Stokes-meter observations of the solar mean magnetic field: Probable manifestations of strong small-scale magnetic fields

For many years, information on the solar mean magnetic field (SMMF) of the Sun—an important heliophysical and astrophysical parameter—was restricted to magnetographic measurements in only one spectral line, FeI λ525.02 nm. More informative observations of the Stokes-meter parameters of the SMMF were first initiated on a regular basis at the Sayan Solar Observatory. The availability of I and V data obtained simultaneously in several spectral lines has made it possible to study fundamentally new physical problems. In this paper, based on a comparison of SMMF observations in several spectral lines, we find high correlations in the data and important systematic differences in the magnetic-field strength B, which we interpret as a manifestation of kilogauss magnetic fields in fine-structure magnetic elements. Results of theoretical modeling of the SMMF strength ratios for the FeI λ525.02 nm-FeI λ524.70 nm and FeI λ630.15 nm-FeI λ630.25 nm lines are presented. The asymmetries of the V profiles of four lines near the FeI λ525.02 nm line are examined; these lines are important diagnostics for studies of small-scale dynamical processes. The Sayan Solar Observatory SMMF measurements are in good consistency with the Wilcox Solar Observatory data for 2003: for a comparison of N = 137 pairs of points in the two data sets, the correlation coefficient ρ is 0.92 for the linear regression between the datasets B_WSO = 0.03(±0.05) + 0.93(±0.03)B_SSO.     

Electromagnetic studies in the central Arctic water basin

The results of the electromagnetic studies, obtained on the North Pole drifting stations, are reviewed. These results are still of current interest. The aspects of similar future works are discussed.     

Polycyclic aromatic hydrocarbons and changes in the trophic structure of polychaete assemblages in sediments of Todos os Santos Bay, Northeastern, Brazil

Polycyclic aromatic hydrocarbons (PAHs) and the trophic structure of polychaete assemblages were studied in sediments at 28 stations in Todos os Santos Bay. Total PAH concentrations varied from 8 to 4163 ng g(-1) dry weight. The indexes used for the determination of PAH origin suggested both pyrolytic and petrogenic sources. A total of 397 individuals of polychaetes was recorded which were classified in three trophic groups. The PCA ordination resulted in the formation of three groups of stations, Group I characterised by sandy sediments, low organic content, low total PAH concentration and percentage of potentially harmful PAH was dominated by subsurface deposit-feeders. The other two groups (IIa and IIb), showed similar percentages of silt and clay, however, Group IIb formed by those stations with high total organic carbon, total nitrogen, sulphur contents, high total PAH concentration and percentage of potentially harmful PAH was dominated by carnivores. Trophic changes could be explained by the level of exposure to PAH effects relative to differences in the life style and feeding strategies between deposit-feeders and carnivores.     

The response of ionospheric convection in the polar cap to substorm activity

We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°-78°. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71° by the time of the expansion phase onset. A westward electrojet, centred at 65.4°, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1° at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the “distant” neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary.     

Cosmogenic nuclide methods for measuring long-term rates of physical erosion and chemical weathering

Understanding the evolution of geochemical and geomorphic systems requires measurements of long-term rates of physical erosion and chemical weathering. Erosion and weathering rates have traditionally been estimated from measurements of sediment and solute fluxes in streams. However, modern sediment and solute fluxes are often decoupled from long-term rates of erosion and weathering, due to storage or re-mobilization of sediment and solutes upstream from the sampling point. Recently, cosmogenic nuclides such as ¹⁰Be and ²⁶Al have become important new tools for measuring long-term rates of physical erosion and chemical weathering. Cosmogenic nuclides can be used to infer the total denudation flux (the sum of the rates of physical erosion and chemical weathering) in actively eroding terrain. Here we review recent work showing how this total denudation flux can be partitioned into its physical and chemical components, using the enrichment of insoluble tracers (such as Zr) in regolith relative to parent rock. By combining cosmogenic nuclide measurements with the bulk elemental composition of rock and soil, geochemists can measure rates of physical erosion and chemical weathering over 1000- to 10,000-year time scales.     

Solar Spectral Irradiance Variability in November/December 2012: Comparison of Observations by Instruments on the International Space Station and Models

Onboard the International Space Station (ISS), two instruments are observing the solar spectral irradiance (SSI) at wavelengths from 16 to 2900 nm. Although the ISS platform orientation generally precludes pointing at the Sun more than 10?–?14 days per month, in November/December 2012 a continuous period of measurements was obtained by implementing an ISS ‘bridging’ maneuver. This enabled observations to be made of the solar spectral irradiance (SSI) during a complete solar rotation. We present these measurements, which quantify the impact of active regions on SSI, and compare them with data simultaneously gathered from other platforms, and with models of spectral irradiance variability. Our analysis demonstrates that the instruments onboard the ISS have the capability to measure SSI variations consistent with other instruments in space. A comparison among all available SSI measurements during November–December 2012 in absolute units with reconstructions using solar proxies and observed solar activity features is presented and discussed in terms of accuracy.     

Periodic orbits based on geometric structure of center manifold around Lagrange points

This study proposes an analytical method that determines the center manifold and identifies the reduced system on the center manifold. The proposed method expresses the center manifold through general equations containing only state variables, and not functions with respect to time. This is the so-called geometric structure of the center manifold. The location of periodic or quasi-periodic orbits is identified after the geometric structure of the center manifold is determined. The reduced system on the center manifold is described using ordinary differential equations, so that periodic or quasi-periodic orbits can be computed by numerically integrating the reduced system. The results indicate that the analytical method proposed in this study has higher precision compared with the Lindstedt-Poincaré method of the same order.