13CO (J = 1 - 0) emission of massive star forming region including 15 ultracompact and 4compact HII regions in Galactic plane was mapped with the 13.7 m millimeter wave telescope of Purple Mountain Observatory. The pr...13CO (J = 1 - 0) emission of massive star forming region including 15 ultracompact and 4compact HII regions in Galactic plane was mapped with the 13.7 m millimeter wave telescope of Purple Mountain Observatory. The present observations provide the first complete structure of the clouds in 13CO with a higher spatial resolution and a wide-field coverage of 28′×45′. Combined with the images of far-infrared emission and dust color temperature obtained from ISSA, various possible dynamical connections between the compact HII regions and associated clouds were found. We presente some reasons to explain the formation of new dense cold core and molecular emission cavity in the massive star formation and early evolution. The luminosities of excitation stars for all HII regions and the main parameters of associated clouds are also derived. The results show that the newborn stars' luminosities are correlated with the 13CO column densities, masses (in 55'beam) and 13CO velocity widths obviously.展开更多
Cloud electrification is one of the oldest unresolved puzzles in the atmospheric sciences. Though many mechanisms for charge separation in clouds have been proposed, a quantitative understanding of their respective co...Cloud electrification is one of the oldest unresolved puzzles in the atmospheric sciences. Though many mechanisms for charge separation in clouds have been proposed, a quantitative understanding of their respective contribution in a given meteorological situation is lacking. Here we suggest and analyze a hitherto little discussed process. A qualitative picture at the molecular level of the charge separation mechanism of lightning in a thundercloud is proposed. It is based on two key physical/chemical natural phenomena, namely, internal charge separation of the atmospheric impurities/aerosols inside an atmospheric water cluster/droplet/ice particle and the existence of liquid water layers on rimers (graupels and hailstones) forming a layer of dipoles with H<sup>+</sup> pointing out from the air-water interface. Charge separation is achieved through strong collisions among ice particles and water droplets with the rimers in the turbulence of the thundercloud. This work would have significant contribution to cloud electrification and lightning formation.展开更多
The planetary boundary layer turbulence and moist convection parameterizations have been modified recently in the NASA Goddard Institute for Space Studies （GISS） Model E2 atmospheric general circulation model （GCM;...The planetary boundary layer turbulence and moist convection parameterizations have been modified recently in the NASA Goddard Institute for Space Studies （GISS） Model E2 atmospheric general circulation model （GCM; post-CMIP5, hereafter P5）. In this study, single column model （SCM_P5） simulated cloud fractions （CFs）, cloud liquid water paths （LWPs） and precipitation were compared with Atmospheric Radiation Measurement （ARM） Southern Great Plains （SGP） groundbased observations made during the period 2002-08. CMIP5 SCM simulations and GCM outputs over the ARM SGP region were also used in the comparison to identify whether the causes of cloud and precipitation biases resulted from either the physical parameterization or the dynamic scheme. The comparison showed that the CMIP5 SCM has difficulties in simulating the vertical structure and seasonal variation of low-level clouds. The new scheme implemented in the turbulence parameterization led to significantly improved cloud simulations in P5. It was found that the SCM is sensitive to the relaxation time scale. When the relaxation time increased from 3 to 24 h, SCM_P5-simulated CFs and LWPs showed a moderate increase （10%-20%） but precipitation increased significantly （56%）, which agreed better with observations despite the less accurate atmospheric state. Annual averages among the GCM and SCM simulations were almost the same, but their respective seasonal variations were out of phase. This suggests that the same physical cloud parameterization can generate similar statistical results over a long time period, but different dynamics drive the differences in seasonal variations. This study can potentially provide guidance for the further development of the GISS model.展开更多
This paper adopts an inertia-centric evolutionary model to study the excitation mechanism of new gravito-electrostatic eigenmode structures in a one-dimensional（1-D） planar self-gravitating dust molecular cloud（DMC...This paper adopts an inertia-centric evolutionary model to study the excitation mechanism of new gravito-electrostatic eigenmode structures in a one-dimensional（1-D） planar self-gravitating dust molecular cloud（DMC） on the Jeans scale.A quasi-neutral multi-fluid consisting of warm electrons,warm ions,neutral gas and identical inertial cold dust grains with partial ionization is considered.The grain-charge is assumed not to vary at the fluctuation evolution time scale.The neutral gas particles form the background,which is weakly coupled with the collapsing grainy plasma mass.The gravitational decoupling of the background neutral particles is justifiable for a higher inertial mass of the grains with higher neutral population density so that the Jeans mode frequency becomes reasonably large.Its physical basis is the Jeans assumption of a self-gravitating uniform medium adopted for fiducially analytical simplification by neglecting the zero-order field.So,the equilibrium is justifiably treated initially as ＂homogeneous＂.The efficacious inertial role of the thermal species amidst weak collisions of the neutral-charged grains is taken into account.A standard multiscale technique over the gravito-electrostatic equilibrium yields a unique pair of Korteweg-de Vries（KdV） equations.It is integrated numerically by the fourth-order Runge-Kutta method with multi-parameter variation for exact shape analyses.Interestingly,the model is conducive for the propagation of new conservative solitary spectral patterns.Their basic physics,parametric features and unique characteristics are discussed.The results go qualitatively in good correspondence with the earlier observations made by others.Tentative applications relevant to space and astrophysical environments are concisely highlighted.展开更多
In this paper, we present the critical mass of magnetized, turbulent and rotating star-forming molecular cloud core (MCc) in the presence of magnetic tension. The critical mass of star-forming magnetized cloud is infl...In this paper, we present the critical mass of magnetized, turbulent and rotating star-forming molecular cloud core (MCc) in the presence of magnetic tension. The critical mass of star-forming magnetized cloud is influenced by the magnetic tension, magnetic pressure and other pressures. Applying the method of theoretical modelling by taking into account the basic equations and assumptions, we formulate the critical mass of magnetized MCc in different cases. Accordingly, the minimum critical masses we find in both cases are different. Energy due to magnetic tension significantly triggers the collapse at relatively larger radius of the core. The model shows that when the initial radius of the parent cloud (Ro) is larger than that of collapsing core radius (Rcore) the magnetic tension also has the larger radius of curvature, so it plays a significant role in supporting gravity to collapse the core. The results indicate gravity without magnetic tension may not overcome magnetic pressure, turbulence pressure and pressure due to rotation. This shows the critical mass of MCc for the collapse depends on the tension force that magnetic field lines apply on the envelope. We conclude that if there is magnetic pressure in star-forming MCc, there is also unavoidable magnetic tension, which triggers the collapse of the core. If there is no magnetic tension, the magnetized MCc needs relatively larger mass and higher density within the small size to collapse.展开更多
A simplified model of clouds' microstructure dynamics under turbulent conditions is presented. The nature of rain stimulation by acoustic waves, based on the drops injection in the region of turbulent coagulation,...A simplified model of clouds' microstructure dynamics under turbulent conditions is presented. The nature of rain stimulation by acoustic waves, based on the drops injection in the region of turbulent coagulation, is de-scribed. The conditions for effective rain stimulating are estimated.展开更多
Understanding how stars form in molecular clouds is one of the ongoing research areas in astrophysics. Star formation is the fundamental process to which our current understanding remains incomplete due to the complex...Understanding how stars form in molecular clouds is one of the ongoing research areas in astrophysics. Star formation is the fundamental process to which our current understanding remains incomplete due to the complexity of the physics that drives their formation within molecular clouds. In this article theoretical modelling of the lowest possible mass of the cloud needed for collapse and the core accretion rate has been presented for the molecular cloud collapsing under its gravity. In many of previous studies the critical mass of star forming cloud under its gravity has been modelled using kinetic energy and gravitational potential energy. However, we test the effect of thermodynamic efficiency factor together with other physical processes in describing the critical mass, and controlling or triggering the rate of mass falling onto the central core. Assuming that, the ratio of radiation luminosity to gravitational energy released per unit time of the collapsing MC is less than unity. Following this conceptual framework we have formulated the critical mass and the core accretion rate of the self-gravitating molecular cloud.展开更多
基金This work was supported by the National Natural Science Foundation of China (Grant No. 19873003) United Laboratory of National Radio Astronomy.
文摘13CO (J = 1 - 0) emission of massive star forming region including 15 ultracompact and 4compact HII regions in Galactic plane was mapped with the 13.7 m millimeter wave telescope of Purple Mountain Observatory. The present observations provide the first complete structure of the clouds in 13CO with a higher spatial resolution and a wide-field coverage of 28′×45′. Combined with the images of far-infrared emission and dust color temperature obtained from ISSA, various possible dynamical connections between the compact HII regions and associated clouds were found. We presente some reasons to explain the formation of new dense cold core and molecular emission cavity in the massive star formation and early evolution. The luminosities of excitation stars for all HII regions and the main parameters of associated clouds are also derived. The results show that the newborn stars' luminosities are correlated with the 13CO column densities, masses (in 55'beam) and 13CO velocity widths obviously.
文摘Cloud electrification is one of the oldest unresolved puzzles in the atmospheric sciences. Though many mechanisms for charge separation in clouds have been proposed, a quantitative understanding of their respective contribution in a given meteorological situation is lacking. Here we suggest and analyze a hitherto little discussed process. A qualitative picture at the molecular level of the charge separation mechanism of lightning in a thundercloud is proposed. It is based on two key physical/chemical natural phenomena, namely, internal charge separation of the atmospheric impurities/aerosols inside an atmospheric water cluster/droplet/ice particle and the existence of liquid water layers on rimers (graupels and hailstones) forming a layer of dipoles with H<sup>+</sup> pointing out from the air-water interface. Charge separation is achieved through strong collisions among ice particles and water droplets with the rimers in the turbulence of the thundercloud. This work would have significant contribution to cloud electrification and lightning formation.
基金supported by the DOE ASR program(Grant No.DESC008468)
文摘The planetary boundary layer turbulence and moist convection parameterizations have been modified recently in the NASA Goddard Institute for Space Studies （GISS） Model E2 atmospheric general circulation model （GCM; post-CMIP5, hereafter P5）. In this study, single column model （SCM_P5） simulated cloud fractions （CFs）, cloud liquid water paths （LWPs） and precipitation were compared with Atmospheric Radiation Measurement （ARM） Southern Great Plains （SGP） groundbased observations made during the period 2002-08. CMIP5 SCM simulations and GCM outputs over the ARM SGP region were also used in the comparison to identify whether the causes of cloud and precipitation biases resulted from either the physical parameterization or the dynamic scheme. The comparison showed that the CMIP5 SCM has difficulties in simulating the vertical structure and seasonal variation of low-level clouds. The new scheme implemented in the turbulence parameterization led to significantly improved cloud simulations in P5. It was found that the SCM is sensitive to the relaxation time scale. When the relaxation time increased from 3 to 24 h, SCM_P5-simulated CFs and LWPs showed a moderate increase （10%-20%） but precipitation increased significantly （56%）, which agreed better with observations despite the less accurate atmospheric state. Annual averages among the GCM and SCM simulations were almost the same, but their respective seasonal variations were out of phase. This suggests that the same physical cloud parameterization can generate similar statistical results over a long time period, but different dynamics drive the differences in seasonal variations. This study can potentially provide guidance for the further development of the GISS model.
基金The financial support from the Department of Science and Technology(DST)of New Delhi,Government of India,extended through the SERB Fast Track Project(Grant No.SR/FTP/PS021/2011)
文摘This paper adopts an inertia-centric evolutionary model to study the excitation mechanism of new gravito-electrostatic eigenmode structures in a one-dimensional（1-D） planar self-gravitating dust molecular cloud（DMC） on the Jeans scale.A quasi-neutral multi-fluid consisting of warm electrons,warm ions,neutral gas and identical inertial cold dust grains with partial ionization is considered.The grain-charge is assumed not to vary at the fluctuation evolution time scale.The neutral gas particles form the background,which is weakly coupled with the collapsing grainy plasma mass.The gravitational decoupling of the background neutral particles is justifiable for a higher inertial mass of the grains with higher neutral population density so that the Jeans mode frequency becomes reasonably large.Its physical basis is the Jeans assumption of a self-gravitating uniform medium adopted for fiducially analytical simplification by neglecting the zero-order field.So,the equilibrium is justifiably treated initially as ＂homogeneous＂.The efficacious inertial role of the thermal species amidst weak collisions of the neutral-charged grains is taken into account.A standard multiscale technique over the gravito-electrostatic equilibrium yields a unique pair of Korteweg-de Vries（KdV） equations.It is integrated numerically by the fourth-order Runge-Kutta method with multi-parameter variation for exact shape analyses.Interestingly,the model is conducive for the propagation of new conservative solitary spectral patterns.Their basic physics,parametric features and unique characteristics are discussed.The results go qualitatively in good correspondence with the earlier observations made by others.Tentative applications relevant to space and astrophysical environments are concisely highlighted.
文摘In this paper, we present the critical mass of magnetized, turbulent and rotating star-forming molecular cloud core (MCc) in the presence of magnetic tension. The critical mass of star-forming magnetized cloud is influenced by the magnetic tension, magnetic pressure and other pressures. Applying the method of theoretical modelling by taking into account the basic equations and assumptions, we formulate the critical mass of magnetized MCc in different cases. Accordingly, the minimum critical masses we find in both cases are different. Energy due to magnetic tension significantly triggers the collapse at relatively larger radius of the core. The model shows that when the initial radius of the parent cloud (Ro) is larger than that of collapsing core radius (Rcore) the magnetic tension also has the larger radius of curvature, so it plays a significant role in supporting gravity to collapse the core. The results indicate gravity without magnetic tension may not overcome magnetic pressure, turbulence pressure and pressure due to rotation. This shows the critical mass of MCc for the collapse depends on the tension force that magnetic field lines apply on the envelope. We conclude that if there is magnetic pressure in star-forming MCc, there is also unavoidable magnetic tension, which triggers the collapse of the core. If there is no magnetic tension, the magnetized MCc needs relatively larger mass and higher density within the small size to collapse.
文摘A simplified model of clouds' microstructure dynamics under turbulent conditions is presented. The nature of rain stimulation by acoustic waves, based on the drops injection in the region of turbulent coagulation, is de-scribed. The conditions for effective rain stimulating are estimated.
文摘Understanding how stars form in molecular clouds is one of the ongoing research areas in astrophysics. Star formation is the fundamental process to which our current understanding remains incomplete due to the complexity of the physics that drives their formation within molecular clouds. In this article theoretical modelling of the lowest possible mass of the cloud needed for collapse and the core accretion rate has been presented for the molecular cloud collapsing under its gravity. In many of previous studies the critical mass of star forming cloud under its gravity has been modelled using kinetic energy and gravitational potential energy. However, we test the effect of thermodynamic efficiency factor together with other physical processes in describing the critical mass, and controlling or triggering the rate of mass falling onto the central core. Assuming that, the ratio of radiation luminosity to gravitational energy released per unit time of the collapsing MC is less than unity. Following this conceptual framework we have formulated the critical mass and the core accretion rate of the self-gravitating molecular cloud.
