Vertically nested nonhydrostatic model for multiscale resolution of flows in the upper troposphere and lower stratosphere

Vertical nesting with refined gridding in coupled mesoscale weather research and forecasting (WRF)/microscale models are presented with a particular emphasis on improved vertical resolution in the upper troposphere and lower stratosphere (UTLS). The finest mesoscale nest is coupled with a sequence of microscale nests with finer resolution in both the horizontal and the vertical. The fully three-dimensional, compressible nonhydrostatic Navier–Stokes equations are solved using a time-split method with a refined grid in the vertical, and improved resolution in the UTLS region. For nesting, both lateral and vertical boundary conditions are treated via implicit relaxation in buffer zones where all fields are relaxed to those obtained from the finest mesoscale nest. Computational results are presented demonstrating the ability of microscale nests to resolve multiscale physics of strongly nonlinear interactions and laminated structures observed in the Terrain-induced rotor experiment (T-REX) campaign of field measurements. Very high resolution real case nested simulations are conducted. The microscale nests fully resolve localized shear layers and sharp gradients of vertical velocity and potential temperature near the tropopause and in the lower stratosphere.     

Development of a selective interference filter for measuring concentrations of trace gases in the stratosphere

A Michelson interferometer set at zero path difference and containing gas samples in its arms can act as a highly selective filter passing only radiation very near the absorption line centres of the gas. An assessment of a variety of instruments having this property is made and the construction of a Mach-Zehnder arrangement is discussed.     

A new model for ideal gases. Decay to the Maxwellian distribution

In this work, a new model in kinetic gas theory for deriving the Maxwellian velocity distribution (MVD) is proposed. We construct an operator that governs the discrete time evolution of the velocity distribution. This operator, which conserves the momentum and the energy of the ideal gas, has the MVD as a fixed point. Moreover, for any initial out-of-equilibrium velocity distribution, it is shown that the gas decays to the equilibrium distribution, that is, to the MVD.     

A simplified two-dimensional diffusion model for calculating the fission-fragment kinetic-energy distribution

The variance \(\sigma _{E_k }^2\) of the fission-fragment kinetic-energy distribution is calculated in describing the dynamics of fission of an excited nucleus by a Fokker-Planck equation for the quantum distribution function of two collective coordinates (the distance between the centers of mass of the nascent fragments and the neck parameter) and their conjugate momenta. In the calculations fluctuations in collective coordinates near scission and prescission kinetic energy have been taken into account simultaneously. The results of statistical model calculations for the case of high friction in fission mode and those of the calculations in the framework of a dynamical model for zero nuclear viscosity are the limiting cases of the proposed model. The dependence of \(\sigma _{E_k }^2\) upon the fissility parameter is studied.     

Diode-laser-seeded optical parametric oscillator for airborne water vapor DIAL application in the upper troposphere and lower stratosphere

Received: 4 May 1998/Revised version: 17 July 1998     

A fast-response near-infrared tunable diode laser absorption spectrometer for in situ measurements of CH4 in the upper troposphere and lower stratosphere

We describe a near-infrared in situ tunable diode laser spectrometer developed for atmospheric measurements of CH₄ in the upper troposphere and lower stratosphere (UT/LS). The instrument is designed to provide fast-response (0.5–1 Hz) measurements and operate autonomously on the NASA WB-57F high-altitude aircraft. A single-mode InGaAsP distributed feedback laser diode operating at 1.6537 μm scans continuously over the R(3) rotation–vibration transition in the 2ν₃ band. We use a direct absorption technique incorporating a custom-designed long path length (252 m) low-volume (3.6 L) astigmatic Herriott cell. The present detection sensitivity is 5×10¹⁰ molecules cm^-3, corresponding to ∼20 ppbv in the UT/LS, with the main limit to instrument precision being background optical interference fringes. In-flight performance is demonstrated by presentation of recent data. Received: 25 January 2002 / Revised version: 5 April 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +1-303/497-5373, E-mail: richard@al.noaa.gov     

Quantum magneto-transport in two-dimensional GaAs electron gases and SiGe hole gases

We have measured the low-temperature transport properties of two-dimensional (2D) GaAs electron gases and 2D SiGe hole gases. Our experimental results fall into three categories. (i) Collapse of spin-splitting and an enhanced Landé g-factor at Landau level filling factors both ν=3 and ν=1 in a 2D GaAs electron gas are observed. Our experimental results show direct evidence that the effective disorder is stronger at ν=1 than that at ν=3 over approximately the same perpendicular magnetic field range. (ii) We present evidence for spin-polarisation of a dilute 2D GaAs electron gas. The Lande g-factor of the system is estimated to be 1.66. This enhanced g value is ascribed to electron–electron interactions at ultra low carrier density limit. (iii) In a high-quality SiGe hole gas, there is a temperature-independent point in the magnetoresistivity ρ_xx and ρ_xy which is ascribed to experimental evidence for a quantum phase transition between ν=3 and ν=5. We also present a study on the temperature(T)-driven flow lines in our system.     

Bose-Einstein condensation in one- and two-dimensional gases

We show that the one- and two-dimensional ideal Bose gases undergo a phase transition if the temperature is lowered at constant pressure. At the pressure-dependent transition temperature T_c (P) and in their thermodynamic limit the specific heat at constant pressure c_p and the particle densityn diverge, the entropyS and specific heat at constant volumec _v fall off sharply but continuously to zero, and the fraction of particles in the ground state N₀/N jumps discontinuously from zero to one. This Bose-Einstein condensation provides a remarkable example of a transition which has most of the properties of a second-order phase transition, except that the order parameter is discontinuous. The nature of the condensed state is described in the large but finiteN regime, and the width of the transition region is estimated. The effects of interactions in real one- and two-dimensional Bose systems and recent experiments on submonolayer helium films are discussed briefly.     

Nonlinear screening in two-dimensional electron gases

We have performed self-consistent calculations of the nonlinear screening of a point charge Z in a two-dimensional electron gas using a density functional theory method. We find that the screened potential for a Z=1 charge supports a bound state even in the high-density limit where one might expect perturbation theory to apply. To explain this behavior, we prove a theorem to show that the results of linear response theory are in fact correct even though bound states exist.     

Entropy and multi-particle correlations in two-dimensional lattice gases

We analyse the statistical entropy of two-dimensional lattice-gas models in terms of the contributions which arise from space correlations of increasing order. The “residual multiparticle entropy”, defined as the contribution to the excess entropy that is associated with correlations involving more than two particles, is calculated for the Ising and Coulomb lattice gases. The thermodynamic behaviour of the residual multiparticle entropy is then discussed in relation to the phase diagram of the model and the existence of underlying signatures of order-disorder phase transitions is also investigated. Received 31 December 1998 and Received in final form 8 March 1999     

A comparison of regularization techniques for atmospheric trace gases retrievals

A comparison of regularization techniques aimed at maximizing the information content for atmospheric trace gas retrievals at an acceptable total error is presented. The total error of a retrieval is associated with the condition number of the regularized inverted matrix, which amplifies the measurement noise when moving from the measurement space to the state space as a noise error, and also together with the characteristics of the stabilizer, injects regularization error into the retrieval. Four different stabilizers: (i) the identity matrix, (ii) the first derivative operator, (iii) the second derivative operator, and (iv) the a-priori covariance matrix are used in this study to characterize the retrieval process under various regularization matrices using the regularized trust region method. For the cases simulated, it is found that the a-priori covariance matrix, which is used in traditional optimal estimation, and the identity matrix, which is used as a regularization in the Levenberg-Marquardt method, produce the highest total error, whereas the discrete one-dimensional Laplace first and second derivative operators produce the least total error at reasonably high information content.     

平流层中部垂直运动年循环异常的模拟研究

利用NCAR提供的包含化学、辐射、动力相互作用的二维模式(SOCRATES)进行模拟试验，进一步探讨年循环年际异常的可能成因.模拟结果的分析表明臭氧高值中心相对于赤道准两年移动是年循环的年际异常的一个重要原因.当臭氧高值区离开赤道偏向夏半球时，夏半球的平流层中部将吸收更多的太阳短波辐射，而冬半球的则相反，因此更大的短波加热率将增大夏半球平流层中部的上升运动，导致年循环的增强；相反地，臭氧高值中心接近赤道时则导致了相对较弱的年循环. 关键词： 臭氧 甲烷 年循环 准两年变率     

A lightweight balloon-borne laser diode sensor for the in-situ measurement of CO2 at 2.68 micron in the upper troposphere and the lower stratosphere

We report the development of a laser sonde operated under stratospheric balloons and devoted to the in-situ measurement of carbon dioxide in the upper troposphere and the lower stratosphere. In the 2.68 micron region, strong CO₂ transitions are suitable for the in-situ monitoring of carbon dioxide, which gives ∼10% absorption depth and, moreover, antimonide laser diodes are nowadays available that show relevant spectral properties for absorption spectroscopy. The light-weight sensor is based on 50-cm single path configuration and is operated open to the atmosphere. We provide details of the design of the instrument and data processing. The performance and the stability of the instrument were evaluated with the Allan variance technique. The spectrometer was test-flown in the Arctic stratosphere from Kiruna, Sweden and we report preliminary flight results.     

超流费米气体中两维孤子的动力学

我们利用解析和数值的方法,研究从Bardeen-Cooper-Schrieffer(BCS)超流到玻色-爱因斯坦凝聚(BEC)渡越的过程里超流费米气体中两维(2D)孤子的形成和演化.基于超流流体力学方程,在准二维和长波近似下,推导描述弱非线性激发带正色散项的Kadomtsev-Petviashvili方程;给出整个BCS-BEC渡越的2D孤子解,以及数值求解孤子在囚禁势中的演化.数值结果显示由于Snake(横向)不稳定性,大振幅的暗孤子会衰变为大量涡旋-反涡旋对,并且这个不稳定性在不同超流区域不同.