Adiabatic betatron acceleration by a geomagnetic storm.
Reversible betatron acceleration mechanism during geomagnetic storm
ADIABATIC EQUATION↗
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An investigation of relationships between meso- and synoptic-scale phenomena
Methods based on the vorticity equation, the adiabatic method, the curvature of the vertical wind profile, and the structure of synoptic waves are used to determine areas of positive vertical motion in the mid-troposphere for a period in each season. Parameters indicative of low-level moisture and conditional instability are areas in which mesoscale systems may be present. The best association between mesoscale and synoptic-scale phenomena was found for a period during December when synoptic-scale systems were well developed. A good association between meso- and synoptic-scale events also was found for a period during March, while the poorest association was found for a June period. Daytime surface heating apparently is an important factor in the formation of mesoscale systems during the summer. It is concluded that the formation of mesoscale phenomena may be determined essentially from synoptic-scale conditions during winter, late fall, and early spring.
Scoggins, J. R.↗
Simple analytical solutions for spherically symmetric production and modulation of energetic solar particles
Exact analytical solutions are presented for the standard time-independent spherically symmetric convection-diffusion-adiabatic deceleration equation governing the transport of cosmic rays in the interplanetary medium for the case in which particles are produced with spherical symmetry at the sun. It is assumed that the solar-wind speed is constant and radial, and that the spatial diffusion coefficient has a power-law dependence on momentum. The Green's function describing the modulation of a monoenergetic production of particles is presented. The solutions provide a useful basis for the study of time-integrated properties of energetic solar-flare particle spectra.
Gross, M. W.↗
Turbulent convection within rapidly rotating superadiabatic fluids with horizontal temperature gradients
A model is developed for small scale thermally driven turbulent convection in rapidly rotating systems. The Boussinesq equations of adiabatic and inviscid flow are perturbed about a basic state which is superadiabatic and which contains a horizontal temperature gradient balanced by a geostrophic wind. The growth rates and length scales of the most unstable modes are determined. It is found that these modes are either zonally or latitudinally symmetric, depending on the latitude and the horizontal temperature gradient. The transports of heat and momentum by the modes are computed. The linear amplitudes are assumed to be limited by shear instability. The model predicts a latitude dependent eddy diffusivity. The applicability of the model to astrophysical and planetary bodies is briefly discussed.
Flasar, F. M.↗
Dynamical implications of the observed thermal contrasts in Venus' upper atmosphere
Observational data on the Venusian upper atmosphere are analyzed to determine the dynamical implications of the large pressure change across the terminator, to study the change in diurnal contrast pattern at the 100 km level, and to investigate the viability of the most straightforward explanation of the cooling, radiative emission by CO2 in the 15 micron bands. Evidence is discussed that a major subsidence or downward vertical contraction of the upper atmosphere occurs across the terminator. The observation that supersonic velocities would be induced in horizontal, inviscid flow by the observed pressure distributions affected by the described flow subsidence is investigated by generalizing the equations for adiabatic inviscid flow along streamtubes to the case of nonhorizontal inviscid flow with heat addition. Nightside cooling is discussed, showing variations in cooling rates. Finally, zonal winds below 100 km are considered.
Seiff, A.↗
Ageostrophic winds and vertical motion fields accompanying upper level jet streak propagation during the Red River Valley tornado outbreak
Preliminary results are shown relating the ageostrophic wind field, through the terms of a semigeostrophic wind equation (assuming adiabatic conditions and the geostrophic momentum approximation) to both air parcel trajectories and their vertical motion fields computed from the parcels' displacement on isentropic surfaces, with respect to pressure. The analysis of results considers both upper-level (324 K) ageostrophic fields and low-level (304 K) fields. Preliminary results tend to support Uccellini and Johnson's (1979) hypothesis concerning upper-level-jet/low-level-jet (ULJ/LLJ) coupling in the exit region of the ULJ. Future plans are described briefly for research intended to clarify the mechanism behind ULJ streak propagation, LLJ development and their relationship to the initiation of severe convection.
Moore, J. T.↗
Normal mode projections of GCM response to tropical forcing
The transient response of a general circulation model (GCM) is examined for the first 10 days of integration after a tropical heating source is switched on. Model output from 10 control and 10 experiment GCM runs are projected onto the normal modes of an adiabatic primitive equation model linearized about a basic state at rest to quantify the contributions from different modes to the 200 mb wind response. The response in the vicinity of the source is similar to that predicted by models linearized about uniform basic states, with important contributions from the internal Rossby and Kelvin modes in the tropics. The heating also excites internal gravity modes with contributions to the 200 mb winds about 40 percent of those of the internal Rossby modes through the 10-day integration time. The response in the external Rossby modes in the extratropics becomes statistically significant after five days.
Zhong, Weili↗
Numerical simulations of galactic wakes
We have performed a series of numerical simulations which examine the simple but realistic case of a galaxy with a smooth potential corresponding to a King profile, and with no interstellar medium. This corresponds to the case of an early-type cluster galaxy that has previously been stripped of its gas. The simulations provide a numerical basis for future work involving galaxies with interstellar media. We use a time-explicit finite difference code (Lufkin & Hawley 1992, ApJ submitted) to obtain solutions to the nonlinear equations for adiabatic flow in axisymmetry. The computational grid covers a region extending 500 kpc from a stationary galaxy radially and along the symmetry axis. We use a graded mesh, allowing for full resolution near the galaxy. Because the assumed potential has a finite depth, no artificial inner boundary condition is necessary; reflection symmetry at the axis is assumed. With a total grid size of 64 radial x 128 vertical, each run requires approximately 5 minutes of cpu time on the NCSA Cray-2.
Lufkin, Eric A.↗
Electron Dynamics in the Magnetotail
The goal of this research has been to study the effects of electrons on magnetotail dynamics and current sheet structure. The approach is to follow ion trajectories in a global model of the magnetotail, use a Boltzmann approximation to include electrons, and then to update the field model according to the currents that are generated by the cross-tail electric field and/or induced fields. Parallel (and perpendicular) electric fields that form are included through the Boltzmann relation. Transverse electron currents are to be included through adiabatic drift equations.
Schriver, David↗
Energy corrections to the Born- Oppenheimer approximation - The best adiabatic approximation
Coupled Schroedinger equations for diatomic molecules internal motion solved using best adiabatic approximation to obtain energy correction to Born-Oppenheimer method
Hirschfelder, J. O.↗
Analytical skin friction and heat transfer formula for compressible internal flows
An analytic, closed-form friction formula for turbulent, internal, compressible, fully developed flow was derived by extending the incompressible law-of-the-wall relation to compressible cases. The model is capable of analyzing heat transfer as a function of constant surface temperatures and surface roughness as well as analyzing adiabatic conditions. The formula reduces to Prandtl's law of friction for adiabatic, smooth, axisymmetric flow. In addition, the formula reduces to the Colebrook equation for incompressible, adiabatic, axisymmetric flow with various roughnesses. Comparisons with available experiments show that the model averages roughly 12.5 percent error for adiabatic flow and 18.5 percent error for flow involving heat transfer.
Dechant, Lawrence J.↗
An Improved Plastically Dilatant Unified Viscoplastic Constitutive Formulation for Multiscale Analysis of Polymer Matrix Composites Under High Strain Rate Loading
Polymer matrix composites are commonly used to fabricate energy-absorbing structures expected to experience impact loading. As such, a detailed understanding of the dynamic response of the constituent materials is necessary. Since the rate, temperature, and pressure dependence of carbon fiber reinforced polymer matrix composites are primarily manifestations of the rate, temperature, and pressure dependence of the polymer matrix, it is crucial that the constitutive behavior of the matrix be accurately characterized. In this work, an existing unified viscoplastic constitutive formulation is extended to ensure thermodynamic consistency and to more accurately account for the tension-compression asymmetry observed in the response of polymeric materials. A new plastic potential function is proposed, and elementary loading conditions are utilized to determine relations between model constants to ensure nonnegative plastic dissipation, a necessary thermodynamic requirement. Expressions for plastic Poisson’s ratios are derived and are bounded by enforcing nonnegative plastic dissipation. The model is calibrated against available experimental data from tests conducted over a range of strain rates, temperatures, and loading cases on a representative thermoset epoxy; good correlation between simulations and experimental data is obtained. Temperature rises due to the conversion of plastic work to heat are computed via the adiabatic heat energy equation. The viscoplastic polymer model is then used as a constitutive model in the generalized method of cells micromechanics theory to investigate the effects of matrix adiabatic heating on the high strain rate response of a unidirectional composite. The thermodynamic consistency of the model ensures plastic dissipation can only cause an increase in temperature. Simulation results indicate that significant thermal softening due to the conversion of plastic work to heat is observed in the composite for matrix dominated deformation modes.
Impact loading↗
Preshock region acceleration of implanted cometary H(+) and O(+)
A self-consistent, three-fluid model of plasma transport and implanted ion acceleration in the unshocked solar wind is presented. The solar wind plasma is depleted by charge exchange with the expanding cometary exosphere, while implanted protons and heavy ions are produced by photoionization and charge transfer and lost by charge exchange. A generalized transport equation describing convection, adiabatic and diffusive velocity change, and the appropriate production terms is used to describe the evolution of the two cometary ion components, while the moments of the Boltzmann equation are used to calculate the solar wind density and pressure. The flow velocity is obtained self-consistently by combining the conservation equations of the three ion species. The results imply that second-order Fermi acceleration can explain the implanted spectra observed in the unshocked solar wind. Comparison of measured and calculated distribution indicates that spatial diffusion of implanted ions probably plays an important role in forming the energetic particle environment in the shock vicinity.
Gombosi, Tamas I.↗
Study of dense aluminum plasmas
Studies directed toward the development of a computer program describing the penetration of a thin aluminum plate by a quartz sphere are reported. The aluminum simulates a bumper plate for micrometeoroids. The ablation of a rock sphere by penetrating a stack of paper sheets is described, and an equation for losses near the surface of the sphere is derived. The expansions of aluminum plasma sphere with initial energies of 44.45, 20.8, and 7.136 eV are investigated, including shock compression during penetration and adiabatic expansion. The equations of state were derived for aluminum and quartz, as well as one of the Mie-Grunesen type. A technique to determine momentum at the bottom surface of the thin plate, and the energy for hypervelocity separation of fragments of the aluminum plate are also considered.
Todd, F. C.↗
A Modeling Study of the Latitudinal Variations in the Nighttime Plasma Temperatures of the Equatorial Topside Ionosphere During Northern Winter at Solar Maximum
Latitudinal variations in the nighttime plasma temperatures of the equatorial topside ionosphere during northern winter at solar maximum have been examined by using values modelled by SUPIM (Sheffield University Plasmasphere Ionosphere Model) and observations made by the DMSP F10 satellite at 21.00 LT near 800 km altitude. The modelled values confirm that the crests observed near 15 deg latitude in the winter hemisphere are due to adiabatic heating and the troughs observed near the magnetic equator are due to adiabatic cooling as plasma is transported along the magnetic field lines from the summer hemisphere to the winter hemisphere. The modelled values also confirm that the interhemispheric plasma transport needed to produce the required adiabatic heating/cooling can be induced by F-region neutral winds. It is shown that the longitudinal variations in the observed troughs and crests arise mainly from the longitudinal variations in the magnetic meridional wind. At longitudes where the magnetic declination angle is positive the eastward geographic zonal wind combines with the northward (summer hemisphere to winter hemisphere) geographic meridional wind to enhance the northward magnetic meridional wind. This leads to deeper troughs and enhanced crests. At longitudes where the magnetic declination angle is negative the eastward geographic zonal wind opposes the northward geographic meridional wind and the trough depth and crest values are reduced. The characteristic features of the troughs and crests depend, in a complicated manner, on the field-aligned flow of plasma, thermal conduction, and inter-gas heat transfer. At the latitudes of the troughs/crests, the low/high plasma temperatures lead to increased/decreased plasma concentrations.
Bailey, G. J.↗
A compilation of studies from Atmospheric Variability Experiment (AVE)
Five methods for obtaining the sign of vertical motion at various levels in the atmosphere were investigated to determine which gave the best explanation for areas of rain and no-rain in the southeastern United States during the period February 19-22, 1964. The methods used were the terrain-induced vertical motion, the kinematic method including the terrain effect, the adiabatic method, the omega equation, and the vorticity equation combined with Dines' Compensation Principle. Stability and moisture availability were considered but not as extensively as vertical motion. Values of vertical motion obtained by the kinetic method, including orographic lifting produced the best agreement with the observed areas. When terms in the omega equation were added through use of constant multipliers, results comparable to the adiabatic method were obtained. Without this addition large uncertainties occurred. Maps showing areas where terms of the omega equation would indicate positive vertical motion did not correlate well with the observed rainfall patterns.
Scoggins, J. R.↗
An artificial energy method for calculating flows with shocks
The artificial-viscosity method, first proposed by von Neumann and Richtmyer, introduces an artificial viscous pressure term in regions of compression such that an increase in entropy occurs in shock transition zones. The paper describes how dissipative flows can be induced by reducing the total energy available for adiabatic processes in shock zones. A class of inviscid fluid flows, called semiflows, is described in which the flows exhibit thermodynamic differences. Induced dissipative flows modify the pressure in regions of compression in a manner analogous to the artificial-viscosity method and for a gas, the effect is equivalent to suitably modifying the gas constant in the equation of state. By employing MacCormack's method and the usual non-adiabatic equations, numerical solutions of a Riemann problem are compared with the modified artificial energy method, showing that the dissipation effect predicted by the analytical formulation is reflected in the numerical method as well.
Rose, M. E.↗
A generalized hyperbolic marching method for chemically reacting 3-D supersonic flow using a splitting technique
A generalized hyperbolic marching method employing a nonorthogonal coordinate system and using a split differencing scheme for calculating steady supersonic flow over aerodynamic shapes is presented. It is a second-order-accurate mixed explicit-implicit procedure that solves the inviscid adiabatic and nondiffusive equations for chemically reacting flow in integral conservation-law form. The relationship between the integral and differential forms of the equations are examined and the relative merits of each discussed. The method admits initial Cauchy data situated on any arbitrary surface and integrates them forward along a general curvilinear coordinate, distorting and deforming the surface as it advances. The chemical kinetics term is split from the convective terms which are themselves dimensionally split, thereby freeing the fluid operators from the restricted step-size imposed by the chemical reactions and increasing the computational efficiency. The accuracy of this splitting technique is analyzed, a sufficient stability criterion is established, and comparisons are made with another method.
Rizzi, A. W.↗