The impacts of cloud-induced mass forcing on the development of the moist potential vorticity (MPV) anomaly associated with torrential rains are investigated by using NCEP/NCAR 1? × 1? data. The MPV ten...The impacts of cloud-induced mass forcing on the development of the moist potential vorticity (MPV) anomaly associated with torrential rains are investigated by using NCEP/NCAR 1? × 1? data. The MPV tendency equation with the cloud-induced mass forcing is derived, and applied to the torrential rain event over the Changjiang River-Huaihe River Valleys during 26–30 June 1999. The result shows that positive anomalies are located mainly between 850 hPa and 500 hPa, while the maximum MPV, maximum positive tendency of the MPV, and maximum surface rainfall are nearly collocated. The cloud-induced mass forcing contributes to the positive tendency of the moist potential vorticity anomaly. The results indicate that the MPV may be used to track the propagation of rain systems for operational applications.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
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
As for the present situation of coronal mass ejection （CME） triggering models, the distributions of Alfv@n waves in flux ropes are different from model to model, and thus examining those distributions in interplanet...As for the present situation of coronal mass ejection （CME） triggering models, the distributions of Alfv@n waves in flux ropes are different from model to model, and thus examining those distributions in interplanetary coronal mass ejection （ICME） is an effective way to connect ICME observations with these theoretical models of CME triggering. However, previous observations of Alfv@nic fluctuations in ICMEs were rare with locations ranging from 0.3 AU to 0.68 AU only, which is usually explained as rapid dissipation of those remnant waves. Here we present an observation of Alfv@n waves in a magnetic cloud （MC） near 1 AU, in situ detected by WIND in February 17,-~20, 2011. The MC was generated by a CME accompanied with the first X-class flare in the 24th solar cycle. The slope of the power spectral densities of magnetic fluctuation in the MC, are similar to those modes in ambient solar wind, but more anisotropic. The results will also be helpful for studies of CME theories and ICME thermodynamics.展开更多
Two cloud-scale experiments with two different ice-phase schemes were carried out for a precipitation event that occurred in eastern China in 2005.The results were analyzed to examine the influences of the change of i...Two cloud-scale experiments with two different ice-phase schemes were carried out for a precipitation event that occurred in eastern China in 2005.The results were analyzed to examine the influences of the change of ice-particle mass and radius on hydrometeors,internal energy,and kinetic energy,as well as the primary factors responsible.It was found that the ice content increases notably and the snow content decreases due to the change.This is the consequence of the modulation of cloud microphysical processes.In particular,the Bergeron process and the accretion of snow and cloud ice are markedly influenced.The differences of internal energy and kinetic energy between the two experiments are caused by adjustments to pressure-flux divergence,the coupling of temperature and divergence,and gravitational work,and the reason is that these three factors result in differences of local changes of internal and kinetic energy.展开更多
Using model like hot air bloom with zero-weighted membrane wrapped hot air, surrounded by cold air, this paper sets up a partial differential equation (PDE) of motion of mushroom cloud by modifying Navier-Stokes (N-S)...Using model like hot air bloom with zero-weighted membrane wrapped hot air, surrounded by cold air, this paper sets up a partial differential equation (PDE) of motion of mushroom cloud by modifying Navier-Stokes (N-S) equations. The obtained equation is a vector PDE. It states that the derivative of velocity is with respect to time proportions to the gradient of temperature with respect to trace. Its solution is obtained by the method of separating variables for scalar function. These results have been compared with well agreement with literatures. Highlight: The Principle of Minimum Energy Release (PMER) is used to prove the pulse-mode of explosion of nuclear weapon, as great Earthquake, and optimum path problems.展开更多
We investigated the evolutionary stages and disk properties of 211 young stellar objects（YSOs） across the Perseus cloud by modeling their broadband optical to mid-infrared（IR） spectral energy distribution（SED）. ...We investigated the evolutionary stages and disk properties of 211 young stellar objects（YSOs） across the Perseus cloud by modeling their broadband optical to mid-infrared（IR） spectral energy distribution（SED）. Our optical gri photometry data were obtained from the recently finished Purple Mountain Observatory Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center（XSTPS-GAC）.About 81% of our sample fall into the Stage II phase which is characterized by having optically thick disks, while 14% into the Stage I phase characterized by having significant infalling envelopes, and the remaining 5% into the Stage Ⅲ phase characterized by having optically thin disks. The median stellar age and mass of the Perseus YSOs are 3.1 Myr and 0.3 M⊙ respectively. By exploring the relationships among the turnoff wave bands λturnoff（longward of which significant IR excesses above the stellar photosphere are observed）, the excess spectral index αexcess as determined for λ 〉 λturnoff, and the disk inner radius Rin（determined from SED modeling） for YSOs at different evolutionary stages, we found that the median and standard deviation of αexcess for YSOs with optically thick disks tend to increase withλturnoff, especially at λturnoff ≥5.8 μm, whereas the median fractional dust luminosities Ldust/L★ tend to decrease with increasing λturnoff. This points to an inside-out process of disk clearing for small dust grains. Moreover, a positive correlation between αexcess and Rin was found at α〉excess ～ 0 and R〉in～ 10 × the dust sublimation radius Rsub, irrespective of λturnoff, Ldust/L★ and disk flaring. This suggests that the outer disk flaring either does not evolve synchronously with the inside-out disk clearing of small dust grains or has little appreciable influence on the spectral slopes at λ〈～ 24 μm. About 23% of our YSO disks are classified as transitional disks, which haveλturnoff ≥ 5.8 μm and Ldust/L★ 〉 10-3. The transitional disks and full disks occupy distinctly different regions on the Ldust/L★ vs. αexcess diagram. Taking Ldust/L★ as an approximate discriminator of disks with（〉0.1） and without（〈0.1） considerable accretion activity, we found that 65% and 35% of the transitional disks may be consistent with being dominantly cleared by photoevaporation and dynamical interaction with giant planets respectively. None of our transitional disks have αexcess（〈0.0） or Ldust/L★（〉0.1） values that would otherwise be suggestive of disk clearing dominanted by grain growth.展开更多
基金by the National Natural Science Foundation of China under Grant Nos.40405007 , 40275015 the OlympicProject under Grant No.KACX1-02 partially sup-ported by the"Outstanding Overseas Chinese Scholars"Project of the Chinese Academy of Sciences under Grant No.2002-1-2.
文摘The impacts of cloud-induced mass forcing on the development of the moist potential vorticity (MPV) anomaly associated with torrential rains are investigated by using NCEP/NCAR 1? × 1? data. The MPV tendency equation with the cloud-induced mass forcing is derived, and applied to the torrential rain event over the Changjiang River-Huaihe River Valleys during 26–30 June 1999. The result shows that positive anomalies are located mainly between 850 hPa and 500 hPa, while the maximum MPV, maximum positive tendency of the MPV, and maximum surface rainfall are nearly collocated. The cloud-induced mass forcing contributes to the positive tendency of the moist potential vorticity anomaly. The results indicate that the MPV may be used to track the propagation of rain systems for operational applications.
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.
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.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences[grant number XDA20060501]the National Basic Research Program of China[grant numbers 2017YFA0604000 and 2016YFB0200800]the National Natural Science Foundation of China[grant number 41530426]。
基金supported by National Natural Science Foundation of China (Nos.40974104,40731056,and 10975012)Doctoral Fund of Ministry of Education of China (20090001110012)National Key Basic Research Science Foundation of China (2011CB811400,2009GB105004)
文摘As for the present situation of coronal mass ejection （CME） triggering models, the distributions of Alfv@n waves in flux ropes are different from model to model, and thus examining those distributions in interplanetary coronal mass ejection （ICME） is an effective way to connect ICME observations with these theoretical models of CME triggering. However, previous observations of Alfv@nic fluctuations in ICMEs were rare with locations ranging from 0.3 AU to 0.68 AU only, which is usually explained as rapid dissipation of those remnant waves. Here we present an observation of Alfv@n waves in a magnetic cloud （MC） near 1 AU, in situ detected by WIND in February 17,-~20, 2011. The MC was generated by a CME accompanied with the first X-class flare in the 24th solar cycle. The slope of the power spectral densities of magnetic fluctuation in the MC, are similar to those modes in ambient solar wind, but more anisotropic. The results will also be helpful for studies of CME theories and ICME thermodynamics.
基金supported by the National Basic Research Program of China (Grant No.2013CB430105)the Key Program of the Chinese Academy of Sciences (Grant No.KZZD-EW-05)+2 种基金the Project of Chinese Academy of Meteorological Sciences (Grant No.2011LASW-B15)the Special Scientific Research Fund of Meteorological Public Welfare of the Ministry of Sciences and Technology (Grant No.GYHY200906004)and the National Natural Science Foundation of China (Grant Nos.41175060,41075098,and 41005005)
文摘Two cloud-scale experiments with two different ice-phase schemes were carried out for a precipitation event that occurred in eastern China in 2005.The results were analyzed to examine the influences of the change of ice-particle mass and radius on hydrometeors,internal energy,and kinetic energy,as well as the primary factors responsible.It was found that the ice content increases notably and the snow content decreases due to the change.This is the consequence of the modulation of cloud microphysical processes.In particular,the Bergeron process and the accretion of snow and cloud ice are markedly influenced.The differences of internal energy and kinetic energy between the two experiments are caused by adjustments to pressure-flux divergence,the coupling of temperature and divergence,and gravitational work,and the reason is that these three factors result in differences of local changes of internal and kinetic energy.
文摘Using model like hot air bloom with zero-weighted membrane wrapped hot air, surrounded by cold air, this paper sets up a partial differential equation (PDE) of motion of mushroom cloud by modifying Navier-Stokes (N-S) equations. The obtained equation is a vector PDE. It states that the derivative of velocity is with respect to time proportions to the gradient of temperature with respect to trace. Its solution is obtained by the method of separating variables for scalar function. These results have been compared with well agreement with literatures. Highlight: The Principle of Minimum Energy Release (PMER) is used to prove the pulse-mode of explosion of nuclear weapon, as great Earthquake, and optimum path problems.
基金support of the National Natural Science Foundation of China (NSFC, Grant No. 11390373)HXZ acknowledges support from the China Postdoctoral Science Foundation (Grant No. 2013M530008)+1 种基金the CAS-CONICYT Postdoctoral Fellowship, administered by the Chinese Academy of Sciences South America Center for Astronomy (CASSACA)MF acknowledges the NSFC (Grant No. 11203081)
文摘We investigated the evolutionary stages and disk properties of 211 young stellar objects（YSOs） across the Perseus cloud by modeling their broadband optical to mid-infrared（IR） spectral energy distribution（SED）. Our optical gri photometry data were obtained from the recently finished Purple Mountain Observatory Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center（XSTPS-GAC）.About 81% of our sample fall into the Stage II phase which is characterized by having optically thick disks, while 14% into the Stage I phase characterized by having significant infalling envelopes, and the remaining 5% into the Stage Ⅲ phase characterized by having optically thin disks. The median stellar age and mass of the Perseus YSOs are 3.1 Myr and 0.3 M⊙ respectively. By exploring the relationships among the turnoff wave bands λturnoff（longward of which significant IR excesses above the stellar photosphere are observed）, the excess spectral index αexcess as determined for λ 〉 λturnoff, and the disk inner radius Rin（determined from SED modeling） for YSOs at different evolutionary stages, we found that the median and standard deviation of αexcess for YSOs with optically thick disks tend to increase withλturnoff, especially at λturnoff ≥5.8 μm, whereas the median fractional dust luminosities Ldust/L★ tend to decrease with increasing λturnoff. This points to an inside-out process of disk clearing for small dust grains. Moreover, a positive correlation between αexcess and Rin was found at α〉excess ～ 0 and R〉in～ 10 × the dust sublimation radius Rsub, irrespective of λturnoff, Ldust/L★ and disk flaring. This suggests that the outer disk flaring either does not evolve synchronously with the inside-out disk clearing of small dust grains or has little appreciable influence on the spectral slopes at λ〈～ 24 μm. About 23% of our YSO disks are classified as transitional disks, which haveλturnoff ≥ 5.8 μm and Ldust/L★ 〉 10-3. The transitional disks and full disks occupy distinctly different regions on the Ldust/L★ vs. αexcess diagram. Taking Ldust/L★ as an approximate discriminator of disks with（〉0.1） and without（〈0.1） considerable accretion activity, we found that 65% and 35% of the transitional disks may be consistent with being dominantly cleared by photoevaporation and dynamical interaction with giant planets respectively. None of our transitional disks have αexcess（〈0.0） or Ldust/L★（〉0.1） values that would otherwise be suggestive of disk clearing dominanted by grain growth.
