The Cusp and the Double Cusp: Observations, Modeling and Implications for
Antiparallel Merging

P. T. Newell, S. Wing, and C.-I. Meng


At least three good explanations for the double cusp exist in the literature,
namely bursty reconnection, merging in opposite hemispheres on different
sides of noon, and simultaneous high and low-latitude merging. The latter two
explanations both require antiparallel merging, and can explain a persistent
double cusp. We present modeling and observational evidence supporting
simultaneous high and low-latitude merging for small magnitude Bz (especially
weakly southward) and large magnitude By. In addition, a great deal of
particle and magnetometer evidence has accumulated over the years about cusp
morphology, much of which supports antiparallel merging. Some recent research
and some older cusp (and related dayside) research directly bearing on the
issue will be reviewed.

_______________
Presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, California, U.S.A., Feb. 9 - 13, 2003.