J. Legarreta

A planetary‐scale disturbance in the most intense Jovian atmospheric jet from JunoCam and ground‐based observations

We describe a huge planetary-scale disturbance in the highest-speed Jovian jet at latitude 23.5°N that was first observed in October 2016 during the Juno perijove-2 approach. An extraordinary outburst of four plumes was involved in the disturbance development. They were located in the range of planetographic latitudes from 22.2° to 23.0°N and moved faster than the jet peak with eastward velocities in the range 155 to 175 m s 1. In the wake of the plumes, a turbulent pattern of bright and dark spots (wave number 20–25) formed and progressed during October and November on both sides of the jet, moving with speeds in the range 100–125 m s 1 and leading to a new reddish and homogeneous belt when activity ceased in late November. Nonlinear numerical models reproduce the disturbance cloud patterns as a result of the interaction between local sources (the plumes) and the zonal eastward jet.

A large active wave trapped in Jupiter’s equator

Context. A peculiar atmospheric feature was observed in the equatorial zone (EZ) of Jupiter between September and December 2012 in ground-based and Hubble Space Telescope (HST) images. This feature consisted of two low albedo Y-shaped cloud structures (Y1 and Y2) oriented along the equator and centred on it (latitude 0.5°-1°N). Aims. We wanted to characterize these features, and also tried to find out their properties and understand their nature. Methods. We tracked these features to obtain their velocity and analyse their cloud morphology and the interaction with their surroundings. We present numerical simulations of the phenomenon based on one- and two-layer shallow water models under a Gaussian pulse excitation. Results. Each Y feature had a characteristic zonal length of ~15° (18?000 km) and a meridional width (distance between the north-south extremes of the Y) of 5° (6000 km), and moved eastward with a speed of around 20-40 m?s-1 relative to Jupiter’s mean flow. Their lifetime was 90 and 60 days for Y1 and Y2, respectively. In November, both Y1 and Y2 exhibited outbursts of rapidly evolving bright spots emerging from the Y vertex. The Y features were not visible at wavelengths of 255 or 890 nm, which suggests that they were vertically shallow and placed in altitude between the upper equatorial hazes and the main cloud deck. Numerical simulations of the dynamics of the Jovian equatorial region generate Kelvin and Rossby waves, which are similar to those in the Matsuno-Gill model for Earth’s equatorial dynamics, and reproduce the observed cloud morphology and the main properties the main properties of the Y features.

Spectral comparison and stability of red regions on Jupiter

A rare red cyclone visible on Jupiter in 1994 and 1995 falls in a class of vortices that are intensely colored, yet low altitude, unlike the Great Red Spot (GRS). Dynamical modeling indicates that the presence of nearby anticyclones both aids in formation and lead to the destruction of the cyclone. A study of absolute spectral reflectance from Hubble Space Telescope imaging data shows that GRS is not typically the “reddest” region of the planet. Rather, transient red cyclones and the reddest parts of the North Equatorial Belt show less reflectance than the GRS at all wavelengths, with enhanced absorption at wavelengths near 500 nm. Temporal analysis shows that the darkest regions of the North Equatorial Belt and transient red cyclones are relatively constant in color from 1995 to 2014, while the spectral slope and absolute brightness of the GRS core vary over time. Laboratory data of colored materials that yield a good qualitative fit to the GRS spectrum do not match the spectra of other regions, and wavelengths from 400 to 700 nm may be most diagnostic of chromophore identification.