Circumstellar disk and the first generation of stars

Circumstellar disk (CD) around the first generation of stars have been numerically investigated here to see if the cooling regimes also play a role in the formation and evolution of the disk associated with the most massive protostars (MMPS). Also, an emphasis is given to exploring the effect of the initial turbulent motion of the metal-free gas on the resulting morphology of the CD. For this, a systematic range of Mach number $ℳ=0.1-1.0$ has been examined. It has been found that the disk-to-star mass ratio $M_{\text{disk}}$/ $M_{\text{star}}$ is larger when the model evolution is based on the first H ${}_2$ line cooling followed by subsequent cooling via collision-induced emission than in the model where only H ${}_2$ line cooling remains operative. Also, irrespective of the initial turbulence in the cloud, the former type of model yields a CD as massive as 7.66 M ${}_{\odot }$ while the latter type produces a disk as massive as 1.29 M ${}_{\odot }$. Moreover, the inner part of the CD is found dominated by higher subsonic turbulent motions in the case of the former type of models than in the latter type. CDs around MMPS in both types of models show stable disk structures.     

Self-gravity driven instabilities of interfaces in the interstellar medium

In order to understand star formation it is important to understand the dynamics of atomic and molecular clouds in the interstellar medium (ISM). Non-linear hydrodynamic flows are a key component to the ISM. One route by which non-linear flows arise is the onset and evolution of interfacial instabilities. Interfacial instabilities act to modify the interface between gas components at different densities and temperatures. Such an interface may be subject to a host of instabilities, including the Rayleigh–Taylor, Kelvin–Helmholtz, and Richtmyer–Meshkov instabilities. Recently, a new density interface instability was identified. This self-gravity interfacial instability (SGI) causes any displacement of the interface to grow on roughly a free-fall time-scale, even when the perturbation wavelength is much less than the Jeans length. In previous work, we used numerical simulations to confirm the expectations of linear theory and examine the non-linear evolution of the SGI. We now continue our study by generalizing our initial conditions to allow the acceleration due to self-gravity to be non-zero across the interface. We also consider the behaviour of the SGI for perturbation wavelengths near the Jeans wavelength. We conclude that the action of self-gravity across a density interface may play a significant role in the ISM either by fuelling the growth of new instabilities or modifying the evolution of existing instabilities.     

A numerical simulation of supersonic thermal convection

A computational scheme has been constructed for solving the equations that describe strong thermal convection in a two-dimensional gas layer that is heated from below and is stratified across many scaleheights by a uniform gravitational field. The purpose of this scheme is to mimic the physical conditions that may have existed in a section of the proto-solar cloud from which the planetary system formed. The vertical temperature gradient of the initial quiescent layer of diatomic gas is strongly superadiabatic and matches that of a polytrope of index m  = 1. The temperature at the upper boundary is kept fixed during the computation. Because of the highly compressible nature of the gas and the steep spatial gradients, a modified version of a flux-corrected transport scheme due to Zalesak is devised. The computations show that after the convection adopts a steady-state configuration, the flow consists of horizontal pairs of giant convective cells of opposing circulation. At the cell boundaries, the downflows are rapid and spatially concentrated while the upflows are broad and sluggish. Supersonic speeds are easily achieved in the downflows. Contrary to the expectations of the mixing length theory of convection, there is a net downward flux of kinetic energy at each level in the layer. The convecting layer is cooler on average compared with the initial temperature profile, and there is a net shift of mass towards the lower boundary. The implications of these results for the modern Laplacian theory of Solar system origin are briefly discussed.     

湍流能量闭合法用于大气模式的初探

湍流能量（TKE）闭合方案是近年来大气边界层（PBL）模式中技推崇的方法,它具有11－2阶精度。大气环流模式的计算容量和垂直网络限制,不允许PBL方案过份精细。本文对TKE方案进行简化及网络稀疏化试验。并用Wangara资料验证。验证结果表明：此方案引入PBL内仅设置5层的大气环流模式是可行的。地面以上400米内模式结果与实测吻合。但中、上部位温计算值偏高。关于本方案在大尺度模式中的应用尚须进一步研究。     

Turbulence Modelling of A Lock-Release Oil Slick

1 .IntroductionWiththe rapidincrease inthe scale of offshore oil depletion and marine oil transport ,the devas-tating and obnoxious effects of marine oil pollution due to oil spills become a matter of internationalconcern,and corresponding numerical simul…     

寒潮冷锋过境期间湍流特征量及其谱分析

利用两台超声风速温度仪于1992年12月至1993年1月间,在中国科学院大气物理研究所气象观测塔47 m和120 m两个高度观测到的风速三个正交分量以及温度的湍流脉动资料,计算分析寒潮冷锋过境时局地湍流特征量的日变化以及风速分量和温度的归一化湍流能谱。它们都在不同程度上反应出较大尺度湍流的特征。     

Stability of stationary and time-varying nongyrotropic particle distributions

The ubiquity of nongyrotropic particle populations in space plasmas warrants the study of their characteristics, in particular their stability. The unperturbed nongyrotropic distribution functions in homogeneous media without sources and sinks (closed phase space) must be rotating and time-varying (TNG), whereas consideration of open phase spaces allows for the occurrence of homogeneous and stationary distributions (SNG). The free energy brought about by the introduction of gyrophase organization in a particle population can destabilize otherwise thoroughly stable magnetoplasmas (or, a fortiori, enhance pre-existing gyrotropic instabilities) and feed intense wave growth both in TNG and SNG environments: The nongyrotropic (electron or ion) species can originate unstable coupling among the gyrotropic characteristic waves. The stability properties of these two types of homogeneous nongyrotropy shall be contrasted for parallel (with respect to the ambient magnetic field) and perpendicular propagation, and their potential role as wave activity sources shall be illustrated resorting to solutions of the appropriate dispersion equations and numerical simulations.     

Transitional, entraining, cloudy, and coastal boundary layers

Atmospheric boundary layers are marvelously varied and complex. Recent research has examined some of that variety. Boundary layers over land undergo drastic changes throughout the day as the sun rises and sets, and as clouds form and dissipate. Air is entrained at the top of the boundary layer at varying rates. As air moves over the coast, the boundary layer reacts to changes in surface forcing. All of these changes affect pollutant transport and weather formation. In this paper, research attempting to understand transitional, cloud-topped, and coastal boundary layers, and boundary-layer top entrainment, is reviewed.