Evolution of the cloud field and wind structure of Jupiter's highest speed jet during a huge disturbance

¹ Grupo de Ciencias Planetarias, Dpto. Física Aplicada I, Escuela Técnica Superior de Ingenieros, EHU-UPV, Alda. Urquijo s/n, 48013 Bilbao, Spain e-mail: naiara.barrado@ehu.es
² Esteve Duran Observatory Foundation, c/Montseny 46, 08553 Seva, Spain

Received: 6 April 2009
Accepted: 31 July 2009

Abstract

Aims. Despite the banded visual aspect of cloud patterns in Jupiter, high resolution images indicate that these regions are markedly turbulent. One region of particular interest is the north temperate belt (NTB) at 21° N planetocentric latitude, where the most intense Jovian jet resides with eastward peak speeds of 160-180 m s^-1. Almost every 15 years, the NTB is known to experience an eruption or disturbance that dramatically changes its appearance, a phenomenon known as NTB disturbance (NTBD). In this work, we characterize the morphology of the disturbed cloud field in the wake of the plumes that caused the perturbation, and check for changes in the velocity or shape of the jet.

Methods. The 2007 disturbance was witnessed with unprecedented resolution by the Hubble Space Telescope and by a long-term survey based on the “International Outer Planet Watch” (IOPW) network. Our analysis is based on the brightness spectral distribution to characterize both the typical spatial frequency of the perturbation and its turbulent and wavy nature. We also compare our characterization with non-linear dynamical simulations of the disturbance using the EPIC dynamical model. Finally, we obtain a renewed wind profile for the region of interest by cloud tracking.

Results. We detect a change in the power spectral slope of the cloud brightness following the disturbance that is related to a change in the typical size of the observed structures. We model the initial disturbance as a Rossby wave. A comparison of the jet profile in the NTB just after the disturbance ended (June 2007) with one observed a year later (July 2008), illustrates a net change occurred in the westward jet at 16° N with a speed change of 25 m s^-1. As implied by the power spectra analysis, the disturbance and its related Rossby wave dissipate. We propose that this dissipation produced a momentum transfer to the anticyclonic side of the NTB jet increasing the speed of the westward jet at 16° N as also supported by numerical simulations.