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Garca-Melendo E.,Fundacio Observatori Esteve Duran | Sanchez-Lavega A.,University of the Basque Country | Legarreta J.,University of the Basque Country | Perez-Hoyos S.,University of the Basque Country | Hueso R.,University of the Basque Country
Geophysical Research Letters | Year: 2010

Here we report the discovery at the upper cloud level of an extremely narrow and strong prograde jet, centered in the middle of the broad equatorial jet. Measurements from images obtained by the Cassini Imaging Science Subsystem (ISS) show that the jet reaches 430 ms-1 16 m s-1 with a peak speed difference of 180 ms-1 relative to nearby latitudes at 60 mbar and 390 ms-1 23 m s-1 at depths > 500 mbar spanning ∼6 about the equator . Contrarily to what is observed in other latitudes, its velocity increases with altitude. This jet is the first of its kind to be discovered on any of the giant planets, and adds to our three-dimensional understanding of Saturn's stratospheric wind field. © 2010 by the American Geophysical Union.

Legarreta J.,University of the Basque Country | Barrado-Izagirre N.,University of the Basque Country | Sanchez-Lavega A.,University of the Basque Country | Gomez-Forrellad J.M.,Fundacio Observatori Esteve Duran
Astronomy and Astrophysics | Year: 2016

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. © 2016 ESO.

Sanchez-Lavega A.,University of the Basque Country | Wesley A.,Acquerra Pty. Ltd. | Orton G.,Jet Propulsion Laboratory | Hueso R.,University of the Basque Country | And 12 more authors.
Astrophysical Journal Letters | Year: 2010

On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55°S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory in the opposite direction and with a lower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4800km east-west and 2500km north-south, with those produced by the SL9 fragments and dynamical calculations of pre-impact orbit indicates that the impactor was most probably an icy body with a size of 0.5-1km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890nm and K (2.03-2.36 μm) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary clouds. © 2010 The American Astronomical Society. All rights reserved.

Garcia-Melendo E.,Fundacio Observatori Esteve Duran | Garcia-Melendo E.,Institute Of Ciencies Of Lespai Csic Ieec | Hueso R.,University of the Basque Country | Sanchez-Lavega A.,University of the Basque Country | And 4 more authors.
Nature Geoscience | Year: 2013

Saturn's Great White Spots are rare planetary-scale storms that have been observed only six times since 1876. The most recent Great White Spot appeared in December 2010 and has been studied from both ground-based and spacecraft observations. The storm developed into an enormous disturbance extending over 10,000 km at cloud level, emitted intense electrostatic discharges over several months, and caused long-standing localized warming in the high stratosphere of about 60 K. Here we analyse the dynamics of the storm's head using high-resolution imagery obtained by the Cassini spacecraft on 26 February 2011. We find strong winds with speeds up to 160 m s-1 and organized into a divergent open anticyclone where massive cumulus-like cloud clusters interact with the ambient zonal flow to generate a storm front. The cloud clusters evolved over a timescale of hours, with cloud tops reaching 44 km above the undisturbed environment. Simulations using a general circulation model, which includes Saturn's zonal winds, reproduce the observations when a persistent heat source is introduced, causing a high-pressure anomaly. We conclude that the complex phenomenology of a mature Great White Spot represents a natural response of the saturnian atmosphere to severe sustained convection in a sheared background flow. © 2013 Macmillan Publishers Limited. All rights reserved.

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