The extension of ionospheric holes into the tail of Venus

Abstract

Ionospheric holes are Cytherian nightside phenomena discovered by the NASA Pioneer Venus Orbiter, featuring localized plasma depletions driven by prominent and unexplained enhancements in the draped interplanetary magnetic field. Observed only during solar maximum, the phenomenon remains unexplained, despite their frequent observation during the first 3 years of the mission and more than 30 years having elapsed since their first description in the literature. We present new observations by the European Space Agency Venus Express showing that ionospheric holes can extend much further into the tail than previously anticipated (1.2 to 2.4 planetary radii) and may be observed throughout the solar cycle and over a wide range of solar wind conditions. We find that ionospheric holes are a manifestation of a deeper underlying phenomenon: tubes of enhanced draped interplanetary magnetic field that emerge in pairs from below the ionosphere and stretch far down the tail. We speculate on two possible explanations for the magnetic fields underlying the phenomena: magnetic pileup due to stagnation of ionospheric flow and internal draping around a metallic core.

Solar Wind Interaction and Impact on the Venus Atmosphere

“…Indeed the ionospheric holes (e.g. Collinson et al 2014b) are not yet well-reproduced by the models. The matter of bulk removal of ionospheric ions by fluid instabilities, and their importance for ion escape (e.g.…”

“…Further out in the tail (1.2-2.4 R V ) the size of the holes is larger and the magnetic enhancements weaker. In fact, for the holes to be observable in the tail the background magnetic field has to be weak, which may explain why only eleven event were detected in the VEX data from 2006-2012 (Collinson et al 2014b). These observations raise the possibility that the dayside penetrated fields and fields in the nightside ionospheric holes fields may be connected, but the participation of the lower atmosphere and interior of Venus in the solar wind interaction is still largely unexplored (but see .…”

The impact of a slow interplanetary coronal mass ejection on Venus

“…We will now discuss the magnetic and plasma conditions inside the ICME and contrast them with the typical solar wind and IMF at Venus. As with previous investigations at Venus [e.g., Marubashi et al , ; Luhmann and Russell , ; Collinson et al , ], with no spacecraft in the immediate vicinity of Venus to monitor upstream conditions, we are forced to use a technique whereby the Venus Express proxies as its own solar wind “monitor.” IMF and solar wind proton moments were averaged during two ≈3 h periods approximately h apart: Inbound to the planet when ICME strength was still increasing and then again outbound, close to the peak of the storm.…”

Vortex Structure in the Plasma Flow Channels of the Venus Wake

“…In fact, along the VEX trajectory in the 19 May 2010 orbit reported in Figure 2 of [8] (between 05:21:37 and 05:30:15 UT) the spacecraft is located by 0.73 < Y < 0.87 R V and between Z = −0.12 and Z = 0.21 R V and thus far from the midnight plane and close to the equatorial plane, and also far from a magnetic polar region since 1.45 < X < 1.72 R V . Consequently, the statement indicated in [8] in the sense that H+ ions fluxes are not measured at the time when the Venus Express is within an ionospheric hole is incorrect. In fact, the spectra of the decelerated solar wind protons shown in Figure 3 were obtained as the spacecraft traveled through a plasma channel in the close vicinity of a magnetic polar region near the midnight plane.…”

“…Vortex Structure in the Plasma Flow Channels of the Venus Wake http://dx.doi.org/10.5772/66762 of ~keV solar wind proton fluxes in an ionospheric hole reported from VEX measurements at large angles from the midnight plane and in the vicinity of the equator [8] (see their Section 4.2). In fact, along the VEX trajectory in the 19 May 2010 orbit reported in Figure 2 of [8] (between 05:21:37 and 05:30:15 UT) the spacecraft is located by 0.73 < Y < 0.87 R V and between Z = −0.12 and Z = 0.21 R V and thus far from the midnight plane and close to the equatorial plane, and also far from a magnetic polar region since 1.45 < X < 1.72 R V . Consequently, the statement indicated in [8] in the sense that H+ ions fluxes are not measured at the time when the Venus Express is within an ionospheric hole is incorrect.…”