Spatial Variations in the Altitude of the CH4 Homopause at Jupiter’s Mid-to-high Latitudes, as Constrained from IRTF-TEXES Spectra
Spatial Variations in the Altitude of the CH4 Homopause at Jupiter’s Mid-to-high Latitudes, as Constrained from IRTF-TEXES Spectra
复制标题
受 IRTF-TEXES 光谱约束的木星中高纬度 CH4 同层顶高度的空间变化
作者：
J. Sinclair;T. Greathouse;R. Giles;A. Antuñano;J. Moses;T. Fouchet;B. Bézard;C. Tao;J. Martín‐Torres;G. Clark;D. Grodent;G. Orton;V. Hue;L. Fletcher;P. Irwin
我们分析了木星中高纬度的IRTF纹理光谱，以检验木星极光地区CH4同层顶高度高于地球其他地方的假设。基于Mosse&Poppe(2017)的一系列光化学模型，在CH4同层顶高度范围内进行了计算。依次采用每个模型，对2019年4月16日和8月20日观测到的H2、S(1)、CH4和CH3排放的纹理光谱进行了反演，允许垂直温度分布发生变化，并用光谱的拟合度来区分模型。在木星主要极光椭圆形赤道以北的纬度(>；62°S，<；54°N，行星中心)，假设同层顶高度低于∼360公里(1巴以上)，观测结果完全符合。在62°N，极光主椭圆内的甲烷同层顶高度为Km，而在同一纬度的主椭圆形外，1σ的上限为370kM。我们的解释是，来自磁层的一部分能量以热量的形式储存在主椭圆形内，这推动了垂直风和/或更高的湍流率，并将CH4及其光化学副产品输送到更高的海拔。在北部主要极光椭圆形内，也需要∼3甲烷丰度增加的因素来拟合光谱。这可能是由于光化学模拟中的不确定性，或者是木星极光区域产生CH3的另一个来源。
We present an analysis of IRTF-TEXES spectra of Jupiter’s mid-to-high latitudes in order to test the hypothesis that the CH4 homopause altitude is higher in Jupiter’s auroral regions compared to elsewhere on the planet. A family of photochemical models, based on Moses & Poppe (2017), were computed with a range of CH4 homopause altitudes. Adopting each model in turn, the observed TEXES spectra of H2 S(1), CH4, and CH3 emission measured on 2019 April 16 and August 20 were inverted, the vertical temperature profile was allowed to vary, and the quality of the fit to the spectra was used to discriminate between models. At latitudes equatorward of Jupiter’s main auroral ovals (>62°S, <54°N, planetocentric), the observations were adequately fit assuming a homopause altitude lower than ∼360 km (above 1 bar). At 62°N, inside the main auroral oval, we derived a CH4 homopause altitude of km, whereas outside the main oval at the same latitude, a 1σ upper limit of 370 km was derived. Our interpretation is that a portion of energy from the magnetosphere is deposited as heat within the main oval, which drives vertical winds and/or higher rates of turbulence and transports CH4 and its photochemical by-products to higher altitudes. Inside the northern main auroral oval, a factor of ∼3 increase in CH3 abundance was also required to fit the spectra. This could be due to uncertainties in the photochemical modeling or an additional source of CH3 production in Jupiter’s auroral regions.