Glacier in the upstream Manla Reservoir in the Nianchu River Basin, Tibet: shrinkage and impacts

Glaciers in the upstream Manla Reservoir in the Nianchu River Basin are crucial for agriculture and hydropower in the "One River and Two Streams" area. Rising temperature has caused widespread retreat of glaciers on the Tibetan Plateau during the last few decades. In this study, glacier variations under climate change in the Nianchu River Basin are quantified and their influence are evaluated by analyzing 1980 aerial topographic maps, 1990 Landsat TM, 2000 Landsat ETM+, and 2005 CBERS remotely sensed images. It is found that from 1980 to 2005, the debris-free glacier area shrank by 7.3% (13.42 km²). Glacier shrinkage will have a positive effect on agriculture, hydropower and eco-environment in the near future. However, because the large number of small glaciers (<2 km²) will rapidly retreat and disappear in future years, melt water will decrease, ultimately resulting in a long term water shortage. Glacial lakes exhibited rapid expansion due to accelerating glacier retreat during 1980–2005, increasing the possibility of glacial lake outburst floods.     

Silicon tetrafluoride on Io

Silicon tetrafluoride (SiF₄) is observed in terrestrial volcanic gases and is predicted to be the major F-bearing species in low-temperature volcanic gases on Io [Schaefer, L., Fegley Jr., B., 2005b. Alkali and halogen chemistry in volcanic gases on Io. Icarus 173, 454-468]. SiF₄ gas is also a potential indicator of silica-rich crust on Io. We used F/S ratios in terrestrial and extraterrestrial basalts, and gas/lava enrichment factors for F and S measured at terrestrial volcanoes to calculate equilibrium SiF₄/SO₂ ratios in volcanic gases on Io. We conclude that SiF₄ can be produced at levels comparable to the observed NaCl/SO₂ gas ratio. We also considered potential loss processes for SiF₄ in volcanic plumes and in Io's atmosphere including ion-molecule reactions, electron chemistry, photochemistry, reactions with the major atmospheric constituents, and condensation. Photochemical destruction (t_chem ∼266 days) and/or condensation as Na₂SiF₆ (s) appear to be the major sinks for SiF₄. We recommend searching for SiF₄ with infrared spectroscopy using its 9.7 μm band as done on Earth.     

Modelling Dust in Galactic SEDs: Application to Semi-Analytical Galaxy Formation Models

We present the basic features and preliminary results of the interface between our spectrophotometric model GRASIL (which calculates galactic SEDs from the UV to the submm with a detailed computation of dust extinction and thermal reemission) with the semi-analytical galaxy formation model GALFORM (which computes galaxy formation and evolution in the hierarchical scenario, providing the star formation history as an input to our model). With these two models we are able to synthesize simulated samples of a few thousand galaxies for statistical studies of galaxy properties to investigate galaxy formation and evolution. There is good agreement with the available SED and luminosity function data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analyses of dust coma morphology of Comet Hyakutake (1996 B2) near perigee: outburst behavior, jet motion, source region locations, and nucleus pole orientation

We present inner-coma dust imaging of Comet Hyakutake (1996 B2) obtained on 11 consecutive nights in late March 1996, an interval including a major outburst and the comet’s closest approach to Earth. The evolution of the outburst morphology is followed, along with the motion along the tail of several outburst fragments. Two spiral dust jets—a primary jet, along with a much weaker secondary jet—are visible throughout the interval and are produced by two source regions on a rotating nucleus. These are examined as a function of rotational phase and viewing geometry, with their appearance changing from a nearly face-on view on March 18 to side-on by March 28. The dust outflow velocity as a function of distance from the nucleus is derived, with the dust continuing to accelerate to a distance of 4000 km or more and reaching an average outflow velocity of 0.38 km s⁻¹ between 3000 and 8000 km. We present details of our Monte Carlo modeling of the jets and our methodology of fitting the model to the images. The modeling yields the pole orientation of the nucleus, with an obliquity of approximately 108°, corresponding to an RA of 13^h41^m and a Dec of −1.1°. For an assumed spherical nucleus, the primary active region is centered at approximately −66° latitude, has a radius of about 56°, and therefore covers about 22% of the surface. The source of the secondary jet is at a latitude of −28°, has a radius of about 16°, and is located at a longitude nearly 180° away from the primary source. Estimated uncertainties for the pole orientation and the source locations and sizes are each about 3°. This solution for the nucleus orientation and source locations explains the strong asymmetry in measured production rates before and after perihelion in radio observations (Biver et al., 1999, Astron. J. 118, 1850-1872). The modeling also tightly constrains the sidereal rotation period as 0.2618 ± 0.0001 day, completely consistent with the expected +0.0003 day difference from the observed solar rotation period of 0.2614 ± 0.0004 day determined by Schleicher and Osip (2002, Icarus 159, 210-233), given the pole orientation and position of the comet in its orbit.     

Photometry and Imaging of Comet C/2000 Wm1 (Linear)

Earth, Moon, and Planets -     

Mobility of trace elements between the river water,the sediments,and the pore water of Las Catonas Stream,Buenos Aires Province,Argentina

The composition of river water, sediments, and pore waters (down to 30 cm below the bed) of Las Catonas Stream was studied to analyze the distribution of trace elements in a peri-urban site. The Las Catonas Stream is one of the main tributaries of Reconquista River, a highly polluted water course in the Buenos Aires Province, Argentina. The semi-consolidated Quaternary sediments of the Luján Formation are the main source of sediments for Las Catonas Stream. The coarse-grained fraction in the sediments is mainly composed of tosca (calcretes), intraclasts, bone fragments, glass shards, quartz, and aggregates of fine-grained sediments together with considerably amounts of vegetal remains. The clay minerals are illite, illite–smectite, smectite, and kaolinite. For the clay-sized fraction, the external surface area values are mostly between 70 and 110 m²g^?1, although the fraction at 15 cm below the bottom of the river shows a lower surface area of 12 m²g^?1. The N₂ adsorption–desorption isotherms at 77 K for this sample display a behavior indicative of non-porous or macroporous material, whereas the samples above and below present a typical behavior of mesoporous materials with pores between parallel plates (slit-shaped). As, Cr, Cu, and Cd concentrations increase down to 15 cm depth in the sediments, where the highest trace element and total organic carbon (TOC) concentrations were found, and then decrease toward the bottom of the core. Except for As, the levels of the other heavy metals show higher concentration in surficial waters than in pore waters. Distribution coefficients between the sediments, pore water, and surficial water phases indicate that As is released from the sediments to the pore and surficial waters. Cu content strongly correlates with TOC (mainly from vegetal remains), suggesting that this element is mainly bound to the organic phase.