99 research outputs found
New Horizons Solar Wind Around Pluto (SWAP) Observations of the Solar Wind From 11-33 AU
The Solar Wind Around Pluto (SWAP) instrument on NASA's New Horizon Pluto
mission has collected solar wind observations en route from Earth to Pluto, and
these observations continue beyond Pluto. Few missions have explored the solar
wind in the outer heliosphere making this dataset a critical addition to the
field. We created a forward model of SWAP count rates, which includes a
comprehensive instrument response function based on laboratory and flight
calibrations. By fitting the count rates with this model, the proton density
(n), speed (V), and temperature (T) parameters are determined. Comparisons
between SWAP parameters and both propagated 1 AU observations and prior Voyager
2 observations indicate consistency in both the range and mean wind values.
These comparisons as well as our additional findings confirm that small and
midsized solar wind structures are worn down with increasing distance due to
dynamic interaction of parcels of wind with different speed. For instance, the
T-V relationship steepens, as the range in V is limited more than the range in
T with distance. At times the T-V correlation clearly breaks down beyond 20 AU,
which may indicate wind currently expanding and cooling may have an elevated T
reflecting prior heating and compression in the inner heliosphere. The power of
wind parameters at shorter periodicities decreases with distance as the longer
periodicities strengthen. The solar rotation periodicity is present in
temperature beyond 20 AU indicating the observed parcel temperature may reflect
not only current heating or cooling, but also heating occurring closer to the
Sun.Comment: 55 pages, 29 Figures, accepted for publication in The Astrophysical
Journal Supplements (ApJS
Dynamics of a geomagnetic storm on 7–10 September 2015 as observed by TWINS and simulated by CIMI
For the first time, direct comparisons of the equatorial ion partial pressure
and pitch angle anisotropy observed by TWINS and simulated by CIMI are
presented. The TWINS ENA images are from a 4-day period, 7–10 September
2015. The simulations use both the empirical Weimer 2K and the
self-consistent RCM electric potentials. There are two moderate storms in
succession during this period. In most cases, we find that the general
features of the ring current in the inner magnetosphere obtained from the
observations and the simulations are similar. Nevertheless, we do also see
consistent contrasts between the simulations and observations. The simulated
partial pressure peaks are often inside the observed peaks and more toward
dusk than the measured values. There are also cases in which the measured
equatorial ion partial pressure shows multiple peaks that are not seen in the
simulations. This occurs during a period of intense AE index. The CIMI
simulations consistently show regions of parallel anisotropy spanning the
night side between approximately 6 and 8 RE, whereas the
parallel anisotropy is seen in the observations only during the main phase of
the first storm. The evidence from the unique global view provided by the
TWINS observations strongly suggests that there are features in the ring
current partial pressure distributions that can be best explained by enhanced
electric shielding and/or spatially localized, short-duration injections.</p
JUPITER's AURORAL RADIO SPECTRUM
Juno's first perijove science observations were carried out on 27 August 2016. The 90° orbit inclination and 4163 km periapsis altitude provide the first opportunity to explore Jupiter's polar magnetosphere. A radio and plasma wave instrument on Juno called Waves provided a new view of Jupiter's auroral radio emissions from near 10 kHz to ~30 MHz. This frequency range covers the classically named decametric, hectometric, and broadband kilometric radio emissions, and Juno observations showed much of this entire spectrum to consist of V-shaped emissions in frequency-time space with intensified vertices located very close to the electron cyclotron frequency. The proximity of the radio emissions to the cyclotron frequency along with loss cone features in the energetic electron distribution strongly suggests that Juno passed very close to, if not through, one or more of the cyclotron maser instability sources thought to be responsible for Jupiter's auroral radio emissions
Response of Jupiter's auroras to conditions in the interplanetary medium as measured by the Hubble Space Telescope and Juno
We present the first comparison of Jupiter's auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought
Magnetosphere dynamics during the 14 November 2012 storm inferred from TWINS, AMPERE, Van Allen Probes, and BATS-R-US–CRCM
During the 14 November 2012 geomagnetic storm, the Van Allen Probes spacecraft observed a number of sharp decreases
(dropouts) in particle fluxes for ions and electrons of different energies. In this paper, we investigate the global
magnetosphere dynamics and magnetosphere–ionosphere (M–I) coupling during the dropout events using multipoint
measurements by Van Allen Probes, TWINS, and AMPERE together with the output of the two-way coupled global BATS-R-US–CRCM
model. We find different behavior for two pairs of dropouts. For one pair, the same pattern was repeated: (1)Â weak
nightside Region 1 and 2 Birkeland currents before and during the dropout; (2) intensification of Region 2 currents after
the dropout; and (3) a particle injection detected by TWINS after the dropout. The model predicted similar behavior of
Birkeland currents. TWINS low-altitude emissions demonstrated high variability during these intervals, indicating high
geomagnetic activity in the near-Earth tail region. For the second pair of dropouts, the structure of both Birkeland
currents and ENA emissions was relatively stable. The model also showed quasi-stationary behavior of Birkeland currents
and simulated ENA emissions with gradual ring current buildup. We confirm that the first pair of dropouts was caused by
large-scale motions of the OCB (open–closed boundary) during substorm activity. We show the new result that this OCB
motion was associated with global changes in Birkeland (M–I coupling) currents and strong modulation of low-altitude ion
precipitation. The second pair of dropouts is the result of smaller OCB disturbances not related to magnetospheric
substorms. The local observations of the first pair of dropouts result from a global magnetospheric reconfiguration, which
is manifested by ion injections and enhanced ion precipitation detected by TWINS and changes in the structure of Birkeland
currents detected by AMPERE. This study demonstrates that multipoint measurements along with the global model results
enable the reconstruction of a more complete system-level picture of the dropout events and provides insight into M–I
coupling aspects that have not previously been investigated
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