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Brandt J. C. Snow M. Yi Y. Larson S. M. Mikuz H. Petersen C. C. Liller W. 《Earth, Moon, and Planets》2002,90(1-4):15-33
The plasma tails of comets clearly show the demarcation of the solar wind into distinct equatorial and polar regions (Brandt
and Snow (2000), Icarus
148, 52–64).The boundary is determined by the maximum extent in latitude of the heliospheric current sheet (HCS). The observational
record contains many well-observed equatorial comets, but observations of comets in the polar region are relatively rare.
In addition to its size and brightness, comet Hale–Bopp had an orbital inclination of 89.4° and was well observed for months
in the polar region. We document the comet's large-scale appearance throughout the apparition, including the polar region
and its transition into the equatorial region. The bright dust tail hampered observations of the plasma tail, particularly
near the head, but images taken with a CO+ filter show a very large disconnection event (DE) on May 7 and May 8, 1997. The time of disconnection is estimated at approximately
May 4.0. This DE is associated with a crossing of the HCS. The model calculations of the HCS indicate that other crossings
might have occurred in late April, but given the uncertainty in the calculation, the comet might have missed the HCS. Sparse
observational coverage and the bright dust tail prevent further investigation of the potential earlier HCS crossings. The
plasma tail shows anomalous orientations at the highest latitudes and possible explanations are discussed. 相似文献
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The paper presents the results of dynamic simulation for the dust tail formation of comet C/1995 O1 (Hale-Bopp). To simulate
the dust tail, the trajectories of 2 × 106 dust particles were traced. The sizes, ejection moments, outflow directions and velocities of the dust particles were defined
by the Monte Carlo algorithm. The obtained three-dimensional tail was projected on the sky plane to compare it with the observed
images. The brightness distribution in the comet tail was fitted to similar model parameters for three different dates. According
to our model experiments, the observed tails could be formed by particles with sizes from 0.3 to 8.0 μm, ejection velocities
from 0.155 to 0.670 km/s, and power index of the exponential size distribution from −3.6 to −3.7. It is shown that the inclusion
of the particles fragmentation processes leads to a noticeable improvement of the simulation results. 相似文献
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Images of comet Hyakutake (C/1996 B2) are analyzed in conjunction with solar wind data from spacecraft to determine the relationship between solar wind conditions and plasma tail morphology. The disconnection event (DE) on March 25, 1996 is analyzed with the aid of data from the IMP-8 and WIND Earth-orbiting spacecraft and the DE is found to be correlated with a crossing of the heliospheric current sheet. The comet was within of Earth at the time of the DE and data from IMP-8 and WIND show no high-speed streams, significant density enhancements or shocks.The latitudinal variation in the appearance and orientation of the plasma tail are interpreted based on results from the Ulysses spacecraft. In the polar solar wind region, the comet has a relatively undisturbed appearance, no DEs were observed, and the orientation of the plasma tail was consistent with a higher solar wind speed. In the equatorial solar wind region, the comet's plasma tail had a disturbed appearance, a major DE was observed, and the orientation of the plasma tail was consistent with a lower solar wind speed. The boundary between the equatorial and polar regions crossed by comet Hyakutake in April 1996 was near 30°N (ecliptic) or 24°N (solar) latitude. 相似文献
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