Photoionization modeling of Titan’s dayside ionosphere

• Previous modeling studies of Titan’s dayside ionosphere predicts electron numberdensities roughly a factor of 2 higher than observed by the RPWS/Langmuir probe. The issuecan equivalently be described as that the ratio between the calculated electron productionrates and the square of the observed electron number densities result in roughly a factor of4 higher effective recombination coefficient than expected from the ion composition and theelectron temperature. Here we make an extended reassessment of Titan’s dayside ionizationbalance focusing on 34 flybys between TA and T120. Using a re-calibrated dataset and bytaking the presence of negative ions into account we arrive at lower effective recombinationcoefficients compared with earlier studies. The values are still higher than expected from theion composition and the electron temperature, but by a factor of ~2 − 3 instead of a factorof ~4. We have also investigated whether the derived effective recombination coefficientsdisplay dependencies on parameters such as the solar zenith angle, the integrated solar EUVintensity (< 80 nm) and the corotational plasma ram direction and found statisticallysignificant trends which may be explained by a declining photoionization against thebackground ionization by magnetospheric particles (SZA, RAM) and altered photochemistry(EUV). We find that a series of flybys that occurred during solar minimum (2008) and withsimilar flyby geometries are associated with enhanced values of the effective recombinationcoefficient compared with the remaining dataset, which also suggests a chemistry dependenton the sunlight conditions.

Ämnesord

NATURVETENSKAP  -- Fysik -- Fusion, plasma och rymdfysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Fusion, Plasma and Space Physics (hsv//eng)

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