SPA-Magnetospheric Physics [SM]
SM53B
ACC:Chichen-Itza Hall
Friday
From Solar Wind to Magnetopause and Cusp II: Posters
Presiding: S Hernandez, Florida Institute of Technology
SM53B-01
Two Distinct Types of Cusp-Like Regions Observed by POLAR
* Niehof, J T
(jniehof@bu.edu), Boston University Center for Space Physics, 725 Commonwealth Avenue, Boston, MA
02215, United States
Fritz, T
(fritz@bu.edu), Boston University Center for Space Physics, 725 Commonwealth Avenue, Boston, MA
02215, United States
Friedel, R H
(friedel@lanl.gov), Los Alamos National Laboratory, Space and Atmospheric Sciences (ISR-1)
MS-D466, Los Alamos, NM 87545, United States
Chen, J
(jschen@bu.edu), Boston University Center for Space Physics, 725 Commonwealth Avenue, Boston, MA
02215, United States
We examine POLAR data for several cusp crossings, observing two different types of cusp-like regions. We apply
the label "quiet cusp" to the traditional cusp of high-density, stagnant solar wind plasma. "Cusp Diamagnetic
Cavities", described previously, are similar but show a strongly depressed and turbulent field and are colocated
with "Cusp Energetic Particle" observations. Within the CDC's, field depressions are strongly correlated to
enhancements in the local plasma density.
SM53B-02
A New Scenario for the Production of Weak Bipolar Fields in Space: "Notch" Instabilities Resulting From Electron Velocity Dispersion*
Newman, D L
(David.Newman@colorado.edu), University of Colorado at Boulder, Center for Integrated Plasma Studies, 390 UCB, Boulder,
CO 80309-0390, United States
* Goldman, M V
(goldman@stripe.colorado.edu), University of Colorado at Boulder, Center for Integrated Plasma Studies, 390 UCB, Boulder,
CO 80309-0390, United States
The bipolar signatures of weak
(eφmax/Te ≪ 1) electron phase-space holes have
now been observed in numerous near-Earth space-plasma
environments such as the polar cusp region1 and the solar
wind2 at 1 AU. While families of stationary solutions of
the Vlasov-Poisson equations consistent with these
observations have been found,3 the question of how
shallow phase-space density depressions supporting
these bipolar fields form remains an open one. While
strong bipolar fields associated with deep
phase-space holes in Earth auroral downward-current region
are consistent with saturated two-stream instabilities
resulting from double-layer electron acceleration,4 the
weak bipolar fields observed in other space environments may
require an alternative generation mechanism. One such
mechanism involves the formation of narrow minima in the
electron velocity-space distribution resulting from
stretching due to velocity dispersion of
phase-space density minima that are initially localized in
physical space (e.g., constant-density regions with
temperatures greater than their surroundings). These
velocity-space minima, which become narrower as they are
dispersively stretched, eventually cross the threshold
condition for a "notch" instability, which saturates by
forming an expanding series of shallow phase-space holes and
their associated weak bipolar fields. 1-D Vlasov-Poisson
simulations show that this process can be a robust mechanism
for generating a large ensemble of shallow
holes. Simulations with different background electron
distributions show that the properties of the holes that
form depend sensitively on the characteristics of the
embedding plasma environment.
* Research supported by NSF, NASA, and DOE.
1 J. R. Franz, et al., JGR, 110, doi:10.1029/2005JA011095 (2005).
2 A. Mangeney, private communication.
3 M. V. Goldman, et al., this meeting.
4 R. E. Ergun, et al., PRL, 87, 045003 (2001);
D. L. Newman, et al. PRL, 87, 255001 (2001).