Comments on 'Density distribution in looplike coronal transients: A comparison of observations and a theoretical model' by D. G. Sime, R. M. MacQueen, and A. J. Hundhausen
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Dryer, M.↗
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Numerical investigation of fluid models with full electron and proton thermal conduction equations for the quiet solar wind
The effect of using full equations (rather than Fourier law expressions) for the electron and proton thermal conductivities in conjunction with community, momentum, and temperature equations for the description of spherically symmetric quiet solar wind states is investigated numerically. For this purpose a time-dependent method is used, and steady state solutions in both subsonic and supersonic regimes between the sun and 5 AU are obtained and presented. The consequences for one-fluid and two-fluid models for the solar wind are summarized and discussed.
Cuperman, S.↗
A multiple type-II burst associated with a coronal transient and its MHD simulation
A large coronal transient took place on May 8, 1981. The transient was related to an M7.7/2B flare and was associated with at least two coronal type-II bursts. The velocities of the type-II bursts were in the range 1100-1800 km/s, in excess of the transient velocity of 1000 km/s. Two dimensional positions of the type-II radio sources are available from both the Clark Lake and the Culgoora Radio Observatories. Two dimensional MHD simulations of the event are carried out, taking into account the observed velocity, position, and size of the type-II bursts. The multiple shocks observed during the event and their interaction are simulated, and results of the simulation are discussed.
Gergely, T. E.↗
Corotating interplanetary streams and associated ionospheric disturbances at Venus and earth
During the summer of 1979, solar corona structure was such that a sequence of recurrent regions produced a corresponding sequence of corotating solar wind streams with pronounced downstream signatures. One of these stream events passed earth on July 3 and was observed later at Venus late on July 11th, with similar characteristics. Corresponding in situ measurements at earth from the Atmospheric Explorer-E satellite and at Venus from the Pioneer Venus Orbiter are examined for evidence of comparable perturbations of the planetary ionospheres. The passage of the stream shock front is found to be associated with pronounced fluctuations in n(O+) which appear as pronounced local depletion of ion concentrations in both ionospheres. The ionosphere disturbances appear to be closely associated with large variations in the solar wind momentum flux. The implied local ionospheric depletions observed at each planet are interpreted to be the consequence of plasma redistribution, rather than actual depletions of plasma.
Taylor, H.↗
Response of earth and Venus ionospheres to corotating solar wind stream of 3 July 1979
Corotating solar wind stream interactions are examined for the earth and Venus in light of data from the plasma detectors aboard ISEE-3, the Pioneer Venus Orbiter (PVO), and Helios-A, as well as in situ ion composition measurements taken by the mass spectrometers aboard the PVO and Atmosphere Explorer-E spacecraft. During May-July 1979, a sequence of distinct, recurrent coronal regions developed at the sun; their analysis indicates a corresponding sequence of corotating streams. Although the planetary environments are distinctly different, it is noted that pronounced and analogous ionospheric responses to the stream passage were observed at both the earth and Venus. The response to the intercepted stream is consistent with independent investigations showing the importance of the variability of the solar wind momentum flux in the solar wind-ionosphere interaction at both planets.
Taylor, H. A., Jr.↗
Calibration of the kinematic method of studying solar wind disturbances on the basis of a one-dimensional MHD solution and a simulation study of the heliosphere disturbances between 22 November and 6 December 1977
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Sun, W.↗
A simulation study of two major events in the heliosphere during the present sunspot cycle
Disturbances in the heliosphere which occurred during two of the most active periods of the sun during the present solar cycle, in June and July 1982 and April and May 1978, are qualitatively simulated using the method of Hakamada and Akasofu (1982). A first-order spatial and temporal construction of flare-generated shocks and their multiple interactions with each other and with cororating interaction regions is obtained. A comparison of the results with solar wind observations from Pioneer 10, 11, and 12 suggests that some major flares occurred behind the solar disk during the two periods. The present method provides some qualitative information on how such a series of intense solar flares can greatly disturb both the inner and outer heliospheres. A long-lasting effect on cosmic rays which occurs in conjunction with such disturbances is discussed.
Akasofu, S. L.↗
A simulation study of two major events in the heliosphere during the present sunspot cycle
The two major disturbances in the heliosphere during the present sunspot cycle, the event of June to August, 1982, and the event of April to June, 1978, are simulated by the method developed by Hakamada and Akasofu (1982). Specifically, an attempt was made to simulate the effects of six major flares from three active regions in June and July, 1982, and April and May, 1978. A comparison of the results with the solar wind observations at Pioneer 12 (approximately 0.8 au), ISEE-3 (approximately 1 au), Pioneer 11 (approximately 7 to 13 au) and Pioneer 10 (approximately 16 to 28 au) suggests that some major flares occurred behind the disk of the sun during the two periods. The method provides qualitatively some information as to how such a series of intense solar flares can greatly disturb both the inner and outer heliospheres. A long lasting effect on cosmic rays is discussed in conjunction with the disturbed heliosphere.
Akasofu, S. I.↗
A piston-driven shock in the solar corona
A solar flare that occurred on the west limb at 20:38 UT on Mar. 25, 1981 generated a massive, rapidly expanding optical coronal transient, which moved outward with an approximately constant velocity of 800 km/s. An associated magnetohydrodynamic shock traveled out ahead of the transient with a velocity estimated to be approximately 1000 km/s. The optical and radio data on the transient and shock fit well with general theories concerning piston-driven shocks and with current MHD models for propagation of such shocks through the solar corona.
Maxwell, A.↗
On heat conduction in multicomponent, non-Maxwellian spherically symmetric solar wind plasmas
A generalized expression for the steady-state heat flux in multicomponent, moderately non-Maxwellian spherically symmetric plasmas is presented and discussed. The work was motivated by the inability of the simple, Fourier-type formula for the thermal conductivity to explain the observed correlations in the solar wind. The results hold for situations not far from local thermodynamic equilibrium. The generalized expression includes not only correlations that have been observed but also correlations not sought for previously.
Cuperman, S.↗
The influence of the energy emitted by solar flare soft X-ray bursts on the propagation of their associated interplanetary shock waves
The relationship between the thermal energy released from 29 solar flares and the propagation features of their associated interplanetary shock waves that were detected at 1 AU is investigated. The 29 interplanetary shock waves were identified unambiguously and their tracking from each solar flare was deduced by tracking their associated interplanetary type-II radio emission. The thermal energy released in the solar flares was estimated from the time-intensity profiles of 1-8 A soft X-ray bursts from each flare. A good relationship is found between the flares' thermal energy with the IP shock-waves' transient velocity and arrival time at the earth - that is, the largest flare energy released is associated with the faster shock waves. Finally, a possible scenario of formation of a shock wave during the early phase of the flare and its propagation features is discussed.
Pinter, S.↗
Interplanetary shock collisions - Forward with reverse shocks
When one interplanetary shock overtakes another, the structure that results depends upon the nature of the interacting shocks. The results of collisions of forward with reverse shocks, in two dimensions, are numerically examined, and it is shown that the results depend primarily upon shock strength. It is also noted that such interactions could explain why many energy outburst on the sun that would be expected to cause geomagnetic effects at the earth, do not.
Smith, Z. K.↗
MHD simulation of the 'geoeffectiveness' of interplanetary disturbances
A series of examples is used to evaluate the 'geoeffectiveness' prediction technique that is based on the classical, initial boundary value problem of MHD. For the nonplanar simulation of a corotating stream, it is shown that the technique can compute relevant solar wind parameters at the earth's location. For the nonplanar simulation of a complex series of events, qualitative agreement is found for large-scale structures, but the phasing and amplitudes are not satisfactory. Preliminary work with a fully three-dimensional, time-dependent simulation of a flare-generated interplanetary shock wave shows that the effect of the latitudinal variation produces attenuation of the heliolongitudinal component of the IMF and of the radial velocity.
Dryer, M.↗
A linear MHD instability analysis of solar mass ejections with gravitation
The linear MHD instability of a cylindrical plasma is used to investigate the origin of solar mass ejections, and the dispersion relation is solved numerically. The initial plasma-flow velocity is found to have a significant effect on the instability criteria and growth rate, and the instability growth-rate is shown to be larger in cases where plasma flow exists, relative to the static case. Results suggest that the plasma column may break into small pieces. Assuming a thin-tube approximation, gravity is found to have little effect on the instability of quasi-horizontal ejection, but to have considerable effect on the vertical ejection. In considering the gravitational force, an exact analytical solution is found for the vertical case, while asymptotic solutions are given for the horizontal and oblique cases.
Song, M. T.↗
Overview of STIP intervals 15-19
Five STIP Intervals for special scientific study of solar and interplanetary phenomena were designated between February 1984 and March 1986. The first two intervals were selected retrospectively after unusual periods of solar activity; the remaining three intervals were selected in advance in conjunction with anticipated spacecraft configurations and measurements. In this overview the historical background of these STIP Intervals and a summary of the rationale in the selection of these particular time periods for concentrated studies are presented.
Shea, M. A.↗
Comparison of MHD simulation for the February 1986 events with interplanetary observations by the spacecraft Sakigake
During the period 3-10 February 1986 a series of major solar flares occurred on the Sun and several intense geomagnetic storms took place on the Earth. To examine the causality between the solar activity and the geomagnetic activity in this period, a magnetohydrodynamic (MHD) numerical simulation was performed using a 2 1/2 -D numerical code. In that period of February 1986, the Japanese spacecraft Sakigake was at 0.84 AU, 57 deg west of the Earth. Besides the in-situ measurements of the interplanetary plasma, Sakigake also provided Doppler scintillation observations. Comparisons between the results of the MHD simulation and the measurements made by the spacecraft Sakigake are presented.
Smith, Z.↗
A numerical study of transient, thermally-conductive solar wind
A numerical analysis of transient solar wind starting at the solar surface and arriving at 1 AU is performed by an implicit numerical method. The model hydrodynamic equations include thermal conduction terms for both steady and unsteady simulations. Simulation results show significant influence of thermal conduction on both steady and time-dependent solar wind. Higher thermal conduction results in higher solar wind speed, higher temperature, but lower plasma density at 1 AU. Higher base temperature at the solar surface gives lower plasma speed, lower temperature, but higher density at 1 AU. Higher base density, on the other hand, gives lower velocity, lower temperature, but higher density at 1 AU.
Han, S. M.↗
Plasma-tail activity and the interplanetary medium at Halley's Comet during Armada Week: 6-14 March 1986
The encounters of five spacecraft with Halley's Comet during 6-14 March 1986 offered a unique opportunity to calibrate the solar-wind interaction with cometary plasmas as recorded by remote wide-field and narrow-field/narrowband imaging. Perhaps not generally recognized in the comet community is the additional opportunity offered by the Halley Armada to study the structure of the solar-wind and interplanetary magnetic field (IMF) in three dimensions using five sets of data obtained over similar time intervals and heliocentric distances, but at somewhat different heliolatitudes. In fact, the two problems, i.e., comet physics and the structure of the interplanetary medium, are coupled if one wants to understand what conditions pertained at the comet between the encounters. This relationship is discussed.
Niedner, Malcolm B., Jr.↗