Composition of solar cosmic rays

Summary The general features of the solar particle composition now seem to be clear. The two most abundant components, protons and helium nuclei, have different velocity spectra, similar, but not exactly identical rigidity spectra, and varying relative abundances. The multiply charged nuclei, on the other hand, appear to have the same spectral shape and relative abundances each time measurements are made, at least in the region from 42 to 135 MeV/nucleon. Further, these relative abundances seem to reflect those of the solar atmosphere insofar as comparison can be made. Electrons are rare, but high energy electrons are not expected to be plentiful due to the probable high rate of energy loss caused by synchrotron radiation at the sun. Energetic neutrons were also not expected in large quantity and have not been observed. Finally, there is positive evidence that very small quantities of deuterons exist, probably in an amount which is about 10^-3 or less of the proton abundance.The experimental data indicate that the propagation phenomenon is not purely rigidity dependent. Although the propagation of solar particles is still not well understood, the development of theories which take into account both the general magnetic field and the inhomogeneities in the field seem to hold some promise of explaining the experimental results. The composition data have also established important restraints which any acceleration theory must satisfy, and thereby contributed greatly to the very difficult problem of determining the acceleration mechanism.The similarity of the relative abundance of the energetic solar particles and the nuclei in the sun's photosphere suggested the possibility of having a new means of estimating the solar neon and helium abundances. This very interesting possibility will have to be explored by further testing of the composition of future solar particle events. Finally, it was seen that the composition was a very strong argument against most stars being the principal source of high energy non-solar cosmic rays, and, therefore, special sources, such as supernovae or possibly quasistellar objects, should be considered as much more likely prospects for the origin of cosmic rays.The results which have been obtained thus far on the composition of solar cosmic rays have indicated that further research in this area of study should be very rewarding and of value to many fields of physics. Further data on the composition and relative, as well as absolute, energy spectra of the various components are needed throughout many events. More experiments also should be performed to determine the properties of the rare components, deuterons, tritons, He³ nuclei, electrons, neutrons, and the heavier nuclei. When these experiments are complete, the knowledge which is needed to aid in answering the solar and astrophysical problems discussed in this review should be at hand.     

Dynamical theory of the solar wind

This paper is a review of the basic theoretical dynamical properties of an atmosphere with an extended temperature strongly bound by gravity. The review begins with the historical developments leading up to the realization that the only dynamical equilibrium of an atmosphere with extended temperature is supersonic expansion. It is shown that sufficient conditions for supersonic expansion are T(r) declining asymptotically less rapidly than 1/r, or the density at the base of the corona being less than N _b given by (40) if no energy is available except through thermal conductivity, or the temperature falling within the limits given by (18) if T N ^-1 throughout the corona. Less extended temperatures lead to equilibria which are subsonic or static. The hypothetical case of a corona with no energy supply other than thermal conduction from its base is considered at some length because the equations may be solved by analytical methods and illustrate the transition from subsonic to supersonic equilibrium as the temperature becomes more extended. Comparison with the actual corona shows that the solar corona is actively heated for some distance into space by wave dissipation.The dynamical stability of the expanding atmosphere is demonstrated, and in a later section the radial propagation of acoustic and Alfvén waves through the atmosphere and wind is worked out. The calculations show that the magnetometer will probably detect waves more easily than the plasma instrument, but that both are needed to determine the mode and direction of the wave. An observer in the wind at the orbit of Earth can listen to disturbances generated in the corona near the sun and in turbulent regions in interplanetary space.The possibility that the solar corona is composed of small-scale filaments near the sun is considered. It is shown that such filamentary structure would not be seen at the orbit of Earth. It is pointed out that the expansion of a non-filamentary corona seems to lead to too high a calculated wind density at the orbit of Earth to agree with the present observations, unless T(r) is constant or increases with r. A filamentary corona, on the other hand, would give the observed wind density for declining T(r).It is shown that viscosity plays no important role in the expansion of an atmosphere either with or without a weak magnetic field. The termination of the solar wind, presumably between 10–10³ AU, is discussed briefly. The interesting development here is the interplanetary L recently observed, which may come from the interstellar neutral hydrogen drifting into the outer regions of the solar wind.Theory is at the present time concerned with the general dynamical principles which pertain to the expansion equilibrium of an atmosphere. It is to be expected that the rapid progress of direct observations of the corona and wind will soon permit more detailed studies to be carried out. It is important that the distinction between detailed empirical models and models intended to illustrate general principles be kept clearly in mind at all times.This work was supported by the National Aeronautics and Space Administration under Grant NASA-NsG-96-60.     

Survey of High-Power Microwave Filters

A summary of research and development work on high-power microwave filters is given here: first, design considerations in high-power microwave filters?power handling capacity, waveform distortion, multimode suppression, and stop and pass band characteristics; second, a discussion of filtering devices and techniques in two broad categories-dominant mode filters and harmonic filters (discussion covers methods of operation and significant characteristics of each filter developed to date); and third, a discussion of applications and limitations of filters in various systems and interference situations. Also included are the availability, cost, size, weight, etc. as functions of frequency for the various filter types.     

Frequency-Dependent Ionospheric Refraction Effects on the Doppler Shift of Satellite Signals

Analysis of four-frequency satellite Doppler data has allowed the separation and measurement of frequency-dependent ionospheric contributions to the Doppler shift, providing information useful in the study of errors incurred when tracking radio signals through the ionosphere. These refraction errors affect the accuracy of navigational position fixes obtained by Doppler satellite tracking systems. Some measured ionospheric refraction errors reported here are of interest because their magnitudes are significantly greater than those heretofore predicted from theoretical considerations.     

Identification of Aircraft Stability and Control Parameters Using Hierarchical State Estimation

Previous attempts to identify aircraft stability and control derivatives from flight test data, using three-degrees-of-freedom (3-DOF) longitudinal or lateral-directional perturbation equation-of-motion models, suffer from the disadvantage that the coupling between the longitudinal and lateral-directional dynamics has been ignored. In this paper, the identification of aircraft stability parameters is accomplished using a more accurate 6-DOF model which includes this coupling. Hierarchical system identification theory is used to reduce the computational effort involved. The 6-DOF system of equations is first decomposed into two 3-DOF subsystems, one for the longitudinal dynamics and the other for the lateral-directional dynamics. The two subsystem parameter identification processes are then coordinated in such a way that the overall system parameter identification problem is solved. Next, a six-subsystem decomposition is considered. Computational considerations and comparison with the unhierarchically structured problem are presented.     

Linear FM Signal Formats for Beacon and Communication Systems

This paper examines the capabilities of the class of linear FM spread-spectrum signals within the context of potential communications systems usage in order to establish some performance criteria and bounds that permit comparison with other spread-spectrum formats. A systematic basis is provided for parameter selection for this class of signals by examining the interaction a mong the frequency-modulation indices, time-bandwidth product, and cross-talk criteria that determine the number of effective linear FM signals (or channels) that can be used within the constraints of a bounded time-frequency region. A general expression is derived relating N, the number of useful signals, R2, a cross-talk parameter, ToWo, the mean time-bandwidth product, and ?max and ?min, the maximum and minimum FM rates of the signal set. Canonic signal processor structures are described for ensembles of linear FM signals that have either constant duration or constant bandwidth. It is then shown that the signal modulation format can be modified in accordance with classical paired-echo theory to expand the utility of this class of signals in both synchronous and nonsynchronous operations to yield the equivalent of time-division and code multiplexing. Possible applications for this signal format are discussed.