CONTROL ID: 2071105 SUBMISSION ROLE: Regular DPS Abstract DATE/TIME CREATED: August 20, 2014, 11:31 AM TITLE: Characterization of the lower layer in the dayside Venus ionosphere ABSTRACT BODY: Abstract (2,250 Maximum Characters): The dayside Venus ionosphere consists of two layers: the V2 layer at 141 km, produced by solar extreme ultraviolet (EUV) photons, and the V1 layer at 127 km, produced by solar soft X-rays. The influence of solar zenith angle (SZA) and solar irradiance has been well characterized for the V2 layer, but not the V1 layer, where previous efforts were limited by data scarcity and incomplete SZA coverage. Here we use over 200 radio occultation profiles from Venus Express to characterize how the V1 peak altitude, peak density, and morphology respond to changes in SZA and solar activity. The V1 and V2 peak altitudes do not vary with SZA, and both peak electron densities vary with SZA in a Chapman-like manner. These results imply that the thermal structures of the atmosphere and ionosphere between 141 km and 127 km vary little with SZA. Also, the V1 peak density increases more with solar activity than the V2 peak density and the V1 morphology can change much more than the V2 morphology. These results are due to the soft X-ray flux increasing relative to the EUV flux as solar activity increases. PRESENTATION TYPE: Poster CURRENT * CATEGORY: Venus | Mars: Atmosphere CURRENT : None | None AUTHORS (FIRST NAME, LAST NAME): Zachary Girazian1, Paul Withers1, Martin Paetzold2, Silvia Tellmann2, Kerstin Peter2 INSTITUTIONS (ALL): 1. Boston Univ., Boston, MA, United States. 2. University of Cologne, Cologne, Germany. Contributing Teams: