Sub-terahertz emission from solar flares: The plasma mechanism of chromospheric emission

We consider the plasma mechanism of sub-terahertz emission from solar flares and determine the conditions for its realization in the solar atmosphere. The source is assumed to be localized at the chromospheric footpoints of coronal magnetic loops, where the electron density should reach n ≈ 10¹⁵ cm^?3. This requires chromospheric heating at heights h ? 500 km to coronal temperatures, which provides a high degree of ionization needed for Langmuir frequencies ν _p ≈ 200–400 GHz and reduces the bremsstrahlung absorption of the sub-THz emission as it escapes from the source. The plasma wave excitation threshold for electron-ion collisions imposes a constraint on the lower density limit for energetic electrons in the source, n ₁ > 4 × 10⁹ cm^?3. The generation of emission at the plasma frequency harmonic ν ≈ 2ν _p rather than the fundamental tone turns out to be preferred. We show that the electron acceleration and plasma heating in the sub-THz emission source can be realized when the ballooning mode of the flute instability develops at the chromospheric footpoints of a flare loop. The flute instability leads to the penetration of external chromospheric plasma into the loop and causes the generation of an inductive electric field that efficiently accelerates the electrons and heats the chromosphere in situ. We show that the ultraviolet radiation from the heated chromosphere emerging in this case does not exceed the level observed during flares.     

The tsunami on Sakhalin on August 2, 2007: Mareograph evidence and numerical simulation

Instrumental data on the tsunami registration on Sakhalin and Hokkaido islands are presented. The numerical simulation of the tsunami propagation in the Tatar Strait was performed. The results of the calculations are in satisfactory agreement with the observed data.     

The modern topography of the Scythian Plate as evidence for deformations in the crystalline basement

This work presents the results of tectonophysical modeling of tectonic deformations in the crystalline basement of the Scythian Plate, including estimated deformation values and stress-field orientations. The morphostructural parameters of the Earth’s surface, which were calculated using the LESSA program, were compared. In addition, some parameters of modern geodynamic processes that occur in the Scythian Plate, such as the level of seismicity and heat flow value, were calculated. The similarity between ancient and modern geodynamic processes allows us to propose that deformational processes in the crystalline basement of the Scythian Plate play a significant role in the formation of the modern topography and makes it possible to use morphostructural parameters of the relief for studying the deep structure of platform covers.     

First Data on the Geochemistry and Age of the Kontay Intrusion in Polar Siberia

The first ever comprehensive geochemical data on the Kontay intrusion, polar Siberia, demonstrate that the intrusion is profoundly differentiated and shows geochemical features typical of intraplate magmatism. The age of the intrusion is Early Paleozoic. The paper summarizes literature data regarded as circumstantial evidence that a large magmatic intraplate (perhaps, plume-related) province of Early Paleozoic age may occur in the northern part of the Siberian Platform, whose only component found as of now is the Kontay intrusion. The intrusion is demonstrated not to possess any precious-metal (Ag–Pd) ore potential, contrary to what was surmised previously.     

The World’s Largest Fouta Djallon–Mandingo Bauxite Province (West Africa): Part III. The Influence of Geomorphic Factors and the Age of Relief on the Spatial Distribution,Size, and Quality of Bauxite Deposits

Geology of Ore Deposits - The scheme of geomorphic evolution of the region was substantially refined, compared to the previous understanding, based on the results of geologic and geomorphic...     

A dynamic theory of type III solar radio bursts

All four large EUV bursts (peak 10–1030 Å flux enhancements 2 ergs cm^–2 s^–1 at 1 AU as deduced from sudden frequency deviations), for which there were available concurrent white light observations of at least fair quality, were detected as white light flares. The rise times and maxima of the white light emissions coincided with rise times and maxima of the EUV bursts. The frequency of strong EUV bursts suggests that white light flares may occur at the rate of five or six per year near sunspot maximum. All of the white light flare areas coincided with intense bright areas of the H flares. These small areas appeared to be sources of high velocity ejecta in H. The white light flares occurred as several knots or patches of 2 to 15 arc-sec diameter, with bright cores perhaps less than 2 arc-sec diameter (1500 km). They preferred the outer penumbral borders of strong sunspots within 10 arc-sec of a longitudinal neutral line in the magnetic field. The peak continuum flux enhancement over the 3500–6500 Å wavelength range is about the same order of magnitude as the peak 10–1030 Å flux enhancement.     

C, О, S,and Sr Isotope Geochemistry and Chemostratigraphy of Ordovician Sediments in the Moyero River Section,Northern Siberian Platform

The ⁸⁷Sr/⁸⁶Sr ratio in gypsum and limestones of the Ordovician section of the Moyero River decreases from the bottom upward from 0.7091?0.7095 in the Irbukli Formation (Nyaian Regional Stage, ~Lower Ordovician Tremadocian Stage) to 0.7080 in the upper part of the Dzherom Formation (Dolborian Regional Stage, ~Upper Ordovician Katian Stage), which is well consistent with biostratigraphic subdivision of the section and existing concept concerning the strontium isotope evolution of the World Ocean. The most characteristic feature of the carbon isotope curve is decrease of δ¹³С values in carbonates from weakly positive values (0.5…1.1‰) in the Irbukli Formation (Nyaian Regional Stage) to sharply negative values (–5.4...–5.8‰) in the middle part of the Kochakan Formation (top of the Kimaian Regional Stage, ~end of the Dapingian–base of the Darriwilian Stage). Increase of δ¹⁸О from 20?22‰ to 26?28‰, the negative correlation of δ¹³С and δ¹⁸О, and decrease of δ³⁴S in gypsum from 30?32‰ to 22?24‰ in this interval indicate that the ¹³С depletion of carbonates was not related to the sulfate reduction and oxidation of organic matter during diagenesis and that the negative δ¹³С excursion was of primary nature. The presence of negative δ¹³С anomalies at this stratigraphic level in Ordovician sections of the South and North America (Buggish et al., 2003; Edwards and Saltzman, 2014; McLaughlin et al., 2016) indicates the global or subglobal distribution of this event, which was possibly related to the emergence of the oldest ground vegetation. Against the general decrease of δ¹³С, the lower part of the section reveals three low-amplitude (1?2‰) positive excursions, the position of which in general confirms the existing correlation scheme of the Moyero River section with the international scale. The upper part of the section is characterized by the alternation of low-δ¹³С intervals (from–2 to–3‰) and brief positive excursions with amplitude of 0.5?1.3‰. The positive δ¹³С excursion terminating the Ordovician section of the Moyero River correlates with the δ¹³С excursion in the middle Katian Stage, while the δ¹³С excursion in the lower part of the Baksian Regional Stage correlates with the excursion marking the Katian–Sandbian boundary.     

Hymenoptera (wasps,bees and ants) in mid-Cretaceous Burmese amber: A review of the fauna

The Burmese amber assemblage of Hymenoptera with its 47 constituent families is now the richest in Cretaceous. A collection of Burmite (Burmese amber) from the Hukawng Valley, Myanmar at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences was examined, revealing that Burmite inclusions contain a very highly diverse hymenopteran fauna with as many as ten families found new for the Burmese fossil assemblage. The mid-Cretaceous hymenopteran fauna of Burmese amber is revised at the family level. A high level of the first family occurrences and endemism is demonstrated suggestive of an insular syndrome affected the mid-Cretaceous Burmese biome, as well as somewhat contradictory features in composition of the hymenopteran families there.     

Kimberlites of the Manchary pipe: a new kimberlite field in Central Yakutia

This paper reports new petrographic and mineralogical data on the Manchary kimberlite pipe, which was discovered south of Yakutsk (Central Yakutia) in 2007–2008, 100 km. The pipe breaks through the Upper Cambrian carbonate deposits and is overlain by Jurassic terrigenous rock masses about 100 m thick. It is composed of greenish-gray kimberlite breccia with a serpentine-micaceous cement of massive structure. The porphyry texture of kimberlite is due to the presence of olivine, phlogopite, and picroilmenite phenocrysts. The SiO₂ and Al₂O₃ contents of the groundmass are indicative of typical noncontaminated kimberlites. The groundmass has a significant content of ore minerals: Fe- and Cr-spinels, perovskite, magnetite, and, less commonly, magnesian Cr-magnetite. Pyropes occur in kimberlites as sharp-edged fragments and show uneven distribution. Chemically, they belong to lherzolite, wehrlite, or nondiamondiferous dunite–harzburgite parageneses. Garnets corresponding to lherzolites of anomalous composition make up 8%; this is close to the garnet content of Middle Paleozoic kimberlites from the Yakutian kimberlite province. The pyropes from the new pipe are compositionally similar to those from diamond-poor Middle Paleozoic kimberlites in the north of the Yakutian diamondiferous province. Chemically, pyropes from the Manchary pipe and those from the modern alluvium of the Kengkeme and Chakyya Rivers differ substantially. Consequently, the rocks of the pipe could not be a source of pyropes for this alluvium. They probably occured from other sources. This fact along with numerous “pipelike” geophysical anomalies, suggest the existence of a new kimberlite field in Central Yakutia.