Abstract.We describe an empirical model to predict the 1-AU •rrival of coronal mass ejections (CMEs). This model is based on an effective interplanetary (IP) acceleration described by Gopalswamy et al. [2000b] that the CMEs are subject to, as they propagate from the Sun to i AU. We have improved this model (1) by minimizing the projection effects (using data from spacecraft in quadrature) in determining the initial speed of CMEs, and (2) by allowing for the cessation of the interplanetary acceleration before i AU. The resulting effective IP acceleration was higher in magnitude than what was obtained from CME measurements from spacecraft along the Sun-Earth line. We evaluated the predictive capability of the CME arrival model using recent two-point measurements from the Solar and Heliospheric Observatory (SOHO), Wind, and ACE spacecraft. We found that The standard assumption that the CME is a rigid cone may not be correct. In fact, the predicted arrival times have a better agreement with the observed arrival times when no projection correction is applied to the SOHO CME measurements. The results presented in this work suggest that CMEs expand and accelerate near the Sun (inside 0.7 AU) more than our model supposes; these aspects will have to be included in future models.

The statistics improved during the 1980s as the SOLWIND (1979)(1980)(1981)(1982)(1983)(1984)(1985) and SMM (1980,(1984)(1985)(1986)(1987)(1988)(1989) However, there were relatively few systematic studies of acceleration. Despite its large 2.5-10 Rs field of view, the SOLWIND coronagraph had a low spatial resolution (-1.25 arc min) and revealed unambiguous accelerations for only a small number of particularly well observed events [Howard et 24,739

No abstract

In an examination of the Solwind coronagraph images obtained during the interval March 28, 1979, to December 31, 1981, we have identified 998 coronal mass ejections and recorded their structural classes, central latitudes, latitudinal spans, speeds, excess brightnesses, and relative importances. A statistical analysis revealed the following general results. (1) The properties of coronal mass ejections (CMEs) depended strongly on their structure. Curved front, halo, and complex CMEs were the most energetic, and single spike, streamer blowout, and diffuse fan CMEs were the least energetic. CMEs occurred over a wide range of position angles, broadly centered on the equator, and had an average angular span of 45°. The leading edge moved at an average of approximately 470 km/s, and the average ejected mass and kinetic energy were 4.1×1015 g and 3.5×1030 erg, respectively. The average CME proton flux at the equator at 1 AU was 2.2×107 cm−2 s−1 or approximately 5% of the measured in situ flux during 1971–1976. (2) During 1979–1981, the average occurrence rate was 1.8/day for all CMEs, 0.9/day for “major” CMEs, and 0.15/day for all CMEs that crossed the equator and had an angular span of at least 45°. (3) The temporal variations in the CME occurrence rate did not show an obvious persistent relation to the variations in the sunspot number on time scales ranging from 7 to 180 days. During 1979–1981 the maximum in the 180‐day average CME rate peaked in the second half of 1980, whereas the 180‐day average sunspot number peaked during the first half of 1980. The 180‐day average rate of fast CMEs (speeds of at least 800 km/s) had a monotonic increase that seemed to be more closely associated with the occurrence rate of large solar flares than with the variation of the sunspot number.

We examine the energetics of coronal mass ejections (CMEs) with data from the large-angle spectrometric coronagraphs (LASCO) on SOHO. The LASCO observations provide fairly direct measurements of the mass, velocity, and dimensions of CMEs. Using these basic measurements, we determine the potential and kinetic energies and their evolution for several CMEs that exhibit Ñux-rope morphologies. Assuming Ñux conservation, we use observations of the magnetic Ñux in a variety of magnetic clouds near the Earth to determine the magnetic Ñux and magnetic energy in CMEs near the Sun. We Ðnd that the potential and kinetic energies increase at the expense of the magnetic energy as the CME moves out, keeping the total energy roughly constant. This demonstrates that Ñux-rope CMEs are magnetically driven. Furthermore, since their total energy is constant, the Ñux-rope parts of the CMEs can be considered a closed system above D2 R _ .

Abstract. We report the properties of all the 841 coronal mass ejections (CMEs) observed by the Solar and Heliospheric Observatory (SOHO) Large Angle Spectroscopic Coronagraph (LASCO) C2 and C3 white-light coronagraphs from January 1996 through June 1998, and we compare those properties to previous observations by other similar instruments. Both the CME rate and the distribution of apparent locations of CMEs varied during this period as expected based on previous solar cycles. The distribution of apparent speeds and the fraction of CMEs showing acceleration were also in agreement with earlier reports. The pointing stability provided by an L-1 orbit and the use of CCD detectors have resulted in superior brightness sensitivity for LASCO over earlier coronagraphs; however, we have not detected a significant population of fainter (i.e., low mass) CMEs. The general shape of the distribution of apparent sizes for LASCO CMEs is similar to those of earlier reports, but the average (median) apparent size of 72 ø (50 ø ) is significantly larger. The larger average apparent size is predominantly the result of the detection of a population of partial and complete halo CMEs, at least some of which appear to be events with a significant longitudinal component directed along the SunEarth line, either toward or away from the Earth. Using full disk solar images obtained by the Extreme ultraviolet Imaging Telescope (EIT) on SOHO, we found that 40 out of 92 of these events might have been directed toward the Earth, and we compared the timing of those with the Kp geomagnetic storm index in the days following the CME. Although the "false alarm" rate was high, we found that 15 out of 21 (71%) of the Kp _> 6 storms could be accounted for as SOHO LASCO/EIT frontside halo CMEs. If we eliminate three Kp storms that occurred following LASCO/EIT data gaps, then the possible association rate was 15 out of 18 (83%). IntroductionThe dynamic processes taking place in the rarified atmosphere of our nearest star are sufficient motivation for many researchers to examine the Sun, the hellosphere, and planetary magnetospheres as plasma physics laboratories. But recent research connecting severe geomagnetic disturbances directly with coronal mass ejections from the Sun [e.g., Gosling, 1993] has renewed interest in a more systemic approach to the arcane specialties of solar and space physics (e.g., collection of This manuscript describes recent observations of coronal mass ejections near the Sun. These sporadic ejections of material through the Sun's atmosphere into interplanetary space can be detected remotely (both by imaging and by inference) at many wavelengths across the electromagnetic spectrum (e.g., X ray, EUV, Ha, and radio). Also the plasma, particle, and magnetic properties of ejected material can be measured in situ in the heliosphere. However, the phrase "coronal mass The understanding of the origin, observation, and effects of CMEs has benefited from significant effort during the past 25 years, and the reader is directed to any of the r...

We have used data from the Naval Research Laboratory (NRL) white light coronagraph on the P78‐1 spacecraft and energetic (E > 4 MeV) proton data from the Goddard Space Flight Center (GSFC) detectors on the IMP 8 and ISEE 3 spacecraft to investigate the association between proton events originating in flares and coronal mass ejections (CME's). The primary data were 50 prompt proton events observed between April 1979 and February 1982 for which reduced coronagraph data were available. H alpha flares could be confidently associated with 27 of these events, and in 26 of these 27 cases an associated CME was found, indicating a high but not perfect association of prompt proton events with CME's. Peak proton fluxes correlate with both the speeds and the angular sizes of the associated CME's. We show that the CME speeds do not significantly correlate with CME angular sizes, so that the peak proton fluxes are correlated with two independent CME parameters. With larger angular sizes, CME's are more likely to be loops and fans rather than jets and spikes and are more likely to intersect the ecliptic. Which of these factors is important to the peak proton flux correlation cannot be determined from the data. We find weak evidence that steeper proton spectra are associated with faster and wider CME's. Two of the 50 proton events of the study and two additional events, all with no associated CME's, share common characteristics: relatively short duration (∼1 day) proton events with low fluxes, parent flares with short (∼10 min) soft X ray duration, close magnetic connection to the earth, and gamma ray and metric type II emission.

Abstract. This work discusses the relations among (1) an interplanetary force-free magnetic cloud containing a plug of cold high-density material with unusual composition, (2) a coronal mass ejection (CME) ,