A. V. Solov’ev

Torsional Alfvén waves in solar magnetic flux tubes of axial symmetry

Aims. Propagation and energy transfer of torsional Alfven waves in solar magnetic flux tubes of axial symmetry is studied. Methods. An analytical model of a solar magnetic flux tube of axial symmetry is developed by specifying a magnetic flux and deriving general analytical formulas for the equilibrium mass density and gas pressure. The main advantage of this model is that it can be easily adopted to any axisymmetric magnetic structure. The model is used to numerically simulate the propagation of nonlinear Alfven waves in such 2D flux tubes of axial symmetry embedded in the solar atmosphere. The waves are excited by a localized pulse in the azimuthal component of velocity and launched at the top of the solar photosphere, and they propagate through the solar chromosphere, the transition region, and into the solar corona. Results. The results of our numerical simulations reveal a complex scenario of twisted magnetic field lines and flows associated with torsional Alfven waves, as well as energy transfer to the magnetoacoustic waves that are triggered by the Alfven waves and are akin to the vertical jet flows. Alfven waves experience about 5% amplitude reflection at the transition region. Magnetic (velocity) field perturbations that experience attenuation (growth) with height agree with analytical findings. The kinetic energy of magnetoacoustic waves consists of 25% of the total energy of Alfven waves. The energy transfer may lead to localized mass transport in the form of vertical jets, as well as to localized heating because slow magnetoacoustic waves are prone to dissipation in the inner corona.

Two stages of granite formation in the Sredinny Range, Kamchatka: Tectonic and geodynamic setting of granitic rocks

The newly formed continental crust in southern Kamchatka was created as a result of the Eocene collision of the Cretaceous-Paleocene Achaivayam-Valagin island arc and the northeastern Asian margin. Widespread migmatization and granite formation accompanied this process in the Sredinny Range of Kamchatka. The tectonic setting and composition of granitic rocks in the Malka Uplift of the Sredinny Range are characterized in detail, and the U-Pb (SHRIMP) zircon ages are discussed. Two main stages of granite formation—Campanian (80–78 Ma ago) and Eocene (52 ± 2 Ma ago) have been established. It may be suggested that granite formation in the Campanian was related to the partial melting of the accretionary wedge due to its under-plating by mafic material or to plunging of the oceanic ridge beneath the accretionary wedge. The Eocene granitic rocks were formed owing to the collision of the Achaivayam-Valagin ensimatic island arc with the Kamchatka margin of Eurasia. In southern Kamchatka (Malka Uplift of the Sredinny Range), the arc-continent collision started 55–53 Ma ago. As a result, the island-arc complexes were thrust over terrigenous sequences of the continental margin. The thickness of the allochthon was sufficient to plunge the autochthon to a considerable depth. The autochthon and the lower portion of the allochthon underwent high-grade metamorphism followed by partial melting and emplacement of granitic magma 52 ± 2 Ma ago. The anomalously rapid heating of the crust was probably caused by the ascent of asthenospheric magma initiated by slab breakoff, while the Eurasian Plate plunged beneath the Achaivayam-Valagin arc.

Lateral structural variability in zone of eocene island-arc-continent collision, Kamchatka

The lateral variability of structural elements in the collision zone of the Cretaceous-Paleocene Achaivayam-Valagin island arc with the northeastern Asian margin is considered. The similarity and difference of Eocene collision structural elements in the north and the south of Kamchatka are shown. In northern Kamchatka, the continent-arc boundary is traced along the Lesnaya-Vatyn Thrust Fault, which completed its evolution about 45 Ma ago. The thin, near-horizontal allochthon of this thrust, composed of island-arc rocks, overlies the deformed but unmetamorphosed terrigeneous sequences of the Asian margin. The general structure of this suture in the Kamchatka Isthmus and southern Koryakia is comparable with the uppermost subduction zone, where a thin lithospheric wedge overlaps intensely deformed sediments detached from the plunging plate. In southern Kamchatka (Malka Uplift of the Sredinny Range), the arc-continent collision started 55–53 Ma ago with thrusting of island-arc complexes over terrigenous rocks of continental margin. However, the thickness of the allochthon was much greater than in the north. Immediately after this event, both the autochthon and lower part of allochthon were deformed and subsided to a significant depth. This subsidence gave rise to metamorphism of both the autochthon (Kolpakov and Kamchatka groups, Kheivan Formation) and lower allochthon (Andrianovka and Khimka formations). The anomalously fast heating of the crust was most likely related to the ascent of asthenospheric masses due to slab breakoff, when the Eurasian Plate was plunging beneath the Achaivayam-Valagin arc.

First fission-track dating of zircons from Mesozoic complexes of the Crimea

The fission-track dating of detrital zircon from Mesozoic terrigenous complexes of the Crimean mountains has been carried out for the first time. A young zircon population from the Tavria Group of sandstones of the Yaman ravine was dated at 220.1 ± 12.6 Ma, and the zircon population from the same deposits of the Crimea’s southern coast, at 193.6 ± 13.1, 167.1 ± 12.1, and 154.0 ± 10.2 Ma. Sandstones from the lowermost parts of the Demerdzhi Formation on Mount Yuzhnaya Demerdzhi comprise the Middle Jurassic young zircon population (169.9 ± 8.6 Ma). The age of the young zircon population from the Chenka Formation in the region of the Settlement of Observatoriya corresponds to the initial Middle Jurassic (178.9 ± 9.1 Ma). The timing of the cooling of the Mount Kastel massif was established at 149.0 ± 10.9 Ma. In all the considered cases, the age of terrigenous complexes is close to the age of enclosed zircons. Volcanic and/or magmatic rocks that formed synchronously with accumulation of terrigenous complexes in the sedimentary basin are likely to have been sources of zircons. Hence, the data obtained allow the timing of the Triassic-Jurassic magmatism in the Crimean mountains to be refined and three stages of magmatism to be distinguished: Late Triassic (Carnian?), poorly expressed Early Jurassic, and Middle Jurassic (Aalenian-Bathonian).

The role of the polarization mechanism for emission of radiation by atoms over a broad photon frequency range

This paper develops an effective method for calculating the bremsstrahlung cross section with allowance for the polarization mechanism. We calculate the cross section of bremsstrahlung produced in the scattering of electrons and positrons by H and Kr atoms. We also demonstrate the important role of polarization bremsstrahlung in the formation of the total emission spectrum over the entire frequency range.

New analytical and numerical models of a solar coronal loop: I. Application to forced vertical kink oscillations

Aims. We construct a new analytical model of a solar coronal loop that is embedded in a gravitationally stratified and magnetically confined atmosphere. On the basis of this analytical model, we devise a numerical model of solar coronal loops. We adopt this model to perform the numerical simulations of its vertical kink oscillations excited by an external driver. Methods. Our model of the solar atmosphere is constructed by adopting a realistic temperature distribution and specifying the curved magnetic field lines that constitute a coronal loop. This loop is described by 2D, ideal magnetohydrodynamic equations that are numerically solved by the FLASH code. Results. The vertical kink oscillations are excited by a periodic driver in the vertical component of velocity, which is acting at the top of the photosphere. For this forced driver with its amplitude 3 km s −1 , the excited oscillations exhibit about 1. 2k m s −1 amplitude in their velocity and the loop apex oscillates with an amplitude in displacement of about 100 km. Conclusions. The newly devised analytical model of the coronal loops is utilized for the numerical simulations of the vertical kink oscillations, which match well with the recent observations of decayless kink oscillations excited in solar loops. The model will have further implications on the study of waves and plasma dynamics in coronal loops, revealing physics of energy and mass transport mechanisms in the localized solar atmosphere.

Numerical simulations of sheared magnetic lines at the solar null line

Aims. We perform numerical simulations of sheared magnetic lines at the magnetic null line configuration of two magnetic arcades that are settled in a gravitationally stratified and magnetically confined solar corona. Methods. We developed a general analytical model of a 2.5D solar atmospheric structure. As a particular application of this model, we adopted it for the curved magnetic field lines with an inverted Y shape that compose the null line above two magnetic arcades, which are embedded in the solar atmosphere that is specified by the realistic temperature distribution. The physical system is described by 2.5D magnetohydrodynamic equations that are numerically solved by the FLASH code. Results. The magnetic field line shearing, implemented about 200 km below the transition region, results in Alfven and magnetoacoustic waves that are able to penetrate solar coronal regions above the magnetic null line. As a result of the coupling of these waves, partial reflection from the transition region and scattering from inhomogeneous regions the Alfven waves experience fast attenuation on time scales comparable to their wave periods, and the physical system relaxes in time. The attenuation time grows with the large amplitude and characteristic growing time of the shearing. Conclusions. By having chosen a di erent magnetic flux function, the analytical model we devised can be adopted to derive equilibrium conditions for a diversity of 2.5D magnetic structures in the solar atmosphere.

New Data on the Baraba Formation Age (the Sredinnyi Range of Kamchatka)

In the Sredinnyi Range of Kamchatka, the Baraba Formation of continental conglomerates is assumed to be of the late Campanian age based on found flora remains, but data of isotopic geochronology suggest the Eocene age of these deposits. New data on radiolarians from cherty pebbles are considered in this work along with results of fission-track dating of zircons from pebbles and matrix of the Baraba conglomerates. Fission-track dates obtained for zircons from matrix approve the Eocene age of the Baraba Formation, and new dates characterizing pebbles are not contradicting this conclusion. The Baraba Formation structural position can hardly be lower, therefore, than that of the Irunei Formation.

Cenozoic volcanic rocks of North Kamchatka: In search of subduction zones

Two belts of subaerial volcanic rocks—the Eocene Kinkil belt and the Neogene belt of the Sredinny Range—extend along the Kamchatka Isthmus. It is suggested that their formation is related to subduction of the oceanic lithosphere beneath the continental margin of North Kamchatka. The oceanic lithosphere consumed in the subduction zones could have been formed as a result of active spreading in the Komandorsky Basin. In the simplest case, both spreading and subduction reflect the northwestward motion of the lithosphere of the Komandorsky Plate relative to Kamchatka, the Shirshov Ridge, and the Aleutian Basin combined into one relatively immobile plate conventionally called the North American Plate. The authors perform a simulation of conjugate spreading and subduction. The most important parameter determining the regional geodynamics—the velocity of the Komandorsky Plate moving relative to the North American Plate—is taken as 2.5, 5.0, and 7.5 cm/yr. The calculated ages of the onset and end of volcanic activity in the aforementioned belts are compared with the dates obtained with the isotopic and paleontological methods. For the Eocene Kinkil belt, where volcanism started 44 Ma ago, the model age of the onset of subduction depends on the accepted velocity of the motion of the Komandorsky Plate and varies from 54 Ma at the velocity of 2.5 cm/yr to 47.5 Ma at the velocity of 7.5 cm/yr. It can be assumed that the model of fast subduction in this age interval is most consistent with the geological data. For the Miocene-Pliocene belt of the Sredinny Range, assuming the velocity of the motion of the Komandorsky Plate at 5.0 and 7.5 cm/yr, multiple rifting at the boundary with the Shirshov Ridge should be assumed. Therefore, for the end of the Neogene, a model with low velocity (2.5–5.0 cm/yr, i.e., about 4.0 cm/yr) is preferable.

Features of the bremsstrahlung accompanying collisions with a hydrogen atom in an excited state

The features of the bremsstrahlung appearing during a collision of a fast charged particle with a hydrogen atom (or hydrogenic ion) in an excited state are investigated. It is shown that the emission spectrum of photons with energies greater than the ionization potential of a given excited state (except the 2s state) displays narrow lines, which are caused by de-excitation of the atom in an intermediate state. It is demonstrated that the scattering of a charged particle on an excited hydrogen atom produces a feature which is not observed in the case of scattering on a ground-state hydrogen atom. Expressions are obtained for the generalized dynamic polarizability of the hydrogen atom and hydrogenic ions in the 1s, 2s, and 3s states. A method is developed for deriving expressions for the generalized dynamic polarizabilities of other excited states through the use of the Coulomb Green’s function and representation of the electronic wave function in terms of the differentiation of the generating functions of Laguerre polynomials. The bremsstrahlung cross sections for electrons and positrons colliding with hydrogen atoms in the 1s, 2s, and 3s states are calculated.