Galileo probe measurements of thermal and solar radiation fluxes in the Jovian atmosphere
Galileo probe measurements of thermal and solar radiation fluxes in the Jovian atmosphere
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伽利略探测器测量木星大气中的热通量和太阳辐射通量
DOI：
10.1029/98je01048
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发表时间：
1998
影响因子：
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通讯作者：
R. Freedman
中科院分区：
文献类型：
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作者：
L. Sromovsky;A. Collard;P. Fry;G. Orton;M. Lemmon;M. Tomasko;R. Freedman
伽利略探测器的净通量辐射计（NFR）测量了木星大气中的辐射通量，范围约为0.44至14巴，使用五个光谱通道来分离太阳和热成分。机载校准结果证实，NFR对辐射的响应大致符合预期。NFR通道也会响应叠加的热扰动，这可以通过盲通道测量和物理约束近似地消除。预期的NH3云的证据可以在太阳直射光束信号的自旋诱导调制的光谱特征中看到。这些结果与覆盖在0.5 μm处光学深度为1.5-2的NH3小冰粒云（半径0.5 - 0.75 μm）相一致。这种云对热通量的影响很小，因此NFR热通道对其性质没有额外的限制。然而，在NFR热通道中，在0.45巴附近加热的证据似乎需要在这个小颗粒云之外的额外不透明源，这意味着云结构不均匀，以避免与太阳调制结果冲突，或者温度下降率恰好在探测器测量值之上发生变化。大的热通量水平意味着水汽混合比在10巴时仅为太阳的6%，但可能随着深度而增加，并且在低于3巴的压力下显著亚饱和氨。如果探测器进入地点的深层NH3混合比是地面推断值的3-4倍，正如探测器无线电信号衰减所表明的那样，那么只需一半的水就可以匹配NFR观测值。在5巴水平附近没有发现水云的证据。5 μm热通道在1.35 bar附近检测到假定的NH4SH云基。这种云的影响也出现在太阳通道上升通量测量中，但没有出现在太阳净通量中，这意味着这种云是阳光的保守散射体。该云的微小热特征与颗粒半径在3 μm附近相一致，但不能排除更小的颗粒。在深度超过3 bar的区域，太阳通道对波长大于0.6 μm的太阳光的吸收出乎意料地大，这可能是由于NH3在0.65 ~ 1.5 μm之间的吸收。
The Galileo probe net flux radiometer (NFR) measured radiation fluxes in Jupiter's atmosphere from about 0.44 to 14 bars, using five spectral channels to separate solar and thermal components. Onboard calibration results confirm that the NFR responded to radiation approximately as expected. NFR channels also responded to a superimposed thermal perturbation, which can be approximately removed using blind channel measurements and physical constraints. Evidence for the expected NH3 cloud was seen in the spectral character of spin-induced modulations of the direct solar beam signals. These results are consistent with an overlying cloud of small NH3 ice particles (0.5–0.75 μm in radius) of optical depth 1.5–2 at 0.5 μm. Such a cloud would have so little effect on thermal fluxes that NFR thermal channels provide no additional constraints on its properties. However, evidence for heating near 0.45 bar in the NFR thermal channels would seem to require either an additional opacity source beyond this small-particle cloud, implying a heterogeneous cloud structure to avoid conflicts with solar modulation results, or a change in temperature lapse rate just above the probe measurements. The large thermal flux levels imply water vapor mixing ratios that are only 6% of solar at 10 bars, but possibly increasing with depth, and significantly subsaturated ammonia at pressures less than 3 bars. If deep NH3 mixing ratios at the probe entry site are 3–4 times ground-based inferences, as suggested by probe radio signal attenuation, then only half as much water is needed to match NFR observations. No evidence of a water cloud was seen near the 5-bar level. The 5-μm thermal channel detected the presumed NH4SH cloud base near 1.35 bars. Effects of this cloud were also seen in the solar channel upflux measurements but not in the solar net fluxes, implying that the cloud is a conservative scatterer of sunlight. The minor thermal signature of this cloud is compatible with particle radii near 3 μm, but it cannot rule out smaller particles. Deeper than about 3 bars, solar channels indicate unexpectedly large absorption of sunlight at wavelengths longer than 0.6 μm, which might be due to unaccounted-for absorption by NH3 between 0.65 and 1.5 μm.