Effect of snow cover on pan-Arctic permafrost thermal regimes     

Hotaek Park  Alexander N. Fedorov  Mikhail N. Zheleznyak  Pavel Y. Konstantinov  John E. Walsh 《Climate Dynamics》2015,44(9-10):2873-2895

This study quantitatively evaluated how insulation by snow depth (SND) affected the soil thermal regime and permafrost degradation in the pan-Arctic area, and more generally defined the characteristics of soil temperature (T_SOIL) and SND from 1901 to 2009. This was achieved through experiments performed with the land surface model CHANGE to assess sensitivity to winter precipitation as well as air temperature. Simulated T_SOIL, active layer thickness (ALT), SND, and snow density were generally comparable with in situ or satellite observations at large scales and over long periods. Northernmost regions had snow that remained relatively stable and in a thicker state during the past four decades, generating greater increases in T_SOIL. Changes in snow cover have led to changes in the thermal state of the underlying soil, which is strongly dependent on both the magnitude and the timing of changes in snowfall. Simulations of the period 2001–2009 revealed significant differences in the extent of near-surface permafrost, reflecting differences in the model’s treatment of meteorology and the soil bottom boundary. Permafrost loss was greater when SND increased in autumn rather than in winter, due to insulation of the soil resulting from early cooling. Simulations revealed that T_SOIL tended to increase over most of the pan-Arctic from 1901 to 2009, and that this increase was significant in northern regions, especially in northeastern Siberia where SND is responsible for 50 % or more of the changes in T_SOIL at a depth of 3.6 m. In the same region, ALT also increased at a rate of approximately 2.3 cm per decade. The most sensitive response of ALT to changes in SND appeared in the southern boundary regions of permafrost, in contrast to permafrost temperatures within the 60°N–80°N region, which were more sensitive to changes in snow cover. Finally, our model suggests that snow cover contributes to the warming of permafrost in northern regions and could play a more important role under conditions of future Arctic warming.  相似文献   

Statistical acceleration of cosmic rays in anisotropic turbulent medium     

Yu. I. Fedorov 《Kinematics and Physics of Celestial Bodies》2011,27(1):1-16

Acceleration of cosmic rays interacting with the anisotropic magnetohydrodynamic turbulent medium is studied. Particle acceleration is caused by a large-scale electric field arising in a turbulent medium due to the α-effect. A comparison is made of equilibrium spectra of cosmic rays, characteristic of the specific acceleration mechanism, with the energy distribution of particles corresponding to the statistical Fermi acceleration.  相似文献   

Temporal Evolution of the Solar-Wind Electron Core Density at Solar Minimum by Correlating SWEA Measurements from STEREO A and B     

A. Opitz  J.-A. Sauvaud  A. Fedorov  P. Wurz  J. G. Luhmann  B. Lavraud  C. T. Russell  P. Kellogg  C. Briand  P. Henri  D. M. Malaspina  P. Louarn  D. W. Curtis  E. Penou  R. Karrer  A. B. Galvin  D. E. Larson  I. Dandouras  P. Schroeder 《Solar physics》2010,266(2):369-377

The twin STEREO spacecraft provide a unique tool to study the temporal evolution of the solar-wind properties in the ecliptic since their longitudinal separation increases with time. We derive the characteristic temporal variations at ～?1 AU between two different plasma parcels ejected from the same solar source by excluding the spatial variations from our datasets. As part of the onboard IMPACT instrument suite, the SWEA electron experiment provides the solar-wind electron core density at two different heliospheric vantage points. We analyze these density datasets between March and August 2007 and find typical solar minimum conditions. After adjusting for the theoretical time lag between the two spacecraft, we compare the two density datasets. We find that their correlation decreases as the time difference increases between two ejections. The correlation coefficient is about 0.80 for a time lag of a half day and 0.65 for two days. These correlation coefficients from the electron core density are somewhat lower than the ones from the proton bulk velocity obtained in an earlier study, though they are still high enough to consider the solar wind as persistent after two days. These quantitative results reflect the variability of the solar-wind properties in space and time, and they might serve as input for solar-wind models.  相似文献   

Methane in the water and bottom sediments of the mouth area of the Severnaya Dvina River during the winter time     

D. N. Gar’kusha  Yu. A. Fedorov 《Oceanology》2014,54(2):160-169

The spatial distribution of methane in the water and bottom sediments of the mouth area of the Severnaya Dvina River shows quite a similar character during the ice-cover and summer periods. It is characterized by the increase of the gas content from the head of the mouth area towards the delta with maximum values at the sites subjected to permanent anthropogenous impact. The difference consists in the higher level of the methane content in the bottom sediments during the winter period. At the same time, the excess of the winter to summer concentrations in the water was registered only at the stations within the impact area of the sources of anthropogenous contamination. As in the summer, the bottom sediments have a prevailing role in the formation of the level of the methane content in the water of the mouth area. The linear dependence between the concentrations of the total hydrogen sulfide and methane in the surface layer of the riverine sediments is probably caused by the parallel and nonconcurrent proceeding of the generation of these gases, which are controlled by the bacterial communities being not inhibitory to each other.  相似文献   

Variations of cosmic-ray energy in interplanetary space     

L. I. Dorman  M. E. Katz  Yu. I. Fedorov  B. A. Shakhov 《Astrophysics and Space Science》1983,94(1):43-95

A consistent theory of energy exchange between high-energy charged cosmic-ray particles and the random inhomogeneities of a magnetic field frozen in the moving solar wind plasma is developed. It is shown that the mode of the particle energy variations at a given law of plasma velocity variation in space is determined by the specific form of the particle distribution function. The equation for the density of cosmic-ray energy is obtained. Consideration is given to the generation of a charged particle energy spectrum in the course of multiple scatterings by the random inhomogeneities of the magnetic field.  相似文献   

On the vertical electric component of the geomagnetic pulsation field     

D.N. Chetaiev  E.N. Fedorov  S.M. Krylov  V.P. Lependin  V.A. Morghounov  V.A. Troitskaya  K.Yu. Zybin 《Planetary and Space Science》1975,23(2):311-314

The existence of a close correlation between the atmospheric electric field and geomagnetic pulsations in the range of Pc 2–4 is demonstrated experimentally and theoretically (from the horizontal propagation of pulsations). The need to take this into account in any geological-geophysical interpretation of experimental data is stressed.  相似文献   

Mass composition of the escaping plasma at Mars     

E. Carlsson  A. Fedorov  E. Budnik  H. Gunell  J.-A. Sauvaud  Y. Futaana  H. Andersson  J.D. Winningham  J.R. Sharber  A.J. Coates  D.O. Kataria  H. Koskinen  P. Riihelä  J. Kozyra  E. Roelof  S. Livi  K.C. Hsieh  M. Grande  J.-J. Thocaven  S. Orsini  M. Maggi  P. Bochsler  J. Woch  K. Asamura 《Icarus》2006,182(2):320-328

Data from the Ion Mass Analyzer (IMA) sensor of the ASPERA-3 instrument suite on Mars Express have been analyzed to determine the mass composition of the escaping ion species at Mars. We have examined 77 different ion-beam events and we present the results in terms of flux ratios between the following ion species: CO⁺₂/O⁺ and O⁺₂/O⁺. The following ratios averaged over all events and energies were identified: CO⁺₂/O⁺ = 0.2 and O⁺₂/O⁺ = 0.9. The values measured are significantly higher, by a factor of 10 for O⁺₂/O⁺, than a contemporary modeled ratio for the maximum fluxes which the martian ionosphere can supply. The most abundant ion species was found to be O⁺, followed by O⁺₂ and CO⁺₂. We estimate the loss of CO⁺₂ to be by using the previous measurements of Phobos-2 in our calculations. The dependence of the ion ratios in relation to their energy ranges we studied, 0.3-3.0 keV, indicated that no clear correlation was found.  相似文献   

On the Temporal Variability of the “Strahl” and Its Relationship with Solar Wind Characteristics: STEREO SWEA Observations     

P. Louarn  C. Diéval  V. Génot  B. Lavraud  A. Opitz  A. Fedorov  J. A. Sauvaud  D. Larson  A. Galvin  M. H. Acuňa  J. Luhmann 《Solar physics》2009,259(1-2):311-321

The “strahl” is a specific population of the solar wind, constituted by strongly field aligned electrons flowing away from the Sun, with energies >60 eV. Using the Solar Wind Electron Analyzer (SWEA) onboard STEREO, we investigate the short time scale fluctuations of this population. It is shown that its phase space density (PSD) at times presents fluctuations larger than 50% at scales of the order of minutes and less. The fluctuations are particularly strong for periods of a few tens of hours in high-speed streams, following the crossing of the corotating interaction region, when the strahl is also the most collimated in pitch angle. The amplitude of the fluctuations tends to decrease in conjunction with a broadening in pitch angle. Generally, the strongly fluctuating strahl is observed when the magnetic field is also highly perturbed. That SWEA is able to perform a very rapid 3D analysis at a given energy is essential since it can be demonstrated that the observed magnetic turbulence can only marginally perturb the PSD measurements.  相似文献   

Venus express: Highlights of the nominal mission     

D. V. Titov  H. Svedhem  F. W. Taylor  S. Barabash  J. -L. Bertaux  P. Drossart  V. Formisano  B. Häusler  O. Korablev  W. J. Markiewicz  D. Nevejans  M. Pätzold  G. Piccioni  J. -A. Sauvaud  T. L. Zhang  O. Witasse  J. -C. Gerard  A. Fedorov  A. Sanchez-Lavega  J. Helbert  R. Hoofs 《Solar System Research》2009,43(3):185-209

Venus Express is the first European (ESA) mission to the planet Venus. Its main science goal is to carry out a global survey of the atmosphere, the plasma environment, and the surface of Venus from orbit. The payload consists of seven experiments. It includes a powerful suite of remote sensing imagers and spectrometers, instruments for in-situ investigation of the circumplanetary plasma and magnetic field, and a radio science experiment. The spacecraft, based on the Mars Express bus modified for the conditions at Venus, provides a versatile platform for nadir and limb observations as well as solar, stellar, and radio occultations. In April 2006 Venus Express was inserted in an elliptical polar orbit around Venus, with a pericentre height of ～250 km and apocentre distance of ～66000 km and an orbital period of 24 hours. The nominal mission lasted from June 4, 2006 till October 2, 2007, which corresponds to about two Venus sidereal days. Here we present an overview of the main results of the nominal mission, based on a set of papers recently published in Nature, Icarus, Planetary and Space Science, and Geophysical Research Letters.  相似文献   

Receiver-Function Velocity Structure of the Lithosphere beneath the Khibiny and Lovozero Massifs,Northeastern Baltic Shield     

Goev  A. G.  Sanina  I. A.  Oreshin  S. I.  Reznichenko  R. A.  Tarasov  S. A.  Fedorov  A. V. 《Izvestiya Physics of the Solid Earth》2021,57(5):605-613

Izvestiya, Physics of the Solid Earth - Abstract—The velocity structure of the lithosphere is studied beneath the Khibiny and Lovozero massifs in the northeastern part of the Baltic shield....  相似文献