An air gun generates acoustic signals for seismic exploration by releasing a high-pressure gas.A large error is always gradually introduced into the ideal-gas model when the pressure in the air-gun chamber exceeds 100...An air gun generates acoustic signals for seismic exploration by releasing a high-pressure gas.A large error is always gradually introduced into the ideal-gas model when the pressure in the air-gun chamber exceeds 100 atm.In the van der Waals non-ideal-gas theory,the gas in the air gun can be regarded as an actual gas,and the error is less than 2%.The van der Waals model is established in combination with the quasi-static open thermodynamic system and bubble-motion equation by considering the bubble rise,bubble interaction,and throttling eff ect.The mismatch between the van der Waals and ideal-gas models is related to the pressure.Theoretically,under high-pressure conditions,the van der Waals air-gun model yields results that are closer to the measured results.Marine vertical cables are extended to the seafl oor using steel cables that connect the cement blocks,but the corresponding hydrophones are suspended in the seawater.Thus,noise associated with ships,ocean surges,and coupling problems is avoided,and the signal-to-noise ratio and resolution of marine seismic data are improved.This acquisition method satisfies the conditions of recording air-gun far-fi eld wavelets.According to an actual vertical-cable observation system,the van der Waals air-gun model is used to model the wavelet of different azimuth and take-off angles.The characteristics of the experimental and simulated data demonstrate good agreement,which indicates that the van der Waals method is accurate and reliable.The accuracy of the model is directly related to the resolution,thus aff ecting the resolution ability of the stratum.展开更多
While Arctic sea ice has been decreasing in recent decades that is largely due to anthropogenic forcing,the extent of Antarctic sea ice showed a positive trend during 1979–2015, followed by an abrupt decrease. The sh...While Arctic sea ice has been decreasing in recent decades that is largely due to anthropogenic forcing,the extent of Antarctic sea ice showed a positive trend during 1979–2015, followed by an abrupt decrease. The shortness of the satellite record limits our ability to quantify the possible contribution of anthropogenic forcing and internal variability to the observed Antarctic sea ice variability. In this study,ice core and fast ice records with annual resolution from six sites are used to reconstruct the annualresolved northernmost latitude of sea ice edge(NLSIE) for different sectors of the Southern Ocean, including the Weddell Sea(WS), Bellingshausen Sea(BS), Amundsen Sea(AS), Ross Sea(RS), and the Indian and western Pacific Ocean(Ind WPac). The linear trends of the NLSIE are analyzed for each sector for the past100–200 years and found to be à0.08°, à0.17°, +0.07°, +0.02°, and à0.03° per decade(!95% confidence level) for the WS, BS, AS, RS, and Ind WPac, respectively. For the entire Antarctic, our composite NLSIE shows a decreasing trend(à0.03° per decade, 99% confidence level) during the 20 th century, with a rapid decline in the mid-1950 s. It was not until the early 1980 s that the observed increasing trend occurred. A comparison with major climate indices shows that the long-term linear trends in all five sectors are largely dominated by the changes in the Southern Annular Mode(SAM). The multi-decadal variability in WS,BS, and AS is dominated by the Interdecadal Pacific Oscillation, whereas that in the Ind WPac and RS is dominated by the SAM.展开更多
基金This work has been supported by the following:the National Natural Science Foundation of China(No.91958206,91858215)the National Key Research and Development Program Pilot Project(No.2018YFC1405901,2017YFC0307401)+1 种基金the Fundamental Research Funds for the Central Universities(No.201964016)the Marine Geological Survey Program of China Geological Survey(No.DD20190819).
文摘An air gun generates acoustic signals for seismic exploration by releasing a high-pressure gas.A large error is always gradually introduced into the ideal-gas model when the pressure in the air-gun chamber exceeds 100 atm.In the van der Waals non-ideal-gas theory,the gas in the air gun can be regarded as an actual gas,and the error is less than 2%.The van der Waals model is established in combination with the quasi-static open thermodynamic system and bubble-motion equation by considering the bubble rise,bubble interaction,and throttling eff ect.The mismatch between the van der Waals and ideal-gas models is related to the pressure.Theoretically,under high-pressure conditions,the van der Waals air-gun model yields results that are closer to the measured results.Marine vertical cables are extended to the seafl oor using steel cables that connect the cement blocks,but the corresponding hydrophones are suspended in the seawater.Thus,noise associated with ships,ocean surges,and coupling problems is avoided,and the signal-to-noise ratio and resolution of marine seismic data are improved.This acquisition method satisfies the conditions of recording air-gun far-fi eld wavelets.According to an actual vertical-cable observation system,the van der Waals air-gun model is used to model the wavelet of different azimuth and take-off angles.The characteristics of the experimental and simulated data demonstrate good agreement,which indicates that the van der Waals method is accurate and reliable.The accuracy of the model is directly related to the resolution,thus aff ecting the resolution ability of the stratum.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA19070103)the National Key Research & Development Program of China (2018YFA0605901)+1 种基金the State Key Laboratory of Cryospheric Science (SKLCS-ZZ-2021)the National Natural Science Foundation of China (42071086, 41425003, 41941009)。
文摘While Arctic sea ice has been decreasing in recent decades that is largely due to anthropogenic forcing,the extent of Antarctic sea ice showed a positive trend during 1979–2015, followed by an abrupt decrease. The shortness of the satellite record limits our ability to quantify the possible contribution of anthropogenic forcing and internal variability to the observed Antarctic sea ice variability. In this study,ice core and fast ice records with annual resolution from six sites are used to reconstruct the annualresolved northernmost latitude of sea ice edge(NLSIE) for different sectors of the Southern Ocean, including the Weddell Sea(WS), Bellingshausen Sea(BS), Amundsen Sea(AS), Ross Sea(RS), and the Indian and western Pacific Ocean(Ind WPac). The linear trends of the NLSIE are analyzed for each sector for the past100–200 years and found to be à0.08°, à0.17°, +0.07°, +0.02°, and à0.03° per decade(!95% confidence level) for the WS, BS, AS, RS, and Ind WPac, respectively. For the entire Antarctic, our composite NLSIE shows a decreasing trend(à0.03° per decade, 99% confidence level) during the 20 th century, with a rapid decline in the mid-1950 s. It was not until the early 1980 s that the observed increasing trend occurred. A comparison with major climate indices shows that the long-term linear trends in all five sectors are largely dominated by the changes in the Southern Annular Mode(SAM). The multi-decadal variability in WS,BS, and AS is dominated by the Interdecadal Pacific Oscillation, whereas that in the Ind WPac and RS is dominated by the SAM.
