Total Solar Irradiance Variation During Rapid Sunspot Growth

Large sunspot areas correspond to dips in the total solar irradiance (TSI), a phenomenon associated with the local suppression of convective energy transport in the spot region. This results in a strong correlation between sunspot area and TSI. During the growth phase of a sunspot other physics may affect this correlation; if the physical growth of the sunspot resulted in surface flows affecting the temperature, for example, we might expect to see an anomalous variation in TSI. In this paper we study NOAA active region 8179, in which large sunspots suddenly appeared near disk center, at a time (March 1998) when few competing sunspots or plage regions were present on the visible hemisphere. We find that the area/TSI correlation does not significantly differ from the expected pattern of correlation, a result consistent with a large thermal conductivity in solar convection zone. In addition we have searched for a smaller-scale effect by analyzing white-light images from MDI (the Michelson Doppler Imager) on SOHO. A representative upper-limit energy consistent with the images is on the order of 3×10³¹ ergs, assuming the time scale of the actual spot area growth. This is of the same order of magnitude as the buoyant energy of the spot emergence even if it is shallow. We suggest that detailed image analyses of sunspot growth may therefore show `transient bright rings' at a detectable level.     

IN-FLIGHT PERFORMANCE OF THE VIRGO LUMINOSITY OSCILLATIONS IMAGER ABOARD SOHO

The Luminosity Oscillations Imager (LOI) is a part of the VIRGO instrument aboard the Solar and Heliospheric Observatory (SOHO). The scientific objective of the LOI experiment is to identify and characterize pressure and internal gravity oscillations of the Sun by observing the radiance variations. The LOI is a low-resolution imager with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 nm. The low resolution capability of the instrument allows the identification of individual azimuthal orders for l = 0 to 7, without suffering the mixing that affects integrated solar disk instruments. The performance, calibrations and instrumental effects of the LOI are described together with the procedures for extracting the solar p modes.     

Sea Ice Leads Detection Using SARAL/AltiKa Altimeter

Sea ice leads play an essential role in ocean-ice-atmosphere exchange, in ocean circulation, geochemistry, and in ice dynamics. Their precise detection is crucial for altimetric estimations of sea ice thickness and volume. This study evaluates the performance of the SARAL/AltiKa (Satellite with ARgos and ALtiKa) altimeter to detect leads and to monitor their spatio-temporal dynamics. We show that a pulse peakiness parameter (PP) used to detect leads by Envisat RA-2 and ERS-1,-2 altimeters is not suitable because of saturation of AltiKa return echoes over the leads. The signal saturation results in loss of 6–10% of PP data over sea ice. We propose a different parameter—maximal power of waveform—and define the threshold to discriminate the leads. Our algorithm can be applied from December until May. It detects well the leads of small and medium size from 200 m to 3–4 km. So the combination of the high-resolution altimetric estimates with low-resolution thermal infra-red or radiometric lead fraction products could enhance the capability of remote sensing to monitor sea ice fracturing.     

Study of Lake Baikal Ice Cover from Radar Altimetry and In–Situ Observations

Comparison of ENVISAT and SARAL missions data shows that AltiKa can be successfully used for ice discrimination methodology and extension of ice conditions time series. Due to shorter wavelength and large bandwidth (480 MHz) which leads to a higher sensitivity to different surface conditions, AltiKa shows more clearly the separation between open water and various ice types. We observe significant decrease of backscatter (25–30 dB) in late spring for both ENVISAT and SARAL and discuss it in the context of ice metamorphism. There is a clear need to continue and expand our dedicated field studies of lake Baikal ice cover to better assess influence of ice structure on altimetric signal.     

Forced regressive deposits of a deglaciation sequence: Example from the Late Quaternary succession in the Lake Saint‐Jean basin (Québec,Canada)

Differentiating between forced regressive deposits from deglacial periods in high latitude domains and forced regressive deposits from the onset of glacial periods in low latitude domains is fundamental for the accurate interpretation of glacial cycles within the geological record and then for the reconstruction of palaeogeography and palaeo‐climate. A forced regressive deglacial sequence is documented from the Lake Saint‐Jean basin (Québec, Canada). In this area, the Late Pleistocene to Holocene sediments have recorded the Laurentide ice sheet retreat accompanied by the invasion of marine waters (Laflamme Gulf) from ca 12·9 cal kyr bp . Subsequently, fluvio‐deltaic and coastal prograding wedges were deposited; they followed the base‐level fall due to glacio‐isostatic rebound. This succession, representing a transition from glacial to post‐glacial periods within a previously glaciated area, was investigated through recent mapping, preserved landforms, facies analysis, and new optical stimulated luminescence and radiocarbon dates. Three basin‐scale geological sections share a common lower part made of isolated ice‐contact fan deposits overlying bedrock. Throughout the entire basin, ice‐contact fans are capped by glacimarine muds. Above, fluvial and coastal prograding systems were deposited and evolved through four steps: (i) deltaic systems progressively increased in width; (ii) coastal influence on sedimentation increased; (iii) hydrographic drainage systems became more organised; and (iv) deltas graded from steep (Gilbert delta) to low‐angle foresets (mouth‐bar delta). Deposited during the base‐level fall from glacio‐isostatic rebound, the complete succession has been designated as a single falling stage system tract referred to as a deglacial falling stage system tract. It is representative of a deglaciation sequence in areas previously covered by ice during glacial periods (i.e. medium to high latitude domains). Diagnostic criteria are provided to identify such a deglacial falling stage system tract in the geological record, which may aid identification of previously unknown glacial cycles.     

Topotactic formation of ferrisicklerite from natural triphylite under hydrothermal conditions

The topotactic oxidation and delithiation reaction from triphylite, Li(Fe,Mn)PO₄, leading to ferrisicklerite, Li_<1(Fe³⁺,Mn²⁺)PO₄, was investigated under hydrothermal conditions. A cuboid cut from a triphylite single-crystal (Palermo Mine, New Hampshire, USA) with the composition Li_0.93(3)(Fe²⁺ _0.733(6),Fe³⁺ _0.015(1),Mn²⁺ _0.210(4),Mg_0.063(2))_1.021(8)P_1.00(2)O₄ in addition with ground bulk material were treated with KMnO₄ and 30 % H₂O₂(aq) as oxidizing agent in a 0.1 N hydrochloric acid solution in the temperature range between 60 and 200 °C. At 120 °C a rim of 0.1 mm thickness of ferrisicklerite had formed around the core of unreacted triphylite. The sharp reaction boundary was clearly visible, due to the reddish brown absorption colors of ferrisicklerite, compared to colorless triphylite. Using single-crystal X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), electron probe micro-analysis (EPMA) and ⁵⁷Fe-Mössbauer spectroscopy the product ferrisicklerite was characterized and its composition determined as Li_0.30(7)(Fe²⁺ _0.049(1)Fe³⁺ _0.65(2)Mn²⁺ _0.218(5)Mg_0.062(2))_0.98(1)P_1.01(3)O₄, with unit cell parameters a?=?4.795(1), b?=?9.992(4), and c?=?5.886(2) Å. EPMA investigations across the reaction boundary showed no changes in the concentrations of Fe, Mn, Mg, and P. In contrast, SIMS measurements clearly proved the delithiated state of the ferrisicklerite product. Polarization microscopy revealed that the orientation of the ferrisicklerite rim was the same as that of the original triphylite single-crystal, confirming the strictly topotactic character of the reaction.     

Combination of multi-scale and multi-edge X-ray spectroscopy for investigating the products obtained from the interaction between kaolinite and metallic iron in anoxic conditions at 90 °C

In the context of radioactive waste repository in geological formation, kaolinite-metallic iron interaction in chlorine solution was conducted in batch experiments, under anoxic conditions at 90 °C during 9 months. After a mineralogical characterization at a global scale, products were analyzed at the micrometer and nanometer scales by X-ray absorption spectroscopic techniques (XAS and STXM). Absorption at Al, Si and Fe edges was investigated to have a complete overview of the distribution and status of constituting elements. Whereas Si K-edge results do not evidence significant evolution of silicon status, investigations at Al K-edge and Fe L-edges demonstrate variations at aggregate and particle scales of ^IVAl:^VIAl and Fe²⁺:Fe³⁺ ratios. Spectroscopic data evidence the systematic crystallization of Fe-serpentines onto the remaining particles of kaolinite and the absence of pure species (kaolinite or Fe-serpentines). Combination of spatially resolved spectroscopic analyses and TEM-EDXS elemental distribution aims to calculate unit cell formulae of Fe-serpentines layers and abundance of each species in mixed particles. For most of the investigated particles, results reveal that the variations of particles composition are directly linked to the relative contributions of kaolinite and Fe-berthierine in mixed particles. However, for some particles, microscale investigations evidence crystallization of two other Fe-serpentines species, devoid of aluminum, cronstedtite and greenalite.