Excitations From Impact: The Affect of CMEs on Venus' Mysterious Oxygen Green Line and Ionospheric Electrons. An Auroral Process?

Friday, 19 December 2014
Candace Gray1, Nancy Chanover1, Tom G Slanger2, Karan Molaverdikhani3, Bernd Häusler4, Silvia Tellmann5 and Kerstin Peter5, (1)New Mexico State University Main Campus, Department of Astronomy, Las Cruces, NM, United States, (2)SRI Intl, Menlo Park, CA, United States, (3)University of Colorado at Boulder - LASP, Boulder, CO, United States, (4)Universität der Bundeswehr, Institut für Raumfahrttechnik, München, Germany, (5)University of Cologne, Cologne, Germany
Observations of nightglow (upper atmospheric emission from atoms and molecules on the nightside of a planet) allow for a multifaceted study of planetary atmospheres. Information on winds, chemistry, and solar effects is gained by observing temporal and spatial variation in nightglow intensity. One of the brightest nightglow features on Earth is the OI (1S-1D) 557.7 nm line (oxygen green line). This emission is primarily due to photodissociation/transport but is also seen in the aurora as electron precipitation. Unlike Earth, the Venusian green line is highly temporally variable. The chemistry and mechanisms responsible are still unknown. We observe the Venusian nightglow before and after solar flares, which produce large amounts of EUV emission, and coronal mass ejections (CMEs) impacts, which inject a large number of higher energy charged particles in the the Venusian atmosphere. We consistently detect green line emission after large charged particles injections from CMEs. However we do not detect the OI (1D) red line at 630.0 nm, which is quenched below 150 km. We propose that the Venusian green line is an auroral-type emission due to electron precipitation and is occurring deep in the atmosphere, near 125 km. To investigate how CMEs and solar flares affect the electron energy, flux, and density in the Venusian nightside atmosphere, we compare data taken by ASPERA and ELS onboard Venus Express (VEX) before and after solar storms. We find that both electron energy and flux increase after CMEs, but only flux increases after solar flares. Additionally, the V1 ionospheric layer at 125 km increases in electron density while the V2 at 150 km decreases in density after CMEs but not after solar flares. We model the nightside Venusian ionosphere using the observed electron energy and fluxes from VEX in an effort to constrain the chemical processes and mechanisms responsible for green line emission. We will present the results of our ground-based observations and modeling.