The Cassini spacecraft detected a surprisingly large temporal temperature variability of 60 Kin Titan's upper atmosphere during multiple flybys. Previous efforts examining such a variability focused on the role of radiative heating but were unable to explain the observations. Analytic estimates of the wave energy fluxes have suggested that wave heating might be an important process affecting the thermal structure of the upper atmosphere. However, approaches to date have been highly idealized and have not described wave propagation rigorously. Here, we implement an anelastic linearized wave model adopting the Wentzel‐Kramers‐Brillouin approximation that adequately describes wave propagation in Titan's upper atmosphere, where the observed vertical wavelengths are several times larger than the density scale height. Our results show that the wave heating and cooling rates generated by molecular diffusion of monochromatic waves are larger than those found in previous studies. The energy fluxes associated with wave dissipation can exceed that of the combined solar extreme ultraviolet (EUV) heating and HCN rotational line cooling. Compared to the wave‐free, mean‐state temperature, the wave energy fluxes associated with certain wave modes can produce a temperature variability as large as 20 K, which is larger than that driven by magnetospheric particle precipitation but still smaller than that observed. Our results suggest that wave heating and cooling are important processes that can modify the thermal structure of Titan's upper atmosphere and also suggest that additional processes such as wave breaking and molecular diffusion of a spectrum of waves should be considered in future studies.

中文翻译：

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土卫六上层大气的温度变化：波耗散的作用

卡西尼号飞船在多次飞越过程中检测到60 Kin Titan的高空的惊人的瞬时温度变化。先前检查这种变异性的努力集中在辐射加热的作用上，但无法解释这些观察结果。波浪能通量的分析估计表明，波浪加热可能是影响高层大气热结构的重要过程。然而，迄今为止的方法已经高度理想化，并且没有严格描述波的传播。在这里，我们采用Wentzel-Kramers-Brillouin近似来实现非弹性线性化波模型，该模型充分描述了在泰坦高层大气中的波传播，在该高层大气中，所观察到的垂直波长是密度标高的几倍。我们的结果表明，由单色波的分子扩散产生的波加热和冷却速率比以前的研究中发现的要大。与波消散相关的能量通量可能超过太阳极紫外（EUV）加热和HCN旋转线冷却相结合的能量通量。与无波平均温度相比，与某些波模相关的波能通量可产生高达20 K的温度变化，该温度变化大于磁层颗粒降水驱动的温度变化，但仍小于观测到的温度变化。我们的结果表明，波浪加热和冷却是可以改变Titan's热结构的重要过程。