Simulation of the Eurasian ice sheet dynamics during the last glaciation

The Eurasian Weichselian glaciation is studied with the SICOPOLIS ice-sheet model and UKMO PMIP climate anomaly forcings. A set of sensitivity tests are completed, including runs in cold-ice mode, different positive-degree-day (PDD) factors and modified climatic data-sets. The model set-up with present-day climatology modified by a glacial index brings forth an areally correct Last Glacial Maximum (LGM) extent in the western areas, but the ice-sheet volume is too small compared to reconstructions from rebound rates. Applying modified climate data results in similar extent as indicated by the Quaternary Environment of the Eurasian North (QUEEN) Late Weichselian ice-sheet reconstruction. The simulation results display freshwater fluxes from melting and calving in phase with Heinrich events H3 at 27, H2 at 22, and H1 at 14 ka ago. These peaks correspond to fast flow areas, with main activity at 27 and 22 ka ago in the Nordic Channel area and later in the Bear Island and Storfjorden region. The activity of these areas seems to be shifting from south to north from LGM to the Holocene. The freshwater pulse at 19–18.5 ka could correspond to Dansgaard–Oeschger oscillation, as well as ice volume flux peaks around 18–17 ka ago on the western margin of the ice sheet.     

Palaeotemperature determinations for the 1.8-ka Taupo ignimbrite,New Zealand,and implications for the emplacement history of a high-velocity pyroclastic flow

Palaeomagnetic data from lithic clasts collected at 46 sites within layers 1 and 2 of the 1.8-ka Taupo ignimbrite, New Zealand, have been used to determine the palaeotemperatures and thermal structure of the deposit on its emplacement. Equilibrium temperatures from sites less than 30–40 km from vent are 150–300 °C, whereas at greater distances site equilibrium temperatures increase up to 400–500 °C. This variation is seen in both layer 1 and 2 deposits, with values for layer 1 being somewhat cooler, and with its increase in temperature occurring at a greater distance from vent. A temperature maximum at ~50 km from vent coincides with a zone of pink thermal-oxidation colouration of pumices previously inferred to reflect higher emplacement temperatures. Additional palaeomagnetic data collected by us and others from pumice clasts show comparable temperature variations, but these temperature estimates are shown here to be due to a chemical remanence and unreliable for accurate temperature estimates. Cooler temperatures in proximal parts of the ignimbrite are consistent with admixture of >20% cold lithic clasts at source and interaction with the pre-eruption Lake Taupo. The similar, but offset, increases in equilibrium temperatures for medial and distal layers 1 and 2 are consistent with both layers being deposited from the same flow. However, any proximal deposits left by the later, hotter material must have been subsequently eroded, or be so thin that our collection failed to sample them. Radial asymmetries in equilibrium temperatures as well as other physical parameters suggest that the deposit emplacement temperature is primarily determined at source, rather than by interaction with air during transport. These data support previous interpretations that a concentrated basal flow played a dominant role in emplacement and deposition of the Taupo ignimbrite.Editorial responsibility: T. Druitt     

Nongravitational forces and meteoroid streams

The action of the solar electromagnetic radiation on the moving interplanetary dust particles in its more complete form than the special case known as the Poynting-Robertson effect is theoretically discussed in application to meteoroid stream of comet Encke.Normal and transversal components of the perturbing nongravitational force are used due to the action of the solar electromagnetic radiation. It is shown that the normal component of the force is negligible. However, transversal component is very important: it can probably completely explain all the observed meteoroid streams situated along the orbit of comet Encke (and, possibly, some asteroids) as the product of the comet Encke alone. Much shorter time is required for producing such a meteoroid stream than is a general conception.If the idea about the significance of the transversal component of the nongravitational force (may be, not produced by electromagnetic radiation) is correct, it may have important consequences for our understanding of ageing of comets, global evolution of the cometary (and, partially, asteroidal) system, and, of course, for a long-term evolution of small interplanetary particles.     

Distribution of macrophytes and condition of the physical environment of streams flowing through agricultural landscape in north-eastern Slovenia

The distribution and abundance of macrophytes, land-use beyond the riparian zone, characteristics of the riparian zone and selected channel properties have been studied in 9 streams flowing through an agricultural landscape in the north-eastern part of Slovenia. The streams studied supported a rich macrophyte community. Altogether, 53 plant taxa were observed on 93 km of the streams. Canonical correspondence analysis indicated that 10 out of the 11 parameters examined significantly influenced macrophyte distribution. Of these, substrate characteristics and riparian vegetation type were the most influential. Species composition analysis revealed that the majority of species indicated moderate nutrient load while, in the more strongly modified reaches, species indicating eutrophic conditions, i.e. Myriophyllum spicatum and different species of genus Potamogeton, were more abundant.     

多普勒天气雷达信息网络服务系统的设计

多普勒天气雷达信息网络服务系统具有较完善的远距离雷达数据传输、数据处理和图像实时显示功能，将雷达站和Web网站捆绑在一起，实现各类观测资料共享及联网服务，便于各层次用户使用。系统用Java类压缩方法和远程调用法建立新的套接字压缩方法，实现网络上大数据量的数据传输。Java语言实现了I／O数据流与网络数据流的单一接口，用Java语言对数据文件压缩，使数据在Internet上快速传输以节省服务器的外存空间。