Variations in fractal characteristics of active regions and flares

A multifractal analysis of the Hα images for an active region has been performed; the singularity spectra and segmented images for a narrow range of fractal dimensions have been computed for them. The segmented images show the presence of singular areas where the singularity index takes on maximum values. These areas mark the active sites of flares.     

Variations in ionospheric parameters during solar flares

Results of studying the ionospheric response to solar flares, obtained based on the incoherent scatter radar observations of the GPS signals and as a result of the model simulations, are presented. The method, based on the effect of partial “shadowing” of the atmosphere by the globe, has been used to analyze the GPS data. This method made it possible to estimate the value of a change in the electron content in the upper ionosphere during the solar flare of July 14, 2000. It has been shown that a flare can cause a decrease in the electron content at heights of the upper ionosphere (h > 300 km) according to the GPS data. Similar effects in the formation of a negative disturbance in the ionospheric F region were also observed during the solar flares of May 21 and 23, 1967, at the Arecibo incoherent scatter radar. The mechanism by which negative disturbances are formed in the upper ionosphere during solar flares has been studied based on the theoretical model of the ionosphere-plasmasphere coupling. It has been shown that an intense ejection of O⁺ ions into the above located plasmasphere under the action of a sharp increase in the ion production rate and the thermal expansion of the ionospheric plasma cause the formation of a negative disturbance in the electron concentration in the upper ionosphere.     

Space Variations of Stress Along the Tyrrhenian Wadati-Benioff Zone

—Gephart and Forsyth’s (1984) algorithm for stress inversion of earthquake fault-plane solutions has been applied to a set of ninety intermediate and deep events occurring in the southern Tyrrhenian region between 1976 and 1995. P- and S-wave data from local seismic networks in southern Italy, the Italian National Network and international bulletins, have been used for hypocenter and focal mechanism computations. Stress inversion runs performed after accurate selection and weighting of fault-plane solutions have allowed us to identify stress space variations at a higher level of detail than available from all previous investigations carried out in the study area. The maximum compressive stress has been shown to follow the depth-decreasing dip of the Wadati-Benioff zone, along the entire zone from a depth of 90 km, to the depth of the deepest events (about 500 km). Variations to such a stress pattern have been found, possibly related to mantle dynamics and the complex composition of the subducting structure. The diffused state of down-dip compression suggests that the Tyrrhenian subduction has already evolved to the point where the lower end of the slab has reached high-strength mantle materials, the load of the excess mass is entirely supported from below and most of the subducted slab is under compression. In agreement with the lack of large, shallow thrusting events in the immersion zone, the findings of the present study appear to agree well with geodynamic models assuming a passive subduction process with eastward roll-back of the Ionian lithosphere in the study area. In this context, the depth-decrease of the slab dip may also find a reasonable explanation.     

Variations in the Geomagnetic Field Intensity with Characteristic Times of Five and One Million Years

Geomagnetism and Aeronomy - Variations in the paleointensity of the geomagnetic field over the Middle Jurassic–Paleogene (167–20 Ma) interval has been studied. It has been found that...     

Variations of the earth's gravity field due to the free nutation

Summary Expressions for the time variation of gravity and for deformations of equipotential surfaces due to the free nutation of the Earth have been derived. The possibility has been shown of determining the polar motion by means of accurate gravity observations under the assumption that the other effects, particularly tidal, may be expressed with sufficient accuracy theoretically. The necessity of introducing gravity corrections due to the polar motion has been pointed out in investigating the secular variations of gravity and in accurate gravity measurements (standard error of the order of 0.01 mgal and less), in general.     

中国境内地磁场变化对SNMR信号的影响

地面核磁共振方法是目前唯一直接探测地下水的地球物理新方法。新方法在我国探查地下水等方面已取得明显的效果,但是,对于SNMR信号,却有很多影响因素。本文论述并分析了诸多影响因素中的地磁场强度和磁倾角对NMR信号的影响特点,进而分析了我国区域地磁场强度和磁倾角对SNIVIR信号的影响规律,对我国进行区域性水文地质调查中运用SNMR方法时提供了重要的参考资料。     

Variations of the geomagnetic field,the climate and weather

Summary Using palaeomagnetic investigations of sedimentary rocks and particularly lake sediments, changes of the geomagnetic field and geomagnetic poles were determined over a period of the last 40 000 years. The correlations between geomagnetic, climatic and meteorological phenomena were investigated with the object of demonstrating the function of the geomagnetic pole and changes in its positions in forming the climate and weather. A tentative model has been proposed to enable the causes of the generation of glacial and interglacial periods, as well as the causes effecting changes of weather to be explained. The possibilities of man-made meliorations of the climate in certain regions are also discussed.Presented at the XVI Gen.Assembly IUGG, Grenoble 1975.     

An Investigation of the Global TEC Behavior from 1999 to 2017 Variations and Deviations

Geomagnetism and Aeronomy - The global TEC (Total Electron Content) behavior has been studied for several decades, but some properties of this behavior have not been understood well, such as the...     

Variations in the amplitude of the chandler wobble

It is shown that within the framework of the Kolmogorov model the “energy” of the pole E(t) = x ₁² + x ₂² can be interpreted as a Markovian process. The exact analytical expression has been obtained for the density of the conditional probability of the quantity E(t) and the problem of the first passage time of the process E(t) has been analyzed. It was shown that the available data on the swing of the function E(t) are not at variance with the Kolmogorov model and a short-period drop of the amplitude of the Chandler wobble in the early 20th century fits this model at Q = 50–200 too; values of Q > 350 are less reasonable.     

Variations in the ULF index of geomagnetic pulsations during strong magnetic storms

The level of wave geomagnetic activity in the morning, afternoon, and nighttime sectors during strong magnetic storms with Dst varying from ?100 to ?150 nT has been statistically studied based on a new ULF wave index. It has been found out that the intensity of geomagnetic pulsations at frequencies of 2–7 mHz during the magnetic storm initial phase is maximal in the morning and nighttime sectors at polar and auroral latitudes, respectively. During the magnetic storm main phase, wave activity is maximal in the morning sector of the auroral zone, and the pulsation intensity in the nighttime sector is twice as low as in the morning sector. It has been indicated that geomagnetic pulsations excited after substorms mainly contribute to a morning wave disturbance during the magnetic storm main phase. During the storm recovery phase, wave activity develops in the morning and nighttime sectors of the auroral zone; in this case nighttime activity is also observed in the subauroral zone.     

Variations of the upper atmosphere air density and electron density during geomagnetic disturbances

The variations of the upper atmosphere air density during geomagnetic disturbances have been investigated by many authors. According to the analysis of satellite orbits, in most cases an increase in the air density may be observed when the indexA _phas a maximum. Having ionospheric data from stations in Europe, Asia and Australia we might be able to study the global behaviour of the electron density in theF ₂ region during such geomagnetic disturbances when an increase of the air density had been observed. In these cases we found, that at the peak of the ionospheric layer, the electron density decreased 0–3 days later than theA _pmaximum.     

Mount Etna: Variations in its internal plumbing

On the basis of historical records of eruptions and the results of recent volcanological, petrological and geophysical investigations, a model for the internal plumbing of Etna is proposed. It is argued that, over about the last 200 years, hawaiite magma has been fed from a deep-seated crustal reservoir at about 20 km depth to be erupted at the surface with no long term high level storage. This is quite a different model for basaltic plumbing from that suggested for Kilauea Volcano on Hawaii. However, the presence on Etna of ignimbrites, more evolved lavas of mugearite and benmoreite composition, calderas and thick pyroclastic sequences indicates that, at times in the prehistoric past, the style of volcanic activity was different to that of the present. At these times there must have been substantial high level storage of magma in the volcano. It is apparent that the internal plumbing of Etna has varied during the history of the volcano. It is considered that the deep seated crustal reservoir plays an important role in the differentiation of the primitive primary magma.Paper presented at the Symposium Volcanoes of the Earth and Planets, held at the University of Lancaster, March 17, 1981.     

Variations in water regime of bogs in Northern and Northwestern Russia under the effect of climatic factors

The mechanism and factors of the impact of climate changes on the level regime of bog water and the runoff from bogs has been established.     

Variations in the geomagnetic field and auroras during the main phase of a large magnetic storm of November 20, 2003

The substorm characteristics during the main phase of a large magnetic storm of November 20, 2003, are studied based on the data of TV observations of auroras and auroral absorption at Tixie Bay station and at the global network of magnetic stations. The contribution of auroral particles, responsible for the emission of discrete auroras, has been estimated based on an analysis of the spatial-time variations in the auroral luminosity intensity. This contribution accounted for ～40% of the total luminous flux, which is approximately twice as large as was previously observed in substorm disturbances. Responses of the solar wind and IMF parameters in substorms and variations in the magnetic indices, characterizing geomagnetic activity in the northern polar cap and ring current (PCN, ASY-H and SYM-H), have been detected. The spatial-time distribution of the equivalent ionospheric currents has been constructed, and the total value of these currents along the meridian has been determined based on the [Popov et al., 2001] method and using the IMAGE magnetic data. It has been obtained that the maximal total equivalent ionospheric current in the premidnight sector (～2000 MLT) leads the minimal value of the SYM-H index by ～1.5 h.     

Variations in the IMF vertical component in isolated solar wind streams

The regularities of the variations in the IMF B _z component have been studied based on the data on the solar wind streams and their solar sources. Isolated solar wind streams such as magnetic clouds and shock layers before them, undisturbed heliospheric current sheets (HCSs), leading edges and bodies of high-speed streams from coronal holes (HSSs from CHs) have been considered. It has been revealed that each type of isolated streams in the interplanetary medium has it own features in the variations in the value and direction of the B _z component related to the stream immanent properties and conditions of propagation in the interplanetary plasma. The appearance of the southward B _z component is obligatory for all these streams which are, therefore, geoeffective.     

MEM Analysis of Geomagnetic Field Variations Over Narssarssuaq

—Maximum entropy spectral analysis (MESA) has been applied to 24 series of hourly daily data and only one daily mean series for the horizontal (H) and vertical (Z) components of the geomagnetic field for the year 1983 as observed at Narssarssuaq, Greenland (71.2°N, 36.7°E) (gm coordinate). The method has isolated some prominent medium frequency signal components. The maximum peaks for H are at 06 hr (0.174 cycles per day (cpd), 3.2 × 10⁴ db) and 08 hr (0.09 cpd, 3.5 × 10⁴ db). Similarly, the maximum peak in Z is observed at 04 hr (0.114 cpd, 5.7 × 10⁴ db). The spectral results for the daily-mean data indicate periods are greater than two days, with 178.5 days (nearly semiannual) being common to both H and Z. Other harmonics have been found for all the series of H and Z components which are mainly caused by the "Effective Period", i.e., the period produced by the combined effect of the sunspot numbers and the sun’s rotation period. Such frequencies correspond very well with those found in the geomagnetic indices A _p ?, C _p and AE. This suggests that the disturbance transient variations are caused by viscous interaction of the solar energies emanating from sunspot regions with the outermost magnetospheric boundary which, in turn, influences the magnetosphere-iono sphere coupling and produces the medium intensity long-duration continuous auroral activities (MILD CAAs) over high latitude regions. Thus, the higher latitude geomagnetic activities are nothing but the "effective period driven MILDCAAs" having a recurrence tendency of 27/n, where n is an integer.     

Variations in the parameters of thunderstorm electromagnetic signals on paths over earthquake regions

The specific features of a method for radiosounding the lower ionosphere over earthquake epicenters using LF electromagnetic signals of thunderstorm sources (atmospherics) have been considered. The effects of shallow-focus earthquakes with magnitudes larger than 4.0 and their precursors manifest themselves in amplitude characteristics of atmospherics. It has been assumed that variations in the signal characteristics are related to disturbances in the lower ionosphere. According to the results of azimuthal scanning, cross-sectional dimensions of disturbed regions, as a rule, correspond to the dimensions of the first two Fresnel zones for signals at a frequency of 10 kHz. Azimuthal scanning also indicated that the positions of disturbed regions during and before earthquakes could have a certain dynamics and differ from the projection onto the earthquake epicenter. The ratio of the amplitudes of electric and magnetic signal components, in the variations of which seismic effects before earthquakes can also be observed, has been considered. An analysis of the ratio makes it possible to increase the probability of predicting earthquakes when using the characteristics of the electromagnetic signals of lightning discharges as an additional method of complex monitoring of disturbances in the lower ionosphere caused by seismic processes.     

Variations in the parameters of VLF signals on the DEMETER satellite during the periods of seismic activity

Two methods for diagnosing ionospheric disturbances using VLF signals received on the DEMETER satellite are considered in connection with two cases of high seismic activity: the method for analyzing a signal reception zone in order to find large-scale spatial variations and the residual signal method used to reveal time variations. Based on an analysis of the VLF signal reception zone, performed in connection with the catastrophic earthquake near Sumatra, it has been found out that the signal amplitude decreased during a month before the earthquake. As a result, it has been concluded that the zone of ionospheric disturbances extends for several thousand kilometers. It has been indicated that the residual signal method showed good agreement between the ground and satellite data when high seismic activity near Japan was analyzed.     

Winter North Atlantic Oscillations Driven by Variations in Total Solar Irradiance

Geomagnetism and Aeronomy - The solar influence on long-term climatic processes of Earth has been studied with the use of long-term series of historical reconstructions of Total Solar Irradiation...     

Long-Term Variations of Danube Delta Coastline

Water Resources - Ground (expedition) and remote (space-based) methods have been used to carry out detail studies of variations of Danube delta coastline (DC). The displacements of the DC (the...