Ionospheric Precursors of Magnetic Storms. 2. Analysis of Slough Station Data

Geomagnetism and Aeronomy - The behavior of the critical frequency of the F2 layer, foF 2, during the 3 days preceding a magnetic storm is analyzed. A total of 254 storms in 1976–2010...     

Solar-Activity Indices in the 24th Cycle and the Behavior of the Ionospheric F2-Layer

Geomagnetism and Aeronomy - This work is a continuation of the author’s earlier analysis of the relationship between the most often used solar-activity index, F10.7, and solar-activity...     

Melt Inclusions in Chromium Spinel of Kimberlites of the Zapolyarnaya Pipe,Upper Muna Field,Siberian Craton

Doklady Earth Sciences - The results of study of primary melt inclusions in сhromium spinel of kimberlites of the middle Paleozoic Zapolyarnaya pipe (Upper Muna field, Siberian Craton) are...     

Smoothing of force functions and the fluctuation spectra of an open star cluster model

We perform the correlation and spectral analysis of phase-space density and potential fluctuations in a model of an open star cluster for various values of the smoothing parameter ? of the force functions in the equations of motion of cluster stars, and compute the mutual correlation functions for the fluctuations of potential U and phase-space density f of the cluster model at different clustercentric distances. We use the Fourier transform of the mutual correlation functions to compute the power spectra and dispersion curves of the potential and phase-space density fluctuations. The spectrum of potential fluctuations proves to be less complex than that of phase-space density fluctuations. The most powerful potential fluctuations are associated with phase-space density fluctuations, and their spectrum lies in the domain of low frequencies ν < 3/τ _v.r.; at intermediate and high frequencies (ν > 3/τ _v.r.), the contribution of potential fluctuations to those of the phase-space density is small or equal to zero (here τ _v.r. is the violent relaxation time scale of the cluster). We find a number of unstable potential fluctuations in the core of the cluster model (up to 30 pairs of fluctuations with different complex conjugate frequencies). We also find and analyze the dependences of the spectra and dispersion curves of phase-space density and potential fluctuations on ?. We find a “repeatability” (significant correlation) of the spectra at some values of parameter ?. The form of the dispersion curve is unstable against small variations of ?. We discuss the astrophysical applications of our results: the break-up in the cluster core of the phase-space density wave running from the cluster periphery toward its center into several waves with frequencies commensurable to that of the external (tidal) influence; emission and reflection of phase-space and potential waves near the cluster core boundary; possible wavelength and phase discretization of the phase-space and potential waves in the cluster model.     

Long-term ocean simulations in FESOM: evaluation and application in studying the impact of Greenland Ice Sheet melting

The Finite Element Sea-ice Ocean Model (FESOM) is formulated on unstructured meshes and offers geometrical flexibility which is difficult to achieve on traditional structured grids. In this work, the performance of FESOM in the North Atlantic and Arctic Ocean on large time scales is evaluated in a hindcast experiment. A water-hosing experiment is also conducted to study the model sensitivity to increased freshwater input from Greenland Ice Sheet (GrIS) melting in a 0.1-Sv discharge rate scenario. The variability of the Atlantic Meridional Overturning Circulation (AMOC) in the hindcast experiment can be explained by the variability of the thermohaline forcing over deep convection sites. The model also reproduces realistic freshwater content variability and sea ice extent in the Arctic Ocean. The anomalous freshwater in the water-hosing experiment leads to significant changes in the ocean circulation and local dynamical sea level (DSL). The most pronounced DSL rise is in the northwest North Atlantic as shown in previous studies, and also in the Arctic Ocean. The released GrIS freshwater mainly remains in the North Atlantic, Arctic Ocean and the west South Atlantic after 120 model years. The pattern of ocean freshening is similar to that of the GrIS water distribution, but changes in ocean circulation also contribute to the ocean salinity change. The changes in Arctic and sub-Arctic sea level modify exchanges between the Arctic Ocean and subpolar seas, and hence the role of the Arctic Ocean in the global climate. Not only the strength of the AMOC, but also the strength of its decadal variability is notably reduced by the anomalous freshwater input. A comparison of FESOM with results from previous studies shows that FESOM can simulate past ocean state and the impact of increased GrIS melting well.

     

Scatter of hmF2 values as an indicator of trends in thermospheric dynamics

Analysis of the variability of the @F2-layer height, @hmF2@, from the 1950s to 1960s to the 1990s is performed on the basis of vertical sounding data for a series of midlatitude ionospheric stations. It is found that the scatter of the @hmF2@ values (standard deviation) increases sharply from the earlier decades to the later ones. This increase is better pronounced in the spring period of the year and does not depend on geomagnetic activity. The increase in the scatter of @hmF2@ indicates, evidently, the presence of systematic changes (trends) in thermospheric dynamics, the existence of these trends having been suggested in the recent publications of the author on the basis of the analysis of the foF2(night)/foF2(day) and R(foF2) parameters.     

New seismic array solution for earthquake observations and hydropower plant health monitoring

We present the novel fusion of seismic safety monitoring data of the hydropower plant in Chirkey (Caucasus Mountains, Russia). This includes new hardware solutions and observation methods, along with technical limitations for three types of applications: (a) seismic monitoring of the Chirkey reservoir area, (b) structure monitoring of the dam, and (c) monitoring of turbine vibrations. Previous observations and data processing for health monitoring do not include complex data analysis, while the new system is more rational and less expensive. The key new feature of the new system is remote monitoring of turbine vibration. A comparison of the data obtained at the test facilities and by hydropower plant inspection with remote sensors enables early detection of hazardous hydrodynamic phenomena.     

Long-Term Variations in the Parameters of the Middle and Upper Atmosphere and Ionosphere (Review)

Geomagnetism and Aeronomy - The article reviews the main publications from the last eight years on long-term trends in the parameters of the middle atmosphere, thermosphere, and ionosphere. It is...