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A Statistical Study of Ionospheric Boundary Wave Formation at Venus.

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Title: A Statistical Study of Ionospheric Boundary Wave Formation at Venus.
Authors: Chong, Ghai Siung1 gschong1@sheffield.ac.uk, Pope, Simon A.1, Walker, Simon N.1, Frahm, Rudy A.2, Zhang, Tielong3,4, Futaana, Yoshifumi5
Source: Journal of Geophysical Research. Space Physics. Sep2018, Vol. 123 Issue 9, p7668-7685. 18p.
Subject Terms: *Atmospheric evolution, Venusian atmosphere, Magnetic fields, Photoelectrons, Planetary ionospheres
Abstract: Previous missions to Venus have revealed that encounters with plasma irregularities of atmospheric origin outside the atmosphere are not uncommon. A number of mechanisms have been proposed to discuss their origins as well as their roles in the atmospheric evolution of Venus. One such mechanism involves an ionopause with a wavelike appearance. By utilizing the magnetic field and plasma data from Venus Express, we present the first observational statistical analysis of the ionospheric boundary wave phenomena at Venus using data from 2006 to 2014. Results from the minimum variance analysis of all the photoelectron dropout events in the ionosphere reveal that the ionopause of Venus does not always appear to be smooth but often exhibits a wavelike appearance. In the northern polar region of Venus, the normal directions of the rippled ionospheric boundary crossings lie mainly in the terminator plane with the largest component predominantly along the dawn‐dusk (YVSO) direction. The average estimated wavelength of the boundary wave is 212 ± 12 km, and the average estimated velocity difference across the ionopause is 104 ± 6 km/s. The results suggest that the rippled boundary is a result of Kelvin‐Helmholtz instability. Analysis reveals a correlation between the normal directions and the locations of the boundary wave with respect to Venus. This indicates that the draping of magnetic field lines may play a role in enhancing the plasma flow along the dawn‐dusk direction, which could subsequently set up a velocity shear that favors the excitation of ionospheric boundary wave by the Kelvin‐Helmholtz instability along the dawn‐dusk direction. Key Points: The ionospheric boundary is not always smooth; it is often observed to exhibit a wavelike appearanceCharacteristics of the boundary wave are consistent with a Kelvin‐Helmholtz instability‐induced waveDraping patterns of magnetic field lines set up favorable conditions for boundary wave excitation [ABSTRACT FROM AUTHOR]
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Abstract:Previous missions to Venus have revealed that encounters with plasma irregularities of atmospheric origin outside the atmosphere are not uncommon. A number of mechanisms have been proposed to discuss their origins as well as their roles in the atmospheric evolution of Venus. One such mechanism involves an ionopause with a wavelike appearance. By utilizing the magnetic field and plasma data from Venus Express, we present the first observational statistical analysis of the ionospheric boundary wave phenomena at Venus using data from 2006 to 2014. Results from the minimum variance analysis of all the photoelectron dropout events in the ionosphere reveal that the ionopause of Venus does not always appear to be smooth but often exhibits a wavelike appearance. In the northern polar region of Venus, the normal directions of the rippled ionospheric boundary crossings lie mainly in the terminator plane with the largest component predominantly along the dawn‐dusk (YVSO) direction. The average estimated wavelength of the boundary wave is 212 ± 12 km, and the average estimated velocity difference across the ionopause is 104 ± 6 km/s. The results suggest that the rippled boundary is a result of Kelvin‐Helmholtz instability. Analysis reveals a correlation between the normal directions and the locations of the boundary wave with respect to Venus. This indicates that the draping of magnetic field lines may play a role in enhancing the plasma flow along the dawn‐dusk direction, which could subsequently set up a velocity shear that favors the excitation of ionospheric boundary wave by the Kelvin‐Helmholtz instability along the dawn‐dusk direction. Key Points: The ionospheric boundary is not always smooth; it is often observed to exhibit a wavelike appearanceCharacteristics of the boundary wave are consistent with a Kelvin‐Helmholtz instability‐induced waveDraping patterns of magnetic field lines set up favorable conditions for boundary wave excitation [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2018JA025644