Neptune's NDS-2018: The Dark Vortex That Would Not Die
Follow-up HST observations instead found that the equatorward motion of the vortex had arrested, or even reversed, with the most recent latitude being 18.3 deg N on 23 June 2020. Under the standard zonal wind profile, which was measured by tracking CH4-ice clouds in Voyager data (Sromovsky et al. 1993, Icarus, DOI 10.1006/icar.1993.1114), simulations predict an equatorward drift about 10 times faster than observed in 2018-2019 (Hadland et al. 2020, MNRAS, DOI 10.1093/mnras/staa1799). We will present numerical simulations using the EPIC code, which indicate that the equatorward migration is slower if the vortex intensity (rotation speed) is reduced, or if there is higher meridional shear in the zonal winds, compared to the Sromovsky et al. (1993) winds.