On the rates of coronal mass ejections: remote solar and in situ observations

Details On the rates of coronal mass ejections: remote solar and in situ observations On the rates of coronal mass ejections: remote solar and in situ observations

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsa21a..01r&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA21A-01

Other

7524 Magnetic Fields, 2101 Coronal Mass Ejections (7513), 2111 Ejecta, Driver Gases, And Magnetic Clouds, 2164 Solar Wind Plasma, 2169 Solar Wind Sources

Scientific paper

In this study we compare the rates of coronal mass ejections (CMEs) as inferred from remote solar observations and interplanetary CMEs (ICMEs) as inferred from in situ observations at both 1 AU and Ulysses for almost an entire solar cycle (1996 through 2004). We find that, while the rates of CMEs and ICMEs track each other well at solar minimum, they diverge significantly in early 1998, during the ascending phase of the solar cycle, with the remote solar observations yielding approximately 20 times more events than are seen in situ at 1 AU. This divergence persists through 2004. We discuss several possible causes, including: (1) the appearance of mid-latitude active regions; (2) the increased rate of high-latitude CMEs; and (3) the strength of the global solar field. We conclude that the most likely interpretation is that this divergence is due to the birth of mid-latitude active regions, which are the sites of a distinct population of CMEs that are only partially intercepted by Earth. This conclusion is supported by the following points: (1) A similar divergence occurs between ICMEs in which magnetic clouds are observed (MCs), and those that are not; and (2) a number of pronounced enhancements in the CME rate, separated by approximately one year, are also mirrored and in ICME rate, but not obviously in the MC rate. We provide a simple geometric argument that shows that the computed CME and ICME rates are consistent with each other. The origins of the individual peaks can be traced back to unusually strong active regions on the Sun. Taken together, these results suggest that whether one observes a flux rope within an ICME is sensitive to the trajectory of the spacecraft through the ICME, i.e., an observational selection effect. This conclusion is supported by models of CME eruption and evolution, which: (1) are incapable of producing a CME that does not contain an embedded flux rope; and (2) demonstrate that glancing intercepts can produce ICME-like signatures without the magnetic structures associated with a flux rope

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