Showing papers on "Coronal mass ejection published in 1993"

The solar flare myth

Abstract: Many years of research have demonstrated that large, nonrecurrent geomagnetic storms, shock wave disturbances in the solar wind, and energetic particle events in interplanetary space often occur in close association with large solar flares. This result has led to a pradigm of cause and effect - that large solar flares are the fundamental cause of these events in the near-Earth space environmemt. This paradigm, which I call 'the solar flare myth,' dominates the popular perception of the relationship between solar activity and interplanetary and geomagnetic events and has provided much of the pragmatic rationale for the study of the solar flare phenomenon. Yet there is good evidence that this paradigm is wrong and that flares do not generally play a central role in producing major transient disturbances in the near-Earth space environment. In this paper I outline a different paradigm of cause and effect that removes solar flares from their central position in the chain of events leading from the Sun to near-Earth space. Instead, this central role is given to events known as coronal mass ejections.

Sizes and locations of coronal mass ejections - SMM observations from 1980 and 1984-1989

Abstract: A statistical description of the sizes and locations of 1209 mass ejections observed with the SMM coronagraph/polarimeter in 1980 and 1984-1989 is presented. The average width of the coronal mass ejections detected with this instrument was close to 40 deg in angle for the entire period of SMM observations. No evidence was found for a significant change in mass ejection widths as reported by Howard et al. (1986). There is clear evidence for changes in the latitude distribution of mass ejections over this epoch. Mass ejections occurred over a much wider range of latitudes at the times of high solar activity (1980 and 1989) than at times of low activity (1985-1986).

Detection of interstellar pick-up hydrogen in the solar system.

Abstract: Interstellar hydrogen ionized primarily by the solar wind has been detected by the Solar Wind Ion Composition Spectrometer instrument on the Ulysses spacecraft at a distance of 4.8 AUs from the sun. This 'pick-up' hydrogen is identified by its distinct velocity distribution function, which drops abruptly at twice the local solar wind speed. From the measured fluxes of pick-up protons and singly charged helium, the number densities of neutral hydrogen and helium in the distant regions of the solar system are estimated to be 0.077 +/- 0.015 and 0.013 +/- 0.003 per cu cm, respectively.

The origin of morphological asymmetries in bipolar active regions. [magnetic field in solar convective envelope]

Abstract: A series of 3D numerical simulations was carried out to examine the dynamical evolution of emerging flux loops in the solar convective envelope. The innermost portions of the loops are anchored beneath the base of the convective zone by the subadiabatic temperature gradient of the underlying overshoot region. It is found that, as the emerging loops approach the photosphere, the magnetic field strength of the leading side of each rising loop is about twice as large as that of the following side at the same depth. The evacuation of plasma out of the leading side of the rising loop results in an enhanced magnetic field strength there compared with the following side. It is argued that this result provides a natural explanation for the fact that the preceding (leading) polarity tends to have a less organized and more fragmented appearance, and that the preceding spots tend to be larger in area and fewer in number, and have a longer lifetime than the following spots.

Reformation of a coronal helmet streamer by magnetic reconnection after a coronal mass ejection

Abstract: A bright feature observed on Jan. 24-26, 1992 with the soft X-ray telescope on the YOHKOH spacecraft and with the coronameter at the Mauna Loa Solar Observatory assumed the appearance of a coronal helmet streamer as it slowly expanded. Mauna Loa observations from Jan. 22-24 indicate that a prominence eruption and coronal mass ejection occurred before this feature was seen. We interpret the Jan. 24-26 observations as evidence for 'reformation' of a magnetically closed helmet structure as a consequence of magnetic reconnection that proceeded along a vertical magnetic neutral sheet formed by the mass ejection.

Signatures of shock drivers in the solar wind and their dependence on the solar source location

Abstract: Solar wind and energetic ion observations following 40 interplanetary shocks with well-established solar source locations have been examined in order to determine whether signatures characteristic of the coronal material forming the shock driver are present. The signatures considered include magnetic-field-aligned bidirectional ion flows observed by the ISEE 3 and IMP 8 spacecraft; bidirectional solar wind electron heat fluxes; solar wind plasma proton and electron temperature depressions; low-beta plasma; enhanced, low-variance magnetic fields; and energetic ion depressions. Several shock driver signatures are commonly observed following shocks originating from within about 50 deg of central meridian, and are generally absent for other events. We conclude that shock drivers generally extend up to about 100 deg in longitude, centered on the solar source longitude. Since shocks from central meridian events are not usually associated with all the shock driver signatures examined, the absence of a driver cannot be confirmed from consideration of one of these signatures alone. We also find evidence that a few bidirectional energetic ion and solar wind electron heat flux events following shocks (in particular from far eastern sources) may occur on open field lines outside of shock drivers.

Interplanetary magnetic clouds: Topology and driving mechanism

Abstract: A model is developed to study the origin and propagation of magnetic clouds. Starting with an equilibrium current loop embedded in an ambient plasma consistent with the solar corona, magnetic energy is injected by increasing the loop current. This causes the loop to rise, propelling plasma and magnetic field away from the Sun. Using a simple model of the interplanetary medium, the subsequent dynamics of the loop is calculated to 1 AU and beyond. The macroscopic properties of the resulting structures at 1 AU closely resemble those of observed magnetic clouds. Thermal effects indicate that clouds remain magnetically connected to the Sun in order to yield observed temperatures near 1 AU.

Large-scale solar-wind structure near the Sun detected by Doppler scintillation

Abstract: STUDIES of the solar wind in the inner heliosphere (between the solar-wind source surface at ∼0.01 AU and 0.3 AU) are hampered by the lack of in situ spacecraft measurements. Radio propagation measurements—using both natural1–7 and spacecraft8–14 radio signals—have provided many insights, but information on large-scale solar-wind structure inside 0.3 AU that can be related to coronal features or direct spacecraft measurements at larger distances has nevertheless remained elusive. Here we report the detection of solar-wind structure between 0.08 and 0.53 AU, based on the response of the 13-cm radio signals from the Pioneer Venus Orbiter to electron-density fluctuations and solar-wind speed within this region. These Doppler scintillation measurements were made during the late declining phase of the most recent cycle of solar activity, when the solar wind exhibited recurrent high-speed streams. Near 0.5 AU, we find narrow regions of enhanced scintillation which appear to be associated with compressed plasma at the leading edges of these streams, consistent with previous scintillation measurements15,16. Inside 0.2 AU, however, scintillation enhancements are conspicuously absent from the fast streams, and instead occur in regions where the average solar wind is slow. They exhibit high variability, and appear to be the interplanetary manifestation of coronal mass ejections. The plasma structures giving rise to these enhanced scintillations apparently undergo significant evolution inside 0.3 AU.

An early solar dynamo prediction : cycle 23 ∼ cycle 22

Abstract: In this paper, we briefly review the “dynamo” and “geomagnetic precursor” methods of long-term solar activity forecasting. These methods depend upon the most basic aspect of dynamo theory to predict future activity, future magnetic field arises directly from the magnification of pre-existing magnetic field. We then generalize the dynamo technique, allowing the method to be used at any phase of the solar cycle, through the development of the “Solar Dynamo Amplitude” (SODA) index. This index is sensitive to the magnetic flux trapped within the Sun's convection zone but insensitive to the phase of the solar cycle. Since magnetic fields inside the Sun can become buoyant, one may think of the acronym SODA as describing the amount of buoyant flux. Using the present value of the SODA index, we estimate that the next cycle's smoothed peak activity will be about 210 ± 30 solar flux units for the 10.7 cm radio flux and a sunspot number of 170 ± 25. This suggests that solar cycle #23 will be large, comparable to cycle #22. The estimated peak is expected to occur near 1999.7 ± 1 year. Since the current approach is novel (using data prior to solar minimum), these estimates may improve when the upcoming solar minimum is reached.

Three-dimensional structure of the solar wind: Variation of density with the solar cycle

Abstract: Interplanetary Scintillation (IPS) measurements obtained from a large number of compact radio sources (nearly 150 sources) distributed over the heliocentric distance range 15–175 solar radii (R(⊙) and heliographic latitude ∼75° N-75° S have been used to study the global three-dimensional density distribution of the solar wind plasma. Contours of constant electron-density fluctuations (ΔNe) in the heliospheric plasma obtained for both the solar minimum and maximum show a strong solar latitude dependence. During low solar activity, the equatorial density-fluctuation value decreases away from the equator towards higher latitudes and is reduced by ∼2.5 times at the poles; the level of turbulence is reduced by a factor of ∼7; the solar-wind mass flux density at the poles is ∼25% lower than the equatorial value. However, during high solar activity, the average distribution of density fluctuations becomes spherically symmetric. In the ecliptic, the variation of ΔNe with the heliocentric distance follows a power law of the formR−2.2 and it does not show any change with solar activity.

A global numerical 3-D MHD model of the solar wind

Abstract: A fully three-dimensional, steady-state global model of the solar corona and the solar wind is developed. A numerical, self-consistent solution for 3-D MHD equations is constructed for the region between the solar photosphere and the Earth's orbit. Boundary conditions are provided by the solar magnetic field observations. A steady-state solution is sought as a temporal relaxation to the dynamic equilibrium in the region of transonic flow near the Sun and then traced to the orbit of the Earth in supersonic flow region. The unique features of the proposed model are: (a) uniform coverage and self-consistent treatment of the regions of subsonic/sub-Alfvenic and supersonic/super-Alfvenic flows, (b) inferring the global structure of the interplanetary medium between the solar photosphere and 1 AU based on large-scale solar magnetic field data. As an experimental test for the proposed technique, photospheric magnetic field data for CR 1682 are used to prescribe boundary condition near the Sun and results of a simulation are compared with spacecraft measurements at 1 AU. The comparison demonstrates a qualitative agreement between computed and observed parameters. While the difference in densities is still significant, the 3-D model better reproduces variations of the solar wind velocity than does the 2-D model presented earlier (Usmanov, 1993).

Polytropic relationship in interplanetary magnetic clouds

Abstract: High time-resolution data from the ISEE 3 and IMP 8 spacecraft are presented for the magnetic field and the proton and electron populations of a number of magnetic clouds, in order to investigate such clouds' thermodynamics and the relationship between their magnetic and thermodynamic structures. It is judged on the basis of these data that while the magnetic flield of the cloud expands, the ions are cooled. Hot electrons are trapped by the magnetic field in the magnetic cloud's core. These conditions are favorable for the generation of ion-acoustic waves.

Solar cycle 21 effects on the Interplanetary Magnetic Field and related parameters at 0.7 and 1.0 AU

Abstract: Magnetometer data obtained over the course of the previous solar cycle by the Pioneer Venus orbiter at about 0.7 AU and IMP 8 at 1.0 AU are used to compare the long-term behavior of the IMF at these two heliocentric distances. Similarities include an enhancement in the typical or median field magnitude during the declining phase of the solar cycle (as compared to solar maximum or minimum), slight decreases in the Parker spiral angle from the declining phase through solar minimum, similar trends in the Alfvenic and magnetosonic Mach numbers, and a remarkably consistent sector structure. Differences include the temporal behavior of the high-field tail of the field distribution, showing that high fields are most frequently observed during solar maximum at the Earth but during the declining phase of activity at Venus. This feature suggests that the perceived occurrence history of large fields from transient disturbances such as coronal mass ejections is a sensitive function of position within the heliosphere.

Coronal mass ejections: The link between solar and geomagnetic activity*

Abstract: Coronal mass ejections are spectacular manifestations of solar activity in which 10+15–10+16 g of solar material are propelled outward into interplanetary space. Recent work has demonstrated that these events are the prime link between solar activity and large, nonrecurrent geomagnetic storms, closing a loop in a body of research extending back more than 130 years.

The origins of planar magnetic structures in the solar wind

Abstract: It is shown that the solar-wind settings of planar magnetic structures (PMSs) are generally inconsistent with their interpretation by Nakagawa et al. (1989) as magnetic loops or tongues resulting from newly emerging magnetic flux in the photosphere. It is suggested that PMS events have two origins: (1) compression and/or draping of preexisting magnetic structures on the leading edge of high-speed streams, especially ahead of coronal mass ejections; and (2) discontinuities near the heliospheric current sheet.

Thermal and nonthermal emissions during a coronal mass ejection

Abstract: Observations were made of thermal and nonthermal radio emissions from a coronal mass ejection (CME) at meter-decameter wavelengths. The speed of the CME was found to be approximately 450 km/sec. It was possible to observe the thermal structure of the CME in radio due to the absence of nonthermal radio emission in the beginning of the event, and the weakness of the following event. Several minutes after the onset of the CME, type III bursts and a nonthermal continuum began. Radio and optical observations are used to show that the CME was not driven by the flare. The thermal structure and geometry of the mass ejection in radio is investigated and compared with the optical evidence. Lastly, a schematic model of the event is developed to show that particle acceleration high in the corona is possible.

Cosmic Ray Decreases and Particle Acceleration in 1978-1982 and the Associated Solar Wind Structures

Abstract: Results of a study of the time histories of particles in the energy range 1 MeV to 1 GeV at the times of greater than 3-percent cosmic ray decreases in the years 1978-1982 are presented. The intensity-time profiles of the particles are used to separate the cosmic ray decreases into four classes which are subsequently associated with three types of solar wind structures. Decreases in class 1 (15 events) and class 2 (26 events) are associated with shocks driven by energetic coronal mass ejections. For class 1 events, the ejecta are detected at 1 AU, whereas this is not usually the case for class 2 events. The shock must therefore play a dominant role in producing the cosmic ray depression in class 2 events. It is argued that since energetic particles (from MEV to GeV energies) seen at earth may respond to solar wind structures which are not detected at earth, consideration of particle observations over a wide range of energies is necessary for a full understanding of cosmic ray decreases.

A CME mass distribution derived from solwind coronagraph observations

Abstract: Using estimates of the masses of nearly 1000 CMEs observed by SOLWIND from Howardet al. (1985), we re-plot the numbers of CMEs as a function of CME mass on a log-linear plot. The plot is significant in that it shows a linear trend over more than a decade of CME masses. The plot indicates a simple form for the distribution of the CME masses and allows an easy determination of the total mass ejected into the solar wind in the form of CMEs. We find that approximately 16% of the solar wind at solar maximum can be comprised of CME mass. There is no indication that the numbers of low-mass CMEs increase in number above the trend set by the more massive ones. Specifically, there is no increase in the numbers of small CMEs such that the whole of the solar wind can be comprised of them.

Bidirectional about 1 MeV/amu ion intervals in 1973-1991 observed by the Goddard Space Flight Center instruments on IMP 8 and ISEE 3/ICE

Abstract: Bidirectional energetic ion flows (BIFs) in the solar wind at 1AU during 1973-1991 are examined on the basis of about 1 MeV/amu data from the Goddard Space Flight Center instruments on ISEE3/ICE and IMP 8. BIFs are observed more frequently around solar maximum, when they are observed about 12 percent of the time compared with about 5 percent at solar minimum. Intervals with durations greater than 4 hr are observed on average approximately every 3-4 d at solar maximum and every 2 wk at solar minimum, with about 33 percent of these intervals following within 2 d of an interplanetary shock. Various coronal mass ejection signatures and BIFs greater than 1 MeV/amu usually do not coincide exactly, and additional bidirectional ion events are identified.

A seasonal dependence for the geoeffectiveness of eruptive solar events

Abstract: The pronounced seasonal variation of the occurrence rate of great geomagnetic storms, attributed to in-ecliptic draping of interplanetary magnetic fields and the Russell-McPherron effect, suggests that the geoeffectiveness of the causative eruptive solar events has a seasonal dependence. Thus an eruptive solar event of a given ‘size’ occurring near the equinoxes might be expected to give rise to a larger geomagnetic storm than would a comparable event occurring near the solstices. We present the following evidence for such a seasonal dependence: (1) the great ‘problem’ storms of the last four solar cycles, i.e., severe storms lacking commensurate preceding solar activity, occurred relatively near the equinoxes, (2) the few great storms that occurred near the solstices were generally preceded by truly outstanding flares, and (3) on average, central meridian proton flares occurring near the equinoxes were followed by significantly larger geomagnetic storms than were similar flares occurring near the solstices. We conclude that the strong semi-annual variation of great storms results from the virtual absence, near the solstices, of great storms associated with disappearing solar filaments and with moderately-sized eruptive solar flares.

The variation in the strength of low-ℓ solar p-modes: 1981–92

Abstract: The acoustic eigenmodes of the Sun are a well-recognized probe of the structure of the solar interior. We report here on a measurement of the strength of the low-l p-mode oscillations throughout a solar cycle. There is an increase of 35 +/- 5 per cent in the strength of the modes from solar maximum to solar minimum, consistent for all the l-values measured. The observations were made with the Birmingham Solar Oscillations Network ('BISON').

Particle acceleration in solar flares

Abstract: We present an overview of the variety of observational data through which particle acceleration is manifested in solar flares These data consist of direct energetic particle measurements, as well as radio, X-ray, gamma-ray and neutron observations, including new data from GAMMA-1, GRANAT and Compton GRO We discuss the evidence showing the existence of impulsive and gradual solar particle events We also discuss recent developments in acceleration theory and in the modelling of particle transport and interactions in solar flares

History of Energetic Solar Protons for the Past Three Solar Cycles Including Cycle 22 Update

Abstract: Solar proton events have been recorded at the earth since 1942 although the detection techniques varied considerably over the past 50 years. From 1942 to 1957 the identification of solar proton events was limited to very high energy events. This situation improved over the next decade after which lower energy solar proton events became routinely identified by satellite measurements. Even though the detection threshold differed between the 19th and more recent cycles, more than 200 solar proton events with a flux of over 10 protons/cm2-sec-ster above 10 MeV have been recorded at the earth in the last three solar cycles. From the composite record of major solar proton events that have occurred during each of the last five solar cycles, it appears that the 20th and 21st solar cycles are deficient in extremely high energy long duration solar particle events. A summary of solar proton events for the past 50 years is given together with information on the flux of solar protons to various spacecraft orbits.

The spin of cosmic dust: rotational bursting of circumsolar dust in the F corona

Abstract: This paper will list, investigate, and evaluate the various spin mechanisms for cosmic dust particles that have been suggested in the literature. This evaluation will concentrate on the possibility of particle fragmentation (rotational bursting) of cosmic dust. The importance of particle fragmentation is manifested by the fact that dust particle size distribution will be changed. More importantly, repeated fragmentation of interplanetary dust particles will give rise to some of the observed “β meteoroids.” Some of these particles are driven out of the solar system and into interstellar space by solar radiation pressure. If this mass loss mechanism is taking place in stellar systems, then it becomes a source for interstellar dust. This paper also addresses the possibility that massive rotational bursting by circumsolar dust particles is taking place in the F corona region. This rotational bursting of F coronal dust could be taking place because of the classical “Paddack effect,” along with a similar spin mechanism suggested by the author, and caused by coronal mass ejections.

Coronal mass ejections and long risetimes of solar energetic particle events

Abstract: We have surveyed the risetimes of all E > 15 MeV solar energetic proton (SEP) events observed on the NOAA GOES spacecraft between 1984 and 1989 and associated with well-connected (W20-W70) solar flares. Twelve events occurred during the times of observations by the coronagraph on the SMM spacecraft, and each event was associated with a coronal mass ejection (CME) observed above the west limb. In each of the three SEP events with the longest flux risetimes a second CME was observed before the time of peak flux. While all the initial CMEs were associated with prominent solar flares, the subsequent CMEs were not accompanied by obvious X ray or radio bursts. We interpret the long risetimes of two of the three SEP events in terms of a second SEP injection due to the second CME.

Association of coronal mass ejections with the heliomagnetic current sheet

Abstract: The distribution of distances of coronal mass ejections (CMEs) with respect to the heliomagnetic current sheet is studied. The analysis is carried out for different times during the last solar cycle. We studied first the site of occurrence of all the CMEs for 1980 and 1984-1986. We further considered those CMEs which are associated with interplanetary shocks for the period 1979-1982. Finally, we considered two-ribbon long duration soft X ray events not related with interplanetary shocks and presumably associated with CMEs. We found that during solar minimum the CMEs in general seem better associated with the heliomagnetic current sheet than at solar maximum and that the two-ribbon not shock-related events are poorly associated with it.