Daytime F2-layer positive storm effect at middle and lower latitudes   总被引：3，自引：0，他引：3  

A. V. Mikhailov  M. G. Skoblin  M. Förster 《Annales Geophysicae》1995,13(5):532-540

Daytime F2-layer positive storm effects at middle and lower latitudes in the winter thermosphere are analyzed using AE-C, ESRO-4 neutral gas composition data, ground-based ionosonde observations and model calculations. Different longitudinal sectors marked by the storm onset as ‘night-time’ and ‘daytime’ demonstrate different F2-layer positive storm mechanisms. Neutral composition changes in the ‘night-time’ sector with increased [O] and [N₂] absolute concentrations, while (N₂/O)_storm/(N₂/O)_quiet\approx1 at F2-layer heights, are shown to contribute largely to the background N_mF2 increase at lower latitudes lasting during daytime hours. Storm-induced surges of the equatorward wind give rise to an additional N_mF2 increase above this background level. The mid-latitude F2-layer positive storm effect in the ‘daytime’ sector is due to the vertical plasma drift increase, resulting from the interaction of background (poleward) and storm-induced (equatorward) thermospheric winds, but not to changes of [O] and [N₂] concentrations.  相似文献   

Coseismic and post-seismic signatures of the Sumatra 2004 December and 2005 March earthquakes in GRACE satellite gravity   总被引：2，自引：0，他引：2  

Isabelle Panet  Valentin Mikhailov  Michel Diament  Fred Pollitz  Geoffrey King  Olivier de Viron  Matthias Holschneider  Richard Biancale  Jean-Michel Lemoine 《Geophysical Journal International》2007,171(1):177-190

The GRACE satellite mission has been measuring the Earth's gravity field and its temporal variations since 2002 April. Although these variations are mainly due to mass transfer within the geofluid envelops, they also result from mass displacements associated with phenomena including glacial isostatic adjustment and earthquakes. However, these last contributions are difficult to isolate because of the presence of noise and of geofluid signals, and because of GRACE's coarse spatial resolution (>400 km half-wavelength). In this paper, we show that a wavelet analysis on the sphere helps to retrieve earthquake signatures from GRACE geoid products. Using a wavelet analysis of GRACE geoids products, we show that the geoid variations caused by the 2004 December ( M _w= 9.2) and 2005 March ( M _w= 8.7) Sumatra earthquakes can be detected. At GRACE resolution, the 2004 December earthquake produced a strong coseismic decrease of the gravity field in the Andaman Sea, followed by relaxation in the area affected by both the Andaman 2004 and the Nias 2005 earthquakes. We find two characteristic timescales for the relaxation, with a fast variation occurring in the vicinity of the Central Andaman ridge. We discuss our coseismic observations in terms of density changes of crustal and upper-mantle rocks, and of the vertical displacements in the Andaman Sea. We interpret the post-seismic signal in terms of the viscoelastic response of the Earth's mantle. The transient component of the relaxation may indicate the presence of hot, viscous material beneath the active Central Andaman Basin.  相似文献   

Why the Sacramento Delta area differs from other parts of the great valley: Numerical modeling of thermal structure and thermal subsidence of forearc basins     

V. O. Mikhailov  T. Parsons  R. W. Simpson  E. P. Timoshkina  C. Williams 《Izvestiya Physics of the Solid Earth》2007,43(1):75-90

Data on present-day heat flow, subsidence history, and paleotemperature for the Sacramento Delta region, California, have been employed to constrain a numerical model of tectonic subsidence and thermal evolution of forearc basins. The model assumes an oceanic basement with an initial thermal profile dependent on its age subjected to refrigeration caused by a subducting slab. Subsidence in the Sacramento Delta region appears to be close to that expected for a forearc basin underlain by normal oceanic lithosphere of age 150 Ma, demonstrating that effects from both the initial thermal profile and the subduction process are necessary and sufficient. Subsidence at the eastern and northern borders of the Sacramento Valley is considerably less, approximating subsidence expected from the dynamics of the subduction zone alone. These results, together with other geophysical data, show that Sacramento Delta lithosphere, being thinner and having undergone deeper subsidence, must differ from lithosphere of the transitional type under other parts of the Sacramento Valley. Thermal modeling allows evaluation of the rheological properties of the lithosphere. Strength diagrams based on our thermal model show that, even under relatively slow deformation (10⁻¹⁷ s⁻¹), the upper part of the delta crystalline crust (down to 20–22 km) can fail in brittle fashion, which is in agreement with deeper earthquake occurrence. Hypocentral depths of earthquakes under the Sacramento Delta region extend to nearly 20 km, whereas, in the Coast Ranges to the west, depths are typically less than 12–15 km. The greater width of the seismogenic zone in this area raises the possibility that, for fault segments of comparable length, earthquakes of somewhat greater magnitude might occur than in the Coast Ranges to the west. The text was submitted by the authors in English.  相似文献   

Long-Term Water Level Variations in the Eastern Sea of Azov and in the Mouth Reach of the Don River     

Mikhailov  V. N.  Povalishnikova  E. S.  Zudilina  S. V.  Tiguntsev  L. A. 《Water Resources》2001,28(6):587-595

Studies of long-term water level variations at marine hydrometeorological stations in the eastern Sea of Azov established a rise in the sea level which accelerated in the past 40 years. Allowance for the tectonic component permitted assessing the average rate of eustatic rise in the level. Oppositely directed long-term level variations were established in the mouth area of the Don River. Water level was found to rise at the downstream gages because of the backwater effect caused by the Sea of Azov level rise and delta deposits subsidence and to drop at the upstream gages mainly because of bed erosion owing to a reduction in sediment runoff after the construction of the Tsimlyanskoe Reservoir.  相似文献   

Disturbed vertical E×B plasma drifts in the equatorial F2 region at solar minimum deduced from observed NmF2 and hmF2 variations     

A. V. Mikhailov  M. Förster  T. Y. Leschinskaya 《Annales Geophysicae》1996,14(7):733-743

Ground-based ionosonde and magnetic-field observations on the equatorial station Huancayo, ESRO4 neutral-composition measurements, and theoretical model calculations were used to analyze disturbed E×B vertical plasma drift during the phase of solar minimum in 1973. Vertical drifts calculated for disturbed days do not show the systematic decrease often mentioned in publications, and demonstrate strong dependence on IMF-B_z changes. It is confirmed with the help of our drift calculations that B_z turnings to a northward direction result in a decrease (up to reversal) of normal Sq (eastward during daytime and westward at nighttime) in the zonal component of electric field. Southward B_z excursions enhance normal E_y both in daytime and nighttime hours. Model predictions of E_y’s reaction to IMF-B_z changes are discussed.  相似文献   

Geodynamic models and their application in the combined interpretation of geological and geophysical data (a review)     

V. O. Mikhailov  V. M. Gordin  E. P. Timoshkina  E. A. Kiseleva  E. I. Smolyaninova 《Izvestiya Physics of the Solid Earth》2007,43(1):2-12

The paper presents a review of investigations in the field of the theory and practice of the interpretation of geological and geophysical data with geodynamic models that were carried out mainly by researchers of the Institute of Physics of the Earth, Russian Academy of Sciences. Evolutionary models of platform structures, passive continental margins, rift zones, and orogens are examined. The review presents formulations of inverse problems and results of interpretation for various regions, including sedimentary basins of the East European Platform, Atlantic Ocean margins, the Caucasus, the South Urals, and others.  相似文献   

Erratum to: Seasonal Variations in the b-Value of the Reservoir-Triggered Seismicity in the Koyna–Warna Region,Western India     

Smirnov  V. B.  Potanina  M. G.  Kartseva  T. I.  Ponomarev  A. V.  Patonin  A. V.  Mikhailov  V. O.  Sergeev  D. S. 《Izvestiya Physics of the Solid Earth》2022,58(4):603-603

Izvestiya, Physics of the Solid Earth - An Erratum to this paper has been published: https://doi.org/10.1134/S1069351322090014  相似文献   

A method to solve the paleotectonic analysis problem     

Valentine O. Mikhailov 《Mathematical Geology》1993,25(7):949-961

The method to determine the rates of tectonic movements is based on the use of dynamic models of sedimentary basins. A standard dataset should be provided as input information: the present-day position of sedimentary layer interfaces (chronostratigraphic boundaries), land surface and basement, the layer ages, and the uncertainty limits within which the depth of sedimentation of each layer may have differed. In terms of dynamic models, the paleotectonic analysis problem is reduced to the determination of such tectonic rates that, at prescribed reference times, the model surface topography within the assumed limits would be constrained. At the final moment, the interfaces would be brought into agreement with the contemporary geologic cross-section. The analysis the problem of tectonic rates determination has shown that it has no unique solution. One of the ways to obtain the unique solution is to seek it within a prescribed class of functions, for example, the Fourier series. This method differs from the paleotectonic analysis methodology in that it treats the tectonic rates of motion as functions of time and spatial variables. Under certain conditions, it proves feasible to reconstruct the rates of tectonic movements not only within the time intervals represented in the deposited strata, but within periods of erosion as well. It also is possible to take into account the deformation-induced changes in thickness of the layers. The method's application is illustrated with an example of the Terek-Caspian Trough. As follows from the computation, the tectonic movements since the Middle Jurassic may be presented as a sum of two components: an overall slowing-down subsidence whose rate is proportional to the square root of the age, and local movements which follow a regular oscillatory time pattern with a period of 60–70 MY. The character of the local movements is such that the profile appears to break into a northern and southern segment. When one was being uplifted, the other segment was sinking, andvice versa. These two segments are separated by a deep-seated fault. This may have been a result of an external compression on the trough.  相似文献   

Frequency of Boundary-Layer-Top Fluctuations in Convective and Stable Conditions Using Laser Remote Sensing   总被引：1，自引：0，他引：1  

Giovanni Martucci  Renaud Matthey  Valentin Mitev  Hans Richner 《Boundary-Layer Meteorology》2010,135(2):313-331

The planetary boundary-layer (PBL) height is determined with high temporal and altitude resolution from lidar backscatter profiles. Then, the frequencies of daytime thermal updrafts and downdrafts and of nighttime gravity waves are obtained applying a fast Fourier transform on the temporal fluctuation of the PBL height. The principal frequency components of each spectrum are related to the dominant processes occurring at the daytime and nighttime PBL top. Two groups of cases are selected for the study: one group combines daytime cases, measured in weak horizontal wind conditions and dominated by convection. The cases show higher updraft and downdraft frequencies for the shallow, convective boundary layer and lower frequencies for a deep PBL. For cases characterized by strong horizontal winds, the frequencies directly depend on the wind speed. The temporal variation of the PBL height is determined also in the likely presence of lee waves. For nighttime cases, the main frequency components in the spectra do not show a real correlation with the nocturnal PBL height. Altitude fluctuations of the top of the nocturnal boundary layer are observed even though the boundary layer is statically stable. These oscillations are associated with the wind shear effect and with buoyancy waves at the PBL top.  相似文献   

Extreme flood on the Danube River in 2006   总被引：2，自引：0，他引：2  

V. N. Mikhailov  V. N. Morozov  N. I. Cheroy  M. V. Mikhailova  Ye. F. Zav'yalova 《Russian Meteorology and Hydrology》2008,33(1):48-54

Causes and features of an extreme flood on the Danube River in spring and summer 2006 are considered. The water levels at some gauge stations on the Middle Danube and at most gauge stations on the Lower Danube exceeded maxima observed during previous 100–130 years. The flood on the Lower Danube lasted from March to July and led to widespread inundations and damage. The flood was caused by melt of large amounts of snow accumulated in the river basin during winter, very warm spring, and abundant rains. In recent decades, the occurrence frequency of extreme hydrological events on the Danube River (large spring-summer floods and catastrophic rainfall freshets) has increased.  相似文献