A Global Average Titan Dayside Ionosphere Model: Comparisons with Cassini Data

Solar photoionization and ionization from electrons originating in the magnetosphere of Saturn interact with the upper atmosphere of Titan and create an ionosphere. On the dayside of Titan, it has been shown that the solar ionization mechanism is the dominant source of the ionosphere. Instruments aboard the Cassini spacecraft have provided in situ data of the composition of the upper atmosphere and the ionosphere. Measurements from the Ion-Neutral Mass Spectrometer (INMS) will be emphasized and used to determine global average neutral densities for the upper atmosphere and ionosphere. Ion production rates are calculated for a variety of solar zenith angles and between 800 and 2000 km. A photochemical model with 78 ion species and 601 reactions uses these ion production rates to predict ion and electron density profiles, which are compared with Cassini data for selected dayside flybys. INMS inferred total electron densities below 1000 km are lower than those reported by RPWS-LP, with the probable explanation being that this is due to heavy ions with mass numbers greater than 100 daltons, which INMS cannot detect. We have updated the heavy mass ion chemistry in our model in order to interpret these results. We also use the model to explore the possible effects of magnetospheric electron precipitation on the dayside ionosphere.