Jupiter's Equatorial Plumes and Hot Spots: Spectral 2 Mapping from Gemini/TEXES and Juno/MWR

We present multi-wavelength measurements of the thermal, chemical, and cloud contrasts associated with the visibly dark formations (also known as 5-m hot spots) and intervening bright plumes on the boundary between Jupiter's Equatorial Zone (EZ) and North Equatorial Belt (NEB). Observations made by the TEXES 5-20 micron spectrometer at the Gemini North Telescope in March 2017 reveal the upper-tropospheric properties of 12 hot spots, which are directly compared to measurements by Juno using the Microwave Radiometer (MWR), JIRAM at 5 m, and JunoCam visible images. MWR and thermal-infrared spectroscopic results are consistent near 0.7 bar. Mid-infrared-derived aerosol opacity is consistent with that inferred from visible-albedo and 5-micron opacity maps. Aerosol contrasts, the defining characteristics of the cloudy plumes and aerosol-depleted hot spots, are not a good proxy for microwave brightness. The hot spots are neither uniformly warmer nor ammonia-depleted compared to their surroundings at p < 1 bar. At 0.7 bar, the microwave brightness at the edges of hot spots is comparable to other features within the NEB. Conversely, hot spots are brighter at 1.5 bar, signifying either warm temperatures and/or depleted NH3 at depth. Temperatures and ammonia are spatially variable within the hot spots, so the precise location of the observations matters to their interpretation. Reflective plumes sometimes have enhanced NH3, cold temperatures, and elevated aerosol opacity, but each plume appears different. Neither plumes nor hot spots had microwave signatures in channels sensing p > 10 bars, suggesting that the hot-spot/plume wave is a relatively shallow feature.

本研究报道了木星赤道带（Equatorial Zone, EZ）与北赤道带（North Equatorial Belt, NEB）边界处，可见暗结构（亦称5微米热点（5-m hot spots））与其间亮羽流所关联的热学、化学与云系多波长观测反差。2017年3月，研究团队借助双子座北望远镜（Gemini North Telescope）搭载的TEXES 5-20微米光谱仪开展观测，揭示了12个热点的对流层上层大气特征，并将该结果与朱诺号（Juno）搭载的微波辐射计（Microwave Radiometer, MWR）、5微米波段JIRAM以及朱诺相机（JunoCam）可见光图像的测量结果进行了直接对比。微波辐射计与热红外光谱观测结果在0.7巴压强处吻合良好。中红外反演得到的气溶胶光学厚度，与从可见光反照率及5微米光学厚度图中推断的结果一致。作为云系羽流与气溶胶贫化热点的标志性特征，气溶胶反差并不能作为微波亮度的有效替代指标。在压强低于1巴的区域，热点既未整体温度高于周边环境，也未出现氨贫化现象。在0.7巴处，热点边缘的微波亮度与北赤道带内的其他大气结构相当；与之相反，在1.5巴处热点的微波亮度更高，这表明其深层大气存在温度升高和/或氨贫化现象。热点内部的温度与氨分布存在空间变化，因此观测的精确位置对结果解读至关重要。具有高反照率的羽流有时会表现出氨富集、温度偏低以及气溶胶光学厚度升高的特征，但每个羽流的特性均存在个体差异。无论是羽流还是热点，在探测压强高于10巴的微波通道中均未呈现出特征信号，这表明热点-羽流结构是一种相对浅层的大气特征。