Engineering topics

Dryer, M.

Publications and source records attributed to Dryer, M..

At least 19 records

NASA NTRS2012

The Influence of Pickup Protons, from Interstellar Neutral Hydrogen, on the Propagation of Interplanetary Shocks from the Halloween 2003 Solar Events to ACE and Ulysses: A 3-D MHD Modeling Study

We describe our 3-D, time ]dependent, MHD solar wind model that we recently modified to include the physics of pickup protons from interstellar neutral hydrogen. The model has a time-dependent lower boundary condition, at 0.1 AU, that is driven by source surface map files through an empirical interface module. We describe the empirical interface and its parameter tuning to maximize model agreement with background (quiet) solar wind observations at ACE. We then give results of a simulation study of the famous Halloween 2003 series of solar events. We began with shock inputs from the Fearless Forecast real ]time shock arrival prediction study, and then we iteratively adjusted input shock speeds to obtain agreement between observed and simulated shock arrival times at ACE. We then extended the model grid to 5.5 AU and compared those simulation results with Ulysses observations at 5.2 AU. Next we undertook the more difficult tuning of shock speeds and locations to get matching shock arrival times at both ACE and Ulysses. Then we ran this last case again with neutral hydrogen density set to zero, to identify the effect of pickup ions. We show that the speed of interplanetary shocks propagating from the Sun to Ulysses is reduced by the effects of pickup protons. We plan to make further improvements to the model as we continue our benchmarking process to 10 AU, comparing our results with Cassini observations, and eventually on to 100 AU, comparing our results with Voyager 1 and 2 observations.

Detman, T. R.↗

NASA NTRS2005

Chandra Observations of Comet 2P/Encke 2003: First Detection of a Collisionally Thin, Fast Solar Wind Charge Exchange System

We report the results of 15 hr of Chandra observations of comet 2P/Encke 2003 on November 24. X-ray emission from comet Encke was resolved on scales of 500-40,000 km, with unusual morphology due to the presence of a low-density, collisionally thin (to charge exchange) coma. A light curve with peak-to-peak amplitude of 20% consistent with a nucleus rotational period of 11.1 hr was found, further evidence for a collisionally thin coma. We confirm emission lines due to oxygen and neon in the 800-1000 eV range but find very unusual oxygen and carbon line ratios in the 200-700 eV range, evidence for low-density, high effective temperature solar wind composition. We compare the X-ray spectral observation results to contemporaneous measurements of the coma and solar wind made by other means and find good evidence for the dominance of a postshock bubble of expanding solar wind plasma, moving at 600 km/s with charge state composition between that of the "fast" and "slow" solar winds.

Lisse, C. M.↗

NASA NTRS1997

The solar minimum X2.6/1B flare and CME of 9 July 1996: Solar data - Pt. 1

The solar observations from GOES-8, the Solar and Heliospheric Observatory (SOHO), and the Yohkoh satellite concerning the events of the X-class flare are discussed. The Michelson Doppler imager (MDI) magnetometer shows a new region of magnetic activity in AR 7978. The rapid development and evolution of this region is shown by the MDI and the extreme-ultraviolet Doppler telescope (EDT) data. The coronal mass ejections (CMEs) observed using coronagraphs are presented. The possible association between the CME and the X-flare is considered.

Andrews, M. D.↗

NASA NTRS1997

The solar minimum X2.6/1B flare and CME of 9 July 1996: Propagation - Pt 2

The interplanetary propagation aspects of the first X-class solar flare and coronal mass ejection are discussed. The solar data relevant to this event are summarized. Data from WIND and charge element and isotope analysis system (CELIAS) show solar wind plasma and interplanetary magnetic field disturbances early on 12 July 1996. It was observed that the extrapolation of the coronal mass ejection back to the flare time suggests a close association between them. Moreover, the coronal mass ejection speed is similar to the type two shock's speed. The results suggest that the coronal mass ejection is intimately related to the shock itself.

Dryer, M.↗

NASA NTRS1995

Interaction of an interplanetary shock with the heliospheric plasma sheet

Interplanetary shocks often propagate along the heliospheric plasma sheet (HPS) where the interplanetary magnetic field (IMF) changes its polarity. This problem is investigated by the time-dependent 2.5-D MHD numerical model in the meridional plane. An example of computation is shown in the figure using density (log) contours and IMF vectors. Values of plasma parameters along the HPS fluctuate in time due to the Kelvin-Helmholtz instability. The HPS with its decreased intensity of the IMF as well as with its increased mass density causes a dimple in the shock structure (relatively weak for the forward shock, significant for the reverse shock, and very large for the contact discontinuity). Beyond the forward shock, the HPS is slightly compressed due to the post-shock increase of the azimuthal IMF component. Then follows expansion of the HPS surrounded by the highly-deformed contact discontinuity. A significant draping of IMF lines occurs around this structure that increases the meridional component of the IMF. This can cause a favorable condition for initiation of a geomagnetic storm.

Odstrcil, D.↗

NASA NTRS1995

MHD simulation of a propagation of loop-like and bubble-like magnetic clouds

Propagation and evolution of magnetic clouds in the ambient solar wind flow is studied self-consistently using ideal MHD equations in three dimensions. Magnetic clouds as ideal force-free objects (cylinders or spheres) are ejected near the Sun and followed beyond the Earth's orbit. We investigate the influence of various initial parameters like the injection velocity, magnetic field strength, magnetic helicity, orientation of the clouds' axis, etc., on their propagation and evolution. We demonstrate that the injection velocity and magnetic field strength have a major influence on propagation. Simulation results are compared with analytical solutions of magnetic cloud evolution.

Vandas, M.↗

NASA NTRS1995

Evolution of Coronal MHD Shocks into Interplanetary MHD Shocks

The energetic particle environment near the Sun, particularly during solar activity, is of major importance to the planning of a solar probe. It is not known if intensive fluxes are generated solely in the impulsive phase of flares or whether they are augmented by, or contained within, the coronal mass ejections and shock waves spatially preceding them. A solar wind model with various ejecta is studied.

sun coronal shocks interplanetary shocks solar pro↗

NASA NTRS1993

Numerical study of 1-D, 3-vector component, thermally-conductive MHD solar wind

In the present study, transient, 1-dimensional, 3-vector component MHD equations are used to simulate steady and unsteady, thermally conductive MHD solar wind expansions between the solar surface and 1 AU (astronomical unit). A variant of SIMPLE numerical method was used to integrate the equations. Steady state solar wind properties exhibit qualitatively similar behavior with the known Weber-Davies Solutions. Generation of Alfven shock, in addition to the slow and fast MHD shocks, was attempted by the boundary perturbations at the solar surface. Property changes through the disturbance were positively correlated with the fast and slow MHD shocks. Alfven shock was, however, not present in the present simulations.

Han, S.↗

NASA NTRS1991

Shear-induced instability and arch filament eruption - A magnetohydrodynamic (MHD) numerical simulation

A situation wherein a bipolar magnetic field embedded in a stratified solar atmosphere undergoes symmetrical shear motion at the footpoints is investigated via a 2D (nonplanar) MHD simulation. It was found that the vertical plasma flow velocities grow exponentially, leading to a new type of global MHD instability. The growth rate increases almost linearly until it reaches the same order of magnitude as the Alfven speed. Then a nonlinear MHD instability occurs beyond this point. It was found that the central loops are pinched by opposing Lorentz forces, and the outer closed loops stretch upward with the vertically-rising mass flow. The nonlinear dynamical shearing instability is illustrated by a numerical example that is given for three different values of the plasma beta that span several orders of magnitude.

Wu, S. T.↗

NASA NTRS1991

The February 1986 solar activity - A comparison of Giotto, Vega-1, and IMP-8 solar wind measurements with MHD simulations

Large disturbances in the interplanetary medium were observed by several spacecraft during a period of enhanced solar activity in early February 1986. The locations of six solar flares and the spacecraft considered here encompassed more than 100 deg of heliolongitude. These flares during the minimum of cycle 21 set the stage for an extensive multispacecraft comparison performed with a two-dimensional, MHD numerical experiment. The plasma instruments on the Giotto spacecraft, on its way to encounter Comet Halley in March 1986, made measurements of the solar wind for up to 8 hours/day during February. Solar wind measurements from the Johnstone Plasma Analyzer experiment on Giotto are compared with the MHD simulation of the interplanetary medium throughout these events. Using plasma data obtained by the IMP-8 satellite in addition, it appears that an extended period of high solar wind speed is required as well as the simulated flares to represent the interplanetary medium in this case. The plasma and magnetometer data from Vega-1 is compared with the MHD simulation. This comparison tends to support an interpretation that the major solar wind changes at both Giotto and Vega-1 on February 8, 1986 were due to a shock from a W 05 deg solar flare on February 6, 1986 (06:25 UT). The numerical experiment is considered, qualitatively, to resemble the observations at the former spacecraft, but it has less success at the latter one.

Dryer, M.↗

NASA NTRS1991

Numerical simulations of high-speed solar wind streams within 1 AU and their signatures at 1 AU

A parametric study of the evolution within, and signatures at, 1 AU of high-speed streams is performed with the use of a MHD two-and-a-half-dimensional time-dependent model. This study is an extension of an earlier one by Smith and Dryer (1990) who examined the ecliptic plane consequences of relatively short-duration, energetic solar disturbances. The present study examines both the erupting and corotating parts of long-duration, high-speed streams characteristic of coronal hole flows. By examining the variation of the simulated plasma velocity, density, temperature, and magnetic field at 1 AU, as well as the location of the solar coronal hole sources relative to the observer at 1 AU, it was possible to provide some insight into the identification of the solar sources of interplanetary disturbances. Two definitions for angle locating the solar source of interplanetary disturbances at 1 AU are presented and discussed. The results are applied to the suggestion by Hewish (1988) that low-latitude coronal holes are suitably positioned to be the sources of major geomagnetic storms when the holes are in the eastern half of the solar hemisphere at the time of the commencement of the storm. The results indicate that, for these cases, the streams emanating from within the hole must be very fast, greater than 1000 km/s, or very wide, greater than 60 deg, at the inner boundary of 18 solar radii.

Smith, Z.↗

NASA NTRS1990

Conversion of piston-driven shocks from powerful solar flares to blast waves in the solar wind

Published observational data on 39 combined type-II/type-IV solar radio bursts from the period 1972-1982 are analyzed, with a focus on the potential use of the type-IV burst duration to predict the time of arrival at earth of piston-driven shock waves (extending and modifying the prediction method proposed by Smart and Shea, 1985). The data and analysis results are presented in tables and graphs and characterized in detail. It is found that a typical shock of this type leaves the solar flare at velocity 1560 km/sec and continues for a distance of 0.12 AU, decelerates as it is convected by the solar wind, and has a travel time of about 48.5 h. The mean deviation between predicted and measured arrival times is 1.40 h, with standard deviation 1.25 h.

Pinter, S.↗

NASA NTRS1990

Thermally conductive magnetohydrodynamic flows in helmet-streamer coronal structures

The behavior of thermally conductive plasma flows in helmet-streamer coronal structures is investigated within the framework of the axisymmetric nonrotating one-fluid MHD model. Continuous subsonic-supersonic solutions satisfying observed boundary conditions at the sun as well as the vanishing of the temperature at infinity are obtained and presented. Special attention is paid to the combined effects of conductive flow (and corresponding thermal force) and rapidly diverging magnetic field on the critical points. In this, the heliocentric distance of the neutral point determining the separation between closed and open field lines (cusp) is treated as a free parameter. These thermally conductive solutions are contrasted with those provided by corresponding isothermal models.

Cuperman, S.↗

NASA NTRS1990

Numerical simulations of solar disturbances and their interplanetary consequences

Time-dependent MHD numerical simulations are used to study responses of the solar atmosphere and interplanetary medium to simulated solar disturbances. A number of 2D and 3D examples of coronal mass ejection (CME) simulations and some current controversies concerning the basic processes of CME initiation are discussed. Footpoint shearing motion is tested to determine whether it can provide a reasonable mechanism for CME development from arch filament configurations. Possible interplanetary consequences to CME-like disturbances are demonstrated by using 3D simulations to determine the dynamic response of the solar wind to a plasmoid injection from an eruptive filament or prominence. The possibility that a plasmoid may be generated in the interplanetary medium by a solar-generated shock that propagates through a heliospheric current sheet is discussed. Application of the 3D model for the interpretation of interplanetary scintillation observations is addressed.

Dryer, M.↗

NASA NTRS1989

Multi-spacecraft testing of time-dependent interplanetary MHD models for operational forecasting of geomagnetic storms

An MHD 2-1/2D, time-dependent model is used, together with observations of six solar flares during February 3-7, 1986, to demonstrate global, large-scale, compound disturbances in the solar wind over a wide range of heliolongitudes. This scenario is one that is likely to occur many times during the cruise, possibly even encounter, phases of the Multi-Comet Mission. It is suggested that a model such as this one should be tested with multi-spacecraft data (such as the MCM and earth-based probes) with several goals in view: (1) utility of the model for operational real-time forecasting of geomagnetic storms, and (2) scientific interpretation of certain forms of cometary activities and their possible association with solar-generated activity.

Dryer, M.↗

NASA NTRS1989

Soliton and strong Langmuir turbulence in solar flare processes

The occurrence of modulational instability in the current sheet of a solar flare is investigated. Special attention is given to the plasma microinstability in this sheet and its relation to the flare process. It is found that solitons or strong Langmuir turbulence are likely to occur in the diffusion region under solar flare conditions in which the electric resistivity could be enhanced by several orders of magnitude in the region, resulting in significant heating and stochastic acceleration of particles. A numerical example is used to demonstrate the transition of the magnetic field velocity and plasma density from the outer MHD region into the diffusive region and then back out again with the completion of the energy conversion process. This is all made possible by an increase in resistivity of four to five orders of magnitude over the classical value.

Song, M. T.↗

NASA NTRS1989

Three-dimensional, time-dependent MHD simulations of interplanetary plasmoids

The paper presents a three-dimensional time-dependent simulation of a solar-ejected diamagnetic plasmoid that retains its closed topology to and beyond earth. It is assumed in this case that, before entering the computational domain, the plasmoid already exists at or near the sun. A simulation is also presented for a plasmoid that is formed in the corona near the sun or in the interplanetary medium as a consequence of the reconnection of opposite-directed IMF lines. The plasma and magnetic properties of the expanding plasmoid as it moves toward an observer at 1 AU are described.

Dryer, M.↗

NASA NTRS1988

Expected IPS variations due to a disturbance described by a 3-D MHD model

The variations of interplanetary scintillation due to a disturbance described by a three-dimensional, time-dependent, MHD model of the interplanetary medium are calculated. The resulting simulated IPS maps are compared with observations of real disturbances and it is found that there is some qualitative agreement. It is concluded that the MHD model with a more realistic choice of input conditions would probably provide a useful description of many interplanetary disturbances.

Tappin, S. J.↗