The eddy covariance technique has emerged as an important tool to directly measure carbon dioxide, water vapor and heat fluxes between the terrestrial ecosystem and the atmosphere after a long history of fundamental r...The eddy covariance technique has emerged as an important tool to directly measure carbon dioxide, water vapor and heat fluxes between the terrestrial ecosystem and the atmosphere after a long history of fundamental research and technological developments. With the realization of regional networks of flux measurements in North American, European, Asia, Brazil, Australia and Africa, a global-scale network of micrometeorological flux measurement (FLUXNET) was established in 1998. FLUXNET has made great progresses in investigating the environmental mechanisms controlling carbon and water cycles, quantifying spatial-temporal patterns of carbon budget and seeking the "missing carbon sink" in global terrestrial ecosystems in the past ten years. The global-scale flux measurement also built a platform for international communication in the fields of resource, ecology and environment sciences. With the continuous development of flux research, FLUXNET will introduce and explore new techniques to extend the application fields of flux measurement and to answer questions in the fields of bio-geography, eco-hydrology, meteorology, climate change, remote sensing and modeling with eddy covariance flux data. As an important part of FLUXNET, ChinaFLUX has made significant progresses in the past three years on the methodology and technique of eddy covariance flux measurement, on the responses of CO2 and H2O exchange between the terrestrial ecosystem and the atmosphere to environmental change, and on flux modeling development. Results showed that the major forests on the North-South Transect of Eastern China (NSTEC) were all carbon sinks during 2003 to 2005, and the alpine meadows on the Tibet Plateau were also small carbon sinks. However, the reserved natural grassland, Leymus chinensis steppe in Inner Mongolia, was a carbon source. On a regional scale, temperature and precipitation are the primary climatic factors that determined the carbon balance in major terrestrial ecosystems in China. Finally, the current research emphasis an展开更多
To differentiate between natural and anthropogenic particulate sources in the atmosphere in Lanzhou City, samples were collected in different sites. The dust flux was calculated and magnetic measurements were conducte...To differentiate between natural and anthropogenic particulate sources in the atmosphere in Lanzhou City, samples were collected in different sites. The dust flux was calculated and magnetic measurements were conducted. Results show a distinct pattern of variation of dust flux within a year and it agrees with the shifts of atmospheric circulation regime. The magnetic parameters indicate that natural sources are the major components of atmospheric particulate during late spring and early summer, while anthropogenic sources contribute much more during winter months. The data also support the earlier findings that magnetic parameters are effective for differentiating between particulate arising from natural sources such as soil erosion and from anthropogenic sources such as coal combustion.展开更多
Hypersonic and high-enthalpy wind tunnels and their measurement techniques are the cornerstone of the hypersonic flight era that is a dream for human beings to fly faster,higher and further.The great progress has been...Hypersonic and high-enthalpy wind tunnels and their measurement techniques are the cornerstone of the hypersonic flight era that is a dream for human beings to fly faster,higher and further.The great progress has been achieved during the recent years and their critical technologies are still in an urgent need for further development.There are at least four kinds of hypersonic and high-enthalpy wind tunnels that are widely applied over the world and can be classified according to their operation modes.These wind tunnels are named as air-directly-heated hypersonic wind tunnel,light-gas-heated shock tunnel,free-piston-driven shock tunnel and detonation-driven shock tunnel,respectively.The critical technologies for developing the wind tunnels are introduced in this paper,and their merits and weakness are discussed based on wind tunnel performance evaluation.Measurement techniques especially developed for high-enthalpy flows are a part of the hypersonic wind tunnel technology because the flow is a chemically reacting gas motion and its diagnosis needs specially designed instruments.Three kinds of the measurement techniques considered to be of primary importance are introduced here,including the heat flux sensor,the aerodynamic balance,and optical diagnosis techniques.The techniques are developed usually for conventional wind tunnels,but further improved for hypersonic and high-enthalpy tunnels.The hypersonic ground test facilities have provided us with most of valuable experimental data on high-enthalpy flows and will play a more important role in hypersonic research area in the future.Therefore,several prospects for developing hypersonic and high-enthalpy wind tunnels are presented from our point of view.展开更多
文摘The eddy covariance technique has emerged as an important tool to directly measure carbon dioxide, water vapor and heat fluxes between the terrestrial ecosystem and the atmosphere after a long history of fundamental research and technological developments. With the realization of regional networks of flux measurements in North American, European, Asia, Brazil, Australia and Africa, a global-scale network of micrometeorological flux measurement (FLUXNET) was established in 1998. FLUXNET has made great progresses in investigating the environmental mechanisms controlling carbon and water cycles, quantifying spatial-temporal patterns of carbon budget and seeking the "missing carbon sink" in global terrestrial ecosystems in the past ten years. The global-scale flux measurement also built a platform for international communication in the fields of resource, ecology and environment sciences. With the continuous development of flux research, FLUXNET will introduce and explore new techniques to extend the application fields of flux measurement and to answer questions in the fields of bio-geography, eco-hydrology, meteorology, climate change, remote sensing and modeling with eddy covariance flux data. As an important part of FLUXNET, ChinaFLUX has made significant progresses in the past three years on the methodology and technique of eddy covariance flux measurement, on the responses of CO2 and H2O exchange between the terrestrial ecosystem and the atmosphere to environmental change, and on flux modeling development. Results showed that the major forests on the North-South Transect of Eastern China (NSTEC) were all carbon sinks during 2003 to 2005, and the alpine meadows on the Tibet Plateau were also small carbon sinks. However, the reserved natural grassland, Leymus chinensis steppe in Inner Mongolia, was a carbon source. On a regional scale, temperature and precipitation are the primary climatic factors that determined the carbon balance in major terrestrial ecosystems in China. Finally, the current research emphasis an
文摘To differentiate between natural and anthropogenic particulate sources in the atmosphere in Lanzhou City, samples were collected in different sites. The dust flux was calculated and magnetic measurements were conducted. Results show a distinct pattern of variation of dust flux within a year and it agrees with the shifts of atmospheric circulation regime. The magnetic parameters indicate that natural sources are the major components of atmospheric particulate during late spring and early summer, while anthropogenic sources contribute much more during winter months. The data also support the earlier findings that magnetic parameters are effective for differentiating between particulate arising from natural sources such as soil erosion and from anthropogenic sources such as coal combustion.
基金the support of the National Natural Science Foundation of China(Nos.11532014,11727901,11672308 and 11672357)the National Key Research and Development Program of China(No.2019YFA0405204)。
文摘Hypersonic and high-enthalpy wind tunnels and their measurement techniques are the cornerstone of the hypersonic flight era that is a dream for human beings to fly faster,higher and further.The great progress has been achieved during the recent years and their critical technologies are still in an urgent need for further development.There are at least four kinds of hypersonic and high-enthalpy wind tunnels that are widely applied over the world and can be classified according to their operation modes.These wind tunnels are named as air-directly-heated hypersonic wind tunnel,light-gas-heated shock tunnel,free-piston-driven shock tunnel and detonation-driven shock tunnel,respectively.The critical technologies for developing the wind tunnels are introduced in this paper,and their merits and weakness are discussed based on wind tunnel performance evaluation.Measurement techniques especially developed for high-enthalpy flows are a part of the hypersonic wind tunnel technology because the flow is a chemically reacting gas motion and its diagnosis needs specially designed instruments.Three kinds of the measurement techniques considered to be of primary importance are introduced here,including the heat flux sensor,the aerodynamic balance,and optical diagnosis techniques.The techniques are developed usually for conventional wind tunnels,but further improved for hypersonic and high-enthalpy tunnels.The hypersonic ground test facilities have provided us with most of valuable experimental data on high-enthalpy flows and will play a more important role in hypersonic research area in the future.Therefore,several prospects for developing hypersonic and high-enthalpy wind tunnels are presented from our point of view.
