Global climate modeling of Saturn's atmosphere. Part IV: stratospheric equatorial oscillation

Abstract

The Composite InfraRed Spectrometer (CIRS) on board Cassini revealed an equatorial oscillation of stratospheric temperature, reminiscent of the Earth's Quasi-Biennial Oscillation (QBO), as well as anomalously high temperatures under Saturn's rings. To better understand these predominant features of Saturn's atmospheric circulation in the stratosphere, we have extended towards higher altitudes the DYNAMICO-Saturn global climate model (GCM), already used in a previous publication to study the tropospheric dynamics, jets formation and planetary-scale waves activity. Firstly, we study the higher model top impact on the tropospheric zonal jets and kinetic energy distribution. Raising the model top prevents energy and enstrophy accumulation at tropopause levels. The reference GCM simulation with 1/2${}^{\circ }$ latitude/longitude resolution and a raised model top exhibits a QBO-like oscillation produced by resolved planetary-scale waves. However, the period is more irregular and the downward propagation faster than observations. Furthermore, compared to the CIRS observation retrievals, the modeled QBO-like oscillation underestimates by half both the amplitude of temperature anomalies at the equator and the vertical characteristic length of this equatorial oscillation. This QBO-like oscillation is mainly driven by westward-propagating waves; a significant lack of eastward wave-forcing explains a fluctuating eastward phase of the QBO-like oscillation. At 20${}^{\circ }$N and 20${}^{\circ }$S latitudes, the DYNAMICO-Saturn GCM exhibits several strong seasonal eastward jets, alternatively in the northern and southern hemisphere. These jets are correlated with the rings' shadowing. Using a GCM simulation without rings' shadowing, we show its impact on Saturn's stratospheric dynamics. Both residual-mean circulation and eddy forcing are impacted by rings' shadowing.

arXiv comment54 pages, 23 figures, revised version submitted to Icarus

References in corpus (10)

• Formation of Jets and Equatorial Superrotation on Jupiter
• Mechanisms of jet formation on the giant planets
• Generation of equatorial jets by large-scale latent heating on the giant planets
• Atmospheric Circulation of Brown Dwarfs and Jupiter and Saturn-like Planets: Zonal Jets, Long-term Variability, and QBO-type Oscillations
• Geophysical turbulence and the duality of the energy flow across scales
• Global climate modeling of Saturn's atmosphere. Part II: multi-annual high-resolution dynamical simulations
• Seasonal Evolution of Saturn's Polar Temperatures and Composition
• Disruption of Saturn's Quasi-Periodic Equatorial Oscillation by the Great Northern Storm
• Stratospheric aftermath of the 2010 Storm on Saturn as observed by the TEXES instrument. I. Temperature structure
• Investigating the Semiannual Oscillation on Mars using data assimilation

Cited by in corpus (4)

• First direct measurement of auroral and equatorial jets in the stratosphere of Jupiter
• Mapping the zonal winds of Jupiter's stratospheric equatorial oscillation
• Storms and convection on Uranus and Neptune: impact of methane abundance revealed by a 3D cloud-resolving model
• Warm Jupiters around M-dwarfs are great opportunities for extensive chemical, cloud and haze characterisation with JWST