Sediment changes upstream and downstream of the Altnahinch Dam in the River Bush in Northern Ireland: a preliminary study

The River Bush must reach a standard of good ecological potential (GEP) by 2015 due to the requirements of the water framework directive. The role of sediments within a water body is extremely important to all aspects of a river’s regime. The aim of this research is to investigate the effects of Altnahinch Dam on sediment distribution in the River Bush (a heavily modified water body) with comparison made against the Glendun River (an unmodified water body). Samples collected from the rivers were analysed by physical (pebble count, sieve analysis) and statistical methods (ANOVA, GRADISTAT). An increase in fine sediments upstream of the dam provides evidence that the dam is impacting sediment distribution. Downstream effects are not shown to be significant. The output of this study also implies similar impacts at other drinking water storage impoundments. This research recommends that a sediment management plan be put in place for Altnahinch Dam and that further studies be carried-out concentrating on fine sediment distribution upstream of the dam.     

北极臭氧年际变化特征及其与极涡的关系

利用风云三号卫星搭载的紫外臭氧总量探测仪(TOU)和国际同类卫星的臭氧总量数据对1979年—2011年北半球春季臭氧特征进行了分析,发现北极臭氧年际变化显著,它与平流层温度变化一致(相关系数为0.75)。北极臭氧损耗异常强弱年的月均和日变化特征有明显差异,春季北极臭氧损耗强年有明显的化学损耗过程(1997年和2011年),而弱年化学作用影响不明显(1999年和2010年)。损耗弱年的日变化型在不同年份特征不同,它的臭氧变化可能更多受天气过程的影响。综合分析北极涛动、极涡和平流层温度等大气环流背景场的变化,表明春季北极臭氧损耗强弱受大气环流变化影响。北极涛动指数正位相,极涡偏强偏冷,北极臭氧损耗异常偏高。北极涛动指数负位相,极涡偏弱偏暖,北极臭氧损耗异常偏低。     

Accurate fundamental parameters for lower main-sequence stars

We derive an empirical effective temperature and bolometric luminosity calibration for G and K dwarfs, by applying our own implementation of the Infrared Flux Method to multiband photometry. Our study is based on 104 stars for which we have excellent   BV ( RI )_C JHK _S  photometry, excellent parallaxes and good metallicities.
Colours computed from the most recent synthetic libraries (ATLAS9 and MARCS) are found to be in good agreement with the empirical colours in the optical bands, but some discrepancies still remain in the infrared. Synthetic and empirical bolometric corrections also show fair agreement.
A careful comparison to temperatures, luminosities and angular diameters obtained with other methods in the literature shows that systematic effects still exist in the calibrations at the level of a few per cent. Our Infrared Flux Method temperature scale is 100-K hotter than recent analogous determinations in the literature, but is in agreement with spectroscopically calibrated temperature scales and fits well the colours of the Sun. Our angular diameters are typically 3 per cent smaller when compared to other (indirect) determinations of angular diameter for such stars, but are consistent with the limb-darkening corrected predictions of the latest 3D model atmospheres and also with the results of asteroseismology.
Very tight empirical relations are derived for bolometric luminosity, effective temperature and angular diameter from photometric indices.
We find that much of the discrepancy with other temperature scales and the uncertainties in the infrared synthetic colours arise from the uncertainties in the use of Vega as the flux calibrator. Angular diameter measurements for a well-chosen set of G and K dwarfs would go a long way to addressing this problem.     

A search for nearby counterparts to the moving objects in the Hubble Deep Field

Ibata et al. have recently discovered very faint, moving objects in the Hubble Deep Field (HDF). The number, apparent magnitudes and proper motions of these objects are consistent with old white dwarfs making up part of the Galactic dark halo. We review a number of ground-based proper motion surveys in which nearby dark-halo white dwarfs might be present, if they have the colours and absolute magnitudes proposed. No such objects have been found, whereas we argue here that several times more would be expected than in the HDF. We conclude that it is unlikely that hydrogen-atmosphere white dwarfs make up a significant fraction of the Galactic dark matter. No limits can be placed as yet on helium-atmosphere dwarfs from optical searches.     

Ground Based Testing of the GAIA Filters

We summarise the case for ground based testing of the GAIA filter system. Two scenarios are evaluated; firstly, that ground based testing be part of the (ongoing) filter design effort, and secondly that the filters be tested on real stars from the ground after they have been finalised. We conclude that the filter design effort would benefit more efficiently and directly from good flux calibrated spectra for representative stars of many types, rather than an immediate and concerted ground based photometric effort. Ground based observations after the filter design has been frozen is highly recommended. We review an initial study of the tolerances needed on the filter central wavelengths and bandwidths in manufacture, assuming millimagnitude photometry. Further work is needed in this area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Exploring CO pollution episodes observed at Rishiri Island by chemical weather simulations and AIRS satellite measurements: long-range transport of burning plumes and implications for emissions inventories

The summer of 2003 was an active forest fire season in Siberia. Several events of elevated carbon monoxide (CO) were observed at Rishiri Island in northern Japan during an intensive field campaign in September 2003. A simulation with a global chemistry-transport model is able to reproduce the general features of the baseline levels and variability in the observed CO, and a source attribution for CO in the model suggests that the contribution from North Asia dominated, accounting for approximately 50% on average, with contributions of 7% from North America and 8% from Europe and 30% from oxidation of hydrocarbons. With consideration of recent emission estimates for East Asian fossil fuel and Siberian biomass burning sources, the model captures the timing and magnitude of the CO enhancements in two pollution episodes well (17 and 24 September). However, it significantly underestimates the amplitude during another episode (11–13 September), requiring additional CO emissions for this event. Daily satellite images from AIRS reveal CO plumes transported from western Siberia toward northern Japan. These results suggest that CO emissions from biomass burning in western Siberia in 2003 are likely underestimated in the inventory and further highlight large uncertainties in estimating trace gas emissions from boreal fires.     

Petrology and Geochemistry of Mantle Peridotite Xenoliths from SE China

Geochemical data on Type I spinel peridotite and garnet peridotitexenoliths in Cenozoic basalts from SE China demonstrate thatthe lithospheric mantle under this region is heterogeneous.The depletion and enrichment shown by these peridotite xenolithsare not related to their locations as suggested earlier. Samplesfrom individual localities, at the continental margin or thecontinental interior, show large variational ranges from depletedharzburgite to fertile Iherzolite. The measured Nd and Sr isotopiccompositions of clinopyroxene separates range from _Nd 49 to160 and from ⁸⁷Sr/⁸⁶Sr 070256 to 070407, respectively. Thedepleted signatures of Sr and Nd isotopic compositions and major-elementcontents (low CaO and Al₂O₃ in most xenoliths require an olddepletion event, probably mid-Proterozftic, and the enrichmentof LREE in the depleted peridotites implies a young metasomaticevent shortly before Cenozoic magmatism. Major-element compositionsof the peridotite xenoliths are controlled largely by the degreeof partial melting, and the extra fertile peridotites (highCaO and Al₂O₃) are probably the products of interaction betweenperidotites and a basaltic component. The equilibrium P–Tconditions, determined from coexisting mineral phases, indicatethat these xenoliths equilibrated over a wide P–T range,from 770 to 1250 C and from 10 to 27 kbar. Calculated oxygenfugacities for most spinel peridotites range from near the FMQbuffer to 25 log units below. The late-stage metasomatism didnot change the redox state in the upper mantle. ^*Corraponding author