Observational limits on intergalactic matter     

Bogdan Wszolek 《Astrophysics and Space Science》1995,227(1-2):151-155

Intergalactic gas and dust are very difficult to detect. Several methods to detect intergalactic gas have been developed. The results of these methods have provided qualitative arguments and quantitative limits on the amount of intergalactic matter in the intergalactic environment. We present here arguments as to why the density of intergalactic matter is higher than previously thought possible.  相似文献   

Modelling sediment (dis)connectivity across a river network to understand locational-transmission-filter sensitivity for identifying hotspots of potential geomorphic adjustment     

Sana Khan  Kirstie Fryirs  Simone Bizzi 《地球表面变化过程与地形》2021,46(14):2856-2869

Rivers act as ‘jerky conveyor belts’ that transmit fluxes of flow and sediment downstream. This transmission of fluxes can be highly variable within a drainage basin resulting in either abrupt or gradational sediment (dis)connectivity patterns and processes. This study assesses sediment (dis)connectivity across a basin as a means to understand the locational, transmission and filter sensitivity properties of a fluvial system. Drawing upon the case study of Richmond River Catchment, New South Wales, Australia we use the concepts of effective catchment area and buffers, along with graph theory and an empirical sediment transport model CASCADE (Catchment Sediment Connectivity and Delivery), to assess (1) the degree to which modelled sediment cascades along the river network are connected or disconnected (2) how the position, pattern and configuration of (dis)connection facilitates or restricts geomorphic adjustment in different parts of a catchment, and (3) use the findings as a basis to explain the locational-transmission-filter sensitivity of the catchment. We use this analysis to segregate supply limited and transport limited reaches and identify various controls on sediment dynamics: in-stream sediment storage units, junctions between different geomorphic river types, tributary confluences and sediment storage units within partly confined floodplain units. Such analysis lays the foundation for network scale identification of potential hotspots of geomorphic adjustment.  相似文献   

广州市土壤—大气界面Hg交换通量研究     

刘飞  成杭新  杨柯 《物探与化探》2014,(2):331-338

运用Tekran 2537 A与动力学通量箱联测技术,对广州市5个绿化带和草地土壤—大气界面汞交换通量进行了实地监测,结果表明,广州市5个监测点土壤—大气界面汞交换通量密度均值为7.341±9.714 ng·m-2·h-1,不同地点土壤—大气汞交换通量密度有显著差异。汞交换通量密度随土壤汞含量的增加而增大,气象条件显著影响汞交换通量,汞交换通量密度与光照和土壤温度呈显著正相关关系,与土壤pH呈负相关关系,降雨和植被显著影响汞交换通量。  相似文献   

Fluxes of riverine nutrient to the Zhujiang River Estuary and its potential eutrophication effect     

Li Zhang  Yumin Yang  Weihong He  Jie Xu  Ruihuan Li 《海洋学报(英文版)》2022,41(6):88-98

The Zhujiang River Estuary is becoming eutrophic due to the impact of anthropogenic activities in the past decades. To understand nutrient dynamics and fluxes to the Lingdingyang water via four outlets(Humen,Jiaomen, Hongqimen and Hengmen), we investigated the spatial distribution and seasonal variation of dissolved nutrients in the Zhujiang River Estuary, based on fourteen cruises conducted from March 2015 to October 2017,covering both wet(April to September) and dry(October to March next year)...  相似文献   

On the variability of vertical eddy heat flux in the upper ocean     

Tianshi Du  Peiran Yang  Zhao Jing 《海洋学报(英文版)》2022,41(10):94-99

Ocean eddies produce strong vertical heat flux (VHF) in the upper ocean, exerting profound influences on the climate and ecosystem. Currently, mooring array provides a standard way to estimate the eddy-induced VHF (EVHF) based on the adiabatic potential density equation. Apart from the validity of adiabatic assumption, it remains unclear to what extent the estimated EVHF at a single location within a limited time period is representative of its climatological mean value. In this study, we analyzed the above issue by systematically evaluating the variability of EVHF simulated by a 1-km ocean model configured over the Kuroshio Extension. It is found that the EVHF at a single location exhibits pronounced variability. Even averaged over one year that is comparable to the current maintenance capacity of mooring array, the EVHF still deviates significantly from its climatological mean value. For more than 49% of locations in our computational domain (31°–40°N, 149°–166°E), the discrepancy between the one-year mean EVHF and its climatological mean value at the peaking depth is larger than the climatological mean itself. The mesoscale eddies play a dominant role in the variability of EVHF but contribute little to the climatological mean EVHF; the opposite is true for submesoscale eddies. Our findings indicate that nested mooring array allowing for isolating the effects of submesoscale eddies will be useful to obtain climatological mean EVHF.  相似文献   

放牧对退化草地近地面辐射的影响     

李小院  张圣微  王帅  李瑞燊  赵星宇  刘敏敏 《中国沙漠》2022,42(1):223-233

随着环境变化,草原地表状态也会改变,尤其是近地面能量收支过程变化更明显。为深入理解半干旱草原地表辐射能量平衡过程对放牧的响应特征,利用内蒙古正镶白旗典型退化草原2020年生长季（6—10月）的辐射通量观测资料,对比分析了禁牧、放牧草地太阳总辐射、地表反射辐射、大气长波辐射、地表长波辐射、净辐射以及地表反照率的日变化和生长季变化规律的差异。结果表明：在生长季,太阳总辐射随着时间推进逐月递减;禁牧区的地表反射辐射总体小于放牧区;各月大气长波辐射日变化幅度很小,处于130—370 W·m^-2;禁牧、放牧条件下地表长波辐射存在明显的季节变化规律,但是二者之间的差异甚微。内蒙古典型退化草原生长季近地面辐射通量有显著单峰型日变化特征。禁牧、放牧草地地表反照率都呈现“U”型日变化规律。生长季放牧草地的反照率明显高于禁牧草地。在禁牧区,辐射分量（地表反射辐射、大气长波辐射）和植被指数（归一化差异植被指数）对净辐射的影响是正向极显著的;而地表反照率和另一辐射分量（地表长波辐射）对净辐射有显著的负向作用。在放牧区,地表反射辐射和大气长波辐射对净辐射有极显著的正向作用;而地表反照率和地表长波辐射对净辐射的作用则是负向显著的。植被状况是影响内蒙古典型退化草原近地表辐射能量收支过程的首要因子。  相似文献   

What Determines the Amplitude of ENSO Events?          下载免费PDF全文

WANG Yu-Xing  YANG Hai-jun  Tore FUREVIK 《大气和海洋科学快报》2013,6(2):90-96

In this paper, the dynamic effect of oceanic upwelling on the intensity of El Nio-Southern Oscillation (ENSO) is studied using a simple coupled model (Zebiak-Cane Model). The term balance analysis in the temperature variability equation shows that the anomalous upwelling of the mean vertical temperature gradient and the mean advection of the anomalous meridional temperature gradient are the two of most important factors that determine the intensity of ENSO events, in which the "vertical oceanic heat flux" in the eastern equatorial Pacific (EEP) is the primary influencing factor. The lag correlation between "vertical heat flux (VHF)" and ENSO intensity shows that the highest correlation occurs when the former leads the latter by one to two weeks. The VHF is positively correlated with the background thermocline strength in the EEP, and an increase of both could result in strong ENSO variability. Comparison of the forced and coupled experiments suggests that the coupled process can affect both the intensity and frequency of ENSO.  相似文献   

Numerical Simulation of CO₂ Concentrations in East Asia with RAMS-CMAQ          下载免费PDF全文

KOU Xing-Xia  ZHANG Mei-Gen  PENG Zhen 《大气和海洋科学快报》2013,(4):179-184

The regional air quality modeling system RAMS-CMAQ(Regional Atmospheric Modeling System and Models-3 Community Multi-scale Air Quality) was developed by incorporating a vegetation photosynthesis and respiration module(VPRM) and used to simulate temporal-spatial variations in atmospheric CO2 concentrations in East Asia,with prescribed surface CO2 fluxes(i.e.,fossil fuel emission,biomass burning,sea-air CO2 exchange,and terrestrial biosphere CO2 flux).Comparison of modeled CO2 mixing ratios with eight ground-based in-situ measurements demonstrated that the model was able to capture most observed CO2 temporal-spatial features.Simulated CO2 concentrations were generally in good agreement with observed concentrations.Results indicated that the accumulated impacts of anthropogenic emissions contributed more to increased CO2 concentrations in urban regions relative to remote locations.Moreover,RAMS-CMAQ analysis demonstrates that surface CO2 concentrations in East Asia are strongly influenced by terrestrial ecosystems.  相似文献   

Intercomparison of Surface Radiative Fluxes in the Arctic Ocean          下载免费PDF全文

SHI Xiao-Xu  LIU Ji-Ping 《大气和海洋科学快报》2013,(6):434-439

Recent satellite data analysis has provided improved data sets relevant to the surface energy budget in the Arctic Ocean. In this paper, surface radiation properties in the Arctic Ocean obtained from the Surface Radiation Budget（SRB3.0） and the International Satellite Cloud Climatology Project（ISCCP-FD） during 1984– 2007 are analyzed and compared. Our analysis suggests that these datasets show encouraging agreement in basin-wide averaged seasonal cycle and spatial distribution of surface albedo; net surface shortwave and all-wave radiative fluxes; and shortwave, longwave, and all-wave cloud radiative forcings. However, a systematic large discrepancy is detected for the net surface longwave radiative flux between the two data sets at a magnitude of ~ 23 W m–2, which is primarily attributed to significant differences in surface temperature, particularly from April to June. Moreover, the largest difference in surface shortwave and all-wave cloud radiative forcings between the two data sets is apparent in early June at a magnitude of 30 W m–2.  相似文献   

The Long-Term Field Experiment Observatory and Preliminary Analysis of Land-Atmosphere Interaction over Hilly Zone in the Subtropical Monsoon Region of Southern China          下载免费PDF全文

LIU Jian-Guo  XIE Zheng-Hui  JIA Bing-Hao  TIAN Xiang-Jun  QIN Pei-Hua  ZOU Jing  YU Yan  SUN Qin  WANG Yuan-Yuan  XIE Jin-Bo  XIE Zhi-Peng 《大气和海洋科学快报》2013,(4):203-209

To improve current understanding of the water cycle,energy partitioning and CO2 exchange over hilly zone vegetative land surfaces in the subtropical monsoon environment of southern China,a long-term field experiment observatory was set up at Ningxiang,eastern Hunan Province.This paper presents a preliminary analysis of the field observations at the observatory collected from August to November 2012.Results show that significant diurnal variations in soil temperature occur only in shallow soil layers(0.05,0.10,and 0.20 m),and that heavy rainfall affects soil moisture in the deep layers(≥ 0.40 m).During the experimental period,significant diurnal variations in albedo,radiation components,energy components,and CO2 flux were observed,but little seasonal variation.Strong photosynthesis in the vegetation canopy enhanced the CO2 absorption and the latent heat released in daylight hours;Latent heat of evaporation was the main consumer of available energy in late summer.Because the field experiment data are demonstrably reliable,the observatory will provide reliable long-term measurements for future investigations of the land-atmosphere interaction over hilly land surfaces in the subtropical monsoon region of southern China.  相似文献