EPIC Modeling of Large Scale Dynamical Features of the Gas Giants Nathan Hadland (1), Ramanakumar Sankar (1), Chloe Klare (1), Csaba Palotai (1), Kevin Farmer (2), and Raymond Paul LeBeau Jr (2) (1) Department of Aerospace, Physics, and Space Sciences, Florida Institute of Technology, USA, (2) Aerospace and Mechanical Engineering, Saint Louis University Main Campus, Saint Louis, USA (nhadland2016@my.fit.edu) Abstract We use the Explicit Planetary Isentropic Coordinate General Circulation Model (EPIC GCM), which in- cludes an explicit calculation of cloud microphysics for various condensing species (e.g. ammonia, wa- ter, methane and hydrogen sulfide) to investigate dy- namical features observed in gas giant atmospheres. The evolution of these features are strongly coupled to the structure of the atmosphere, and thus, these mod- els help constrain the temperature structure, composi- tion and winds speeds on these planets. We present results from our study of Jupiter’s 24°N jet and Nep- tune’s dark spots. On Jupiter, we simulate the forma- tion of convective plumes, which are driven by latent heat release from water condensation. Our initial re- sults show that the convective activity is strongly con- strained to specific latitude bands, likely due to the meridional temperature structure. On Neptune, we study the shape oscillations and latitudinal drift of the GDS-89 and more recent vortices such as the Northern Dark Spot (NDS-2018). The dark spot shows a sharp contrast in the methane vapor density within and out- side the vortex. We present results of the drift rate and shape oscillation, which match previous studies, and also a radiative transfer analysis relating the change in albedo within the vortex to the dynamics of the atmo- sphere. 1. Neptune Vortices A recent observation as part of Hubble Outer Planet Atmosphere Legacy (OPAL) program revealed a new dark spot with bright companion clouds in Neptune’s northern hemisphere, NDS-2018. The structure is the most recent of large scale geophysical features to be observed on the ice giants, and their dynamical prop- erties need to be further constrained. The anticy- clonic structures exhibit surprising variability in terms of vortex evolution, shape, drift, cloud distribution, and shape oscillations. In the case of the Great Dark Spot observed by the Voyager spacecraft (GDS-89), equatorial drift was observed [1, 2] as opposed to the poleward drift of other recent dark spots, such as the SDS-2015 [3, 4]. These observations can be used to diagnose the local atmospheric conditions. An analysis of overlying orographic cloud features shows promising insight into the dynamics of clouds on Neptune, as the features are directly impacted by the underlying atmospheric structure. To that end, it is necessary to apply a cloud microphysical model to make a more complete representation of dark spots. Consequently, we use an updated microphysics calcu- lation implemented in the Explicit Planetary Isentropic Coordinate (EPIC) GCM [5, 6] to account for the con- densation of methane, and we investigate the dynamics of vapor and subsequent cloud formation on Neptune by modelling large scale vortices. We seek to answer the following questions: (i) What causes the "darkness" of large scale vortices? (ii) How does the effect of active methane condensation affect the evolution of the vortex? (iii) How is the vorticity in the spot coupled to the vapor field? To investigate these questions, we use an increased grid resolution and increased number of vertical layers in the column compared to previous studies. 1.1 Results We run up to 100 day simulations to investigate sta- bility, drift rate, and companion clouds throughout the model, with the ultimate goal of achieving similari- ties to the observations of GDS-89 and other vortices. Influencing factors include initial vortex coordinates, size, and velocity as well as atmospheric deep abun- dance and relative humidity of methane. As shown in Figure 1, we match the equatorial drift of the GDS and show that in terms of vapor, the spot grows as the vor- EPSC Abstracts Vol. 13, EPSC-DPS2019-745-1, 2019 EPSC-DPS Joint Meeting 2019 c  Author(s) 2019. CC Attribution 4.0 license.