Behavior of the cosmic ray density during the initial phase of the Forbush effect

Variations in the cosmic ray density during the initial phase of the Forbush effect during the first hours after the arrival of the interplanetary shock wave have been studied with the use of data on variations in the cosmic ray density with a rigidity of 10 GV obtained by the global survey method by the world network of neutron monitors in 1957?2012. It is found that behavior of this parameter after the arrival of the shock wave demonstrates high variability. A small (~1/5 of total number), though distinct, group of Forbush effects, in which the density of the cosmic ray increases (not decreases) after the arrival of the shock wave, is defined. As a whole, the initial variation in cosmic ray density is correlated with the Forbush effect magnitude and the strength of the associated geomagnetic disturbance.     

青藏高原全新世降水序列的集成重建

青藏高原全新世降水变化对于过去全球变化研究有重要意义。在过去全球变化研究中, 大尺度区域降水序列重建缺乏可行、有效的方法, 本文以青藏高原作为研究区, 构建了分区古降水空间模拟－多区面积加权的集成方法, 重建全新世青藏高原降水序列。本研究以孢粉为环境证据, 选取有空间代表性的10 条由孢粉重建的高原样点降水序列, 获得716 条具有年代的定量降水记录, 建立全新世古降水记录数据集。借助GIS分析, 基于现代高原降水空间分布的地理因子模拟, 并与古降水记录相集成, 定量重建了高原全新世200 年分辨率的降水序列。结果显示:早全新世高原降水迅速增多, 并在9.0 kaBP达到极大值500 mm, 较现代高170 mm;9.0~5.6 kaBP是旺盛的湿润期, 降水总体比现代高出80 mm, 但呈现明显的下降趋势;5.6 kaBP以来降水减少, 降水与现代相当, 但波动幅度较小;集成序列与其他高低分辨率环境记录有很好的可比性, 说明集成序列有很好的代表性和一定的准确性。     

Microbial community dynamics and biodegradation of polycyclic aromatic hydrocarbons in polluted marine sediments in Hong Kong

Dynamics of microbial community and biodegradation of polycyclic aromatic hydrocarbons (PAHs) in polluted marine sediments, artificially spiked with a mixture of PAHs (fluorene, phenanthrene, fluoranthene and pyrene), were examined for a period of 60 days. Microbial communities were characterised by bacterial counts, ester-linked fatty acid methyl ester (EL-FAME) analysis and denaturing gradient gel electrophoresis (DGGE). A noted reduction in species diversity occurred only in the high PAH level treatment at onset. Both EL-FAME and DGGE demonstrated a marked shift in microbial community, in all the PAH level treatments, afterwards, with increases in the number of fatty acid degraders, the relative abundance of fatty acid biomarkers for gram-negative bacteria and a decrease in species diversity. The shift was also accompanied by the significant decrease in PAH concentrations. By the end of the experiment, diversity indices, based on both approaches, recovered when PAH concentrations declined to their background levels, except in the high PAH level treatment.     

Chemical composition of waters and the phytoplankton of the lakes within the delta of the Selenga river

Field observations showed that the characteristics of chemical composition of waters and the development of plankton algae in the lakes within the delta of the Selenga river are determined by their flowage. The most open Lake Nekipelovskoe communicates with the Selenga outlets throughout a year, and Lake Zavernyaikha only at the period of an open channel. Lake Semenovskoe and Lake Khlystov Zaton are located in the islands and are isolated from the outlets. According to composition of main ions, the lakes under investigation refer to the hydrocarbonate class, the calcium group. The sum of ions in the water of Lake Nekipelovskoe approaches the one in the Selenga (86?221 mg/dm³), and the highest sums of ions were recorded in the wintertime in the lakes isolated from the outlets (446?743 mg/dm³). The lakes of the delta are characterized by a high trophicity. The maximum concentrations of total phosphorus in Lake Nekipelovskoe and Lake Zavernyaikha were 68 and 122 μg mg/dm³, and in Lake Semenovskoe and Lake Khlystov Zaton ?0.8 and ?0.63 μg mg/dm³, respectively. The most intense development of algae is observed in Lake Zavernyaikha, which is due to the high population of Baikal endemics. Lake Zavernyaikha showed a close negative correlation between the concentration of NO ₃ ^? , mineral phosphorus and phytoplankton biomass; the correlation coefficient was ?0.8 and ?0.63, respectively. The lakes exhibited increased contents readily hydrolysable organic matter, and a decrease in dissolved oxygen concentration in winter; hydrogen sulfide was repeatedly recorded in Lake Khlystov Zaton. The water quality in the lakes during the springtime varies from “quite clean” to “weakly polluted”; at low-water periods, especially in winters, it can drop to the category of “exceedingly dirty”. The water quality of the Selenga can be influenced by the lakes during spring floods when material accumulated during the wintertime is transported to the river outlets and further to Lake Baikal.     

Variability of parameters of the <Emphasis Type="Italic">F</Emphasis>2-layer maximum in the quiet midlatitude ionosphere under low solar activity: 1. Statistical properties

Results of statistical analysis of the properties of variability of F2-layer maximum parameters (critical frequency foF2 and the height hmF2) in quiet midlatitude ionosphere under low solar activity in the daytime (1000–1500 LT) and nighttime (2200–0300 LT) hours are presented on the basis of Irkutsk station data for 2007–2008. It is found that the distribution density of δfoF2 could be presented as consisting of two distinctly different normal laws of this distribution, one of which corresponds to weak (|δfoF2| < 10%) fluctuations in foF2 and the other corresponds to strong (30% > |δfoF2| > 10%) fluctuations. Weak fluctuations in foF2 to a substantial degree are related to ionospheric variability at times less of than 1–3 h and determine the δfoF2 variability in the daytime hours. Strong fluctuations in foF2 are mainly related to day-to-day variability of the ionosphere at a fixed local time, the variability increasing by approximately a factor of 3 during the transition from day to night and determining the δfoF2 variability in the nighttime hours. The distribution density of ΔhmF2 is close to the normal distribution law. An interpretation of the different character of the distribution densities of δfoF2 and ΔhmF2 is given.     

On the possible hazard on the major cities caused by asteroid impact in the Pacific ocean

Semi-quantitative investigation is made of hazard expected from an asteroidal impact in the Pacific. An impact ofd (diameter) = 200 m asteroid has a probability of hitting somewhere in the Pacific once in 15000 y. By carrying out a Monte Carlo simulation, such an impact, on average, is shown to create a tsunami as high as 16, 14, 15, and 21 m at Japan, Taiwan, Shanghai and Hawaii, respectively. Wooden houses, stone and brick houses, and reinforced concrete buildings are likely to be demolished by tsunamis of height 2, 7 and 20 m respectively. Thus, there is a probability of 1% or so that most of the artificial constructions on the coast lines of the Pacific be destroyed in the next century by an asteroidal impact.     

Retrospective Assessment of Bottom Deposits in Kondopoga Bay,Lake Onega

Long-term observations of the chemical composition of bottom sediments in Kondopoga Bay, Lake Onega, are considered. The present-day state of bottom sediments is characterized, and regularities of variations in the composition and properties of sediments occurring in the zone of influence of wastewaters from a pulp and paper plant (PPP).