Other
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsa13b..03m&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SA13B-03
Other
2162 Solar Cycle Variations (7536), 2708 Current Systems (2409), 2722 Forecasting, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
The primary mechanism of energy input to the magnetosphere is dayside magnetic reconnection. The rate at which energy is input depends on the rate at which southward (GSM) magnetic flux is delivered to the dayside magnetopause (VBs) and reconnection efficiency (alpha). In the past efficiency has been assumed to be independent of geometry. Recent studies, however, indicate that it is a maximum when the IMF is antiparallel to the dipole moment (specific universal times) near equinox and a minimum when the dipole is maximally tilted either toward or away from the Sun (solstice). Through the Russell-McPherron effect average IMF Bz is a function of season (DOY) and universal time (UT) as is the average solar wind velocity (heliospheric latitude effect). Reconnection efficiency seems to be a function of both variables as well. Magnetic indices are used as proxies for internal dissipation of the energy input to the magnetosphere. The indices that measure ionospheric currents depend on ionospheric conductivity as well. Conductivity depends on DOY and UT differently than the other variables. Thus we can write that Index = K*Sigma*alpha*V*Bs where K is a constant of proportionality and the remaining quantities are functions of both DOY and UT. The product VBs has been shown to obey the predictions of the Russell-McPherron effect. The reconnection efficiency appears to be described by the Svalgaard function (dependent on the tilt toward and away from Sun) [O'Brien and McPherron, JGR, 107(A11)]. The pattern of conductivity is also complex. We expect that the UT-DOY pattern for an index to be distinctly different from the prediction of the R-M effect since it is the product of the various patterns, each of which have time delays that must also be considered. In this paper we will review the evidence supporting this model and discuss consequences of these geometric effects at different time scales. We will show that there are systematic variations in the behavior of magnetic indices with universal time, season, and solar cycle that are consequences of these geometric effects.
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