Io's contracting atmosphere post 2011 perihelion: Further evidence for partial sublimation support on the anti-Jupiter hemisphere

New 19 μm spectroscopy of Io's SO2 atmosphere in 2012 and 2013, when combined with our earlier observations starting in 2001, provides a near-yearly record of atmospheric density in the lowest scale height, spanning almost an entire jovian year. We find that the anti-Jupiter hemisphere atmospheric density is decreasing following Jupiter's 2011 perihelion passage, confirming our model (Tsang, C.C.C., Spencer, J.R., Lellouch, E., Lopez-Valverde, M.A., Richter, M.J., Greathouse, T.K., [2012]. Icarus 217, 277-296) that the anti-jovian atmosphere has a large sublimation-supported component that peaks near perihelion.