Large scale motions of Neptune's bow shock: Evidence for control of the shock position by the rotation phase of Neptune's magnetic field

Technical Report · Tue Jan 01 04:00:00 EST 1991

OSTI ID:5515178

Cairns, I H; Smith, C W; Kurth, W S; Gurnett, D A; Moses, S L

The Voyager 2 spacecraft observed high levels of Langmuir waves before the inbound crossing of Neptune's bow shock, thereby signifying magnetic connection of the bow shock. The Langmuir waves occurred in multiple bursts throughout two distinct periods separated by an 85 minute absence of wave activity. The times of onsets, peaks, and disappearances of the waves were used together with the magnetic field directions and spacecraft position, to perform a 'remote-sensing' analysis of the shape and location of Neptune's bow shock prior to the inbound bow shock crossing. The bow shock is assumed to have a parabolidal shape with a nose location and flaring parameter determined independently for each wave event. The remote-sensing analysis give a shock position consistent with the time of the inbound shock crossing. The flaring parameter of the shock remains approximately constant throughout each period of wave activity but differs by a factor of 10 between the two periods. The absence of waves between two periods of wave activity coincides with a large rotation of the magnetic field and a large increase in the solar wind ram pressure. The planetwards motion of the shock's nose from 38.5 R(sub N) to 34.5 R(sub N) during the second time period occurred while the solar wind ram pressure remained constant to within 15 percent. This second period of planetwards motion of the shock is therefore strong evidence for Neptune's bow shock moving in response to the rotation of Neptune's oblique, tilted magnetic dipole. Normalizing the ram pressure, the remotely-sensed shock moves sunwards during the first wave period and planetwards in the second wave period. The maximum standoff distance occurs while the dipole axis is close to being perpendicular to the Sun-Neptune direction. The remote-sensing analysis provides strong evidence that the location of Neptune's bow shock is controlled by Neptune's rotation phase.

• Research Organization: Iowa Univ., Iowa City, IA (United States)
• OSTI ID: 5515178
• Report Number(s): N-91-22954; NASA-CR--188059; NAS--1.26:188059; UI--91-3; CNN: NAGW-2040
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
DATA
DIPOLES
EXPERIMENTAL DATA
INFORMATION
MAGNETIC DIPOLES
MAGNETIC FIELDS
MOTION
MULTIPOLES
NEPTUNE PLANET
NUMERICAL DATA
PLANETS
ROTATION
SHOCK WAVES
SOLAR ACTIVITY
SOLAR WIND