The World’s Largest Fouta Djallon–Mandingo Bauxite Province (West Africa): Part I. Background

Geology of Ore Deposits - The recognition of the Fouta Djallon–Mandingo territory as an independent bauxite province is substantiated. It is confined to the morphostructure of the same name...     

On the connection between the atmospheric electric field measured at the surface and the ionospheric electric field in the Central Antarctica

Regular measurements of the atmospheric electric field made at Vostok Station (φ=78.45°S; λ=106.87°E, elevation 3500 m) in Antarctica demonstrate that extremely intense electric fields (1000–5000 V/m) can be observed during snow storms. Usually the measured value of the atmospheric electric field at Vostok is about 100–250 V/m during periods with “fair weather” conditions. Actual relation between near-surface electric fields and ionospheric electric fields remain to be a controversial problem. Some people claimed that these intense electric fields produced by snowstorms or appearing before strong earthquakes can re-distribute electric potential in the ionosphere at the heights up to 300 km. We investigated interrelation between the atmospheric and ionospheric electric fields by both experimental and theoretical methods. Our conclusion is that increased near-surface atmospheric electric fields do not contribute notably to distribution of ionospheric electric potential.     

Distances to dwarf galaxies of the Canes Venatici I cloud

We determined the spatial structure of the scattered concentration of galaxies in the Canes Venatici constellation. We redefined the distances for 30 galaxies of this region using the deep images from the Hubble Space Telescope archive with the WFPC2 and ACS cameras.We carried out a high-precision stellar photometry of the resolved stars in these galaxies, and determined the photometric distances by the tip of the red giant branch (TRGB) using an advanced technique and modern calibrations. High accuracy of the results allows us to distinguish the zone of chaotic motions around the center of the system. A group of galaxies around M94 is characterized by the median velocity V _LG = 287 km/s, distance D = 4.28 Mpc, internal velocity dispersion σ = 51 km/s and total luminosity L _B = 1.61 × 10¹⁰ L _?. The projection mass of the system amounts to M _p = 2.56 × 10¹² M _?, which corresponds to the mass-luminosity ratio of (M/L) _p = 159 (M/L)_?. The estimate of the mass-luminosity ratio is significantly higher than the typical ratio M/L _B ～ 30 for the nearby groups of galaxies. The CVn I cloud of galaxies contains 4–5 times less luminous matter compared with the well-known nearby groups, like the Local Group, M81 and CentaurusA. The central galaxy M94 is at least 1^m fainter than any other central galaxy of these groups. However, the concentration of galaxies in the Canes Venatici may have a comparable total mass.     

Longitude and latitude structure of the polar activity of the Sun in the 21st cycle

A catalog of observations of polar faculae by the Mountain Astronomical Station of the Pulkovo Observatory (Kislovodsk) for the 21st polar-activity cycle of the Sun (1972–1976) has been compiled. The mean annual and semiannual longitude distributions of the facular surface density have been constructed for latitude bands from 35 to 85° with steps of 10° in latitude and 30° in longitude in polar (the “wind roses”) and cylindrical projections, using a Bartels coordinate-grid rotation system. Coherent spatial structures in these distributions, which are characteristically elongated in two mutually perpendicular directions (i.e., they have an “X”-like appearance), can be identified. The high-latitude activity in the northern and southern hemispheres tends to be in spatial antiphase. This behavior corresponds to a four-sector global polar-activity structure. This indicates the presence of a magnetic-field source that is not associated with the differential rotation of the sun and modulates the evolution of local magnetic fields.     

Study of the factors determining anomalous variability of carbon dioxide total column amount over St. Petersburg

Results of spectroscopic measurements of the carbon dioxide total column amount near St. Petersburg during forest fires in the period from August to September 2002 are analyzed. The HYSPLIT model is used to calculate air-mass trajectories and CO distribution on a mesoscale in this period. The HYSPLIT model simulations and measurements of carbon dioxide total column amount yield an estimate of the specific intensity of CO emission in a Pskov forest fire on August 28–September 8, 2002, equal to 0.17–0.26 kg m². This estimate can be used for an estimation of the integral CO emission from fires in northwestern Russian forests and for model simulations of atmospheric CO concentration fields. The estimate of the CO emission from forest fires that is obtained from ground-based measurements can also be made on the basis of satellite measurements if they contain information on CO in the lower tropospheric layers (0 to 2 km).     

KDG218, a nearby ultra-diffuse galaxy

We present properties of the low-surface-brightness galaxy KDG218 observed with the HST/ACS. The galaxy has a half-light (effective) diameter of a _e = 47″ and a central surface brightness of SB _V (0) = 24.^m4/□″. The galaxy remains unresolved with the HST/ACS, which implies its distance of D > 13.1 Mpc and linear effective diameter of A _e > 3.0 kpc. We notice that KDG218 is most likely associated with a galaxy group around the massive lenticular NGC4958 galaxy at approximately 22 Mpc, or with the Virgo Southern Extension filament at approximately 16.5 Mpc. At these distances, the galaxy is classified as an ultra-diffuse galaxy (UDG) similar to those found in the Virgo, Fornax, and Coma clusters. We also present a sample of 15 UDG candidates in the Local Volume. These sample galaxies have the following mean parameters: 〈D〉 = 5.1 Mpc, 〈A _e 〉 = 4.8 kpc, and 〈SB _B (e)〉 = 27.^m4/□″. All the local UDG candidates reside near massive galaxies located in the regions with the mean stellar mass density (within 1 Mpc) about 50 times greater than the average cosmic density. The local fraction of UDGs does not exceed 1.5% of the Local Volume population. We notice that the presented sample of local UDGs is a heterogeneous one containing irregular, transition, and tidal types, as well as objects consisting of an old stellar population.     

Spatial–Temporal CO2 Variations near St. Petersburg Based on Satellite and Ground-Based Measurements

Izvestiya, Atmospheric and Oceanic Physics - The results of studying spatial–temporal CO2 variations near St. Petersburg in 2014–2017 based on satellite measurements (OCO-2 satellite)...     

Series of classical solar activity indices: Kislovodsk data

We present data on the series of solar activity indices, Wolf sunspot numbers W and total sunspot areas S, obtained at the Kislovodsk high-altitude station of the Pulkovo Observatory. The problem of properly extending the 133-year-long Zürich series of W and the 102-year-long Greenwich series of S, which were discontinued in 1980 and 1976, respectively, is emphasized. We stress that the Kislovodsk data have retained mutual homogeneity with the classical series until now and that they are preferred for extension. The question under consideration is of fundamental importance in studying the solar activity variations on long time scales and related processes in the Sun-Earth system.     

“Hot” particles of the Yenisei River: Radioisotope composition,structure, and behavior in natural conditions

The radioisotope compositions, structure, and behavior of “hot” particles under the natural conditions of the Yenisei River in the nearby influence zone of Krasnoyarsk mining and chemical combine were examined in this study. By the composition of gamma-radiating isotopes, all particles are divided into three groups: mono-isotopic, bi-isotopic and poly-isotopic. Mono-isotopic “hot” particles, containing only ⁶⁰Co were discovered for the first time. Transuranium elements (²⁴¹Am and ²⁴³Cm) were revealed in poly-isotopic particles. Investigation of poly-isotopic particles by means of a scan electron microscope showed that the presence of UO₂ together with the lack of activation of ¹⁵²Eu testifies to the reactor origin of this particle. Experiments showed that in natural conditions “hot” particles under the influence of filtrating water and moisture of pore solutions are gradually dissolved and radionuclides are repeatedly drawn into migration.     

Time variability of the total methane content in the atmosphere over the vicinity of St. Petersburg

The results of measuring the methane content in the entire atmospheric thickness over the St. Petersburg region are given for 1991–2007. It is shown that, within this period, the mean annual cycle of the total methane content is characterized by its maximum values in December–January and its minimum values in June–August when the annual-cycle amplitude amounts to ∼3.6%. In this case, the annual variations in the total methane content may differ significantly from the mean annual cycle obtained in some years. A statistically significant linear trend of the total CH₄ content has not been revealed for 1991–2007. The obtained values of the linear-trend index have opposite signs in the winter and summer months (positive for January 0.6 ± 0.2%/year and February 0.4 ± 0.2%/year and negative for July 0.3 ± 0.2%/year and August 0.2 ± 0.1%/year). This fact suggests the tendency for an increase in the amplitude of the annual cycle of the total CH₄ content. The results of a spectral analysis of a series of data on the total CH₄ content show that, for 1991–2007, the following harmonics are pronounced with a confidence of 95%: 12 months (annual harmonic), 32 months (quasi-biennial oscillations), and 55 months (4.5 years), which are also pronounced in the series of meteorological parameters and total ozone content.