Long-term Near-IR Observations of Neptunes Atmosphere

Using near-infrared data spanning from 2001 to 2021 taken with NIRC2 on the Keck telescope, the Shane Telescope at Lick Observatory, the Hubble Space Telescope, and amateur astronomer data, we conducted long-term observations of clouds in Neptunes atmosphere. Analysis included calculating cloud coverage, characteristic cloud brightness, I/F measurements of the disk, and drift rates of major cloud features. Drift rates were calculated from cloud features visible on multiple days between 2018 and 2020 in H band (1.6 m), K band (2.2 m), and 845nm data. These were combined with drift rates of major cloud features appearing in the amateur data and were compared to previously calculated zonal wind profiles. From our analysis of Neptunes cloud coverage, characteristic cloud brightness, and I/F measurements using H band and 845nm data, we noted a distinct period of reduced cloud activity and disk brightness in late 2019 and throughout 2020. This observation, together with the discovery of Neptunes Northern Great Dark Spot in 2018 (Simon et al., 2019, GRL, 10.1029/2019GL081961) is suggestive of recent changes in the dynamics of Neptunes deeper atmosphere.