ALBERT

Description: Solar activity is characterized by complex dynamics superimposed to an almost periodic, about 11 years cycle. One of its main features is the presence of a marked, time-varying hemispheric asymmetry, the deeper reasons of which have not yet been completely uncovered. Traditionally, this asymmetry has been studied by considering amplitude and phase differences. Here, we use visibility graphs, a novel tool of nonlinear time series analysis, to obtain complementary information on hemispheric asymmetries in dynamical properties. Our analysis provides deep insights into the potentials and limitations of this method, revealing a complex interplay between factors relating to statistical and dynamical properties, i.e., effects due to the probability distribution and the regularity of observed fluctuations. We demonstrate that temporal changes in the hemispheric predominance of the graph properties lag those directly associated with the total hemispheric sunspot areas. Our findings open a new dynamical perspective on studying the North–South sunspot asymmetry, which is to be further explored in future work.

Description: Solar activity is characterized by complex dynamics superimposed onto an almost periodic, approximately 11-year cycle. One of its main features is the presence of a marked, time-varying hemispheric asymmetry, the deeper reasons for which have not yet been completely uncovered. Traditionally, this asymmetry has been studied by considering amplitude and phase differences. Here, we use visibility graphs, a novel tool of nonlinear time series analysis, to obtain complementary information on hemispheric asymmetries in dynamical properties. Our analysis provides deep insights into the potential and limitations of this method, revealing a complex interplay between factors relating to statistical and dynamical properties, i.e., effects due to the probability distribution and the regularity of observed fluctuations. We demonstrate that temporal changes in the hemispheric predominance of the graph properties lag those directly associated with the total hemispheric sunspot areas. Our findings open a new dynamical perspective on studying the north–south sunspot asymmetry, which is to be further explored in future work.

Description: Slot-check dam system is commonly used to control sediment transport associated with debris flows and mitigate debris flow hazards. This paper aims to estimate the performance of the slot-check dam system in the field and set up a verification to evaluate the efficiency of a slot-check dam system and each subsystem in debris flow sediment control. Field survey on a group of a series of slot-check dams at Shengou Basin in Yunnan, China reveals that the conserving sediment volume of each dam is related to its relative location in the group, gradually decreasing from upstream to downstream. The cumulative sediment volume within a subsystem of slot-check dams closely related to the characteristics of the catchment controlled by the subsystem. It increases with the controlled catchment area of the most downstream dam in subsystem and the distance from the dam to the upstream most. Evaluation models for the conserving efficiency of a slot-check dam system on debris flow control in a river basin and each subsystem within the group associate to the controlled catchment characteristics have been proposed. The layout principle of a slot-check dam system in a river basin has been developed based on the conserving efficiency of a subsystem of slot-check dams which would allow the slot-check dam system to be designed in a more scientific way.

Description: In this study, online monitoring instruments were used to monitor ozone, NOx and VOCs at the Guangzhou Panyu Atmospheric Composition Station (GPACS) of the China Meteorological Administration from June 2011 to May 2012, so as to obtain their characteristic seasonal and diurnal variations, as well as the impacts of NOx and VOCs on local ozone formation and Guangzhou ozone control strategies. The results show that during the observation period the seasonal variation of ozone concentration was lower in the spring and winter and higher in the summer and autumn, which is contrary that of NOx and VOCs. At around 09:00 LT in the summer, autumn and winter, both the ozone concentration and NO2/NO ratio begin to increase, and the NO2/NO ratio reached its maximum after a peak of ozone concentration, but this variation was not particularly evident in the spring. Aromatics and alkenes are the largest components for ozone formation potential, among which aromatic toluene, m-xylene, p-xylene and 1,3,5-trimethylbenzene are the most important components, with a total contribution of about 31.6% to ozone formation potential. Through the analysis on local ozone control by the VOC/NOX ratio, it was found that when the ozone concentration reached a peak in the summer and autumn in which high concentrations of ozone were prone to occur, ozone generation was NOx limited, thus NOx emissions must be controlled to regulate the occurrence of high-concentration ozone events. In the spring and winter, ozone generation was always VOCs controlled. Due to the relatively low ozone concentration, although NOx emissions could be controlled to increase ozone concentration, high-concentration ozone events would not occur. Therefore, for the control of ozone in Guangzhou, in addition to the control of VOCs emissions, more attention must be paid to reducing NOx emissions, so as to achieve the purpose of controlling high-concentration ozone.

Description: In recent years, photochemical smog has been a major cause of air pollution in the metropolitan area of Guangzhou, China, with a continuing increase in the concentrations of photochemical pollutants. The concentration of peroxyacetyl nitrate (PAN) has often been found to reach very high levels, posing a potential threat to the public health. To better understand the changes in PAN concentration and its sources, a study was carried from January to December of 2012 at the Guangzhou Panyu Atmospheric Composition Station (GPACS) to measure the atmospheric concentrations of PAN as well as those of ozone (O3), nitrogen oxides (NOx), and non-methane hydrocarbon (NMHC). These data were analyzed to investigate the quantitative relationships between PAN and its precursors. In the study period, the hourly concentrations of PAN varied from below instrument detection limit to 12.0 ppbv. The yearly mean concentration of PAN was 0.84 ppbv, with the daily mean concentration exceeding 5 ppbv in 32 of the total observation days. Calculations indicate that among the measured NMHC species, alkenes accounted for 53 % of the total NMHC contribution to the PAN production, with aromatics and alkanes accounting for about 11 and 7 % of the total, respectively. During the period of our observation only a modest correlation was found between the concentrations of PAN and O3 for daytime hours, and observed PAN concentrations were relatively high even though the observed NMHCs/NOx ratio was low. This suggests regional air mass transport of pollutants had a major impact on the PAN concentrations in Guangzhou area.

Description: Guangzhou, one of China's megacities, is beset with frequent occurrence of high-concentration ozone events. In this study, online instruments were used to simultaneously monitor ozone, nitrogen oxides (NOx) and volatile organic compounds (VOCs) at GPACS (the Guangzhou Panyu Atmospheric Composition Station) of the China Meteorological Administration, from June 2011 to May 2012, in order to determine their characteristics, the effect of VOCs on ozone photochemical production and the relationship between VOC / NOx ratio and ozone formation. The results showed that during the observation period, the seasonal variation of ozone concentration was lower in spring and winter compared to summer and autumn, which is opposite that for VOCs and NOx. In terms of VOCs, aromatics had the largest ozone formation potential, among which toluene, xylenes, ethylbenzene, 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene were the most important species, with a total contribution of about 44%. As the VOC / NOx ratios were very high during high-concentration ozone events that occur all year round, we speculate ozone production was likely to be NOx-limited regime (12:00–16:00 LT) in Guangzhou. Further investigation based on numerical models is needed in the future to obtain more detailed and robust conclusions.