-polar CHs are divided into three groups depending on the GMF value and a rate of the structural GMF rearrangement.