Imaging studies with the Very Large Array(VLA) have revealed H I emission associated with the extended circumstellar shells of red giants. We analyze the spectral map obtained on Y CVn, a J-type carbon star on the A...Imaging studies with the Very Large Array(VLA) have revealed H I emission associated with the extended circumstellar shells of red giants. We analyze the spectral map obtained on Y CVn, a J-type carbon star on the Asymptotic Giant Branch. The H I line profiles can be interpreted with a model of a detached shell resulting from the interaction of a stellar outflow with the local interstellar medium.We reproduce the spectral map by introducing a distortion along a direction corresponding to the star's motion in space. We then use this fitting to simulate observations expected from the Five-hundred-meter Aperture Spherical radio Telescope(FAST), and discuss its potential for improving our description of the outer regions of circumstellar shells.展开更多
Incoherent scatter radar (ISR) extra-wide coverage experiments during the period of 1978-2011 at Millstone Hill are used to investigate longitudinal differences in electron density. This work is motivated by a recent ...Incoherent scatter radar (ISR) extra-wide coverage experiments during the period of 1978-2011 at Millstone Hill are used to investigate longitudinal differences in electron density. This work is motivated by a recent finding of the US east-west coast difference in TEC suggesting a combined effect of changing geomagnetic declination and zonal winds. The current study provides strong supporting evidence of the longitudinal change and the plausible mechanism by examining the climatology of electron density Ne on both east and west sides of the radar with a longitude separation of up to 40o for different heights within 300-450 km. Main findings include: 1) The east-west difference can be up to 60% and varies over the course of the day, being positive (East side Ne > West side Ne) in the late evening, and negative (West side Ne > East side Ne) in the pre-noon. 2) The east-west difference exists throughout the year. The positive (relative) difference is most pronounced in winter; the negative (relative) difference is most pronounced in early spring and later summer. 3) The east-west difference tends to enhance toward decreasing solar activity, however, with some seasonal dependence; the enhancements in the positive and negative differences do not take place simultaneously. 4) Both times of largest positive and largest negative east-west differences in Ne are earlier in summer and later in winter. The two times differ by 12-13 h, which remains constant throughout the year. 5) Variations at different heights from 300-450 km are similar. Zonal wind climatology above Millstone Hill is found to be perfectly consistent with what is expected based on the electron density difference between the east and west sides of the site. The magnetic declination-zonal wind mechanism is true for other longitude sectors as well, and may be used to understand longitudinal variations elsewhere. It may also be used to derive thermospheric zonal winds.展开更多
Cold ions of plasmaspheric origin have been observed to abundantly appear in the magnetospheric side of the Earth's magnetopause. These cold ions could affect the magnetic reconnection processes at the magnetopaus...Cold ions of plasmaspheric origin have been observed to abundantly appear in the magnetospheric side of the Earth's magnetopause. These cold ions could affect the magnetic reconnection processes at the magnetopause by changing the Alfvén velocity and the reconnection rate, while they could also be heated in the reconnection layer during the ongoing reconnections. We report in situ observations from a partially crossing of a reconnection layer near the subsolar magnetopause. During this crossing, step-like accelerating processes of the cold ions were clearly observed, suggesting that the inflow cold ions may be separately accelerated by the rotation discontinuity and slow shock inside the reconnection layer.展开更多
Earth’s ecosystems and human activities are threatened by a broad spectrum of hazards of major importance for the safety of ground infrastructures,space systems and space flight:solar activity,earthquakes,atmospheric...Earth’s ecosystems and human activities are threatened by a broad spectrum of hazards of major importance for the safety of ground infrastructures,space systems and space flight:solar activity,earthquakes,atmospheric and climatic disturbances,changes in the geomagnetic field,fluctuations of the global electric circuit.Monitoring and understanding these major hazards to better predict and mitigate their effects is one of the greatest scientific and operational challenges of the 21st century.Though diverse,these hazards share one feature in common:they all leave their characteristic imprints on a critical layer of the Earth’s environment:its ionosphere,middle and upper atmosphere(IMUA).The objective of the International Meridian Circle Program(IMCP),a major international program led by the Chines Academy of Sciences(CAS),is to deploy,integrate and operate a global network of research and monitoring instruments to use the IMUA as a screen on which to detect these imprints.In this article,we first show that the geometry required for the IMCP global observation system leads to a deployment of instruments in priority along the 120°E-60°W great meridian circle,which will cover in an optimal way both the dominant geographic and geomagnetic latitude variations,possibly complemented by a second Great Circle along the 30°E-150°W meridians to capture longitude variations.Then,starting from the Chinese Meridian Project(CMP)network and using it as a template,we give a preliminary and promising description of the instruments to be integrated and deployed along the 120°E-60°W great circle running across China,Australia and the Americas.展开更多
基金the Vietnam National Satellite Centre(VNSC/VAST)the NAFOSTED funding agency+3 种基金the World Laboratorythe Odon Vallet Foundationthe Rencontres du Viet Namthe PCMI programme of the CNRS for financial support
文摘Imaging studies with the Very Large Array(VLA) have revealed H I emission associated with the extended circumstellar shells of red giants. We analyze the spectral map obtained on Y CVn, a J-type carbon star on the Asymptotic Giant Branch. The H I line profiles can be interpreted with a model of a detached shell resulting from the interaction of a stellar outflow with the local interstellar medium.We reproduce the spectral map by introducing a distortion along a direction corresponding to the star's motion in space. We then use this fitting to simulate observations expected from the Five-hundred-meter Aperture Spherical radio Telescope(FAST), and discuss its potential for improving our description of the outer regions of circumstellar shells.
基金supported by the National Natural Science Foundation of China (Grant No. 40890164)the US National Science Foundation under Cooperative Agreements (Grant Nos. ATM-0733510 and ATM-6920184)
文摘Incoherent scatter radar (ISR) extra-wide coverage experiments during the period of 1978-2011 at Millstone Hill are used to investigate longitudinal differences in electron density. This work is motivated by a recent finding of the US east-west coast difference in TEC suggesting a combined effect of changing geomagnetic declination and zonal winds. The current study provides strong supporting evidence of the longitudinal change and the plausible mechanism by examining the climatology of electron density Ne on both east and west sides of the radar with a longitude separation of up to 40o for different heights within 300-450 km. Main findings include: 1) The east-west difference can be up to 60% and varies over the course of the day, being positive (East side Ne > West side Ne) in the late evening, and negative (West side Ne > East side Ne) in the pre-noon. 2) The east-west difference exists throughout the year. The positive (relative) difference is most pronounced in winter; the negative (relative) difference is most pronounced in early spring and later summer. 3) The east-west difference tends to enhance toward decreasing solar activity, however, with some seasonal dependence; the enhancements in the positive and negative differences do not take place simultaneously. 4) Both times of largest positive and largest negative east-west differences in Ne are earlier in summer and later in winter. The two times differ by 12-13 h, which remains constant throughout the year. 5) Variations at different heights from 300-450 km are similar. Zonal wind climatology above Millstone Hill is found to be perfectly consistent with what is expected based on the electron density difference between the east and west sides of the site. The magnetic declination-zonal wind mechanism is true for other longitude sectors as well, and may be used to understand longitudinal variations elsewhere. It may also be used to derive thermospheric zonal winds.
基金supported by the National Natural Science Foundation of China(41574138,41604139)the Shandong Provincial Natural Science Foundation(JQ201412)+5 种基金the Chinese Meridian ProjectReading University was supported by STFC consolidated(ST/M000885/1)The Norwegian contribution was supported by the Research Council of Norway(230996.S.R.Z.)support from the U.S.NASA LWS Project(NNX15AB83G)the U.S.Do D MURI Project(ONR15-FOA-0011)supported by the U.S.NSF Geospace Facility program under an agreement AGS-1242204 with Massachusetts Institute of Technology
文摘Cold ions of plasmaspheric origin have been observed to abundantly appear in the magnetospheric side of the Earth's magnetopause. These cold ions could affect the magnetic reconnection processes at the magnetopause by changing the Alfvén velocity and the reconnection rate, while they could also be heated in the reconnection layer during the ongoing reconnections. We report in situ observations from a partially crossing of a reconnection layer near the subsolar magnetopause. During this crossing, step-like accelerating processes of the cold ions were clearly observed, suggesting that the inflow cold ions may be separately accelerated by the rotation discontinuity and slow shock inside the reconnection layer.
基金This work was supported by the International PartnershipProgram of Chinese Academy of Sciences(Grant No.183311KYSB20200003)the Beijing Municipal Science and Technology Commission(Grant No.Z181100002918001).
文摘Earth’s ecosystems and human activities are threatened by a broad spectrum of hazards of major importance for the safety of ground infrastructures,space systems and space flight:solar activity,earthquakes,atmospheric and climatic disturbances,changes in the geomagnetic field,fluctuations of the global electric circuit.Monitoring and understanding these major hazards to better predict and mitigate their effects is one of the greatest scientific and operational challenges of the 21st century.Though diverse,these hazards share one feature in common:they all leave their characteristic imprints on a critical layer of the Earth’s environment:its ionosphere,middle and upper atmosphere(IMUA).The objective of the International Meridian Circle Program(IMCP),a major international program led by the Chines Academy of Sciences(CAS),is to deploy,integrate and operate a global network of research and monitoring instruments to use the IMUA as a screen on which to detect these imprints.In this article,we first show that the geometry required for the IMCP global observation system leads to a deployment of instruments in priority along the 120°E-60°W great meridian circle,which will cover in an optimal way both the dominant geographic and geomagnetic latitude variations,possibly complemented by a second Great Circle along the 30°E-150°W meridians to capture longitude variations.Then,starting from the Chinese Meridian Project(CMP)network and using it as a template,we give a preliminary and promising description of the instruments to be integrated and deployed along the 120°E-60°W great circle running across China,Australia and the Americas.