New Observations and Modelling of a QBO-Like Oscillation in Jupiter's Stratosphere

Abstract

We present a new analysis of the “quasi-quadrennial” oscillation (QQO), a quasi-periodic oscillation of longitude-mean temperatures and winds occurring at low latitudes in Jupiter's stratosphere that may be a phenomenon closely related to Earth's quasi-biennial oscillation (Leovyet al.1991,Nature354, 380–382). Measurements of 7.8-μm thermal emission from the jovian stratosphere acquired during the period 1991–1995 extend observations of this oscillation for an additional cycle beyond those presented in Ortonet al.(1991,Science252, 537–542), showing that this ∼4-yr-period signal has persisted for at least 15 yr. Numerical simulations of the QQO are performed to compare the brightness temperature patterns obtained to the groundbased measurements. By coupling these simulations with a radiative transfer model, we find that the amplitude of the oscillation must be significantly larger than previously estimated by Leovyet al.(1991). Long-period, large-scale equatorial waves on Jupiter are found to be ineffective in driving a QQO that produces the observed amplitude of the brightness temperature oscillations. Simulations in which the wave driving occurs through the interaction of small-scale, short-period gravity waves with their critical levels produce a QQO whose associated brightness temperature variations are in much better agreement with the observations. The amplitude of the QQO predicted by these simulations is large, suggesting that it may have a very significant effect on Jupiter's stratospheric thermal structure at low latitudes, some of which may be apparent in the vertical temperature profiles measured by the Galileo Atmospheric Structure Instrument and by the Voyager 1 radio occultation experiment.