Field Research in the Baltic Sea on Cruise 55 of the P/V Akademik Ioffe

Oceanology - New data on the structure of the water column, upper layer of bottom sediments, and biological communities of the Gdansk and Gotland deeps and the Gulf of Finland in the Baltic Sea...     

Dayside isotropic precipitation of energetic protons

Recently it has been shown that isotropic precipitation of energetic protons on the nightside is caused by a non-adiabatic effect, namely pitch-angle scattering of protons in curved magnetic field lines of the tail current sheet. Here we address the origin of isotropic proton precipitation on the dayside. Computations of proton scattering regions in the magnetopheric models T87, T89 and T95 reveal two regions which contribute to the isotropic precipitation. The first is the region of weak magnetic field in the outer cusp which provides the 1–2° wide isotropic precipitation on closed field lines in a 2–3 hour wide MLT sector centered on noon. A second zone is formed by the scattering on the closed field lines which cross the nightside equatorial region near the magnetopause which provides isotropic precipitation starting 1.5–2 h MLT from noon and which joins smoothly the precipitation coming from the tail current sheet. We also analyzed the isotropic proton precipitation using observations of NOAA low altitude polar spacecraft. We find that isotropic precipitation of >30 to > 80 keV protons continues around noon forming the continuous oval-shaped region of isotropic precipitation. Part of this region lies on open field lines in the region of cusp-like or mantle precipitation, its equatorward part is observed on closed field lines. Near noon it extends 1–2° below the sharp boundary of solar electron fluxes (proxy of the open/closed field line boundary) and equatorward of the cusp-like auroral precipitation. The observed energy dispersion of its equatorward boundary (isotropic boundary) agrees with model predictions of expected particle scattering in the regions of weak and highly curved magnetic field. We also found some disagreement with model computations. We did not observe the predicted split of the isotropic precipitation region into separate nightside and dayside isotropic zones. Also, the oval-like shape of the isotropic boundary has a symmetry line in 10–12 MLT sector, which with increasing activity rotates toward dawn while the latitude of isotropic boundary is decreasing. Our conclusion is that for both dayside and nightside the isotropic boundary location is basically controlled by the magnetospheric magnetic field, and therefore the isotropic boundaries can be used as a tool to probe the magnetospheric configuration in different external conditions and at different activity levels.     

Late-quaternary transgression of the White Sea as deduced from data on GIS-Based bottom relief analysis

We examine the use of geoinformation systems and relevant software applications in marine geomorphology in terms of the digital elevation model of the White Sea region. The geomorphological development of the contemporary shoreline is shown on the basis of comparing the parameters of adjacent surfaces. The technique is suggested for identifying relative tectonic deformations by determining the morphoblock division of the seabed surface. In this case, the boundaries of the time interval used in investigating the tectonic dislocations are specified indirectly by the scale coefficient of the initial digital model. This indirect relationship is determined on the basis of the well-known expression of a dependence of oscillations of a massive object in an elastic medium. By analyzing the structure of seabed relief, we determined areas with a high value of tectonic deformations for the period involved (Holocene) relative to the level of marine sedimentation. A neotectonic regionalization of the surface of the White Sea bed allowed us to identify, on the basis of statistical dependencies, large planate subhorizontal surfaces of the seabed. Upon comparing the graphical analytical information obtained with geomorphological characteristics of these surfaces, we determined four submarine terraces of an abrasion-accumulative origin and drew the corresponding boundaries within which the ancient White Sea existed over the course of the Holocene. By analyzing the position of the marine terraces, we identified a relative intensification of marine abrasion processes at a particular evolutionary stage of the water area. This is associated with a crucial marker event in the development of the White Sea water area, namely its connection with the Word Ocean in the early Holocene.     

Detection,Estimation of Magnitude,and Relative Location of Weak Aftershocks Using Waveform Cross-Correlation: The Earthquake of August 7, 2016, in the Town of Mariupol

The study of the stress-strain state of a medium in seismically quiet areas is difficult because of the absence of strong events. Under such circumstances, each earthquake, even relatively weak, is of high importance. In this case, all possible information on tectonic stresses and their dynamics, e.g., information on time, location, and magnitude of aftershocks, should be obtained from available seismic data. The earthquake near the town of Mariupol which occurred on August 7, 2016, had a body wave magnitude of 4.5–4.9 from the data of the different seismological centers. We detected 12 aftershocks that occurred within 5 days after the main shock using two seismic arrays (AKASG and BRTR) and one three-component station (KBZ) of the International Monitoring System, as well as two array stations of the Institute of Geosphere Dynamics, Russian Academy of Sciences. For six aftershocks, signals were found at three or more stations. The other aftershocks were detected from the data at two out of three nearest stations. Signal detection and association with aftershocks of the main shock, as well as estimation of magnitude and relative location of the found aftershocks, were carried out using the method of waveform cross-correlation (WFCC). The signals from the main shock that acted as the only master event (ME) for the WFCC method were used as waveform templates. To increase the signal-to-noise ratio and to determine the exact onset time of regular seismic waves from aftershocks, we used waveform templates of different length, from 10 to 180 s depending on the wave type and distance to the station, as well as band filtering in narrow frequency bands. The highest sensitivity of the detector and accuracy of the P-wave onset time estimates were reached when a waveform template included all regular waves from P to L _g . Association of signals with aftershocks was based on back projection of signal arrival times to origin times using the travel time from a master event to the station, which was measured with a very low error, being equal to almost half of the digitization step length. To develop a seismic event hypothesis, the origin times at two or more stations should be spaced within a 2-s interval.     

Importance of the Variability of Geocryological Conditions in the Determination of the Significance of the Lakes in the Structure of Regional Water Discharge

Water Resources - The dynamics of the talik zones, associated both with the internal cyclical nature of their development and with climate changes, leads to temporary differences in the volume of...     

X-ray and optical variability of the seyfert galaxy NGC 7469

Based on our UBV RI observations and X-ray data from the RXTE satellite, we have investigated the variability of the galaxy NGC 7469 over the period 1995–2009. In 1995–2000, the optical brightness of the galactic nucleus changed almost by 1 ^m in the U band. In 2000–2009, the amplitude of the optical variations was considerably lower. Regular X-ray observations began only in 2003. The X-ray fractional variability amplitude is higher than the optical one. The optical variability amplitude decreases with increasing wavelength. The full width at half maximum of the X-ray and B-band autocorrelation functions is about 8 and 62 days, respectively. The structure functions (SF) in the X-ray range on time scales up to 7 days and in the optical range on time scales up to 100 days have the form of a power law SF(τ) ∼ τ ^b , where τ is the time shift. On time scales of more than a day, where both structure functions have been determined rather reliably, their slopes differ markedly: b = 1.34 ± 0.06 and b = 0.25 ± 0.05 for the optical and X-ray ranges, respectively. The X-ray and B-band structure functions begin to flatten, respectively, near 6–8 days and on time scales of about 90 days. The observed structure functions can be described by the model of a superposition of independent Gaussian flares whose number changes with duration ω as n(ω) ∼ ω ^α and whose amplitudes depend on duration as A(ω) ∼ ω ^β. The flux distribution and the flux-amplitude relation are consistent with the model of a light curve in the form of a superposition of random flares. Once the fast intensity variations have been filtered out on long time scales, the X-ray light curve correlates well with the optical one. No lag of the X-ray variations relative to those in the B band is detected. The light variations in the R and I bands lag behind those in the B band calculated from the centroid of the cross-correlation function by 2.6 and 3.5 days, respectively, at a 3σ confidence level.     

Pulsations of optical radiation during the flare of YZ CMi occurred on February 9, 2008

One of the most powerful and long-lived flares on the active red dwarf YZ CMi is considered. The flare was observed in the U band at the Terskol Peak Observatory on February 9, 2008. During the formation of the flare over the course of 30 seconds, the flare-induced stellar luminosity increased and became more than 180 times the preflare value. The total duration of the flare was approximately one hour. At the flare maximum, quasi-periodic pulsations having a specified period of approximately 11 s, an initial modulation depth of 5.5%, and an exponential damping time of 29 s were discovered using wavelet analysis. Assuming that the pulsations were caused by fast magnetohydrodynamic oscillations of a flare loop, the following parameters were determined in the region of energy release using coronal seismology methods: plasma concentration (2 × 10¹⁰ cm⁻³), temperature (3 × 10⁷ K), and magnetic field strength (0.015 T).     

Dipolarization fronts in the magnetotail plasma sheet

We present a THEMIS study of a dipolarization front associated with a bursty bulk flow (BBF) that was observed in the central plasma sheet sequentially at X=−20.1, −16.7, and −11.0R_E. Simultaneously, the THEMIS ground network observed the formation of a north-south auroral form and intensification of westward auroral zone currents. Timing of the signatures in space suggests earthward propagation of the front at a velocity of 300 km/s. Spatial profiles of current and electron density on the front reveal a spatial scale of 500 km, comparable to an ion inertial length and an ion thermal gyroradius. This kinetic-scale structure traveled a macroscale distance of 10R_E in about 4 min without loss of coherence. The dipolarization front, therefore, is an example of space plasma cross-scale coupling. THEMIS observations at different geocentric distances are similar to recent particle-in-cell simulations demonstrating the appearance of dipolarization fronts on the leading edge of plasma fast flows in the vicinity of a reconnection site. Dipolarization fronts, therefore, may be interpreted as remote signatures of transient reconnection.     

Analytical model of explosions in a rarefied atmosphere

A new model of explosion products expansion in rarified gas is obtained. This model is based on an approach taking into account the energy dissipation in the ??snowplow?? model, thus making it possible to obtain an exact analytical solution and results which are in good agreement with experimental data. A comparison of the new model with the currently existing models (Simple Snowplow Model, Stuart??s model and Holway??s model) is indicative of the fact that the latter can be described in the framework of the new model. Alongside with that, the new model is able to take into account yet more processes not considered in the existing models. A comparison with the Spolokh-1 experiment demonstrates good agreement with data obtained in this experiment.     

Taxonomic composition and biostratigraphic value of the Early Riphean organic-walled microfossil association from the Ust’-Il’ya Formation of the Anabar Uplift,Northern Siberia

It is demonstrated on the basis of the first monographic study of multiple and taxonomically variable organic-walled microfossils from the Ust’-Il’ya Formation of the Anabar Uplift that both prokaryotic and eukaryotic forms are present in the composition of this microbiota. They are divided into four formal groups on the basis of the specifics of the morphological indicators of the identified taxa. The review of the data on the isotopic age of hosting deposits showed that the Ust’-Il’ya Formation is of the Early Riphean in age which are currently evaluated as 1750 ± 10–1400 Ma. Relatively large and morphologically complex eukaryotic forms present in the Ust’-Il’ya Formation served in due time as the basis for an erroneous conclusion on the Late Riphean age of the specified formation and the overlying Lower Kotuikan Subformation of the Anabar Uplift. The paper provides a global comparative analysis of the Early Riphean microbiotas, demonstrates the position of the Ust’-Il’ya and Kotuikan microbiotas amidst the microbiotas of the same age, and shows that the relatively large acanthomorphic acritarchs Tappania, Valeria, Dictiosphaera, Satka, and Shuiyousphaeridium appeared in the geological history already during the Early Riphean Erathem. Moreover, the paper discusses the recently published data on the distribution of aerobic and anaerobic conditions in the Early Riphean paleobasins and provides the conclusion on the impact of the lateral change of these conditions on the taxonomic composition of the microbiota.