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A theoretical study of the chemical and gas dynamical processes resulting from the release of reactive gases into the daytime ionosphere is discussed. Only point releases, such as from an explosion or a pulsed jet, are considered. Some scientific uses of the artificial reduction of the ionospheric plasma are considered.
The progress of the Astronomy Spacelab Payloads Project at the Goddard Space Flight Center is reported. Astronomical research in space, using the Spacelab in conjunction with the Space Shuttle, is described. The various fields of solar astronomy or solar physics, ultraviolet and optical astronomy, and high energy astrophysics are among the topics discussed. These fields include scientific studies of the sun and its dynamical processes, of the stars in wavelength regions not accessible to ground based observations, and the exciting new fields of X-ray, gamma ray, and particle astronomy.
Examples of feedback among radiative, chemical and dynamical processes are discussed. The characteristics of the two dimensional (2-D) and three dimensional (3-D) models used in stratospheric ozone studies are discussed. The status of these multidimensional atmospheric photochemical models, their current capabilities and limitations, and possible impact on the chlorofluoromethane problem are presented. Requirements, techniques and problems of the parameterization of transport in 3-D models are described, the observational needs of multidimensional models are presented, and a summary is provided.
Recent and ongoing planetary missions have provided extensive observations of the variations of the Interplanetary Magnetic Field (IMF) both in time and with heliocentric distance from the sun. Large time variations in both the IMF and its fluctuations were observed. These are produced predominantly by dynamical processes in the interplanetary medium associated with stream interactions. Magnetic field variations near the sun are propagated to greater heliocentric distances, also contributing to the observed variablity of the IMF. Temporal variations on a time-scale comparable to or less than the corotation period complicate attempts to deduce radial gradients of the field and its fluctuations from the various observations. However, recent measurements inward to 0.46 AU and outward to 5 AU suggest that the radial component of the field on average decreases approximately as r to the minus second power, while the azimuthal component decreases more rapidly than the r to the minum first power dependence predicted by simple theory. This, and other observations, are discussed.
Current knowledge of the temperature structure of the atmosphere of Venus is briefly summarized. The principal features to be explained are the high surface temperature, the small horizontal temperature contrasts near the cloud tops in the presence of strong apparent motions, and the low value of the exospheric temperature. In order to understand the role of radiative and dynamical processes in maintaining the thermal balance of the atmosphere, a great deal of additional data on the global temperature structure, solar and thermal radiation fields, structure and optical properties of the clouds, and circulation of the atmosphere are needed. The ability of the Pioneer Venus Orbiter and Multiprobe Missions to provide these data is indicated.
The use of satellite remote sensing data for resource management is discussed. The evaluation of the need for management data is reviewed, and some legislative programs which require the monitoring of environmental resources are summarized. Several characteristics of data used in the monitoring of dynamic processes are analyzed, and the implications of routine processing of extensive remote sensing data for the development of a new world view are considered.
Scheduled for launch in the second quarter of calendar year 1978, the Seasat-A satellite is designed to provide all-weather global monitoring of sea surface temperature, significant wave height, surface wind speed and direction and departures from the marine geoid corresponding to ocean dynamic processes. These data will be obtained from an array of microwave instruments, two active ones (short pulse radar altimeter and wind field scatterometer) and one passive (scanning multichannel microwave radiometer). An experimental L-band synthetic aperture radar, operated on a selected basis for approximately four percent of the time, will provide land and ocean images with a resolution of 25 meters and a swath width close to 100 km for the study of coastal processes, sea ice and ocean wave characteristics. The mission objectives focus on an evaluation of the performance of the instruments in terms of their capabilities to characterize the desired geophysical quantities and the utility of such measurements to the study and exploitation of the world's oceans.
Results are presented for an analysis of X-ray and XUV emission from the solar flare that occurred on September 5, 1973. X-ray emission was monitored by ionization chambers aboard the Solrad 9 satellite, and the XUV emission in the wavelength range 170-345 A was recorded by a slitless objective-grating spectroheliograph on Skylab. The physical parameters of the flare plasma, including temperature, density, volume, and magnetic-field configuration, are evaluated. A geometrical loop model is used to determine the volumes of the various emitting regions. The structure of the flare in the rise and decay phases is examined in detail, and conclusions about the effect of various dynamic processes in the flare plasma are made. A major finding is that continued energy release is required well into the flare decay phase. In the rise phase, energy is apparently released only along a small portion of a loop, and in the decay phase apparently throughout most of its length.
Computational techniques applicable to turbulent boundary layers are classified into solutions of Reynolds-averaged equations, in which all the effects of the turbulence are modelled, and solutions of three-dimensional, time dependent Navier-Stokes equations, in which the large eddies are calculated and only the turbulence at scales smaller than the computational mesh spacings has to be modelled. Current computation costs place engineering computations in the first of these categories; large eddy simulations are appropriate currently for special studies of the dynamical processes of turbulence in idealized flow fields. It is shown that the two methods are interrelated and that each can gain from advances in the other. The degree of success of a pair of increasingly complex Reynolds stress models to broaden their range of applicability is examined through comparisons with experimental data for a variety of flow conditions. An example of a large-eddy simulation is presented, compared with experimental results, and used to evaluate the models for pressure rate-of-strain correlations and dissipation in the Reynolds-averaged equations.
The paper reviews the dynamical processes by which condensed matter in the solar nebula accumulates into planets. The basic processes are: (1) gravitational instability; (2) conversion of the radial gradient of orbital motion into random motion between planetesimals; and (3) collisions, which damp the random motion and result in aggregation and/or fragmentation of planetesimals. Each of these processes is defined analytically, and models, based on these results, of planetary growth, axial rotation rates, and formation of satellite systems are formulated.
The source of long-period comets was investigated using a Monte Carlo simulation of comet evolution under the influence of a combination of physical and dynamical processes. The perturbation of cometary orbits by major planets and by non-gravitational forces was modeled, as was physical loss of comets due to random disruption (splitting) and planetary collision; a model was also derived for loss of all volatiles. The importance of each of these processes was examined. The primary end states found for long-period comets were: ejection on hyperbolic orbit, 65.2%; random disruption, 27.6%; and formation of silicate crusts, 7.1%. The basic correctness of the Ort hypothesis was confirmed.
The acoustic pressure fluctuations due to large-scale finite amplitude disturbances in a free turbulent shear flow are calculated. The flow is decomposed into three component scales; the mean motion, the large-scale wave-like disturbance, and the small-scale random turbulence. The effect of the large-scale structure on the flow is isolated by applying both a spatial and phase average on the governing differential equations and by initially taking the small-scale turbulence to be in energetic equilibrium with the mean flow. The subsequent temporal evolution of the flow is computed from global energetic rate equations for the different component scales. Lighthill's theory is then applied to the region with the flowfield as the source and an observer located outside the flowfield in a region of uniform velocity. Since the time history of all flow variables is known, a minimum of simplifying assumptions for the Lighthill stress tensor is required, including no far-field approximations. A phase average is used to isolate the pressure fluctuations due to the large-scale structure, and also to isolate the dynamic process responsible. Variation of mean square pressure with distance from the source is computed to determine the acoustic far-field location and decay rate, and, in addition, spectra at various acoustic field locations are computed and analyzed. Also included are the effects of varying the growth and decay of the large-scale disturbance on the sound produced.
The gravitational field of Venus obtained by tracking the Pioneer Venus Orbiter is examined. For each spacecraft orbit, two hours of Doppler data centered around periapsis were used to estimate spacecraft position and velocity and the velocity residuals obtained were spline fit and differentiated to produce line of sight gravitational accelerations. Consistent variations in line of sight accelerations from orbit to orbit reveal the presence of gravitational anomalies. A simulation of isostatic compensation for an elevated region on the surface of Venus indicates that the mean depth of compensation is no greater than about 100 km. Gravitational spectra obtained from a Fourier analysis of line of sight accelerations from selected Venus orbits are compared to the earth's gravitational spectrum and spherical harmonic gravitational potential power spectra of the earth, the moon and Mars. The Venus power spectrum is found to be remarkably similar to that of the earth, however systematic variations in the harmonics suggest differences in dynamic processes or lithospheric behavior.
On the basis of conservative assumptions, a phenomenological approach is used to address the source strength of Jupiter for interplanetary electrons. It is estimated that Jupiter emits approximately 10 to the 24th - 10 to the 26th electrons per sec with energies in excess of 6 MeV, which sources may be compared with the population of approximately 3 x 10 to the 28th electrons of the same energy in the Jovian outer magnetosphere. It is concluded that Jupiter accelerates particles at a rate exceeding that of ordinary trapped particle dynamic processes.
Magnetospheric physics is presently in a transition from the exploratory stage to one in which satellite missions and ground-based observations are planned with the specific object of achieving a global understanding and self-consistent quantitative description of the cause-and-effect relationship among the principal dynamic processes involved. Measurements turn to lower and lower energies and to higher ion mass species, in order to encompass the entire particle population, and to a broader range of the frequency spectrum of magnetic and electric field variations. In the present paper, the current status of our knowledge on magnetospheric plasma physics is reviewed, with particular reference of such fundamental advances as the discovery of layers of streaming plasma in the magnetosphere beneath its boundary surface, the identification of the terrestrial magnetosphere as a celestial source of kilometric radiation and relativistic particles, the identification of parallel electric field regions within the magnetosphere and their role in auroral particle acceleration, and the discovery of large fluxes of energetic heavy ions trapped in the magnetosphere.
The dynamical processes in the cometary system represent unusual examples of very important, widespread natural phenomena. Topics covered include: (1) the comet as an obstacle in the solar wind; (2) the nature of the plasma flow; (3) collisionless shocks; and (4) plasma processes in the comet tail.
A survey of the reduced gravity fluid management technology program is presented. Information on reduced gravity fluid behavior, techniques for thermal control of cryogenic tankage, and design for fluid management systems are discussed. The development of Spacelab experiments, propellant management systems for orbit transfer vehicles, and computer techniques for simulating reduced gravity fluid dynamic processes is reported.
Transfer function techniques were developed to calculate the isostatic component of the geoid signal over trench/island arc/back arc systems. Removal of this isostatic component from geoid profiles determined by GEOS 3 radar altimetry leaves a residual geoid that can be attributed to the effect of mass inhomogeneities below the depth of compensation. Efforts are underway to extend the analysis to all the major trench/island arc systems of the world in order to provide more detailed understanding of the dynamic processes occurring beneath island arcs.