Program: GN-2019B-Q-212

In the three decades since Voyager 2 encountered Neptune, sporadic thermal infrared (7-20 micron) observations have revealed puzzling temporal variations in the atmospheric circulation of this archetypal ice giant. Despite considerable variability in Neptune's weather activity observed in the past decade, our last Gemini/TEXES characterisation of Neptune's atmosphere (2007), near Neptune's southern summer solstice, is being used as the benchmark for planning JWST observations. Surprisingly, these observations did not detect the enhanced emission from Neptune's southern summer vortex, despite its presence since at least 2003. We propose to repeat our successful 2007 observations to assess variability over the past decade, searching for evidence of seasonal evolution and hydrocarbon enhancements within the summer polar vortex, changes in stratospheric ethane emission related to time-variable dynamics, and spatial contrasts in temperatures associated with forcing by storm activity. These observations, proposed shortly after Neptune's 2019 opposition, will establish a new, well-calibrated baseline ahead of JWST observations in 2021-22. Spectral mapping of Neptune in 2019, compared with identical measurements 12 years (one Neptunian month) earlier, would constrain the variability of Neptune's stratospheric circulation and chemistry as the archetype for a seasonally-influenced ice giant.