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NASA NTRS1980

Distribution functions of type III electrons observed in interplanetary space

Simultaneous energetic electron and solar radio observations from the ISEE-3 spacecraft of several solar type III radio bursts are analyzed and discussed. Two types of electron events are found: (1) normal flare associated electron events in the 20 to greater than 100 keV range, and (2) low energy, 2 to 10 keV, electron events which appear to be associated with individual type III bursts from low frequency type III storms. The arrival direction and frequency of the radio emission are identified and the temporal behavior of the in situ radio intensity and the electron intensity are compared. Calculations of the electron velocity distribution function parallel to the magnetic field are made, implying that for electron events above 20 keV, scattering in the pitch angle is significant in modifying this function.

Lin, R. P.↗

NASA NTRS1984

Type III bursts in interplanetary space - Fundamental or harmonic?

ISEE-3 spacecraft observation of 120 relatively simple, isolated bursts in the 30-1980 kHz range are the basis of the present study of Type III bursts in the solar wind. Several characteristics are identified for many of these bursts which imply that the mode of emission changes from predominantly fundamental plasma radiation during the rise phase to predominantly second harmonic during decay. The fundamental emission begins in time coincidence with the start of Langmuir waves, confirming the conventional belief in these waves' causation of Type III bursts. Attention is given to the characteristics of fundamental components, by comparison to harmonics, at km-wavelengths.

Dulk, G. A.↗

NASA NTRS1983

The effect of solar-wind convection on charged particle transport in interplanetary space

In the formulation of focused transport without convection, approximate solutions of the Boltzmann equation are described in terms of small perturbations of its two fundamental steady-state solutions. In the presence of convection, the same approach is applicable, provided that the analysis is carried out in a system moving with the solar wind. The approximate transport equations that apply in this system are very similar to those that apply in the absence of convection. The new equations assume that the wind blows in the direction of the guiding field and is constant in space and time. Nevertheless, these equations are more general than existing formulations, for they retain their validity when the solar wind velocity is large, and they describe the coherent modes of transport that appear when the mean free path is greater than 1 AU. An interesting implication of the new formulation is that coherent disturbances are swept along with the wind. In this respect, they differ from truly scatter-free modes, which are not affected by the wind.

Earl, J. A.↗

NASA NTRS1986

A perturbation approach to cosmic ray transients in interplanetary space

A perturbation approach is used to model the linear response of the cosmic ray distribution as a function of perturbations in the solar wind transport parameters. The analytical technique permits examination of the effects of the different solar wind parameters, i.e., velocity, drift velocity and the diffusion tensor, which are additive. Cosmic ray changes in the solar wind are neglected. Variations in the diffusion coefficient and the convection-diffusion equation are applied to describing Forbush decreases and the 11-yr solar cycle variations. The treatment is limited to energies above 100 MeV, yet is considered valid enough to have identified a hysteresis effect in the 11-yr variation, wherein high-energy particles lead low-energy particles to a magnitude that increases with increasing heliocentric distance within the inner heliosphere. The calculations also indicate that the Forbush decreases are a cumulative effect of precipitous precursors accompanied by slow recoveries from travelling solar wind perturbations.

Chih, P. P.↗

NASA NTRS1991

Naturally induced secondary radiation in interplanetary space: Preliminary analyses for gamma radiation and radioisotope production from thermal neutron activation

Thermal neutron activation analyses were carried out for various space systems components to determine gamma radiation dose rates and food radiation contamination levels. The space systems components selected were those for which previous radiation studies existed. These include manned space vehicle radiation shielding, liquid hydrogen propellant tanks for a Mars mission, and a food supply used as space vehicle radiation shielding. The computational method used is based on the fast neutron distribution generated by the BRYNTRN and HZETRN transport codes for Galactic Cosmic Rays (GCR) at solar minimum conditions and intense solar flares in space systems components. The gamma dose rates for soft tissue are calculated for water and aluminum space vehicle slab shields considering volumetric source self-attenuation and exponential buildup factors. In the case of the lunar habitat with regolith shielding, a completely exposed spherical habitat was assumed for mathematical convenience and conservative calculations. Activation analysis of the food supply used as radiation shielding is presented for four selected nutrients: potassium, calcium, sodium, and phosphorus. Radioactive isotopes that could represent a health hazard if ingested are identified and their concentrations are identified. For nutrients soluble in water, it was found that all induced radioactivity was below the accepted maximum permissible concentrations.

Plaza-Rosado, Heriberto↗

NASA NTRS1995

Interplanetary space science data base and access/display tool on the NSSDC heliospheric CD-ROM

The National Space Science Data Center (NSSDC) has accumulated a rich archive of heliospheric, magnetospheric, and ionospheric data, as well as data from most other NASA-involved science disciplines. To facilitate access to and use of these data, NSSDC has begun to put selected data onto CD-ROM's. This paper describes one such CD-ROM, and the access and display software developed at NSSDC to support its use. The data on the CD-ROM consist primarily of hourly solar wind magnetic field and plasma data from many near-Earth spacecraft (OMNI) and deep space spacecraft (Voyagers, Pioneers, Helios, Pioneer Venus Orbiter). In addition, 5-minute resolution IMP-8 and ISEE-3 magnetic field and plasma data are also included. Data are stored in both ASCII and CDF formats.

Papitashvili, N. E.↗

NASA NTRS1997

High minor ion outflow speeds in the inner corona and observed ion charge states in interplanetary space

The study carried out in order to demonstrate that high minor ion outflow speeds of the order of O(5+) outflow speed are consistent with charge state observations is presented. The calculations were based on atomic data, observational constraints concerning electron temperatures, electron densities and flow speeds. Minor ion charge state observations were used in order to place limits on solar wind acceleration and heating mechanisms. The charge states of C, O, Fe and Si ions measured in situ were compared to those calculated from two solar wind models. The use of the planned ultraviolet and charge state observations in order to constrain both the ion outflow speeds and electron temperature is discussed.

Esser, R.↗

NASA NTRS2001

Cosmic Rays in Interplanetary Space

The science problem I have tackled in this grant is the derivation of the diffusion tensor of energetic particles in turbulent magnetic fields, with a sensible mean field. The new approach was to use quasi-linear theory with a consistent treatment of those scattering terms leading to diffusion perpendicular to the mean magnetic field; and, to use modern data and formats for three-dimensional turbulence.

Forman, Miriam A.↗

NASA NTRS2002

Microphysics of Waves and Instabilities in the Solar Wind and Their Macro Manifestations in the Corona and Interplanetary Space

A breakthrough resulted from the investigation of plasma heating by ion-cyclotron waves in rapidly expanding flow tubes, often referred to as coronal funnels and expected to originate in the low transition region where the temperature gradient in the solar atmosphere rises very sharply. The investigation was made using a three-fluid plasma consisting of protons, electrons and alpha particles. It was found that these waves heat the solar wind plasma by directly heating the heavier species, namely the alphas. Although only alpha particles dissipate the waves, the strong Coulomb coupling between alpha particles and protons, and between protons and electrons, makes it possible for protons and electrons to be heated also to more than one million degrees, i.e. to coronal temperatures. Interestingly, the extreme heating of the alpha particles, however, is such that they end up being hotter and faster, and are no longer in thermal equilibrium with the protons and electrons. once the rapid expansion of the flow tube is complete, the particles return to thermal equilibrium. The observational signatures of these results are such that if spectral lines formed below a million degrees are observed at different heights in the corona, the inferred outflow velocities may vary by a factor of 5 to 6. In addition, if minor ions are indeed much faster than protons and electrons at temperatures below a million degrees, then one cannot reliably determine the bulk outflow velocity of the solar wind in that region from inferences of minor ion outflow velocities. A detailed parameter study on the resonant interaction between ion cyclotron waves and alpha particles and other minor ions is also under way. It is found that the highest frequency of the waves, or the location of the heating determines whether a thermal equilibrium can be established between minor ions and protons. As the maximum frequency is increased, alpha particles and protons become farther away from thermal equilibrium. As the maximum frequency becomes smaller, alpha particles and protons are more likely to be in thermal equilibrium. However, if the maximum frequency is below a critical value, ion cyclotron resonance occurs at a greater height and a hot corona cannot be produced.

Habbal, Shadia Rifai↗

NASA NTRS2003

Microphysics of Waves and Instabilities in the Solar Wind and their Macro Manifestations in the Corona and Interplanetary Space

Investigations of the physical processes responsible for the acceleration of the solar wind were pursued with the development of two new solar wind codes: a hybrid code and a 2-D MHD code. Hybrid simulations were performed to investigate the interaction between ions and parallel propagating low frequency ion cyclotron waves in a homogeneous plasma. In a low-beta plasma such as the solar wind plasma in the inner corona, the proton thermal speed is much smaller than the Alfven speed. Vlasov linear theory predicts that protons are not in resonance with low frequency ion cyclotron waves. However, non-linear effect makes it possible that these waves can strongly heat and accelerate protons. This study has important implications for study of the corona and the solar wind. Low frequency ion cyclotron waves or Alfven waves are commonly observed in the solar wind. Until now, it is believed that these waves are not able to heat the solar wind plasma unless some cascading processes transfer the energy of these waves to high frequency part. However, this study shows that these waves may directly heat and accelerate protons non-linearly. This process may play an important role in the coronal heating and the solar wind acceleration, at least in some parameter space.

Habbal, Shadia R.↗

NASA NTRS2004

Microphysics of Waves and Instabilities in the Solar Wind and their Macro Manifestations in the Corona and Interplanetary Space

Investigations of the physical processes responsible for coronal heating and the acceleration of the solar wind were pursued with the use of our recently developed 2D MHD solar wind code and our 1D multifluid code. In particular, we explored (1) the role of proton temperature anisotropy in the expansion of the solar wind, (2) the role of plasma parameters at the coronal base in the formation of high speed solar wind streams at mid-latitudes, and (3) the heating of coronal loops.

Gurman, Joseph↗

NASA NTRS2005

Microphysics of Waves and Instabilities in the Solar Wind and Their Macro Manifestations in the Corona and Interplanetary Space

Investigations of the physical processes responsible for coronal heating and the acceleration of the solar wind were pursued with the use of our recently developed 2D MHD solar wind code and our 1D multifluid code. In particular, we explored: (1) the role of proton temperature anisotropy in the expansion of the solar (2) the role of plasma parameters at the coronal base in the formation of high (3) a three-fluid model of the slow solar wind (4) the heating of coronal loops (5) a newly developed hybrid code for the study of ion cyclotron resonance in wind, speed solar wind streams at mid-latitudes, the solar wind.

Habbal, Shadia Rifai↗

NASA NTRS2000