The Evolution of Large Scale Solar Wind Disturbances and the Predictability of Their Geomagnetic Effects

Details The Evolution of Large Scale Solar Wind Disturbances and the Predictability of Their Geomagnetic Effects The Evolution of Large Scale Solar Wind Disturbances and the Predictability of Their Geomagnetic Effects

Aug 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt........37l&link_type=abstract

Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, LOS ANGELES, 1996.Source: Dissertation Abstracts International, Volume: 57-03, Sectio

Computer Science

Coronal Mass Ejections

Scientific paper

Although it is understood which properties of stream interactions, coronal mass ejections (CMEs) and interplanetary shocks make them geomagnetically effective, predicting their geomagnetic effects from solar or in-situ observations is not currently possible for several reasons. First, solar observations provide measurements of coronal density and the radial component of the photospheric fields. Also, coronal CME plane-of-sky speed (the speed of a CME projected 90^circ to the Earth-Sun line) is the only speed that can be determined. Solar wind-geomagnetic coupling involves parameters not currently derived from solar observations: solar wind speed in the directions of the Earth and non-radial field components. Further, we do not fully understand how the disturbance associated solar magnetic fields evolve from their solar source to 1 AU. This work investigates the evolution of solar wind disturbances as they transit the heliosphere and how well their geomagnetic effects can be predicted. It is found that CMEs produce the largest geomagnetic storms during all phases of the solar cycle. CMEs usually produce geomagnetic storms more often than stream interaction regions except during the late declining phase of the solar cycle. Solar wind velocity deflections afford the determination of the orientation with respect to the ecliptic of either stream interfaces or CMEs. The orientation of a stream interface or a CME determines to a large extent the geomagnetic effect of the disturbance. For both CMEs and stream interfaces, disturbances highly inclined with respect to the ecliptic are associated with higher than average speeds and larger than average Bz and tend to be more geomagnetically effective. Highly inclined CMEs are associated with high speeds and large Bz. The orientation of CMEs and stream interfaces is still difficult to determine from solar observations, however, orientations do not appear to vary significantly between 0.72 AU and 1.0 AU. The effects of a disturbance observed at 0.72 AU may be predicted at 1 AU by a simple scaling of density and Bz if the monitoring spacecraft at 0.72 AU is aligned with the Earth-Sun line.

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