Stability of the sunlit cometary ionopause

Journal Article · Mon Dec 01 04:00:00 EST 1986 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/164840· OSTI ID:6541345

Ershkovich, A I; Flammer, K R; Mendis, D A

The stability of the sheared MHD flow at the sunlit cometary ionopause at several heliocentric distances is examined, taking into account the effects of ion-neutral drag, sources, curvature, and compressibility. If the ionosphere is regarded as a magnetic field-free cavity, whether it is stable or unstable to the Kelvin-Helmholtz (K-H) mode depends on the value of the velocity shear assumed. Also, for any assumed value of the shear the instability is greater for smaller wavelengths (about 100 km) than for larger (at least 1000 km). It is also shown that even if the ionopause is initially unstable, a modest penetration of the interplanetary magnetic field into the ionosphere could lead to its restabilization. Which of the three instabilities, K-H, flute, or drag, dominates depends on the relative magnitude of the shear, the rather uncertain ion-neutral drag coefficient, and the density ratio across the ionopause. The apparent marginal instability of the ionopause of comet Giacobini-Zinner and the stability of the ionopause of comet Halley are explained essentially in terms of the different solar wind conditions encountered by the two comets. 27 references.

• Research Organization: California Univ., La Jolla
• OSTI ID: 6541345
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 311; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COMETS
FLUID MECHANICS
HELMHOLTZ INSTABILITY
HYDRODYNAMICS
INSTABILITY
INTERACTIONS
INTERPLANETARY MAGNETIC FIELDS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MECHANICS
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
SOLAR ACTIVITY
SOLAR WIND