Polarization of Microwave Radio Emission of Flare-Producing Solar Active Regions     

Vladimir M. Bogod  Leonid V. Yasnov 《Solar physics》2009,255(2):253-271

On the basis of our multiwavelength observations made with the one-dimensional RATAN-600 radio telescope, we study the inversion of the circular polarization in the solar microwave emission at different frequencies. The inversion is detected in the emission of flare-producing active regions (FPARs) at various stages of their development, starting from the pre-flare stage. During the latest 23rd solar cycle maximum, numerous FPARs revealed spectral inhomogeneities in their polarized microwave radiation (Bogod and Tokhchukova, 2003, Astron. Lett. 29, 263). Here, we discuss a particular case of such inhomogeneities, the frequency-dependent double inversion of the sign of circular polarization, which probably reflects some essential processes in FPARs. We consider several mechanisms for the double inversion: linear interaction of waves in the region of a quasitransverse magnetic field, the propagation of waves through a region of zero magnetic field, the scattering of radio waves on waves of high-frequency plasma turbulence, the influence of the current fibrils on the propagation of the radio emission, and the magnetic “dips,” in which the direction of magnetic field lines changes the sign relative to the observer. All of them have shortcomings, but the last mechanism explains the observations the best.  相似文献   

Fog and stratus formation on the coast of Brazil   总被引：1，自引：0，他引：1  

Natalia Fedorova  Vladimir Levit  Dmitry Fedorov   《Atmospheric Research》2008,87(3-4):268

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Solar activity variations of thermospheric temperatures on Mars and a problem of CO in the lower atmosphere     

Vladimir A. Krasnopolsky 《Icarus》2010,207(2):638-647

Long-term MGS drag density observations at 390 km reveal variations of the density with season L_S (by a factor of 2) and solar activity index F_10.7 (by a factor of 3 for F_10.7 = 40-100). According to Forbes et al. (Forbes, J.M., Lemoine, F.G., Bruinsma, S.L., Smith, M.D., Zhang, X. [2008]. Geophys. Res. Lett. 35, L01201, doi:10.1029/2007GL031904), the variation with F_10.7 reflects variations of the exospheric temperature from 192 to 284 K. However, the derived temperature range corresponds to variation of the density at 390 km by a factor of 8, far above the observed factor of 3. The recent thermospheric GCMs agree with the derived temperatures but do not prove their adequacy to the MGS densities at 390 km. A model used by Forbes et al. neglects effects of eddy diffusion, chemistry and escape on species densities above 138 km. We have made a 1D-model of neutral and ion composition at 80-400 km that treats selfconsistently chemistry and transport of species with F_10.7, T_∞, and [CO₂]_80 km as input parameters. Applying this model to the MGS densities at 390 km, we find variation of T_∞ from 240 to 280 K for F_10.7 = 40 and 100, respectively. The results are compared with other observations and models. Temperatures from some observations and the latest models disagree with the MGS densities at low and mean solar activity. Linear fits to the exospheric temperatures are T_∞ = 122 + 2.17F_10.7 for the observations, T_∞ = 131 + 1.46F_10.7 for the latest models, and T_∞ = 233 + 0.54F_10.7 for the MGS densities at 390 km. Maybe the observed MGS densities are overestimated near solar minimum when they are low and difficult to measure. Seasonal variations of Mars’ thermosphere corrected for the varying heliocentric distance are mostly due to the density variations in the lower and middle atmosphere and weakly affect thermospheric temperature. Nonthermal escape processes for H, D, H₂, HD, and He are calculated for the solar minimum and maximum conditions.Another problem considered here refers to Mars global photochemistry in the lower and middle atmosphere. The models gave too low abundances of CO, smaller by an order of magnitude than those observed. Our current work shows that modifications in the boundary conditions proposed by Zahnle et al. (Zahnle, K., Haberle, R.M., Catling, D.C., Kasting, J.F. [2008]. J. Geophys. Res. 113, E11004, doi:10.1029/2008JE003160) are reasonable but do not help to solve the problem.  相似文献   

Thermal instability of the fluid column in a borehole: application to the Yaxcopoil hole (Mexico)     

Vladimir Cermak  Jan Safanda  Louise Bodri 《International Journal of Earth Sciences》2010,99(6):1437-1451

Observational evidence proved that even when a borehole is in “fully” stabilized conditions, temperature data may exhibit certain unrest resembling irregular oscillations in the order of hundredths or (in the extreme case) even tenths of degree. Temperature was monitored in complicated hydrogeological conditions in the Yaxcopoil-1 hole (Chicxulub impact structure, Mexico). Two experiments are reported: (a) 20-day monitoring when a logger was located in the center of the high temperature gradient anomaly produced by the cold wave slowly propagating downwards and (b) simultaneous three-loggers 18-day monitoring with loggers located above, in and below the anomaly. All observed temperature–time series displayed intermittent oscillations of temperature with sharp gradients and large fluctuations over all observed time scales. While the “upper” and “lower” records revealed quasi-periodic temperature variations, the “central” record shows fast temperature oscillations with strong up-and-down reversals, all with amplitudes up to a few tenths of degree. The observed temperature–time series were processed by recurrence and recurrence interval quantification as well as by spectral analyses. It is shown that fluid in a borehole, subject to thermal gradient, is stable, as far as the gradient remains below a certain critical value. At higher Rayleigh numbers, the periodic character of oscillations typical for “quiescent” regime is superseded by stochastic features. This “oscillatory” convection occurs due to instability of the horizontal boundary layers. In the specific case of the Yaxcopoil hole, the time series above and below the cold wave (characterized by relatively lower temperature gradients between 20 and 50 mK/m) contain a clear low frequency component produced by tidal forcing. This component dominates over the high frequency domain (periods from 10–15 to 1 min), which exhibit a scaling behavior. This pattern conspicuously changes in the center part of the cold wave, where the local temperature gradient exceeds 200 mK/m and where tidal forcing composes only ~3% of the signal.  相似文献   

North Atlantic warming: patterns of long-term trend and multidecadal variability   总被引：1，自引：1，他引：0  

Igor V. Polyakov  Vladimir A. Alexeev  Uma S. Bhatt  Evgenia I. Polyakova  Xiangdong Zhang 《Climate Dynamics》2010,34(2-3):439-457

Climate fluctuations in the North Atlantic Ocean have wide-spread implications for Europe, Africa, and the Americas. This study assesses the relative contribution of the long-term trend and variability of North Atlantic warming using EOF analysis of deep-ocean and near-surface observations. Our analysis demonstrates that the recent warming over the North Atlantic is linked to both long-term (including anthropogenic and natural) climate change and multidecadal variability (MDV, ~50–80 years). Our results suggest a general warming trend of 0.031 ± 0.006°C/decade in the upper 2,000 m North Atlantic over the last 80 years of the twentieth century, although during this time there are periods in which short-term trends were strongly amplified by MDV. For example, MDV accounts for ~60% of North Atlantic warming since 1970. The single-sign basin-scale pattern of MDV with prolonged periods of warming (cooling) in the upper ocean layer and opposite tendency in the lower layer is evident from observations. This pattern is associated with a slowdown (enhancement) of the North Atlantic thermohaline overturning circulation during negative (positive) MDV phases. In contrast, the long-term trend exhibits warming in tropical and mid-latitude North Atlantic and a pattern of cooling in regions associated with major northward heat transports, consistent with a slowdown of the North Atlantic circulation as evident from observations and confirmed by selected modeling results. This localized cooling has been masked in recent decades by warming during the positive phase of MDV. Finally, since the North Atlantic Ocean plays a crucial role in establishing and regulating the global thermohaline circulation, the multidecadal fluctuations discussed here should be considered when assessing long-term climate change and variability, both in the North Atlantic and at global scales.  相似文献   

Extended Self-Similarity in Geophysical and Geological Applications     

Vladimir I. Nikora  Derek G. Goring 《Mathematical Geology》2001,33(3):251-271

In this paper we demonstrate application of the Extended Self-Similarity (ESS) concept, recently developed in turbulence physics, for geological and geophysical phenomena. The theoretical background is discussed first and then the ESS properties in fluvial turbulence, sand wave dynamics, Martian topography, river morphometry, gravel-bed mobility, and atmospheric barometric pressure are explored. The main attention is paid to fluvial turbulence and sand waves, while other examples are presented to support the generality of the ESS concept in earth sciences. The results show that the ESS properties of the considered phenomena are remarkably similar to those reported for turbulence, in spite of different underlying mechanisms. This suggests that a general rule should exist which governs a wide class of complex natural phenomena.  相似文献   

Neue Vorstellungen über den Tiefbau von Vorsenken     

Igor Alexandrovič Rezanov  Vladimir Ivanovič Ševčenko 《International Journal of Earth Sciences》1973,62(3):958-968

Zusammenfassung Der geologische Tiefenbau und die Entwicklungsgeschichte der Kopetdag-, Terek-Kaspi-, Indol-Kuban- und Karpaten-Vorsenke sind ähnlich. Es zeigt sich, daß die genannten Vorsenken keine Zonen kurzzeitiger Durchbiegungen sind, die sich in der orogenen Schlußentwicklungsetappe des alpidischen Faltengebietes gebildet haben, sondern daß sie langlebige negative Strukturen darstellen. Die Intensität ihrer Durchbiegung zu Beginn des alpidischen geotektonischen Zyklus (in der Jura und Kreidezeit) ist mit der Größe der Absenkung im Neogen-Quartär vergleichbar. Im Verlaufe des gesamten alpidischen Zyklus entwickelten sich die Senken posthum.Überall dort, wo notwendige geophysikalische Untersuchungen durchgeführt wurden, wurde unter diesen Senken unterhalb eines mächtigen alpidischen Gesteinskomplexes ein genauso mächtiger Sedimentkomplex variszischen Alters festgestellt. Territorial fallen die Zonen der maximalen Mächtigkeiten des variszischen und alpidischen Gesteinskomplexes zusammen.

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Structure and development of the Pre-Copetdag, Terek-Caspian, Indol-Kuban, and Pre-Carpathian fore deeps are similar. The fore deeps were not zones of short term subsidence during the final stage of orogenic development of the Alpine folded belt, but they were long term subsidence zones. The rates of subsidence at the beginning of the Alpine geotectonic cycle (during Jurassic and Cretaceous) and at the end of the cycle (during Neogene and Quaternary) are comparable.Wherever geophysical investigations were carried out in this zone, beneath the Alpine sediments a Hercynian sediment complex of equal thickness was found. The areas of maximum thickness in both complexes coincide.

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Résumé La structure géologique et le développement historique des avant-fosses de Copetdag, Terek-Caspienne, Indol-Kouban et des Carpates sont semblables. Il appert que ces dépressions ne sont pas des zones d'inflexion de courte durée qui se sont formées pendant l'étape finale du plissement alpin, mais qu'ils présentent des structures négatives de longue durée. L'intensité de leur affaissement au commencement du cycle géotectonique alpin (au Jurassique et au Crétacé) est comparable, en grandeur, avec celui de la période néogène-quaternaire. Au cours de l'ensemble du cycle alpin, les dépressions se sont développées de façon posthume.Partout où ont eu lieu des explorations géophysiques, nous avons découvert sous ces avant-fosses, un épais complexe de roches alpines, et sous elles un complexe aussi puissant de sédiments varisques. Spatialement les zones des puissances maximum des complexes alpins et varisques coïncident.

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Définition morphologique de la phase des composantes de l'écoulement en italie     

Vladimir Frolow  Aimée Péreau 《Pure and Applied Geophysics》1954,27(1):159-166

Résumé Les moyennes mensuelles des débits mesurés à 229 stations de jaugeage des cours d'eau italiens ont permis le calcul de la composante annuelle et de la composante semi-annuelle par la méthode des combinaisons linéaires d'ordonnées de M. et MmeH. Labrouste. L'examen de la répartition géographique de la phase de chacune de ces composantes fait ressortir les différentes influences du relief continental et de la forme des côtes sur la mise en place dans le temps de ces deux fractions permanentes de l'écoulement.

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Summary The monthly average values of the run-off of italian rivers, measured in 229 gauging stations enabled the autors to calculate the annual component and the semi-annual component by the linear combinations of ordinates method (established by M. and MmeH. Labrouste). The geographical repartition of the phase of each component shows the different bearings of continental relief and coast outline on the time-distribution of these two permanent fractions of the flow.

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Detection of the Long-Term Microwave `Darkening' Before the 14 July 2000 Flare     

Tokhchukova  Susanna  Bogod  Vladimir 《Solar physics》2003,212(1):99-109

The latitudinal distribution of sunspot groups over a solar cycle is investigated. Although individual sunspot groups of a solar cycle emerge randomly at any middle and low latitude, the whole latitudinal distribution of sunspot groups of the cycle is not stochastic and, in fact, can be represented by a probability density function of the distribution having maximum probability at about 15.5°. The maximum amplitude of a solar cycle is found to be positively correlated against the number of sunspot groups at high latitude (35°) over the cycle, as well as the mean latitude. Also, the relation between the asymmetry of sunspot groups and its latitude is investigated, and a pattern of the N-S asymmetry in solar activity is suggested.  相似文献   

Stability Analysis of the Climate-Vegetation System in the Northern High Latitudes   总被引：6，自引：0，他引：6  

Victor Brovkin  Samuel Levis  Marie-France Loutre  Michel Crucifix  Martin Claussen  Andrey Ganopolski  Claudia Kubatzki  Vladimir Petoukhov 《Climatic change》2003,57(1-2):119-138

The stability of the climate-vegetation system in the northern high latitudesis analysed with three climate system models of different complexity: A comprehensive 3-dimensional model of the climate system, GENESIS-IBIS, and two Earth system models of intermediate complexity (EMICs), CLIMBER-2 andMoBidiC. The biogeophysical feedback in the latitudinal belt 60–70° N, although positive, is not strong enough to support multiple steady states: A unique equilibriumin the climate-vegetation system is simulated by all the models on a zonal scale for present-day climate and doubled CO₂ climate.EMIC simulations with decreased insolation also reveal a unique steady state. However, the climate sensitivity to tree cover, T_F, exhibits non-linear behaviour within the models. For GENESIS-IBIS and CLIMBER-2, T_F islower for doubled CO₂ climate than for present-day climate due to a shorter snow season and increased relative significance ofthe hydrological effect of forest cover. For the EMICs, T_F is higher for low tree fraction than for high treefraction, mainly due to a time shift in spring snow melt in response to changes in tree cover. The climate sensitivity to tree coveris reduced when thermohaline circulation feedbacks are accounted for in the EMIC simulations. Simpler parameterizations of oceanic processes have opposite effects on T_F: T_F is lower in simulations with fixed SSTs and higher in simulations with mixed layer oceans. Experiments with transient CO₂ forcing show climate and vegetation not in equilibrium in the northern high latitudes at the end of the 20thcentury. The delayed response of vegetation and accelerated global warming lead to rather abrupt changes in northern vegetation cover in the first halfof the 21st century, when vegetation cover changes at double the present day rate.  相似文献