N. Barrado-Izagirre

Jupiter’s zonal winds and their variability studied with small-size telescopes

Context. The general circulation of Jupiter’s atmosphere at cloud level is dominated by a system of zonal jets that alternate in direction with latitude. The winds, measured in high-resolution images obtained by different space missions and the Hubble Space Telescope, are overall stable in their latitude location with small changes in intensity at particular jets. However, the atmosphere experiences repetitive changes in the albedo of particular belts and zones that are subject to large-scale intense disturbances that may locally influence the profile. Aims. The lack of high-resolution images has not allowed the wind system to be studied with the regularity required to assess its stability with respect to these major changes or to other types of variations (e.g., seasonality). To amend that, we present a study of the zonal wind profile of Jupiter using images acquired around the 2011 opposition by a network of observers operating small-size telescopes with apertures in the range 0.20−1 m. Methods. Using an automatic correlation technique, we demonstrate the capability to extract the mean zonal winds in observing periods close to the opposition. A broad collaboration with skilled amateur astronomers opens the possibility to regularly study shortand long-term changes in the jets of Jupiter. Results. We compare the 2011 Jovian wind profile to those previously obtained. The winds did not experience significant short-term changes over 2011 but show noteworthy variations at particular latitudes when compared with wind profiles from previous years. Most of these variations are related to major changes in the cloud morphology of the planet, in particular at 7◦ N where an intense eastward jet varies around 40 ms−1 in its intensity according to the development or not of the “dark projection” features, confirming previous results.

An Enduring Rapidly Moving Storm as a Guide to Saturn's Equatorial Jet's Complex Structure

Saturn has an intense and broad eastward equatorial jet with a complex three-dimensional structure mixed with time variability. The equatorial region experiences strong seasonal insolation variations enhanced by ring shadowing, and three of the six known giant planetary-scale storms have developed in it. These factors make Saturns equator a natural laboratory to test models of jets in giant planets. Here we report on a bright equatorial atmospheric feature imaged in 2015 that moved steadily at a high speed of 450 ms−1 not measured since 1980–1981 with other equatorial clouds moving within an ample range of velocities. Radiative transfer models show that these motions occur at three altitude levels within the upper haze and clouds. We find that the peak of the jet (latitudes 10° N to 10° S) suffers intense vertical shears reaching +2.5 ms−1 km−1, two orders of magnitude higher than meridional shears, and temporal variability above 1 bar altitude level.

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.

Turbulence in Jupiter’s Clouds

We have studied the spatial distribution of Jupiter’s higher clouds in order to characterize the turbulent regime and the presence of waves in this planet’s atmosphere. We have used images from the Hubble Space Telescope (HST) 1995’s archive and from Cassini’s ISS camera during its Jupiter fly-by in its way to Saturn in 2000 in three wavelengths: near infrared (∼940nm), blue (∼430nm) and ultraviolet (∼260nm). These images were cylindrically projected and composed to obtain complete planispheres of Jupiter that cover the latitudinal range from 60∘N to 60∘S. When applying the Fast Fourier Transform (FFT) to each latitude reflectivity scan, we obtain brightness power spectra and periodograms that show the presence of wavy phenomena. From the spectra we study the decay of the slopes and their possible correlation with the underlying turbulent regime. We compare the turbulent structure of Jupiter’s clouds with the dynamic structure characterized by the latitudinally alternating zonal wind regime (East–West) and with the meridional wind shear.