| Summary: | Using near-infrared observations of Neptune from the Keck and Lick Observatories, and the Hubble Space Telescope in combination with amateur datasets, we calculated the drift rates of prominent infrared-bright cloud features on Neptune between 2018 and 2021. These features had lifespans of ~ 1 day to ≥ 1 month and were located at mid-latitudes and near the south pole. Our observations permitted determination of drift rates via feature tracking. These drift rates were compared to three zonal wind profiles describing Neptune's atmosphere determined from features tracked in H band (1.6 µm), K' band (2.1 µm), and Voyager 2 data at visible wavelengths. Features near -70 deg measured in the F845M filter (845 nm) were particularly consistent with the K' wind profile. The southern mid-latitudes hosted multiple features whose lifespans were ≥ 1 month, providing evidence that these latitudes are a region of high stability in Neptune's atmosphere. We also used HST F467M (467 nm) data to analyze a dark, circumpolar wave at -60° latitude observed on Neptune since the Voyager 2 era. Its drift rate in recent years (2019–2021) is 4.866 ± 0.009°/day. This is consistent with previous measurements by Karkoschka (2011), which predict a 4.858 ± 0.022°/day drift rate during these years. It also gained a complementary bright band just to the north. © 2023 Elsevier Inc. Thank you to the two anonymous referees whose comments helped improve the manuscript tremendously. This work has been supported by the National Science Foundation, NSF Grant AST-1615004 to UC Berkeley. Many of the images were obtained with the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation, United States. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of ...
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