Seasonal variation of meteor decay times observed at King Sejong Station (62.22°S, 58.78°W), Antarctica

We analyzed meteor decay times measured by a VHF radar at King Sejong Station by classifying strong and weak meteors according to their estimated electron line densities. The height profiles of monthly averaged decay times show a peak whose altitude varies with season at altitudes of 80?85 km. The higher peak during summer is consistent with colder temperatures that cause faster chemical reactions of electron removal. By adopting temperature dependent empirical recombination rates from rocket experiments and meteor electron densities of 2×10⁵?2×10⁶ cm^?3 in a decay time model, we are able to account for decreasing decay times below the peak for all seasons without invoking meteor electron removal by hypothetical icy particles.     

Spatial variability of biochemical responses in resident fish after the M/V Hebei Spirit Oil Spill (Taean, Korea)

This study describes the spatial variation and the duration of the impacts from the Hebei Spirit oil spill using specific biochemical indices in resident benthic fish. Enzymatic activities and biliary PAHs metabolites were higher at the site closer to the spill area in four months after spill incident. Regarding our results of detoxification response, markers of Phase I followed a similar trend in accordance with levels of biliary metabolites, while markers of phase II and GST appeared relatively unchanged.     

Assessing non-linear variation of temperature and precipitation for different growth periods of maize and their impacts on phenology in the Midwest of Jilin Province,China

In the past two decades, the regional climate in China has undergone significant change, resulting in crop yield reduction and complete failure. The goal of this study is to detect the variation of temperature and precipitation for different growth periods of maize and assess their impact on phenology. The daily meteorological data in the Midwest of Jilin Province during 1960–2014 were used in the study. The ensemble empirical mode decomposition method was adopted to analyze the non-linear trend and fluctuation in temperature and precipitation, and the sensitivity of the length of the maize growth period to temperature and precipitation was analyzed by the wavelet cross-transformation method. The results show that the trends of temperature and precipitation change are non-linear for different growth periods of maize, and the average temperature in the sowing-jointing stage was different from that in the other growth stages, showing a slight decrease trend, while the variation amplitude of maximum temperature is smaller than that of the minimum temperature. This indicates that the temperature difference between day and night shows a gradually decreasing trend. Precipitation in the growth period also showed a decreasing non-linear trend, while the inter-annual variability with period of quasi-3-year and quasi-6-year dominated the variation of temperature and precipitation. The whole growth period was shortened by 10.7 days, and the sowing date was advanced by approximately 11 days. We also found that there was a significant resonance period among temperature, precipitation, and phenology. Overall, a negative correlation between phenology and temperature is evident, while a positive correlation with precipitation is exhibited. The results illustrate that the climate suitability for maize has reduced over the past decades.     

Machine learning approaches to coastal water quality monitoring using GOCI satellite data

Since coastal waters are one of the most vulnerable marine systems to environmental pollution, it is very important to operationally monitor coastal water quality. This study attempts to estimate two major water quality indicators, chlorophyll-a (chl-a) and suspended particulate matter (SPM) concentrations, in coastal environments on the west coast of South Korea using Geostationary Ocean Color Imager (GOCI) satellite data. Three machine learning approaches including random forest, Cubist, and support vector regression (SVR) were evaluated for coastal water quality estimation. In situ measurements (63 samples) collected during four days in 2011 and 2012 were used as reference data. Due to the limited number of samples, leave-one-out cross validation (CV) was used to assess the performance of the water quality estimation models. Results show that SVR outperformed the other two machine learning approaches, yielding calibration R² of 0.91 and CV root-mean-squared-error (RMSE) of 1.74 mg/m³ (40.7%) for chl-a, and calibration R² of 0.98 and CV RMSE of 11.42 g/m³ (63.1%) for SPM when using GOCI-derived radiance data. Relative importance of the predictor variables was examined. When GOCI-derived radiance data were used, the ratio of band 2 to band 4 and bands 6 and 5 were the most influential input variables in predicting chl-a and SPM concentrations, respectively. Hourly available GOCI images were useful to discuss spatiotemporal distributions of the water quality parameters with tidal phases in the west coast of Korea.     

Regional variations in trace element concentrations in tissues of black tiger shrimp Penaeus monodon (Decapoda: Penaeidae) from South Vietnam

The goal of the present study was to examine the specific bioaccumulation of 22 trace elements in muscle, exoskeleton and hepatopancreas of black tiger shrimp Penaeus monodon from the Mekong River Delta (MRD), and the South Key Economic Zone (SKEZ), South Vietnam. The general tendency in most trace element concentrations among different tissues were hepatopancreas>exoskeleton>muscle. Comparisons of trace element levels in tissues between the two regions showed that concentrations of Se in muscle and As in all three tissues were higher in SKEZ; whereas in MRD, the higher concentrations of most elements such as Mn, Cu, Cd, Ba, Hg, were observed in tissues. These geographical variations in trace element levels may reflect the differences in human activities between the two regions of South Vietnam. The target hazard quotient (THQ) values for trace elements (<1) indicate that local residents are not exposed to potential health risks via the consumption of shrimp.     

High-resolution simulations for Vietnam - methodology and evaluation of current climate

To assist the government of Vietnam in its efforts to better understand the impacts of climate change and prioritise its adaptation measures, dynamically downscaled climate change projections were produced across Vietnam. Two Regional Climate Models (RCMs) were used: CSIRO’s variable-resolution Conformal-Cubic Atmospheric Model (CCAM) and the limited-area model Regional Climate Model system version 4.2 (RegCM4.2). First, global CCAM simulations were completed using bias- and variance-corrected sea surface temperatures as well as sea ice concentrations from six Coupled Model Intercomparison Project Phase 5 (CMIP5) global climate models. This approach is different from other downscaling approaches as it does not use any atmospheric fields from the GCMs. The global CCAM simulations were then further downscaled to 10 km using CCAM and to 20 km using RegCM4.2. Evaluations of temperature and precipitation for the current climate (1980-2000) were completed using station data as well as various gridded observational datasets. The RCMs were able to reproduce reasonably well most of the important characteristics of observed spatial patterns and annual cycles of temperature. Average and minimum temperatures were well simulated (biases generally less than 1oC), while maximum temperatures had biases of around 1oC. For precipitation, although the RCMs captured the annual cycle, RegCM4.2 was too dry in Oct.-Nov. (-60% bias), while CCAM was too wet in Dec.- Mar. (130% bias). Both models were too dry in summer and too wet in winter (especially in northern Vietnam). The ability of the ensemble simulations to capture current climate increases confidence in the simulations of future climate.     

2006年青海玉树5.0、5.6、5.4级地震灾害损失及震害特点

2006年7月18、19日在青海玉树发生了5．0、5．6、5．4级地震,地震造成了玉树县上拉秀乡、杂多县萨呼腾镇的房屋破坏,震后青海省地震局会同玉树州地震局、玉树地震台对玉树地震的灾害损失进行了现场评估,并对玉树地震的震害特点进行了总结,最后提出了相关建议。     

Acoustic density measurements of consolidating cohesive sediment beds by means of a non-intrusive “Micro-Chirp” acoustic system

A non-intrusive “Micro-Chirp” acoustic system and a signal-processing protocol have been developed to estimate the bulk density of consolidating cohesive sediment beds. Using high-frequency (300–700 kHz) Chirp acoustic waves, laboratory measurements were conducted with clay–water mixtures. Because acoustic echo strength is proportional to variations in acoustic impedance, and the speed of sound in the clay bed hardly changed during consolidation, the bulk density could be successfully estimated without disturbing the sediment bed. Based on acoustic signal analysis, this study demonstrates that the reflection coefficient and bulk density at the water–sediment interface increase with consolidation time, and that a single speed of sound value can be used for practical bulk density estimation in muddy environments.     

Photochemical escape of oxygen from Mars: A comparison of the exobase approximation to a Monte Carlo method

The non-thermal escape of neutral O atoms from Mars at the current epoch is largely due to dissociative recombination of :

     

Analysis of benzene transport in a two‐dimensional aquifer model

In this study, the fate and transport of aqueous benzene was investigated in a laboratory‐scale homogeneous aquifer by conducting a two‐dimensional plume test. Benzene solution was introduced as a pulse type along the width of the aquifer model through a recharge zone situated at the upper‐left part of the model and followed by a steady state flow. Solution samples were collected at various locations on the front side of the model to capture two‐dimensional plumes at discrete time intervals. The benzene plumes showed a moderate retardation relative to chloride plumes observed from the previous study conducted for the same aquifer model. The retardation factor was obtained from the ratio of travel distances of benzene peaks to chloride peaks from the injection point, computed using a line integral method. Mass recovery of aqueous benzene revealed that there was a significant reduction of benzene mass, indicating the occurrence of volatilization and/or irreversible sorption during transport. Thus, retardation along with volatilization and/or irreversible sorption may be important processes affecting the fate and transport of aqueous benzene in the aquifer model. Copyright © 2005 John Wiley & Sons, Ltd.