Temporal Behavior of Stratospheric Ammonia Abundance and Temperature Following the SL9 Impacts
Temporal Behavior of Stratospheric Ammonia Abundance and Temperature Following the SL9 Impacts
复制标题
SL9 撞击后平流层氨丰度和温度的时间行为
DOI：
10.1006/icar.2001.6804
复制
发表时间：
2002
期刊：
影响因子：
3.2
通讯作者：
T. Livengood
中科院分区：
文献类型：
--
作者：
K. Fast;T. Kostiuk;P. Romani;F. Espenak;T. Hewagama;A. Betz;R. T. Boreiko;T. Livengood
1994年7月，苏梅克-利维9号彗星碎片与木星在碎片G和K的撞击地点发生碰撞，观测到了平流层氨(NH3)的红外发射线。A.Betz等人获得了10.7μm附近的红外外差光谱。(见Shoemaker-Levy 9彗星特别会议摘要，行星科学部第26次会议，华盛顿特区，1994年10月31日-11月4日，第25页)使用威尔逊山上的一个红外空间干涉仪望远镜系统。在撞击后，在∼107的分辨率下多次测量了多达三条不同NH3发射线的线形。我们给出了多个振荡线的全分辨谱线形状的辐射传递分析。这一分析提供了撞击后18d内温度结构和NH3丰度分布及其时间变化的信息。这些结果与光化学模型进行了比较，以确定SL9撞击后木星平流层中NH3的破坏和稀释中光化学和其他机制的作用。在G撞击后的一天，推算出0.001毫巴高度以上的温度为283±13K，与最近的烟柱溅射模型一致。第四天平流层上层冷却到204K，一周后静止，这与简单的灰色大气辐射通量计算和与冷木星空气的混合是一致的。在撞击后的前4天，NH3主要存在于1mbar以上的高度，1d后的柱密度为(7.7±1.6)×1017 cm−2，4d后的柱密度为(3.7±0.8)×1017 cm−2。(错误代表精度。)我们从一个大的彗星碎片中获得的NH3是氮的2.5倍，这表明NH3主要来自木星。到撞击后18d，G区恢复到静止的平流层上层温度，平流层下部NH3柱密度为7.3×1017 cm−2或更大，这可能是由于NH3上涌穿过冲击加热的湍流对流层顶提供的，这可能被初始的沙尘和霾所掩盖。在1mbar水平以上，最大回收柱密度降至6.5×1016 cm−2。与光化学模型的比较表明，即使忽略了NH3的化学转化，单靠光解也不足以解释到那时NH3在1mbar以上的损失。我们推测，羽流物质在高海拔(1mbar以上)的弥散是撞击后几天观察到的光谱变化的原因。关于K撞击区域的数据提供了定性一致的结果。
Abstract Infrared emission lines of stratospheric ammonia (NH 3 ) were observed following the collisions of the fragments of Comet Shoemaker–Levy 9 with Jupiter in July of 1994 at the impact sites of fragments G and K. Infrared heterodyne spectra near 10.7 μm were obtained by A. Betz et al. (in Abstracts for Special Sessions on Comet Shoemaker-Levy 9, The 26th Meeting of the Division for Planetary Sciences, Washington DC, 31 Oct.–4 Nov. 1994 , p. 25) using one of the Infrared Spatial Interferometer telescope systems on Mount Wilson. Lineshapes of up to three different NH 3 emission lines were measured at a resolving power of ∼10 7 at multiple times following the impacts. We present here our radiative transfer analysis of the fully resolved spectral lineshapes of the multiple rovibrational lines. This analysis provides information on temperature structure and NH 3 abundance distributions and their temporal changes up to 18 days after impact. These results are compared to photochemical models to determine the role of photochemistry and other mechanisms in the destruction and dilution of NH 3 in the jovian stratosphere after the SL9 impacts. One day following the G impact, the inferred temperature above 0.001 mbar altitude is 283±13 K, consistent with a recent plume splashback model. Cooling of the upper stratosphere to 204 K by the fourth day and to quiescence after a week is consistent with a simple gray atmosphere radiative flux calculation and mixing with cold jovian air. During the first 4 days after impact, NH 3 was present primarily at altitudes above 1 mbar with a column density of (7.7±1.6)×10 17 cm −2 after 1 day and (3.7±0.8)×10 17 cm −2 after 4 days. (Errors represent precision.) We obtained >2.5 times more NH 3 than can be supplied by nitrogen from a large cometary fragment, suggesting a primarily jovian source for the NH 3 . By 18 days postimpact, a return to quiescent upper stratospheric temperature is retrieved for the G region, with an NH 3 column density of 7.3×10 17 cm −2 or more in the lower stratosphere, possibly supplied by NH 3 upwelling across an impact-heated and turbulent tropopause, which may have been masked by initial dust and haze. Above the 1-mbar level, the maximum retrieved column density decreased to 6.5×10 16 cm −2 . Comparison to photochemical models indicates that photolysis alone is not sufficient to account for the loss of NH 3 above 1 mbar by that time, even when chemical reformation of NH 3 is ignored. We speculate that the dispersion of plume material at high altitudes (above 1 mbar) is responsible for the change in the spectra observed a few days postimpact. Data on the K impact region provide qualitatively consistent results.