Properties of coronal mass ejections: SOHO LASCO observations from January 1996 to June 1998

Abstract

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...

Space Weather: Physics, Effects and Predictability

“…CMEs are characterized by their speed, angular width, and central position angle in the sky plane. Their speeds are often fairly constant over the first few solar radii (St Cyr et al 2000) and range between 300 and 3,000 km s -1 (Bothmer and Zhukov 2006). CMEs have mass and kinetic energy in range 5 9 10 12 -5 9 10 13 kg and 10 23 -10 24 J, respectively, and they have angular widths between 24°-72° (Bothmer and Zhukov 2006).…”

Space Storms and Space Weather Hazards

“…Events occur at a rate of roughly 0.5 per day at solar minimum and between 2 and 3 a day at solar maximum (Hundhausen, 1993;Webb and Howard, 1994;St Cyr et al, 2000). This does not seem to have changed between solar cycles 22 and 23.…”

“…The immense efforts documented in Hundhausen (1999) andSt Cyr et al (2000) provide us with the best overviews of CMEs we have. The analysis of data from SOHO, Yohkoh, ACE, Wind and Ulysses (as well as NEAR and other non-CME-focussed missions) will take the best part of the next decade, and will almost certainly resolve some outstanding questions by 2010 (but not, in my view, the all-important question of the cause of the eruption).…”

“…This does not seem to have changed between solar cycles 22 and 23. CMEs typically come from near the equator at solar minimum, and occur over a wider range of latitudes at solar maximum (Hundhausen, 1993;St Cyr et al, 2000), on occasions occurring north or south of 60 o . According to Hundhausen (1993), the distribution of latitudes does not correspond to those of sunspots of flares, but does correspond to larger structures such as prominences and a bright background corona and streamers.…”

Probability of Solar Flares Turn out to Form a Coronal Mass Ejections Events due to the Characterization of Solar Radio Burst Type II and III

“…It expands and is expelled by magnetic forces in CMEs. The front speeds could exceed up to 3000 kms -1 [61][62][63]. This phenomenon can exhibit a variety of forms, some having the classical "three-part" structure [64].…”