Atmospheric Waves and Their Possible Effect on the Thermal Structure of Saturn's Thermosphere

Abstract

Atmospheric waves have been discovered for the first time in Saturn's neutral upper atmosphere (thermosphere). Waves may be generated from instabilities, convective storms or other atmospheric phenomena. The inferred wave amplitudes change little with height within the sampled region, raising the possibility of the waves being damped, which in turn may enhance the eddy friction within the thermosphere. Using our Saturn Thermosphere Ionosphere General Circulation Model, we explore the parameter space of how an enhanced Rayleigh drag in different latitude regimes would affect the global circulation pattern within the thermosphere and, in turn, its global thermal structure. We find that Rayleigh drag of sufficient magnitude at midlatitudes may reduce the otherwise dominant Coriolis forces and enhance equatorward winds to transport energy from poles toward the equator, raising the temperatures there to observed values. Without this Rayleigh drag, energy supplied into the polar upper atmosphere by magnetosphere‐atmosphere coupling processes remains trapped at high latitudes and causes low‐latitude thermosphere temperatures to remain well below the observed levels. Our simulations thus suggest that giant planet upper atmosphere global circulation models need to include additional Rayleigh drag in order to capture the effects of physical processes otherwise not resolved by the codes.

Saturn’s near-equatorial ionospheric conductivities from in situ measurements

“…1a). The profiles marked "model" are the Pedersen conductivities based on the GCM 24 and are shown for reference. www.nature.com/scientificreports www.nature.com/scientificreports/ time between orbits is nearly constant, ≈6.5 days).…”

Magnetosphere‐Ionosphere‐Thermosphere Coupling at Jupiter Using a Three‐Dimensional Atmospheric General Circulation Model

“…In actuality, Jupiter's magnetic field is tilted with respect to its rotation axis and has very complex structure (e.g., Connerney et al, 2018). The next step in the development of the presented model is to include a more realistic magnetic field model (e.g., Connerney et al, 2018) including realistic mapping from the magnetosphere to the ionosphere and LT variation, a more detailed ionosphere model (e.g., Blelly et al, 2019), and parameterizations allowing for the incorporation of atmospheric waves (e.g., Tao et al, 2009;Müller-Wodarg et al, 2019). Such a complex asymmetric interaction region would lead to different neutral flow and heating structures which cannot be simulated with the current model setup.…”

“…The JIM and JTGCM models, while not self-consistently coupling the atmosphere and magnetosphere, do employ more realistic magnetic field models at the planet, which is one of the main reasons that their findings are different from those presented above. The next step in the development of the presented model is to include a more realistic magnetic field model (e.g., Connerney et al, 2018) including realistic mapping from the magnetosphere to the ionosphere and LT variation, a more detailed ionosphere model (e.g., Blelly et al, 2019), and parameterizations allowing for the incorporation of atmospheric waves (e.g., Tao et al, 2009;Müller-Wodarg et al, 2019). This model will be the most realistic three-dimensional representation of Jupiter's coupled magnetosphere-atmosphere system.…”

“…Other sources of heat, such as wave heating (Müller-Wodarg et al, 2019;Tao et al, 2009), need to be included in the model as well as a better understanding of the distant magnetospheric plasma flows. Other sources of heat, such as wave heating (Müller-Wodarg et al, 2019;Tao et al, 2009), need to be included in the model as well as a better understanding of the distant magnetospheric plasma flows.…”

“…Jupiter's thermosphere is ∼ 700 K (∼ 4.5 times) hotter than predicted (e.g., Seiff et al, 1998;Strobel & Smith, 1973;Yelle & Miller, 2004). Recently, Müller-Wodarg et al (2019) discovered atmospheric waves present in Saturn's thermosphere. This is known as the giant planet energy crisis.…”