Thermal variability driven by gravity waves in Triton's atmosphere

Context. The thermal structure of Triton’s upper atmosphere has been recognized to be primarily influenced by magnetospheric electron precipitation and solar extreme ultraviolet (EUV) radiation. Gravity waves (GWs) may also act as an important mechanism for redistributing thermal energy, although they have not been directly observed in Triton’s atmosphere. Potential sources of GWs include geyser-like plumes near the surface, energetic particle deposition, and solar radiation. Aims. This study aims to investigate the effects of GWs on the thermal variations in Triton’s upper atmosphere. We investigated the propagation and dissipation of waves with different horizontal wavelengths and phase speeds, and their impacts on the thermospheric temperature structure. Methods. We used a linear full-wave model, in which a Gaussian source is introduced to represent waves excited by geyser-like plumes near the surface. The model examines wave propagation and dissipation over a broad range of temporal and spatial scales and evaluates the resulting heating and cooling effects on the background atmosphere. Results. Our simulations indicate that GWs propagate adiabatically in the lower atmosphere, with density and temperature perturbations anti-phased and with horizontal and vertical velocities in phase. Wave dissipation due to molecular viscosity and thermal conduction occurs in the upper atmosphere, resulting in phase shifts between temperature, density, and velocity perturbations. Wave amplitudes increase with horizontal wavelength and phase speed, with peak amplitudes occurring below 200 km for short-wavelength low-phase speed modes and reaching altitudes of up to 300 km for long-wavelength high-phase speed modes. The maximum temperature and density perturbations are below 5% for short-wavelength modes but increase to nearly 10% for waves with longer horizontal wavelengths. Wave-induced heating is dominated by the sensible heat flux, leading to heating in the lower atmosphere and cooling in the upper atmosphere, with rates on the order of 10−10 erg cm−3 s−1 and an associated energy flux of up to 10−3 erg cm−2 s−1. The associated temperature increase at the exobase ranges from a few kelvins to several tens of kelvins, depending on the horizontal wavelength, and is comparable to heating from solar EUV radiation and magnetospheric particle precipitation. Conclusions. This study demonstrates that GWs play a critical role in modulating the thermal structure of Triton’s upper atmosphere.