Premium
Solar cycle modulation of Titan's ionosphere
Author(s) -
Edberg N. J. T.,
Andrews D. J.,
Shebanits O.,
Ågren K.,
Wahlund J.‒E.,
Opgenoorth H. J.,
Cravens T. E.,
Girazian Z.
Publication year - 2013
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/jgra.50463
Subject(s) - ionosphere , atmospheric sciences , physics , solar cycle 23 , solar zenith angle , solar minimum , titan (rocket family) , solar cycle , solar maximum , solar irradiance , electron density , computational physics , plasma , astronomy , solar wind , quantum mechanics
During the six Cassini Titan flybys T83–T88 (May 2012 to November 2012) the electron density in the ionospheric peak region, as measured by the radio and plasma wave science instrument/Langmuir probe, has increased significantly, by 15–30%, compared to previous average. These measurements suggest that a long‒term change has occurred in the ionosphere of Titan, likely caused by the rise to the new solar maximum with increased EUV fluxes. We compare measurements from TA, TB, and T5, from the declining phase of solar cycle 23 to the recent T83–T88 measurements during cycle 24, since the solar irradiances from those two intervals are comparable. The peak electron densities normalized to a common solar zenith angle N norm from those two groups of flybys are comparable but increased compared to the solar minimum flybys (T16–T71). The integrated solar irradiance over the wavelengths 1–80nm, i.e., the solar energy flux, F e , correlates well with the observed ionospheric peak density values. Chapman layer theory predicts thatN norm ∝ F e k , with k =0.5. We find observationally that the exponent k =0.54±0.18. Hence, the observations are in good agreement with theory despite the fact that many assumptions in Chapman theory are violated. This is also in good agreement with a similar study by Girazian and Withers (2013) on the ionosphere of Mars. We use this power law to estimate the peak electron density at the subsolar point of Titan during solar maximum conditions and find it to be about 6500cm −3 , i.e., 85–160% more than has been measured during the entire Cassini mission.