Evaluation and analysis of water quality variations were performed with integrated consideration of water quality parameters, hydrological-meteorologic and anthropogenic factors in Cao-E River, Zhejiang Province of Ch...Evaluation and analysis of water quality variations were performed with integrated consideration of water quality parameters, hydrological-meteorologic and anthropogenic factors in Cao-E River, Zhejiang Province of China. Cao-E River system has been polluted and the water quality of some reaches are inferior to Grade V according to National Surface Water Quality Standard of China （GB2002）. However, mainly polluted indices of each tributary and mainstream are different. Total nitrogen （TN） and total phosphorus （TP） in the water are the main polluted indices for mainstream that varies from 1.52 to 45.85 mg/L and 0.02 to 4.02 mg/L, respectively. TN is the main polluted indices for Sub-watershed Ⅰ, Ⅱ, Ⅳ and Ⅴ（0.76 to 18.27 mg/L）. BOD5 （0.36 to 289.5 mg/L）, CODMn （0.47 to 78.86 mg/L）, TN （0.74 to 31.09 mg/L） and TP （0 to 3.75 mg/L） are the main polluted indices for Sub-watershed Ⅲ. There are tow pollution types along the river including nonpoint source pollution and point source pollution types. Remarkably temporal variations with a few spatial variations occur in nonpoint pollution type reaches （including mainstream, Sub-watershed Ⅰ and Ⅱ） that mainly drained by arable field and/or dispersive rural dwelling district, and the maximum pollutant concentration appears in flooding seasons. It implied that the runoff increases the pollutant concentration of the water in the nonpoint pollution type reaches. On the other hand, remarkably spatial variations occur in the point pollution type reaches （include Sub-watershed Ⅲ, Ⅳ and Ⅴ） and the maximum pollutant concentration appears in urban reaches. The runoff always decreases the pollutant concentration of the river water in the seriously polluted reaches that drained by industrial point sewage. But for the point pollution reaches resulted from centralized town domestic sewage pipeline and from frequent shipping and digging sands, rainfall always increased the concentration of pollutant （TN） in the river water too. Pollution controls were respectively suggested for these tow types according to different pollution causes.展开更多
The temporal variations in storm rainfall during the first rainy season (FRS) in South China (SC) are investigated in this study. The results show that the inter-annual variations in storm rainfall during the FRS in S...The temporal variations in storm rainfall during the first rainy season (FRS) in South China (SC) are investigated in this study. The results show that the inter-annual variations in storm rainfall during the FRS in SC seem to be mainly influenced by the frequency of storm rainfall, while both frequency and intensity affect the inter-decadal variations in the total storm rainfall. Using the definitions for the beginning and ending dates of the FRS, and the onset dates of the summer monsoon in SC, the FRS is further divided into two sub-periods, i.e., the frontal and monsoon rainfall periods. The inter-annual and inter-decadal variations in storm rainfall during these two periods are investigated here. The results reveal a significant out-of-phase correlation between the frontal and monsoon storm rainfall, especially on the inter-decadal timescale, the physical mechanism for which requires further investigation.展开更多
The results of field observation carried out in May 2003 were used to examine pH and total alkalinity behaviors in the Changjiang Estuary. It was showed that pH and total alkalinity took on clear spatial variations in...The results of field observation carried out in May 2003 were used to examine pH and total alkalinity behaviors in the Changjiang Estuary. It was showed that pH and total alkalinity took on clear spatial variations in values with the minima in the low salinity region. Like salinity, transect distributions of pH and total alkalinity （TA） in a downriver direction had a sharp gradient each. These gradients appeared in such a sequence that the TA gradient was earlier than salinity and pH gradients, and the salinity gradient was earlier than the pH gradient. These distribution characteristics seemed to be strongly influenced by the mixing process of freshwater and seawater, for both pH and total alkalinity had significant linear relationships with salinity and temperature. For pH, phytoplankton activities also had a significant impact upon its spatial distribution. During a period of 48 h, pH and total alkalinity changed within wide ranges for every layer of the two anchor stations, namely, Stas 13 and 20, which were located at the mixed water mass and seawater mass, respectively. For both Stas 13 and 20, pH and TA fluctuation of every layer could be very wide during a 4 h period. As a whole, the data of the two anchor stations showed that neither variations in salinity and temperature nor phytoplankton activities were the main factors strongly influencing the total alkalinity temporal variability on a small time scale. The data of Sta. 20 implied that both salinity variation and phytoplankton activities had a significant influence on pH temporal variability, but the same conclusion could not be drawn from the data of Sta. 13.展开更多
The size-fractionated phytoplankton biomass, and the spatial and temporal variations in abundance of Synechococcus (SYN) and picoeukaryotes (PEUK) were measured in the Taiwan Strait during three cruises (August 1997, ...The size-fractionated phytoplankton biomass, and the spatial and temporal variations in abundance of Synechococcus (SYN) and picoeukaryotes (PEUK) were measured in the Taiwan Strait during three cruises (August 1997, February-March 1998, and August 1998). The results show that picophytoplankton and nanophytoplankton dominate the phytoplankton biomass, in average of 38% and 40%, respectively. SYN and PEUK varied over time in abundance and carbon biomass, greater in summer than in winter, in range of (7.70–209.2)×106 and (0.75–15.4)×106 cells/cm2 in the abundance, and 1.93–52.3 and 1.57–32.4 μgC/cm2 in the carbon biomass, for SYN and PEUK, respectively. The horizontal distributions of both groups were diurnal but heterogeneous in abundance, depending on the groups and layer of depths. Temperature is the key controlling factor for picophytoplankton distribution (especially in winter) in the Strait.展开更多
Aridity index reflects the exchanges of energy and water between the land surface and the atmosphere,and its variation can be used to forecast drought and flood patterns,which makes it of great significance for agricu...Aridity index reflects the exchanges of energy and water between the land surface and the atmosphere,and its variation can be used to forecast drought and flood patterns,which makes it of great significance for agricultural production.The ratio of potential evapotranspiration and precipitation is applied to analyse the spatial and temporal distributions of the aridity index in the Belt and Road region under the 1.5℃and 2.0℃global warming scenarios on the basis of outputs from four downscaled global climate models.The results show that:(1)Under the 1.5℃warming scenario,the area-averaged aridity index will be similar to that in 1986-2005(around 1.58),but the changes vary spatially.The aridity index will increase by more than 5%in Central-Eastern Europe,north of West Asia,the monsoon region of East Asia and northwest of Southeast Asia,while it is projected to decrease obviously in the southeast of West Asia.Regarding the seasonal scale,spring and winter will be more arid in South Asia,and the monsoon region of East Asia will be slightly drier in summer compared with the reference period.While,West Asia will be wetter in all seasons,except winter.(2)Relative to 1986-2005,both areal averaged annual potential evapotranspiration and precipitation are projected to increase,and the spatial variation of aridity index will become more obvious as well at the 2.0℃warming level.Although the aridity index over the entire region will be maintained at approximately 1.57 as that in 1.5℃,the index in Central-Eastern Europe,north of West Asia and Central Asia will grow rapidly at a rate of more than 20%,while that in West Siberia,northwest of China,the southern part of South Asia and West Asia will show a declining trend.At the seasonal scale,the increase of the aridity index in Central-Eastern Europe,Central Asia,West Asia,South Asia and the northern part of Siberia in winter will be obvious,and the monsoon region in East Asia will be drier in both summer and autumn.(3)Under the scenario of an additional 0.5℃increase in global temperature from 1.5℃to 2.0℃,the aridity index will increase significantly in Central Asia and north of West Asia but decrease in Southeast Asia and Central Siberia.Seasonally,the aridity index in the Belt and Road region will slightly increase in all other seasons except spring.Central Asia will become drier annually at a rate of more than 20%.The aridity index in South Asia will increase in spring and winter,and that in East Asia will increase in autumn and winter.(4)To changes of the aridity index,the attribution of precipitation and potential evapotranspiration will vary regionally.Precipitation will be the major influencing factor over southern West Asia,southern South Asia,Central-Eastern Siberia,the non-monsoon region of East Asia and the border between West Asia and Central Asia,while potential evapotranspiration will exert greater effects over Central-Eastern Europe,West Siberia,Central Asia and the monsoon region of East Asia.展开更多
The rapid expansion of China’s urban agglomerations in recent decades has resulted in over-occupied ecological spaces and increased ecological pressure that are restricting healthy regional development.This paper exa...The rapid expansion of China’s urban agglomerations in recent decades has resulted in over-occupied ecological spaces and increased ecological pressure that are restricting healthy regional development.This paper examines the structure and characteristics of distribution of“production-living-ecological”spaces in five mega-urban agglomerations in China:Beijing-Tianjin-Hebei(BTH),the Yangtze River Delta(YRD),Guangdong-Hong Kong-Macao Greater Bay Area(GBA),Chengdu-Chongqing(CY),and the middle reaches of the Yangtze River(MYR).We analyze spatial and temporal variations in the ecological spaces and factors influencing them from 1990 to 2020,and examine the comprehensive ecological carrying capacity and status of ecological spaces in the past 30 years based on the available water resources,regulation of water and air quality,and leisure and recreation.The results show the following:(1)Urban agglomerations in different stages of formation and development represent varying area ratios of“ecological-production-living”spaces.The modes of expansion and evolution of the living spaces are dominated by multi-center combinations as well as the spatial structure of ecological spaces,including barrier,compact,discrete,and fully enveloping spaces.(2)From 1990 to 2020,the area occupied by living spaces in urban agglomerations continued to increase significantly while that of spaces for ecological production decreased.Except in the GBA,ecological spaces have exhibited a trend of increase in area,especially in the past 10 years.The area ratios and spatio-temporal variations in the“production-living-ecological”spaces indicate that the main functions of production and ecological spaces in mega-urban agglomerations have shifted from supply to regulation and culture,and reflect the transition from rapid urbanization to sustainable urbanization in China.(3)The comprehensive ecological carrying capacities of 78.6%,73.1%,54.5%,56.3%,and 25.8%of cities in BTH,YRD,GBA,CY and MYR are severely overburdened.Water supply and the regulation of water quality are the main factors restricting the ecological carrying capacity of BTH and YRD while leisure and recreation services have hindered the capacities of GBA and CY.Policymakers thus need to pay attention to the conservation and rational layout of ecological spaces to reduce the ecological pressure in urban agglomerations.The work here can provide a scientific basis for the green and sustainable development of urban agglomerations as well as the optimized configuration of“production-living-ecological”spaces.展开更多
To investigate the air quality change during the COVID-19 pandemic,we analyzed spatiotemporal variations of six criteria pollutants in nine typical urban agglomerations in China using ground-based data and examined me...To investigate the air quality change during the COVID-19 pandemic,we analyzed spatiotemporal variations of six criteria pollutants in nine typical urban agglomerations in China using ground-based data and examined meteorological influences through correlation analysis and backward trajectory analysis under different responses.Concentrations of PM2.5,PM10,NO2,SO2 and CO in urban agglomerations respectively decreased by 18%–45%(30%–62%),17%–53%(22%–39%),47%-64%(14%–41%),9%–34%(0%–53%)and 16%-52%(23%–56%)during Lockdown(Post-lockdown)period relative to Pre-lockdown period.PM2.5 pollution events occurred during Lockdown in Beijing-Tianjin-Hebe(BTH)and Middle and South Liaoning(MSL),and daily O3 concentration rose to gradeⅡstandard in Post-lockdown period.Distinct from the nationwide slump of NO2 during Lockdown period,a rebound(~40%)in Post-lockdown period was observed in Cheng-Yu(CY),Yangtze River Middle-Reach(YRMR),Yangtze River Delta(YRD)and Pearl River Delta(PRD).With slightly higher wind speed compared with 2019,the reduction of PM2.5(51%–62%)in Post-lockdown period is more than2019(15%–46%)in HC(Harbin-Changchun),MSL,BTH,CP(Central Plain)and SP(ShandongPeninsula),suggesting lockdown measures are effective to PM2.5 alleviation.Although O3 concentrations generally increased during the lockdown,its increment rate declined compared with 2019 under similar sunlight duration and temperature.Additionally,unlike HC,MSL and BTH,which suffered from additional(>30%)air masses from surrounding areas after the lockdown,the polluted air masses reaching YRD and PRD mostly originated from the long-distance transport,highlighting the importance of joint regional governance.展开更多
To investigate the life cycle of marine sulfate aerosols, chemicophysical characteristics of marine aerosolswere measured during five cruises in the Pacific Ocean. Dimethyl sulfide concentrations in seawater and in th...To investigate the life cycle of marine sulfate aerosols, chemicophysical characteristics of marine aerosolswere measured during five cruises in the Pacific Ocean. Dimethyl sulfide concentrations in seawater and in the air were also measured. The geographic variation of sulfate-aerosol concentrations was studied in relation to biogenic and anthropogenic sources,transport with air trajectories, and chemical transformations in the atmosphere. The highest concentrations were found near Asian and American ports, indicating anthropogenic pollution is the major sulfate aerosols source. Higher concentrations were observed in the upwelling regions than in the oligotrophic areas. Along the coastal regions, both mass and number concentrations of sulfate aerosols depended on wind direction and wind speed, and land-breeze and sea-breeze oscillations; no clear diurnal variation was detected. In pelagic areas, along the equator, the concentrations of small sulfate particles showed a maximum in the afternoon and the minimum at night , indicating photo-oxidation as an important process for gas-to-particle conversion. Higher sulfate-aerosol concentrations were observed in spring than in autumn and higher concentrations were found during the La Nina anomaly than during the El Nino anomaly. Biogenic source of sulfate aerosols has an important role in the remote ocean. Case studies of sulfate-aerosol distributions are discussed.展开更多
Complex empirical orthogonal function (CEOF) and Fourier analyses are applied to 500 hPa geopotential height anomaly for two selected latitude belts in the Northern Hemisphere from Dec 1978 through Feb 1979 based on t...Complex empirical orthogonal function (CEOF) and Fourier analyses are applied to 500 hPa geopotential height anomaly for two selected latitude belts in the Northern Hemisphere from Dec 1978 through Feb 1979 based on the ECMWF FGGE Hl-b data. The positive anomalies in the three leading CEOFs for the high-latitude belt mainly show the preferred locations for blocking activity in the North Atlantic, the North Pacific and to the west of the Ural Mountains. The negative anomalies in the three leading CEOFs for the mid-latitude belt mainly show the preferred locations for cyclogenesis in the east coasts of Asia and North America, and the Mediterranean; weak cyclogenesis is also seen in the western United States and off the coasts of Spain and Morocco. The travelling components of the positive anomalies in the high-latitude belt mainly propagate westward, weakening as approaching the east side of some mountain chains while intensifying to the west side. On the contrary, the travelling components of the negative anomalies in the mid-latitude belt mainly propagate eastward, intensifying over the lee side of mountain and/or approaching the east coasts of the two continents. These preferred locations for blocking and cyclogenesis are basically consistent with the climatological results, and related to some teleconnection patterns found earlier.The temporal variation of blocking highs seems to relate with the vacillation of the potential vorticity (PV) index defined by Weng (1992). There are two build-up stages of the PV index during the winter. Each build-up stage corresponds to a westward propagation of a large-scale positive anomaly in the high-latitude belt, resulting in the occurrence of a series of blocking highs over the western Eurasia, Scandinavia, Greenland and the Pacific. In general, the temporal variation of cyclogenesis is less reflected by the PV index than blocking highs. The duration of a PV index cycle of build-up and break-down is about 30-50 days. Within this low-frequency envelope, there is a global quasi-two-week vacillation of the PV index, reflecting one of the preferred time scales of mid-latitude cyclone and anticyclone activity in some preferred locations during the 1978 / 79 winter.展开更多
In this paper, we use the daily ranges of the vertical magnetic intensity of approximately 76 geomagnetic stations from January 1, 2008 to December 31, 2010 to analyze the spatial and temporal characteristics of Z ran...In this paper, we use the daily ranges of the vertical magnetic intensity of approximately 76 geomagnetic stations from January 1, 2008 to December 31, 2010 to analyze the spatial and temporal characteristics of Z ranges. The results are summarized as follows: (1) Temporally, we use regressive analysis and FFT analysis to analyze the data. The results show that the Z component daily ranges of all stations have an obvious cyclical variation, the computed Fourier spectra of all data sets have clearly resolved the required periodicities in the data, in the form of distinct peaks at days 365, 183, 22, and 73, and the power spectra of day 365 is the highest in all periods. (2) In terms of spatial variation, the daily ranges show nonlinear variation with latitude in China. The results show the existence of a point of inflexion (maximal value point) nearby at about 25°N, the daily ranges of Z rise from 15°~25°N and have a good linear decrease variation along with 25°~50°N. (3) Compared with the spatial and temporal variations of Z daily ranges with the Sq current inversion, we found that the spatial and temporal characteristics of Z ranges are decided mainly by the spatio-temporal evolution of the Sq current system. (4) If the latitudes of the maximum amplitudes of variation of the vertical component in the geomagnetic quiet days are roughly taken as the latitudes corresponding to the foci of Sq overhead current system, we can see that these latitudes of foci become higher in summer, are lowest in winter and highest during Equinoxes, displaying conspicuous monthly and daily variations. For two successive geomagnetic quiet days, the latitudes of foci may vary ten degrees.展开更多
The seaweeds Chaetomorpha antennina, Gymnogongrus griffithsiae and Ulva fasciata were studied regarding tissue concentrations of total nitrogen, total phosphorus, total protein, hydrosoluble protein, total carbohydrat...The seaweeds Chaetomorpha antennina, Gymnogongrus griffithsiae and Ulva fasciata were studied regarding tissue concentrations of total nitrogen, total phosphorus, total protein, hydrosoluble protein, total carbohydrate, chlorophyll a and total carotenoid throughout a 39-month survey in two coastal environments of Rio de Janeiro State, Brazil. One of the sites (Itapuca Stone) has high concentrations of dissolved nutrients and an intense long-term process of cultural eutrophication;the second site (Bananal Inlet) is thought to have lower concentrations of dissolved nutrients and no relevant anthropic impact. Seaweeds experienced changes in the concentrations of the substances in the thalli;however they did not show any cyclic seasonal pattern, except for pigments, with lower values in summer in both sites. The differences found for each species in each sampling at the sites were small (e.g. U. fasciata, more total nitrogen at Itapuca Stone) or absent (e.g. C. antennina, no significant differences for hydrosoluble protein in the sites). Differences in the concentrations of dissolved nutrients in the sites did not generate contrasting chemical profiles in the seaweeds. There is no evidence of nitrogen- or phosphorus-limitation in any season. It is presumable that the concentrations of dissolved nutrients at the nutrient-poorer site are sufficient to generate high concentrations of the substances in the thalli of the species tested, similar to the concentrations measured in the eutrophic site. Experimental data are needed to elucidate the factors that promote the success of the species tested under contrasting nutrient availability and environmental disturbance.展开更多
Daily maximum/minimum temperatures and relative humidity records from 510 stations in China for the period 1960–2008 were used to investigate geographical patterns and temporal variations of heatwave （HW） events. D...Daily maximum/minimum temperatures and relative humidity records from 510 stations in China for the period 1960–2008 were used to investigate geographical patterns and temporal variations of heatwave （HW） events. Dry and wet HW events were compared by different definitions. Regionally, both dry and wet HW events are commonly located in southeastern China in the monsoon area, with neither type occurring in the northeast part of Northeast China and Southwest China, while the north-northwest region of the country experiences dry HW events and a few wet HW events. In the southeast of the country, site dry HW events occurred from April to September and mostly in June, while site wet HW events occurred from April to October and mostly in September. In total, 163 regional wet HW events were identified. The ten longest regional wet HW events lasted for more than 20 days, while the mean duration for 163 events was about 11 days. For the top ten events, six occurred after the 1990s, compared with four before this time. Global surface warming was clear since 1979, but the frequency and severity of regional wet HW events were relatively low in the 1980s, increasing remarkably since the 1990s. Possible reasons for this might be the strong interdecadal and interannual variations in regional atmospheric circulations, as well as water transport related directly to temperature contrasts in different regions, rather than global-mean temperature changes.展开更多
High PM_(2.5) concentrations and frequent air pollution episodes during late autumn and winter in Jilin Province have attracted attention in recent years. To describe the spatial and temporal variations of PM_(2.5) co...High PM_(2.5) concentrations and frequent air pollution episodes during late autumn and winter in Jilin Province have attracted attention in recent years. To describe the spatial and temporal variations of PM_(2.5) concentrations and identify the decisive influencing factors, a large amount of continuous daily PM_(2.5) concentration data collected from 33 monitoring stations over 2-year period from 2015 to 2016 were analyzed. Meanwhile, the relationships were investigated between PM_(2.5) concentrations and the land cover, socioeconomic and meteorological factors from the macroscopic perspective using multiple linear regressions(MLR) approach. PM_(2.5) concentrations across Jilin Province averaged 49 μg/m^3, nearly 1.5 times of the Chinese annual average standard, and exhibited seasonal patterns with generally higher levels during late autumn and over the long winter than the other seasons. Jilin Province could be divided into three kinds of sub-regions according to 2-year average PM_(2.5) concentration of each city. Most of the spatial variation in PM_(2.5) levels could be explained by forest land area, cultivated land area, urban greening rate, coal consumption and soot emissions of cement manufacturing. In addition, daily PM_(2.5) concentrations had negative correlation with daily precipitation and positive correlation with air pressure for each city, and the spread and dilution effect of wind speed on PM_(2.5) was more obvious at mountainous area in Jilin Province. These results indicated that coal consumption, cement manufacturing and straw burning were the most important emission sources for the high PM_(2.5) levels, while afforestation and urban greening could mitigate particulate air pollution. Meanwhile, the individual meteorological factors such as precipitation, air pressure, wind speed and temperature could influence local PM_(2.5) concentration indirectly.展开更多
Based on the nearly diurnal resonance in the tidal gravity observations, the temporal variations in period of the Earth＇s free core nutation （FCN） are investigated by using the tidal gravity observations of 18-year...Based on the nearly diurnal resonance in the tidal gravity observations, the temporal variations in period of the Earth＇s free core nutation （FCN） are investigated by using the tidal gravity observations of 18-year duration recorded continu- ously with a superconducting gravimeter （SG） at Brussels. The effects of the global oceanic tide loading and local barometric pressure on the SG observations have been removed by using eleven high-precision global digital models of oceanic tides and barometric pressure measurements recorded simultaneously at the same site. The results indicate that there exist decade-scale variations in the FCN period. The results should be further confirmed by the measurements using other space-based geodetic techniques （such as the very long baseline interferometry） and the SG observations from globally distributed stations.展开更多
Temporal variation of rock mass properties,especially the strength degradation due to drying-wetting cycles as well as the acidic wetting fluid(rainfall or reservoir water)is crucial to stability of reservoir rock slo...Temporal variation of rock mass properties,especially the strength degradation due to drying-wetting cycles as well as the acidic wetting fluid(rainfall or reservoir water)is crucial to stability of reservoir rock slopes.Based on a series of drying-wetting cycling and experiments considering the influences of pH values,the degradation degree models of the reduced cohesion𝑐𝑐′,friction angle𝜑𝜑′are developed.2D stability analysis of the slope is subsequently carried out to calculate the factor of safety(Fs)via limit equilibrium method(LEM)and a predictive model of Fs is built using multivariate adaptive regression splines(MARS),revealing the effect of the drying-wetting cycles and pH value.The reliability analysis by Monte Carlo simulation is performed to rationally consider the uncertainty and the temporal variation of the shear strength parameters of rock mass.Results indicate that the MARS-based model can estimate the Fs accurately.The Fs and the reliability indexβdecrease with increase of drying-wetting cycles,and the temporal variation of rock mass properties has significant influence on the slope reliability.Overlooking the temporal variation of rock properties may overestimate the Fs and reliability indexβin the longer term.展开更多
Temporal variations in multimodal structures of diurnal( D_1) and semidiurnal( D_2) internal tides were investigated on the continental slope of the Dongsha Plateau, based on 2-month moored acoustic Doppler current pr...Temporal variations in multimodal structures of diurnal( D_1) and semidiurnal( D_2) internal tides were investigated on the continental slope of the Dongsha Plateau, based on 2-month moored acoustic Doppler current profiler observations. Harmonic analysis indicated that the D_1 components( K_1 and O_1) dominated the internal tide field. The vertical structure of the K_1 constituent presented a first-mode structure while the M_2 constituent seemed to exhibit a high-mode structure. Amplitude spectra analysis of the current data revealed differences in baroclinic current amplitudes between different water depths. Temporal variations in modal structures ware analyzed, based on the D_1 and D_2 baroclinic tides extracted from the baroclinic velocity field with band-pass filters. Analysis showed that the magnitude of the D_1 internal tide current was much larger than the D_2 current, and temporal variations in the modal structure of the D_1 internal tide occurred on an approximately fortnightly cycle. The EOF analyses revealed temporal transformation of multimodal structures for D_1 and D_2 internal tides. The enhancement of the D_1 internal tide was mainly due to the superposition of K_1 and O_1, according to the temporal variation of coherent kinetic energy.展开更多
The spatial and temporal variations of the instrument-based evaporation and actual evaporation in autumn during a 45-year period from 1960 to 2004 are studied using the observation data from 66 stations over South Chi...The spatial and temporal variations of the instrument-based evaporation and actual evaporation in autumn during a 45-year period from 1960 to 2004 are studied using the observation data from 66 stations over South China. The results reveal that there are two main anomalous centers of the instrument-based evaporation in autumn in the central and northwestern parts of South China respectively. The instrument-based evaporation over the central part of South China in autumn experiences not only a decreasing trend but also a main interdecadal variation. The solar radiation is best correlated with the instrument-based evaporation among all affecting factors. For the actual evaporation, two main anomalous centers are located at the central and western parts of the South China respectively. The actual evaporation over the two regions illustrates an interannual variation. Among the affecting factors, precipitation is the most remarkable. The actual evaporation is usually 40 percent of the instrument-based one, and the overall rate has a slightly increasing trend from the southern part to the northern part of the South China in autumn.展开更多
Water is one of the essential life’s basic needs. However, the purity and quality of water from groundwater sources in developing countries are still in doubt due to contamination by different anthropogenic activitie...Water is one of the essential life’s basic needs. However, the purity and quality of water from groundwater sources in developing countries are still in doubt due to contamination by different anthropogenic activities. This study assessed the temporal variations in physico-chemical parameters of water sources in Kibujjo Village, Wakiso District, Uganda. Water samples were collected from four water sources: two (2) wells and two (2) boreholes. The levels of both physical and chemical parameters were assessed using APHA standard analytical methods. The results indicated that most of the measured water quality variables did not exceed the UNBS and WHO standards for drinking water, and the majority of the water parameters positively correlated. Borehole waters had a better quality than well waters. The highest levels of most of the variables were recorded during the wet season. There was a significant statistical difference (p SO<sup>2-</sup>4</sub> showed a significant difference in the dry season amongst the water sources but no significant difference during the wet season (p > 0.05). Therefore, water from wells is not recommended for drinking before treatment, most especially during the wet season.展开更多
Based on the data of meteorological elements and concentration of negative ions in the county town station,Luguhe station and Yunjishan station during 2020-2024,the temporal and spatial variations in the concentration...Based on the data of meteorological elements and concentration of negative ions in the county town station,Luguhe station and Yunjishan station during 2020-2024,the temporal and spatial variations in the concentration of negative ions and their influencing factors in Xinfeng County were analyzed.The results show that the concentration of negative ions was the highest in summer,followed by spring;it was lower in autumn and the lowest in winter.In terms of diurnal variations,it was higher in the early morning and night,and lower in the noon and afternoon,which was closely related to the diurnal variations of human activities and meteorological conditions.The factors that affect the concentration of negative ions in the air are more complex.Besides meteorological factors,vegetation,altitude,human activities and other factors should be considered.展开更多
Vegetation plays an important role in global or regional environmental change.In this study,the spatial–temporal variations of NDVI and its response to climate in China and its seven sub-regions were investigated bas...Vegetation plays an important role in global or regional environmental change.In this study,the spatial–temporal variations of NDVI and its response to climate in China and its seven sub-regions were investigated based on MODIS NDVI data,ERA5-land precipitation(PRE)and temperature(TEM)data from 2001 to 2020.The inter-annual growth rate of NDVI in China was 0.0021/yr in the past 20 years.The inter-annual growth rates of NDVI in seven sub-regions had significant differences at regional or seasonal scales.The ratio of improved vegetation area to the total studied area reached about 70%.In summer,vegetation degradation was concentrated in East China and Southwest China.The vegetation in Central China and South China improved more obviously in autumn than in the other seasons.The vegetation of Northeast China had a remarkable degradation in autumn and winter,especially in winter.The influence degree of PRE(q=0.54,P<0.01)was greater than that of TEM(q=0.27,P<0.01)in the control of the spatial distribution of NDVI.The interaction influence degree q of PRE∩TEM was about 0.71 in the last 20 years.However,the PRE and TEM played different roles in vegetation growth in seven sub-regions.展开更多
文摘Evaluation and analysis of water quality variations were performed with integrated consideration of water quality parameters, hydrological-meteorologic and anthropogenic factors in Cao-E River, Zhejiang Province of China. Cao-E River system has been polluted and the water quality of some reaches are inferior to Grade V according to National Surface Water Quality Standard of China （GB2002）. However, mainly polluted indices of each tributary and mainstream are different. Total nitrogen （TN） and total phosphorus （TP） in the water are the main polluted indices for mainstream that varies from 1.52 to 45.85 mg/L and 0.02 to 4.02 mg/L, respectively. TN is the main polluted indices for Sub-watershed Ⅰ, Ⅱ, Ⅳ and Ⅴ（0.76 to 18.27 mg/L）. BOD5 （0.36 to 289.5 mg/L）, CODMn （0.47 to 78.86 mg/L）, TN （0.74 to 31.09 mg/L） and TP （0 to 3.75 mg/L） are the main polluted indices for Sub-watershed Ⅲ. There are tow pollution types along the river including nonpoint source pollution and point source pollution types. Remarkably temporal variations with a few spatial variations occur in nonpoint pollution type reaches （including mainstream, Sub-watershed Ⅰ and Ⅱ） that mainly drained by arable field and/or dispersive rural dwelling district, and the maximum pollutant concentration appears in flooding seasons. It implied that the runoff increases the pollutant concentration of the water in the nonpoint pollution type reaches. On the other hand, remarkably spatial variations occur in the point pollution type reaches （include Sub-watershed Ⅲ, Ⅳ and Ⅴ） and the maximum pollutant concentration appears in urban reaches. The runoff always decreases the pollutant concentration of the river water in the seriously polluted reaches that drained by industrial point sewage. But for the point pollution reaches resulted from centralized town domestic sewage pipeline and from frequent shipping and digging sands, rainfall always increased the concentration of pollutant （TN） in the river water too. Pollution controls were respectively suggested for these tow types according to different pollution causes.
基金supported jointly by the National Key Technologies R&D Program of China(Grant No.2008BAK50B02)the National Basic Research Program of China(Grant No.2009CB421405)the National Natural Science Foundation of China(Grant No.40730952)
文摘The temporal variations in storm rainfall during the first rainy season (FRS) in South China (SC) are investigated in this study. The results show that the inter-annual variations in storm rainfall during the FRS in SC seem to be mainly influenced by the frequency of storm rainfall, while both frequency and intensity affect the inter-decadal variations in the total storm rainfall. Using the definitions for the beginning and ending dates of the FRS, and the onset dates of the summer monsoon in SC, the FRS is further divided into two sub-periods, i.e., the frontal and monsoon rainfall periods. The inter-annual and inter-decadal variations in storm rainfall during these two periods are investigated here. The results reveal a significant out-of-phase correlation between the frontal and monsoon storm rainfall, especially on the inter-decadal timescale, the physical mechanism for which requires further investigation.
基金This study was supported by the Qingdao Special Program for Leading Scientists under contract No.04-3-JJ-03the Knowledge Innovation Program of the Chinese Academy of Sciences under contract No.KZCX1-SW-01-08the“100 Talents Project”of the Chinese Academy of Sciences and the National Science Foundation for Outstanding Young Scientists of China under contract No.49925614.
文摘The results of field observation carried out in May 2003 were used to examine pH and total alkalinity behaviors in the Changjiang Estuary. It was showed that pH and total alkalinity took on clear spatial variations in values with the minima in the low salinity region. Like salinity, transect distributions of pH and total alkalinity （TA） in a downriver direction had a sharp gradient each. These gradients appeared in such a sequence that the TA gradient was earlier than salinity and pH gradients, and the salinity gradient was earlier than the pH gradient. These distribution characteristics seemed to be strongly influenced by the mixing process of freshwater and seawater, for both pH and total alkalinity had significant linear relationships with salinity and temperature. For pH, phytoplankton activities also had a significant impact upon its spatial distribution. During a period of 48 h, pH and total alkalinity changed within wide ranges for every layer of the two anchor stations, namely, Stas 13 and 20, which were located at the mixed water mass and seawater mass, respectively. For both Stas 13 and 20, pH and TA fluctuation of every layer could be very wide during a 4 h period. As a whole, the data of the two anchor stations showed that neither variations in salinity and temperature nor phytoplankton activities were the main factors strongly influencing the total alkalinity temporal variability on a small time scale. The data of Sta. 20 implied that both salinity variation and phytoplankton activities had a significant influence on pH temporal variability, but the same conclusion could not be drawn from the data of Sta. 13.
基金Supported by Natural Science Foundation of China (No.40730846 40521003)
文摘The size-fractionated phytoplankton biomass, and the spatial and temporal variations in abundance of Synechococcus (SYN) and picoeukaryotes (PEUK) were measured in the Taiwan Strait during three cruises (August 1997, February-March 1998, and August 1998). The results show that picophytoplankton and nanophytoplankton dominate the phytoplankton biomass, in average of 38% and 40%, respectively. SYN and PEUK varied over time in abundance and carbon biomass, greater in summer than in winter, in range of (7.70–209.2)×106 and (0.75–15.4)×106 cells/cm2 in the abundance, and 1.93–52.3 and 1.57–32.4 μgC/cm2 in the carbon biomass, for SYN and PEUK, respectively. The horizontal distributions of both groups were diurnal but heterogeneous in abundance, depending on the groups and layer of depths. Temperature is the key controlling factor for picophytoplankton distribution (especially in winter) in the Strait.
文摘Aridity index reflects the exchanges of energy and water between the land surface and the atmosphere,and its variation can be used to forecast drought and flood patterns,which makes it of great significance for agricultural production.The ratio of potential evapotranspiration and precipitation is applied to analyse the spatial and temporal distributions of the aridity index in the Belt and Road region under the 1.5℃and 2.0℃global warming scenarios on the basis of outputs from four downscaled global climate models.The results show that:(1)Under the 1.5℃warming scenario,the area-averaged aridity index will be similar to that in 1986-2005(around 1.58),but the changes vary spatially.The aridity index will increase by more than 5%in Central-Eastern Europe,north of West Asia,the monsoon region of East Asia and northwest of Southeast Asia,while it is projected to decrease obviously in the southeast of West Asia.Regarding the seasonal scale,spring and winter will be more arid in South Asia,and the monsoon region of East Asia will be slightly drier in summer compared with the reference period.While,West Asia will be wetter in all seasons,except winter.(2)Relative to 1986-2005,both areal averaged annual potential evapotranspiration and precipitation are projected to increase,and the spatial variation of aridity index will become more obvious as well at the 2.0℃warming level.Although the aridity index over the entire region will be maintained at approximately 1.57 as that in 1.5℃,the index in Central-Eastern Europe,north of West Asia and Central Asia will grow rapidly at a rate of more than 20%,while that in West Siberia,northwest of China,the southern part of South Asia and West Asia will show a declining trend.At the seasonal scale,the increase of the aridity index in Central-Eastern Europe,Central Asia,West Asia,South Asia and the northern part of Siberia in winter will be obvious,and the monsoon region in East Asia will be drier in both summer and autumn.(3)Under the scenario of an additional 0.5℃increase in global temperature from 1.5℃to 2.0℃,the aridity index will increase significantly in Central Asia and north of West Asia but decrease in Southeast Asia and Central Siberia.Seasonally,the aridity index in the Belt and Road region will slightly increase in all other seasons except spring.Central Asia will become drier annually at a rate of more than 20%.The aridity index in South Asia will increase in spring and winter,and that in East Asia will increase in autumn and winter.(4)To changes of the aridity index,the attribution of precipitation and potential evapotranspiration will vary regionally.Precipitation will be the major influencing factor over southern West Asia,southern South Asia,Central-Eastern Siberia,the non-monsoon region of East Asia and the border between West Asia and Central Asia,while potential evapotranspiration will exert greater effects over Central-Eastern Europe,West Siberia,Central Asia and the monsoon region of East Asia.
基金The Strategic Priority Research Program of the Chinese Academy of Sciences,No.XDA20010202,No.XDA20010302。
文摘The rapid expansion of China’s urban agglomerations in recent decades has resulted in over-occupied ecological spaces and increased ecological pressure that are restricting healthy regional development.This paper examines the structure and characteristics of distribution of“production-living-ecological”spaces in five mega-urban agglomerations in China:Beijing-Tianjin-Hebei(BTH),the Yangtze River Delta(YRD),Guangdong-Hong Kong-Macao Greater Bay Area(GBA),Chengdu-Chongqing(CY),and the middle reaches of the Yangtze River(MYR).We analyze spatial and temporal variations in the ecological spaces and factors influencing them from 1990 to 2020,and examine the comprehensive ecological carrying capacity and status of ecological spaces in the past 30 years based on the available water resources,regulation of water and air quality,and leisure and recreation.The results show the following:(1)Urban agglomerations in different stages of formation and development represent varying area ratios of“ecological-production-living”spaces.The modes of expansion and evolution of the living spaces are dominated by multi-center combinations as well as the spatial structure of ecological spaces,including barrier,compact,discrete,and fully enveloping spaces.(2)From 1990 to 2020,the area occupied by living spaces in urban agglomerations continued to increase significantly while that of spaces for ecological production decreased.Except in the GBA,ecological spaces have exhibited a trend of increase in area,especially in the past 10 years.The area ratios and spatio-temporal variations in the“production-living-ecological”spaces indicate that the main functions of production and ecological spaces in mega-urban agglomerations have shifted from supply to regulation and culture,and reflect the transition from rapid urbanization to sustainable urbanization in China.(3)The comprehensive ecological carrying capacities of 78.6%,73.1%,54.5%,56.3%,and 25.8%of cities in BTH,YRD,GBA,CY and MYR are severely overburdened.Water supply and the regulation of water quality are the main factors restricting the ecological carrying capacity of BTH and YRD while leisure and recreation services have hindered the capacities of GBA and CY.Policymakers thus need to pay attention to the conservation and rational layout of ecological spaces to reduce the ecological pressure in urban agglomerations.The work here can provide a scientific basis for the green and sustainable development of urban agglomerations as well as the optimized configuration of“production-living-ecological”spaces.
基金supported by the National Natural Science Foundation of China(No.21777094)the Science and Technology Commission of Shanghai Municipality(CN)(Nos.19DZ1205004,20DZ1204004)。
文摘To investigate the air quality change during the COVID-19 pandemic,we analyzed spatiotemporal variations of six criteria pollutants in nine typical urban agglomerations in China using ground-based data and examined meteorological influences through correlation analysis and backward trajectory analysis under different responses.Concentrations of PM2.5,PM10,NO2,SO2 and CO in urban agglomerations respectively decreased by 18%–45%(30%–62%),17%–53%(22%–39%),47%-64%(14%–41%),9%–34%(0%–53%)and 16%-52%(23%–56%)during Lockdown(Post-lockdown)period relative to Pre-lockdown period.PM2.5 pollution events occurred during Lockdown in Beijing-Tianjin-Hebe(BTH)and Middle and South Liaoning(MSL),and daily O3 concentration rose to gradeⅡstandard in Post-lockdown period.Distinct from the nationwide slump of NO2 during Lockdown period,a rebound(~40%)in Post-lockdown period was observed in Cheng-Yu(CY),Yangtze River Middle-Reach(YRMR),Yangtze River Delta(YRD)and Pearl River Delta(PRD).With slightly higher wind speed compared with 2019,the reduction of PM2.5(51%–62%)in Post-lockdown period is more than2019(15%–46%)in HC(Harbin-Changchun),MSL,BTH,CP(Central Plain)and SP(ShandongPeninsula),suggesting lockdown measures are effective to PM2.5 alleviation.Although O3 concentrations generally increased during the lockdown,its increment rate declined compared with 2019 under similar sunlight duration and temperature.Additionally,unlike HC,MSL and BTH,which suffered from additional(>30%)air masses from surrounding areas after the lockdown,the polluted air masses reaching YRD and PRD mostly originated from the long-distance transport,highlighting the importance of joint regional governance.
文摘To investigate the life cycle of marine sulfate aerosols, chemicophysical characteristics of marine aerosolswere measured during five cruises in the Pacific Ocean. Dimethyl sulfide concentrations in seawater and in the air were also measured. The geographic variation of sulfate-aerosol concentrations was studied in relation to biogenic and anthropogenic sources,transport with air trajectories, and chemical transformations in the atmosphere. The highest concentrations were found near Asian and American ports, indicating anthropogenic pollution is the major sulfate aerosols source. Higher concentrations were observed in the upwelling regions than in the oligotrophic areas. Along the coastal regions, both mass and number concentrations of sulfate aerosols depended on wind direction and wind speed, and land-breeze and sea-breeze oscillations; no clear diurnal variation was detected. In pelagic areas, along the equator, the concentrations of small sulfate particles showed a maximum in the afternoon and the minimum at night , indicating photo-oxidation as an important process for gas-to-particle conversion. Higher sulfate-aerosol concentrations were observed in spring than in autumn and higher concentrations were found during the La Nina anomaly than during the El Nino anomaly. Biogenic source of sulfate aerosols has an important role in the remote ocean. Case studies of sulfate-aerosol distributions are discussed.
基金"Contribution No. 336" of Geophysical Fluid Dynamics Institute, FSU.
文摘Complex empirical orthogonal function (CEOF) and Fourier analyses are applied to 500 hPa geopotential height anomaly for two selected latitude belts in the Northern Hemisphere from Dec 1978 through Feb 1979 based on the ECMWF FGGE Hl-b data. The positive anomalies in the three leading CEOFs for the high-latitude belt mainly show the preferred locations for blocking activity in the North Atlantic, the North Pacific and to the west of the Ural Mountains. The negative anomalies in the three leading CEOFs for the mid-latitude belt mainly show the preferred locations for cyclogenesis in the east coasts of Asia and North America, and the Mediterranean; weak cyclogenesis is also seen in the western United States and off the coasts of Spain and Morocco. The travelling components of the positive anomalies in the high-latitude belt mainly propagate westward, weakening as approaching the east side of some mountain chains while intensifying to the west side. On the contrary, the travelling components of the negative anomalies in the mid-latitude belt mainly propagate eastward, intensifying over the lee side of mountain and/or approaching the east coasts of the two continents. These preferred locations for blocking and cyclogenesis are basically consistent with the climatological results, and related to some teleconnection patterns found earlier.The temporal variation of blocking highs seems to relate with the vacillation of the potential vorticity (PV) index defined by Weng (1992). There are two build-up stages of the PV index during the winter. Each build-up stage corresponds to a westward propagation of a large-scale positive anomaly in the high-latitude belt, resulting in the occurrence of a series of blocking highs over the western Eurasia, Scandinavia, Greenland and the Pacific. In general, the temporal variation of cyclogenesis is less reflected by the PV index than blocking highs. The duration of a PV index cycle of build-up and break-down is about 30-50 days. Within this low-frequency envelope, there is a global quasi-two-week vacillation of the PV index, reflecting one of the preferred time scales of mid-latitude cyclone and anticyclone activity in some preferred locations during the 1978 / 79 winter.
基金supported by the special fundamental research fund of Institute of Geophysics,CEA for Central Public Welfare Research Institutes(DQJB11C10)the fund for the Task of Tracing Earthquake Trend of China Earthquake Administration(Grant No.2010020705)
文摘In this paper, we use the daily ranges of the vertical magnetic intensity of approximately 76 geomagnetic stations from January 1, 2008 to December 31, 2010 to analyze the spatial and temporal characteristics of Z ranges. The results are summarized as follows: (1) Temporally, we use regressive analysis and FFT analysis to analyze the data. The results show that the Z component daily ranges of all stations have an obvious cyclical variation, the computed Fourier spectra of all data sets have clearly resolved the required periodicities in the data, in the form of distinct peaks at days 365, 183, 22, and 73, and the power spectra of day 365 is the highest in all periods. (2) In terms of spatial variation, the daily ranges show nonlinear variation with latitude in China. The results show the existence of a point of inflexion (maximal value point) nearby at about 25°N, the daily ranges of Z rise from 15°~25°N and have a good linear decrease variation along with 25°~50°N. (3) Compared with the spatial and temporal variations of Z daily ranges with the Sq current inversion, we found that the spatial and temporal characteristics of Z ranges are decided mainly by the spatio-temporal evolution of the Sq current system. (4) If the latitudes of the maximum amplitudes of variation of the vertical component in the geomagnetic quiet days are roughly taken as the latitudes corresponding to the foci of Sq overhead current system, we can see that these latitudes of foci become higher in summer, are lowest in winter and highest during Equinoxes, displaying conspicuous monthly and daily variations. For two successive geomagnetic quiet days, the latitudes of foci may vary ten degrees.
基金FAPERJ(Rio de Janeiro State Research Support Foundation)for the financial support to this study.
文摘The seaweeds Chaetomorpha antennina, Gymnogongrus griffithsiae and Ulva fasciata were studied regarding tissue concentrations of total nitrogen, total phosphorus, total protein, hydrosoluble protein, total carbohydrate, chlorophyll a and total carotenoid throughout a 39-month survey in two coastal environments of Rio de Janeiro State, Brazil. One of the sites (Itapuca Stone) has high concentrations of dissolved nutrients and an intense long-term process of cultural eutrophication;the second site (Bananal Inlet) is thought to have lower concentrations of dissolved nutrients and no relevant anthropic impact. Seaweeds experienced changes in the concentrations of the substances in the thalli;however they did not show any cyclic seasonal pattern, except for pigments, with lower values in summer in both sites. The differences found for each species in each sampling at the sites were small (e.g. U. fasciata, more total nitrogen at Itapuca Stone) or absent (e.g. C. antennina, no significant differences for hydrosoluble protein in the sites). Differences in the concentrations of dissolved nutrients in the sites did not generate contrasting chemical profiles in the seaweeds. There is no evidence of nitrogen- or phosphorus-limitation in any season. It is presumable that the concentrations of dissolved nutrients at the nutrient-poorer site are sufficient to generate high concentrations of the substances in the thalli of the species tested, similar to the concentrations measured in the eutrophic site. Experimental data are needed to elucidate the factors that promote the success of the species tested under contrasting nutrient availability and environmental disturbance.
基金supported jointly by the National Natural Science Foundation of China (Grant No.40975039),GYHY201006018the Key Technologies R&D Program (Grant No. 2009BAC51B00)
文摘Daily maximum/minimum temperatures and relative humidity records from 510 stations in China for the period 1960–2008 were used to investigate geographical patterns and temporal variations of heatwave （HW） events. Dry and wet HW events were compared by different definitions. Regionally, both dry and wet HW events are commonly located in southeastern China in the monsoon area, with neither type occurring in the northeast part of Northeast China and Southwest China, while the north-northwest region of the country experiences dry HW events and a few wet HW events. In the southeast of the country, site dry HW events occurred from April to September and mostly in June, while site wet HW events occurred from April to October and mostly in September. In total, 163 regional wet HW events were identified. The ten longest regional wet HW events lasted for more than 20 days, while the mean duration for 163 events was about 11 days. For the top ten events, six occurred after the 1990s, compared with four before this time. Global surface warming was clear since 1979, but the frequency and severity of regional wet HW events were relatively low in the 1980s, increasing remarkably since the 1990s. Possible reasons for this might be the strong interdecadal and interannual variations in regional atmospheric circulations, as well as water transport related directly to temperature contrasts in different regions, rather than global-mean temperature changes.
基金Under the auspices of National Natural Science Foundation of China(No.41601607,41771138,41771161)Strategic Planning Project from Institute of Northeast Geography and Agroecology(IGA),Chinese Academy of Sciences(No.Y6H2091001-3)
文摘High PM_(2.5) concentrations and frequent air pollution episodes during late autumn and winter in Jilin Province have attracted attention in recent years. To describe the spatial and temporal variations of PM_(2.5) concentrations and identify the decisive influencing factors, a large amount of continuous daily PM_(2.5) concentration data collected from 33 monitoring stations over 2-year period from 2015 to 2016 were analyzed. Meanwhile, the relationships were investigated between PM_(2.5) concentrations and the land cover, socioeconomic and meteorological factors from the macroscopic perspective using multiple linear regressions(MLR) approach. PM_(2.5) concentrations across Jilin Province averaged 49 μg/m^3, nearly 1.5 times of the Chinese annual average standard, and exhibited seasonal patterns with generally higher levels during late autumn and over the long winter than the other seasons. Jilin Province could be divided into three kinds of sub-regions according to 2-year average PM_(2.5) concentration of each city. Most of the spatial variation in PM_(2.5) levels could be explained by forest land area, cultivated land area, urban greening rate, coal consumption and soot emissions of cement manufacturing. In addition, daily PM_(2.5) concentrations had negative correlation with daily precipitation and positive correlation with air pressure for each city, and the spread and dilution effect of wind speed on PM_(2.5) was more obvious at mountainous area in Jilin Province. These results indicated that coal consumption, cement manufacturing and straw burning were the most important emission sources for the high PM_(2.5) levels, while afforestation and urban greening could mitigate particulate air pollution. Meanwhile, the individual meteorological factors such as precipitation, air pressure, wind speed and temperature could influence local PM_(2.5) concentration indirectly.
基金supported by the Key Project of the Knowledge Innovation of Chinese Academy of Sciences (Grant No. KZCX2-YW-133, KZCX2-YW-Q08-2)National Natural Science Foun-dation of China (Grant No. 40874038 and 40730316)
文摘Based on the nearly diurnal resonance in the tidal gravity observations, the temporal variations in period of the Earth＇s free core nutation （FCN） are investigated by using the tidal gravity observations of 18-year duration recorded continu- ously with a superconducting gravimeter （SG） at Brussels. The effects of the global oceanic tide loading and local barometric pressure on the SG observations have been removed by using eleven high-precision global digital models of oceanic tides and barometric pressure measurements recorded simultaneously at the same site. The results indicate that there exist decade-scale variations in the FCN period. The results should be further confirmed by the measurements using other space-based geodetic techniques （such as the very long baseline interferometry） and the SG observations from globally distributed stations.
基金the financial support from Natural Science Foundation of Chongqing,China(cstc2018jcyjAX0632)the Venture&Innovation Support Program for Chongqing Overseas Returnees(cx2017123)+1 种基金as well as Chongqing Engineering Research Center of Disaster Prevention&Control for Banks and Structures in Three Gorges Reservoir Area(SXAPGC18ZD01,SXAPGC18YB03)In addition,the authors would like to express their appreciation to Liu et al.[Liu,Zhang and Fu(2014)]for making their test results available for this work.
文摘Temporal variation of rock mass properties,especially the strength degradation due to drying-wetting cycles as well as the acidic wetting fluid(rainfall or reservoir water)is crucial to stability of reservoir rock slopes.Based on a series of drying-wetting cycling and experiments considering the influences of pH values,the degradation degree models of the reduced cohesion𝑐𝑐′,friction angle𝜑𝜑′are developed.2D stability analysis of the slope is subsequently carried out to calculate the factor of safety(Fs)via limit equilibrium method(LEM)and a predictive model of Fs is built using multivariate adaptive regression splines(MARS),revealing the effect of the drying-wetting cycles and pH value.The reliability analysis by Monte Carlo simulation is performed to rationally consider the uncertainty and the temporal variation of the shear strength parameters of rock mass.Results indicate that the MARS-based model can estimate the Fs accurately.The Fs and the reliability indexβdecrease with increase of drying-wetting cycles,and the temporal variation of rock mass properties has significant influence on the slope reliability.Overlooking the temporal variation of rock properties may overestimate the Fs and reliability indexβin the longer term.
基金Supported by the State Ministry of Science and Technology of China(Nos.2013AA122803,2013AA09A502)the National Natural Science Foundation of China(Nos.41206001,41371496)+1 种基金the Natural Science Foundation of Shandong Province of China(No.ZR2014DM017)National Key Technology Research and Development Program(No.2013BAK05B04)
文摘Temporal variations in multimodal structures of diurnal( D_1) and semidiurnal( D_2) internal tides were investigated on the continental slope of the Dongsha Plateau, based on 2-month moored acoustic Doppler current profiler observations. Harmonic analysis indicated that the D_1 components( K_1 and O_1) dominated the internal tide field. The vertical structure of the K_1 constituent presented a first-mode structure while the M_2 constituent seemed to exhibit a high-mode structure. Amplitude spectra analysis of the current data revealed differences in baroclinic current amplitudes between different water depths. Temporal variations in modal structures ware analyzed, based on the D_1 and D_2 baroclinic tides extracted from the baroclinic velocity field with band-pass filters. Analysis showed that the magnitude of the D_1 internal tide current was much larger than the D_2 current, and temporal variations in the modal structure of the D_1 internal tide occurred on an approximately fortnightly cycle. The EOF analyses revealed temporal transformation of multimodal structures for D_1 and D_2 internal tides. The enhancement of the D_1 internal tide was mainly due to the superposition of K_1 and O_1, according to the temporal variation of coherent kinetic energy.
基金Significant Technical Addressing Project from Guangdong Bureau of Science and Technology (2007Z1-E0101)
文摘The spatial and temporal variations of the instrument-based evaporation and actual evaporation in autumn during a 45-year period from 1960 to 2004 are studied using the observation data from 66 stations over South China. The results reveal that there are two main anomalous centers of the instrument-based evaporation in autumn in the central and northwestern parts of South China respectively. The instrument-based evaporation over the central part of South China in autumn experiences not only a decreasing trend but also a main interdecadal variation. The solar radiation is best correlated with the instrument-based evaporation among all affecting factors. For the actual evaporation, two main anomalous centers are located at the central and western parts of the South China respectively. The actual evaporation over the two regions illustrates an interannual variation. Among the affecting factors, precipitation is the most remarkable. The actual evaporation is usually 40 percent of the instrument-based one, and the overall rate has a slightly increasing trend from the southern part to the northern part of the South China in autumn.
文摘Water is one of the essential life’s basic needs. However, the purity and quality of water from groundwater sources in developing countries are still in doubt due to contamination by different anthropogenic activities. This study assessed the temporal variations in physico-chemical parameters of water sources in Kibujjo Village, Wakiso District, Uganda. Water samples were collected from four water sources: two (2) wells and two (2) boreholes. The levels of both physical and chemical parameters were assessed using APHA standard analytical methods. The results indicated that most of the measured water quality variables did not exceed the UNBS and WHO standards for drinking water, and the majority of the water parameters positively correlated. Borehole waters had a better quality than well waters. The highest levels of most of the variables were recorded during the wet season. There was a significant statistical difference (p SO<sup>2-</sup>4</sub> showed a significant difference in the dry season amongst the water sources but no significant difference during the wet season (p > 0.05). Therefore, water from wells is not recommended for drinking before treatment, most especially during the wet season.
文摘Based on the data of meteorological elements and concentration of negative ions in the county town station,Luguhe station and Yunjishan station during 2020-2024,the temporal and spatial variations in the concentration of negative ions and their influencing factors in Xinfeng County were analyzed.The results show that the concentration of negative ions was the highest in summer,followed by spring;it was lower in autumn and the lowest in winter.In terms of diurnal variations,it was higher in the early morning and night,and lower in the noon and afternoon,which was closely related to the diurnal variations of human activities and meteorological conditions.The factors that affect the concentration of negative ions in the air are more complex.Besides meteorological factors,vegetation,altitude,human activities and other factors should be considered.
基金funded by the National Natural Science Foundation[grant number 71971002]the Anhui Provincial Natural Science Foundation[grant number 2108085QD154]+1 种基金the Major Science and Technology Project of Anhui Province[grant number 202003a06020016]the Key R&D Project of Anhui Province[grant number 202004a07020050].
文摘Vegetation plays an important role in global or regional environmental change.In this study,the spatial–temporal variations of NDVI and its response to climate in China and its seven sub-regions were investigated based on MODIS NDVI data,ERA5-land precipitation(PRE)and temperature(TEM)data from 2001 to 2020.The inter-annual growth rate of NDVI in China was 0.0021/yr in the past 20 years.The inter-annual growth rates of NDVI in seven sub-regions had significant differences at regional or seasonal scales.The ratio of improved vegetation area to the total studied area reached about 70%.In summer,vegetation degradation was concentrated in East China and Southwest China.The vegetation in Central China and South China improved more obviously in autumn than in the other seasons.The vegetation of Northeast China had a remarkable degradation in autumn and winter,especially in winter.The influence degree of PRE(q=0.54,P<0.01)was greater than that of TEM(q=0.27,P<0.01)in the control of the spatial distribution of NDVI.The interaction influence degree q of PRE∩TEM was about 0.71 in the last 20 years.However,the PRE and TEM played different roles in vegetation growth in seven sub-regions.
