On the mechanism of the post-midnight winter NmF2 enhancements: dependence on solar activity     

A. V. Mikhailov  M. Förster  T. Y. Leschinskaya 《Annales Geophysicae》2000,18(11):1422-1434

The mechanism of the N_mF₂ peak formation at different levels of solar activity is analyzed using Millstone Hill IS radar observations. The h_mF₂ nighttime increase due to thermospheric winds and the downward plasmaspheric fluxes are the key processes responsible for the N_mF₂ peak formation. The electron temperature follows with the opposite sign the electron density variations in this process. This mechanism provides a consistency with the Millstone Hill observations on the set of main parameters. The observed decrease of the nighttime N_mF₂ peak amplitude with solar activity is due to faster increasing of the recombination efficiency compared to the plasmaspheric flux increase. The E × B plasma drifts are shown to be inefficient for the N_mF₂ nighttime peak formation at high solar activity.  相似文献   

Structure and optical properties of soot aerosol in a moist atmosphere: 2. Influence of hydrophilicity of particles on the extinction, scattering, and absorption coefficients     

E. F. Mikhailov  S. S. Vlasenko 《Izvestiya Atmospheric and Oceanic Physics》2007,43(2):195-207

The optical coefficients of soot particles are measured in a flow-through optical cell at the wavelength 635 nm in a dry atmosphere and in an atmosphere saturated with water vapor. Two types of systems modeling atmospheric soot aerosols and differing in the degree of hygroscopicity of their particles are investigated and compared. One of the systems contains hydrophobic acetylene soot, and the other contains hydrophilic soot obtained through modification of the initial soot by vapors of glutaric acid. The results show that the optical properties of hydrophobic soot depend only slightly on the conditions of moistening, whereas the optical properties of hydrophilic soot change abruptly upon its moistening because of the formation of a hydrate shell. In the atmosphere saturated with water-vapor, the monomolecular layer of a hydrophilic organic substance leads to the watering of particles and an abrupt (more than twofold) increase in the cross section of light scattering. A further growth of the hydrophilic component of soot particles initiates the formation of micron drops on them, thus resulting not only in the natural effect of light scattering enhancement but also in a noticeable light absorption increase. In particular, a light absorption enhancement by a factor of 3.5 is characteristic of particles of enriched hydrophilic soot.  相似文献   

Structure and optical properties of soot aerosol in a moist atmosphere: 1. Structural changes of soot particles in the process of condensation     

E. F. Mikhailov  S. S. Vlasenko 《Izvestiya Atmospheric and Oceanic Physics》2007,43(2):181-194

A laboratory setup and a procedure for measuring the volume coefficients and mean cross sections of extinction, scattering, and absorption of soot particles in the medium of saturated water vapor are described. A method for hydrophilization of the surface of soot particles, which makes it possible to obtain model objects with specified hygroscopic properties, is presented. The processes of transformation of soot particles are analyzed with the use of data of electron-microscopic investigations on the basis of the fractal approach. The structural parameters of hydrophobic soot are shown to depend on the conditions of moistening, whereas hydrophilic particles are subject to substantial structural changes indicative of their watering. Investigation of the coagulation of soot particles with drops shows that hydrophobic particles form a weakly bound system; they coagulate on the surface of drops and cause no changes in the structure of soot aggregates. During the coagulation, hydrophilic soot particles penetrate inside a drop and irreversibly form a mixed system.  相似文献   

Determining the foF2 critical frequency at the path midpoint from oblique sounding data based on the Smith method     

G. V. Kotovich  A. G. Kim  S. Ya. Mikhailov  V. P. Grozov  Ya. S. Mikhailov 《Geomagnetism and Aeronomy》2006,46(4):517-521

A simple method for finding the critical frequency at a path midpoint from the distance-frequency characteristic measured on the one-hop path, based on the Smith method (the transmission curve method). The proposed method is the solution of the problem for the regular ionosphere along the path; therefore the method accuracy is also estimated as applied to irregular paths. The modeling results for the Khabarovsk-Irkutsk path are considered, and the experimental results for the Magadan-Irkutsk path are presented.  相似文献   

Numerical Modeling of Transient Seismic Fields in Viscoelastic Media Based on the Laguerre Spectral Method     

B. G. Mikhailenko  A. A. Mikhailov  G. V. Reshetova 《Pure and Applied Geophysics》2003,160(7):1207-1224

--The wave propagation in real media can be described within the theory of linear viscoelasticity. The presence of convolutional integral in Boltzmann's superposition principle poses the main difficulties in implementing the direct numerical methods in time domain. The paper presents a new algorithm, based on the application of the spectral Laguerre method for the approximation of temporal derivatives and convolution as applied to the problem of seismic wave propagation in the heterogeneous viscoelastic medium. Examples of the calculation of synthetic seismograms for different models of viscoelastic media are presented.  相似文献   

Hypergene Metallogeny of the Urals     

B. M. Mikhailov 《Lithology and Mineral Resources》2004,39(2):114-134

The presented overview of hypergene metallogeny of the Urals is largely based on original data of the author. All bauxite, Co–Ni oxide–silicate, and high-grade ferromanganese our deposits, gold, platinum, and diamond placers, as well as brown coal, kaoline, refractory, and other economic-grade mineral deposits, currently mined in the Urals are hosted in hypergene zones and related hypergene blankets of different ages. Prospects for diverse mineral deposits are estimated with a special emphasis on thermal hypergene deposits (Ni, Au, and others) that are atypical for the Urals but favorable for mining under conditions of the market economy owing to the presence of high-grade ore bodies.  相似文献   

Physical mechanism of strong negative storm effects in the daytime ionospheric F2 region observed with EISCAT   总被引：1，自引：0，他引：1  

A. Mikhailov  K. Schlegel 《Annales Geophysicae》1998,16(5):602-608

A self-consistent method for daytime F-region modelling was applied to EISCAT observations during two periods comprising the very disturbed days 3 April 1992 and 10 April 1990. The observed strong N_e decrease at F2-layer heights originated from different physical mechanisms in the two cases. The negative F2-layer storm effect with an N_mF2 decrease by a factor of 6.4 on 3 April 1992 was produced by enhanced electric fields (E 85 mV/m) and strong downward plasma drifts, but without any noticeable changes in thermos-pheric parameters. The increase of the O⁺ + N₂ reaction rate resulted in a strong enrichment of the ionosphere with molecular ions even at F2-layer heights. The enhanced electric field produced a wide mid-latitude daytime trough on 03 April 1992 not usually observed during similar polarization jet events. The other strong negative storm effect on 10 April 1990 with a complete disappearance of the F2-layer maximum at the usual heights was attributed mainly to changes in neutral composition and temperature. A small value for the shape parameter S in the neutral temperature profile and a low neutral temperature at 120 km indicate strong cooling of the lower thermosphere. We propose that this cooling is due to increased nitric oxide concentration usually observed at these heights during geomagnetic storms.  相似文献   

Comparative study of temporal variations in the earth’s gravity field using GRACE gravity models in the regions of three recent giant earthquakes     

V. O. Mikhailov  I. Panet  M. Hayn  E. P. Timoshkina  S. Bonvalot  V. Lyakhovsky  M. Diament  O. de Viron 《Izvestiya Physics of the Solid Earth》2014,50(2):177-191

Comparative analysis of coseismic and postseismic variations of the Earth’s gravity field is carried for the regions of three giant earthquakes (Andaman-Sumatra, December 26, 2004, magnitude M _w = 9.1; Maule-Chile, February 27, 2010, M _w = 8.8, and Tohoku-Oki, March 11, 2011, M _w = 9.0) with the use of GRACE satellite data. Within the resolution of GRACE models, the coseismic changes of gravity caused by these seismic events manifest themselves by large negative anomalies located in the rear of the subduction zone. The real data are compared with the synthetic anomalies calculated from the rupture surface models based on different kinds of ground measurements. It is shown that the difference between the gravity anomalies corresponding to different rupture surface models exceeds the uncertainties of the GRACE data. There-fore, the coseismic gravity anomalies are at least suitable for rejecting part of the models that are equivalent in the ground data. Within the first few months after the Andaman-Sumatra earthquake, a positive gravity anomaly started to grow above the deep trench. This anomaly rapidly captured the area of the back-arc basin and largely compensated the negative coseismic anomaly. The processes of viscoelastic stress relaxation do not fully allow for these rapid changes of gravity. According to the calculations, even with a sufficiently low viscosity of the upper mantle, relaxation only covers about a half of the observed change of the field. In order to explain the remaining temporal variations, we suggested the process of downdip propagation of the coseismic rupture surface. The feasibility of such a process was supported by numerical simulations. The sum of the gravity anomalies caused by this process and the anomaly generated by the processes of viscoelastic relaxation accounts well for the observed changes of the gravity field in the region of the earthquake. The similar postseismic changes of gravity were also detected for the region of the Tohoku-Oki earthquake. Just as in the case discussed above, this earthquake was also followed by a rapid growth of a positive postseismic anomaly, which partially counterbalanced the negative coseismic anomaly. The time variations of the gravity field in the region of the Maule-Chile earthquake differ from the pattern of changes observed in the island arcs described above. The postseismic gravity variations are in this case concentrated in a narrower band above the deep trench and shelf, and they do not spread over the continental territory, where the negative coseismic anomaly is located. These discrepancies reflect the difference in the geodynamical settings of the studied earthquakes.  相似文献   

SIMP-1 model: Mapping of <Emphasis Type="Italic">fo F</Emphasis>2 monthly medians over the Northern Hemisphere     

T. Yu. Leshchinskaya  V. V. Mikhailov 《Geomagnetism and Aeronomy》2016,56(6):733-741

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The response of river mouths to large-scale variations in sea level and river runoff: Case study of rivers flowing into the Caspian Sea     

V. N. Mikhailov  D. V. Magritsky  V. I. Kravtsova  M. V. Mikhailova  M. V. Isupova 《Water Resources》2012,39(1):11-43

Regularities in the response of the mouths of major rivers, flowing into the Caspian Sea, to large-scale variations in its level and river water runoff and sediment yield are considered. Changes in the morphological structure and hydrological regime of the Volga, Terek, Sulak, Ural, and Kura mouths have been analyzed in both geological past and separately for three modern periods: a considerable drop in Caspian Sea level before 1978, its abrupt rise in 1978–1995, and a relative stabilization in the subsequent years. Specific features were identified in the hydrological-morphological processes in different mouths, caused by the differences in river sediment yields, and the slopes of delta surface and mouth nearshore beds. Some theoretical and methodological approaches were verified in the analysis and evaluation of the processes under consideration. The obtained results of studies of the mouths of rivers flowing into the Caspian Sea can be regarded as examples and analogues in the assessment of processes, which take place at the mouths of other Russian and world rivers at present and can take place in the future under anticipated natural and anthropogenic variations in sea level and river runoff.  相似文献