Showing papers on "Coronal mass ejection published in 1984"

Associations between coronal mass ejections and solar energetic proton events

Abstract: A comparison between proton events and coronal mass ejections (CMEs) based on nearly three years of observations around the recent maximum of solar activity is presented. Peak proton fluxes are found to correlate with both the speeds and the angular sizes of the associated CMEs. It is shown that CME speeds do not significantly correlate with CME angular sizes, so that peak proton fluxes are correlated with two independent CME parameters. With larger angular sizes, CMEs are more likely to be loops and fans rather than jets and spikes and are more likely to intersect the ecliptic.

Coronal mass ejections observed during the Solar Maximum Mission: Latitude distribution and rate of occurrence

Abstract: Sixty-five coronal mass ejections have been identified in a systematic examination of white-light coronal images obtained between March and September 1980 by the coronagraph/polarimeter flown on the solar maximum mission spacecraft. These ejections were more uniformly distributed in position angle (or 'projected' solar latitude) than the similar events observed during the Skylab mission in 1973-1974; 27 percent of the solar maximum mission mass ejections were centered at positions more than 45 deg from the solar equator. The average rate of occurrence of the observed mass ejections for the entire solar maximum mission epoch, based on the assumption that one coronagraph image per spacecraft orbit is sufficient for detection, was 0.9 + or 0.15 per 24-hour day. Application of the same sampling assumption to the Skylab data set leads to a rate of 0.75 per 24-hour day and thus a change in this rate from the Skylab era (on the declining phase of sunspot cycle 20) to solar maximum mission (near the maximum of sunspot cycle 21) of only approximately 20 percent.

The energetics of chromospheric evaporation in solar flares

Abstract: The Solar Maximum Mission (SMM) spacecraft has provided high time resolution observational data regarding the soft X-ray emission from solar-flare plasma during 1980. The present investigation is concerned with the characteristics of a soft X-ray flare and the energetics of the impulsive phase on the basis of the data collected with the aid of two of the instruments on board the SMM, taking into account the Hard X-ray Burst Spectrometer (HXRBS) and the Bent Crystal Spectrometer (BCS). Attention is given to an analysis of soft X-ray flare spectra, the relative motion of the soft X-ray sources, the phenomenology of the soft X-ray flare, energy and mass transport during the impulsive phase, and energy deposition in the chromosphere during evaporation.

Coronal Mass Ejections

Abstract: Sudden expulsions of dense clouds of plasma from the outer atmosphere of the Sun, termed "coronal mass ejections" (CMEs), are the focus of intense observational and theoretical efforts. CMEs are a type of coronal transient, the general name given the disruption of coronal structure. The mass ejection phenomenon, known for barely a dozen years, is rapidly generating interest within the areas of solar, stellar, and solar-terrestria l physics. Flares, eruptive prominences, and nonequilibrium magnetic field con­ figurations are among the postulated origins of CMEs. Not surprisingly, large-scale magnetic fields are also related to mass ejections. The slowly evolving coronal density structure is now recognized as marking the location of fields and, ultimately, the instantaneous state of the solar dynamo. A new class of CMEs has been found that perhaps shows the continuous renewal of surface fields by interior circulation. Understanding CMEs, the refo re, may lead to insights about flares and other solar phenomena. The CME may be described as an ejection of magnetized plasma out of the gravitational potential well of a central star (56). Thus, phenomena analogous to CMEs should also be occurring in other stars whose magnetic fields and gravitational potentials are Sun-like. Those techniques at radio wavelengths that allow ground-based CME observations at large elon­ , \ \ \ ,. / / " '" ",,' '" - ..... ..... � � � \ \ \ \ ; g � ' ,

Are interplanetary magnetic clouds manifestations of coronal transients at 1 AU

Abstract: Using proxy data for the occurrence of those mass ejections from the solar corona which are directed earthward, the association between the post-1970 interplanetary magnetic clouds of Klein and Burlaga (1982) and coronal mass ejections is investigated. The evidence linking magnetic clouds following shocks with coronal mass ejections is striking; six of nine clouds observed at earth were preceded an appropriate time earlier by meter-wave type II radio bursts indicative of coronal shock waves and coronal mass ejections occurring near central meridian. During the selected control periods when no clouds were detected near earth, the only type II bursts reported were associated with solar activity near the limbs. Where the proxy solar data to be sought are not so clearly suggested, that is, for clouds preceding interaction regions and clouds within cold magnetic enhancements, the evidence linking the clouds and coronal mass ejections is not as clear; proxy data usually suggest many candidate mass-ejection events for each cloud.

Structure and evolution of the large scale solar and heliospheric magnetic fields

Abstract: Structure and evolution of large scale photospheric and coronal magnetic fields in the interval 1976-1983 were studied using observations from the Stanford Solar Observatory and a potential field model. The solar wind in the heliosphere is organized into large regions in which the magnetic field has a componenet either toward or away from the sun. The model predicts the location of the current sheet separating these regions. Near solar minimum, in 1976, the current sheet lay within a few degrees of the solar equator having two extensions north and south of the equator. Soon after minimum the latitudinal extent began to increase. The sheet reached to at least 50 deg from 1978 through 1983. The complex structure near maximum occasionally included multiple current sheets. Large scale structures persist for up to two years during the entire interval. To minimize errors in determining the structure of the heliospheric field particular attention was paid to decreasing the distorting effects of rapid field evolution, finding the optimum source surface radius, determining the correction to the sun's polar field, and handling missing data. The predicted structure agrees with direct interplanetary field measurements taken near the ecliptic and with coronameter and interplanetary scintillation measurements which infer the three dimensional interplanetary magnetic structure. During most of the solar cycle the heliospheric field cannot be adequately described as a dipole.

3He-RICH SOLAR FLARES

Abstract: The formation of the observed solar cosmic ray (SCR) composition remains an open question. It has become particularly acute after the discovery of 3He-rich events. The 3He/4He abundance ratio revealed in such events exceeds substantially (up to four orders of magnitude) that in the solar atmosphere. The data available on the 3He-rich events are discussed and a list of all such events known up to date is presented. Most of the 3He-rich SCR events can be associated with the corresponding optical flares on the Sun, with X-ray and radiobursts. An analysis of the models of 3He enrichement proposed up to now shows that only preferential 3He heating by plasma mechanisms can provide the observed high enrichment levels (3He/4He ≈ 1). A model involving preferential heating of 3He by induced scattering on ions of the ion acoustic waves generated by flare associated electrons in the solar atmosphere is considered in detail. This model can account for the major properties of the 3He-rich flares. Observational implications of the 3He-rich solar flare model are analyzed; the predictions of the theory are compared with the experimental data available, and promising avenues of further relevant experimental and theoretical research are considered. However it is shown that all main conclusions made based on the expressions ((3.2), (3.11), (3.12)) remain the same.

Extension of the reconnection theory of two-ribbon solar flares

Abstract: The magnetic reconnection theory for two-ribbon flares and flare loops hypothesizes that the gradual energy release during the decay phase is a direct result of dissipative relaxation of the open coronal magnetic configuration created by an eruptive prominence/coronal transient precursor. This scenario is here developed quantitatively to the point where a realistic comparison with observational data can be attempted. Our major refinements are (i) to use an analytical description of the reconnecting field geometry specifically chosen to characterize the spatial scale of the active region where a flare occurs, and (ii) to take account of the fact that the volume occupied by X-ray-emitting plasma (hot loops) generally increases with time during the flare.

Solar Terrestrial Physics: Present and Future

Abstract: The following topics relating to solar-terrestrial interactions are considered: (1) reconnection of magnetic fields; (2) particle acceleration; (3) solar magnetic flux; (4) magnetohydrodynamic waves and turbulence in the Sun and interplanetary medium; (5) coupling of the solar wind to the magnetosphere; (6) coronal transients; (7) the connection between the magnetosphere and ionosphere; (8) substorms in the magnetosphere; (9) solar flares and the solar terrestrial environment; (10) shock waves in the solar terrestrial environment; (11) plasma transport and convection at high latitudes; and (12) high latitude ionospheric structure

Interpretation of 3 He abundance variations in the solar wind

Abstract: The ion composition instrument (ICI) on ISEE-3 observed the isotopes of helium of mass 3 and 4 in the solar wind almost continuously between August 1978 and July 1982. This period included the increase towards the maximum of solar activity cycle 21, the maximum period, and the beginning of the descent towards solar minimum. Observations were made when the solar wind speed was between 300 and 620 km/s. For part of the period evidence for regular interplanetary magnetic sector structure was clear and a number of He-3 flares occurred during this time.

Characteristics of flares producing metric type II bursts and coronal mass ejections

Abstract: We attempt to study the origin of coronal shocks by comparing several flare characteristics for two groups of flares: those with associated metric type II bursts and coronal mass ejections (CMEs) and those with associated metric type II bursts but no CMEs CMEs accompany about 60% of all flares with type II bursts for solar longitudes greater than 30°, where CMEs are well observed with the NRL Solwind coronagraph Hα flare areas, 1–8 A X-ray fluxes, and impulsive 3 cm fluxes are all statistically smaller for events with no CMEs than for events with CMEs It appears that both compact and large mass ejection flares are associated with type II bursts The events with no CMEs imply that at least many type II shocks are not piston-driven, but the large number of events of both groups with small 3 cm bursts does not support the usual assumption that type II shocks are produced by large energy releases in flare impulsive phases The poor correlation between 3 cm burst fluxes and the occurrence of type II bursts may be due to large variations in the coronal Alfven velocity

Mgix and Sixi line ratios in the sun

Abstract: New theoretical emission line ratios for the Be-sequence ions Mgix and Sixi are presented A comparison with observational data for two solar flares and an active region loop obtained with the Harvard EUV spectrometer and NRL XUV spectroheliograph aboard Skylab reveals that these plasmas are in ionization equilibrium at coronal temperatures Unfortunately most of the density diagnostics are not particularly useful under solar plasma conditions, as they vary only slightly over the electron density range 108–1013cm−3 However the Sixi ratioI(3Pe2 -3Po2)/I(3Po1 –1Se0) is density sensitive in the range 108 to 1010cm−3, which is representative of electron densities found in solar active regions or small flares

Magnetohydrodynamic modelling of interplanetary disturbances between the sun and earth

Abstract: A time-dependent, nonplanar, two-dimensional magnetohydrodynamic computer model is used to simulate a series, separately examined, of solar flare-generated shock waves and their subsequent disturbances in interplanetary space between the sun and the earth's magnetosphere. The 'canonical' or ansatz series of shock waves include initial velocities near the sun over the range 500 to 3500 km/s. The ambient solar wind, through which they propagate, is taken to be a steady state homogeneous plasma (that is, independent of heliolongitude) with a representative set of plasma and magnetic field parameters. Complete sets of solar wind plasma and magnetic field parameters are presented and discussed. Particular attention is addressed to the MHD model's ability to address fundamental operational questions vis-a-vis the long-range forecasting of geomagnetic disturbances. These questions are: (1) will a disturbance (such as the present canonical series of solar flare shock waves) produce a magnetospheric and ionospheric disturbance, and, if so, (2) when will it start, (3) how severe will it be, and (4) how long will it last? The model's output is used to compute various solar wind indices of current interest as a demonstration of the model's potential for providing 'answers' to these questions.

He I 10830 observations of the 3N/M4.0 flare of 4 September, 1982

Abstract: Hei 10830 A spectroheliograms of a major 3N two-ribbon flare occurring in Boulder Region 3885/3886 early on 4 September, 1982 are discussed and compared with Hα and soft X-ray observations of the event. This flare, observed for more than 60 hr in Hei 10830, was associated with the eruption of a large filament in the active region complex, the formation of coronal holes, a long-duration soft X-ray event, and was the probable source of a earthward coronal mass ejection and the largest geomagnetic storm of this solar cycle. The results of this study suggest the Hei flare is a chromospheric manifestation of the X-ray coronal loop structures associated with flares.

Interplanetary radio storms. I - Extension of solar active regions through the interplanetary medium

Abstract: About 100 storms of type-III solar radio bursts have been identified in the ISEE-3 radio-experiment data during the 4-yr period around the maximum of the 21st solar cycle. They demonstrate the very frequent presence of streams of suprathermal electrons. Their durations range from 1 to 10 d or more. They are observed up to 100-170 solar radii. Their rate of occurrence is 2 to 3 per solar rotation near solar maximum. It is shown that the time variations of the daily radio-emission intensities correlate with the sunspot-number variations and with the solar activity in general. More specifically, a very good correlation is found with the meter-wave type-III and type-I storms, which demonstrates that the suprathermal electrons responsible for the radio emission have been accelerated below 2 solar radii heliocentric. The different lags observed between the sunspot-number variations, the S-component, and the type-I and type-III storms are discussed.

ISEE-3 distant geotail results

Abstract: The ISEE-3 spacecraft spent most of 1983 in the geomagnetic tail, between 60 and 240 earth radii. This extended mission phase has provided an opportunity to study the effects of the solar wind-magnetosphere interaction in previously unexplored downstream regions. Analyses have been conducted concerning such fundamental questions as the nature and structure of the distant tail, the role played by the tail in magnetospheric substorms, and the possibility of processes that lead to the heating and energization of the ambient plasma. Determinations have already been made on the very high plasmasheet velocities, the two-lobe structure of the tail, and the penetration of the IMF into the tail.

Heliospheric current sheet displacements during the solar cycle evolution

Abstract: The purpose of the present study is to confirm the view of a heliospheric current sheet moving with respect to the solar equator, in relation to the solar cycle phases. For this reason, we have analyzed both observed and high-accuracy inferred daily interplanetary magnetic field (IMF) polarities between the maxima of solar cycles 18 and 21 (1947–1980). Statistically significant north-south and “away”-“toward” differences of the IMF mean sector widths (MSW) have been detected around the solar activity minima while no significant differences have been observed around the maxima or the solar polarity reversals. This peculiar variability of the MSW differences in the solar activity extrema can be finally interpreted by assuming a variable placement of the heliospheric current sheet with respect to the solar equator and the solar cycle phases. Actually, in the epochs of the solar polarity reversal our observations are consistent with a current sheet located symmetrically to the solar equator, almost vertical to it and extending to high heliolatitudes. In the opposite, in the epochs of the solar minima the interpretation of our observations could be due to a current sheet which is southward depressed in the northern but symmetrical in the southern hemisphere. The various placements of the current sheet on both sides of the solar equator in relation to the solar cycle phases, are supposed to originate in north-south asymmetric solar activity which has been found by several authors to predominate in the solar minima. The MSW differences detected in the last minimum (1975–1977) of the time span under consideration give reasons to venture the prediction that in the solar minima of the time period 1976–1998 the heliospheric current sheet will appear northward depressed in the southern hemisphere but symmetrical in the northern hemisphere. Systematic meridional and high-latitude observations of both solar wind parameters and IMF patterns would contribute significantly in giving a final answer to the question of possible heliospheric current sheet displacements during the solar cycle evolution.

Comparison of the solar cosmic ray events on May 7, 1978, and November 22, 1977

Abstract: Neutron monitor data from the IMP 7 and 8 satellites are used in the present analysis of the cosmic ray events of Nov. 22, 1977, and May 7, 1978, in order to determine the energy spectra of the solar protons from 50 MeV to 10 GeV, together with pitch angle distributions, intensity-time profiles, and anisotropy-time profiles. The solar proton energy spectra obtained agree with the overlapping energy range when the pitch angle distribution is taken into account, and it is noted that the energy spectra covering three decades of energy and eight of intensity, together with their time variations, were very similar for the two events. The May 1978 event is important for the study of solar particle acceleration and their subsequent injection into the interplanetary medium. Although the solar proton propagation of the November 1977 event was diffusive, the solar particle injection was also time-extended and energy-dependent.

Impulsive phase heating and a coronal explosion in a solar flare

Abstract: The flare of 12 November 1980, 02∶50 UT, in Active Region 2779 (NOAA classification) was studied by using X-ray images obtained with the Hard X-Ray Imaging Spectrometer aboard NASA's Solar Maximum Mission. In a ten-minute period, between about 02∶44 and 02∶54 UT, some five short-lived impulsive bursts occurred. We found that the so-called ‘hard’ bursts (≳ 15 keV) are also detectable in low energy images. During that 10 min period - the impulsive phase - the heat input into the flare and the total number of energetic electrons increased practically exponentially, to reach their maximum values at 02∶54 UT. At the end of that period, when the thermal energy content of the flare was largest, a burst was observed, for the first time, to spread in a broad southern direction from an initially small area with a speed of about 50 km s−1. We have called this phenomenon a coronal explosion.

Magnetic field amplification in the solar nebula through interaction with the T-Tauri wind

Abstract: As carbonaceous chondrites are the least thermally-evolved and hence the most primitive of the meteorites, their residual magnetization can, in principle, be used to estimate the intensity of the magnetic field in the primordial solar nebular, which varies between 0.2 and 1 G (refs 1–4), and could be as high as 2–3 G (ref. 4). The presence of palaeomagnetic fields of such magnitude is of importance in reconstructing the early history of the Solar System and of planetary formation. Levy and Sonnet5, for example, have stressed this point in comparing the respective merits of four alternative sources of the primordial magnetic field. They claim only two of these are possible: (1) a large solar magnetic field spread into the solar nebula; (2) a hydromagnetic dynamo field generated in the solar nebula itself. We show here that there is in fact a further possibility that fits the requirements for strong magnetic field generation and energetic particle irradiation of the grains6: magnetic field enhancement at the point of stagnation between the solar nebula and the intense solar outflows. This mechanism, which involves the interaction of the T-Tauri wind with the solar nebular, is straightforward and is supported by results from recent space research.