Previous satellite measurements and model simulations have shown that the Asian summer monsoon（ASM） anticyclone is co-located with higher concentrations of pollutants, which are emitted in the continental atmospheri...Previous satellite measurements and model simulations have shown that the Asian summer monsoon（ASM） anticyclone is co-located with higher concentrations of pollutants, which are emitted in the continental atmospheric boundary layer（ABL）. Backward trajectory calculations show that the air at the 150-hPa level has the maximum frequency of ABL sources within 30 days over the most intensive convection regions and their downwind areas, which are not located within the ASM anticyclone,but rather at the southern flank or periphery of the ASM anticyclone. The upper tropospheric airs originated from the ABL sources include two parts： one from the ocean, which has the dominant impact to the south of 20°N, particularly over the South China Sea（SCS） and the west tropical Pacific Ocean; and another from the continent, which is dominant between 10°N and 30°N, particularly over the Bay of Bengal（BoB）, continental India, the Arabian Sea, and the Arabian Peninsula. It is the latter part that forms the higher pollutant concentration within the ASM anticyclone as shown by satellite measurements. Air in the ABL sources（both polluted and unpolluted） converges to the intensive convection region in the lower troposphere, and then traverses the middle troposphere through a wide group of upward pipes, and finally to the upper troposphere. These pipes in the middle troposphere are defined by the ASM intensive convections and cover the south of continental India,the BoB, the Tibetan Plateau, the Indochina Peninsula, the SCS, and the Philippine Sea.展开更多
The relationship between the North Atlantic Oscillation(NAO) and the tropical cyclone frequency over the western North Pacific(WNPTCF) in summer is investigated by use of observation data. It is found that their linka...The relationship between the North Atlantic Oscillation(NAO) and the tropical cyclone frequency over the western North Pacific(WNPTCF) in summer is investigated by use of observation data. It is found that their linkage appears to have an interdecadal change from weak connection to strong connection. During the period of 1948–1977, the NAO was insignificantly correlated to the WNPTCF. However, during the period of 1980–2009, they were significantly correlated with stronger(weaker) NAO corresponding to more(fewer) tropical cyclones in the western North Pacific. The possible reason for such a different relationship between the NAO and the WNPTCF during the former and latter periods is further analyzed from the perspective of large-scale atmospheric circulations. When the NAO was stronger than normal in the latter period, an anomalous cyclonic circulation prevailed in the lower troposphere of the western North Pacific and the monsoon trough was intensified, concurrent with the eastward-shifting western Pacific subtropical high as well as anomalous low-level convergence and high-level divergence over the western North Pacific. These conditions favor the genesis and development of tropical cyclones, and thus more tropical cyclones appeared over the western North Pacific. In contrast, in the former period, the impact of the NAO on the aforementioned atmospheric circulations became insignificant, thereby weakening its linkage to the WNPTCF. Further study shows that the change of the wave activity flux associated with the NAO during the former and latter periods may account for such an interdecadal shift of the NAO–WNPTCF relationship.展开更多
The spectral characteristics of air pollution gas sulfur dioxide and hydrogen sulfide has been studied experimentally and theo-retically in the range of 0.2-2.6 THz. The gases absorption spectra of sulfur dioxide and ...The spectral characteristics of air pollution gas sulfur dioxide and hydrogen sulfide has been studied experimentally and theo-retically in the range of 0.2-2.6 THz. The gases absorption spectra of sulfur dioxide and hydrogen sulfide, as measured by terahertz Time-Domain Spectroscopy (THz-TDS) technique, show equi-spaced absorption peaks. The peak intervals are varied for different gas and may relate with the molecule structures and rotation modes. We have calculated the intervals of rotational transition frequency according to the gases molecule structure and the rotational modes. The results are consistent with experimental results which confirm the suggestion that the absorption is coming from the molecular rotational transition. The study suggests a technique to detect air pollutants by THz-TDS and the rotational modes of gas molecules.展开更多
基金supported by the National Natural Science Foundation of China[grant number 91337214],[grand number41675040]
文摘Previous satellite measurements and model simulations have shown that the Asian summer monsoon（ASM） anticyclone is co-located with higher concentrations of pollutants, which are emitted in the continental atmospheric boundary layer（ABL）. Backward trajectory calculations show that the air at the 150-hPa level has the maximum frequency of ABL sources within 30 days over the most intensive convection regions and their downwind areas, which are not located within the ASM anticyclone,but rather at the southern flank or periphery of the ASM anticyclone. The upper tropospheric airs originated from the ABL sources include two parts： one from the ocean, which has the dominant impact to the south of 20°N, particularly over the South China Sea（SCS） and the west tropical Pacific Ocean; and another from the continent, which is dominant between 10°N and 30°N, particularly over the Bay of Bengal（BoB）, continental India, the Arabian Sea, and the Arabian Peninsula. It is the latter part that forms the higher pollutant concentration within the ASM anticyclone as shown by satellite measurements. Air in the ABL sources（both polluted and unpolluted） converges to the intensive convection region in the lower troposphere, and then traverses the middle troposphere through a wide group of upward pipes, and finally to the upper troposphere. These pipes in the middle troposphere are defined by the ASM intensive convections and cover the south of continental India,the BoB, the Tibetan Plateau, the Indochina Peninsula, the SCS, and the Philippine Sea.
基金supported by the Special Fund for Public Welfare Industry(Meteorology)(Grant No.GYHY201306026)the National Natural Science Foundation of China(Grant No.41275078)the National Basic Research Program of China(Grant No.2009CB421407)
文摘The relationship between the North Atlantic Oscillation(NAO) and the tropical cyclone frequency over the western North Pacific(WNPTCF) in summer is investigated by use of observation data. It is found that their linkage appears to have an interdecadal change from weak connection to strong connection. During the period of 1948–1977, the NAO was insignificantly correlated to the WNPTCF. However, during the period of 1980–2009, they were significantly correlated with stronger(weaker) NAO corresponding to more(fewer) tropical cyclones in the western North Pacific. The possible reason for such a different relationship between the NAO and the WNPTCF during the former and latter periods is further analyzed from the perspective of large-scale atmospheric circulations. When the NAO was stronger than normal in the latter period, an anomalous cyclonic circulation prevailed in the lower troposphere of the western North Pacific and the monsoon trough was intensified, concurrent with the eastward-shifting western Pacific subtropical high as well as anomalous low-level convergence and high-level divergence over the western North Pacific. These conditions favor the genesis and development of tropical cyclones, and thus more tropical cyclones appeared over the western North Pacific. In contrast, in the former period, the impact of the NAO on the aforementioned atmospheric circulations became insignificant, thereby weakening its linkage to the WNPTCF. Further study shows that the change of the wave activity flux associated with the NAO during the former and latter periods may account for such an interdecadal shift of the NAO–WNPTCF relationship.
基金supported by the Science and Technology Program of Beijing Educational Committee (Grant No. KM200910028005)the Natural Science Foundation of Beijing (Grant No. 4102016)
文摘The spectral characteristics of air pollution gas sulfur dioxide and hydrogen sulfide has been studied experimentally and theo-retically in the range of 0.2-2.6 THz. The gases absorption spectra of sulfur dioxide and hydrogen sulfide, as measured by terahertz Time-Domain Spectroscopy (THz-TDS) technique, show equi-spaced absorption peaks. The peak intervals are varied for different gas and may relate with the molecule structures and rotation modes. We have calculated the intervals of rotational transition frequency according to the gases molecule structure and the rotational modes. The results are consistent with experimental results which confirm the suggestion that the absorption is coming from the molecular rotational transition. The study suggests a technique to detect air pollutants by THz-TDS and the rotational modes of gas molecules.
