HR: 0800h
AN: SM51A-02    [Abstracts]
TI: The Cusp for High and Low Merging Rates
AU: * Newell, P T
EM: Patrick.Newell@jhuapl.edu
AF: Johns Hopkins U./Appl. Phys. Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
AU: Wing, S
EM: Simon.Wing@jhuapl.edu
AF: Johns Hopkins U./Appl. Phys. Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
AU: Rich, F J
EM: Frederick.Rich@hanscom.af.mil
AF: Space Vehicles Directorate, Air Force Research Laboratory, Hanscom AFB, Bedford, MA 01731, United States
AB: The traditional distinction between a northward and southward IMF cusp is deficient, in that northward IMF cusp encounters often closely resemble southward IMF encounters. Partly for that reason, "southward" IMF cusps have been far more often examined than "northward." Recently Newell et al. [2007] showed that the magnetopause merging rate, dFMP/dt, much better predicts cusp latitude than does Bz (or Bs). Here, we investigate the extent to which high and low merging rate conditions better separate cusp encounters into mutually distinct classes. Indeed, high merging rate cusps (those with dFMP/dt > 2*<dFMP/dt>) differ sharply from low merging rate cusps (those with dFMP/dt < 0.5<dFMP/dt>). High energy (tens of keV) ions, apparently of magnetospheric origin, do not extend into the high merging rate cusp, but frequently do for low merging rates. The local time extent of the cusp is 2.33 hours MLT for low merging rate conditions and 3.45 hours MLT for high merging rate conditions. All high merging rate cusps show clear forward dispersion (declining energy with increasing latitude) with low-energy ion cutoffs within that dispersion. Low merging rates cusps rarely show forward merging, but about half show reverse dispersion. "Double" cusps, some with very clear latitudinal separation, occur in some high merging rate cases, but never for low merging rates. The high merging rates cases also typically have a "shadow" region of electron only precipitation at roughly polar rain energies and intensities. For low-merging rate conditions, the region equatorward of the cusp contains ions as well as electrons, and forms a boundary layer.
UR: http:sd-www.jhuapl.edu/Aurora/PressRelease/docs/2006JA012015.pdf
DE: 2431 Ionosphere/magnetosphere interactions (2736)
DE: 2716 Energetic particles: precipitating
DE: 2724 Magnetopause and boundary layers
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly