Characterising Saturn's vertical temperature structure from Cassini/CIRS
Characterising Saturn's vertical temperature structure from Cassini/CIRS
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DOI：
10.1016/j.icarus.2007.02.006
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发表时间：
2007-08-01
期刊：
影响因子：
3.2
通讯作者：
Taylor, F. W.
中科院分区：
文献类型：
--
作者：
Fletcher, L. N.;Irwin, P. G. J.;Taylor, F. W.
卡西尼号复合红外光谱仪以15厘米(-1)的光谱分辨率和1度-2度的空间分辨率获得了土星在10-1400厘米(-1)范围内的热红外光谱[Flasar，F.M.和44名同事，2004年。太空科学。第115版，169-297版]。使用最优估计检索代码来分析在18个月的观测期间获得的数千个光谱[Irwin，P.G.J.，Parrish，P.，Fuchet，T.，Calutt，S.B.，Taylor，F.W.，Simon-Miller，A.A.，Nixon，C.A.，2004。伊卡洛斯172，37-49]，以恢复土星北半球(冬季)和南半球(夏季)的温度结构和对氢分布。为了研究对流层顶高度(65-90mbar)的季节不对称性、辐射-对流边界的位置(350-500mbar)以及温度膝部(150-300mbar)随纬度的变化，对垂直温度结构进行了详细的分析，这是在Voyager/IRIS光谱的反演中首次观察到的[Hanel，R.，和15个同事，1981]。科学212,192-200；Hanel，R.，Conrath，B.，Flasar，F.M.，坤德，V.，Maguire，W.，珀尔，J.C.，Pirraglia，J.，Samuelson，R.，Cruikshank，D.P.，Gautier，D.，Gierasch，P.J.，Horn，L.，Ponnamperuma，C.，1982。科学215,544-548]。由于光谱吸收的模型(碰撞诱导吸收系数、对流层雾霾、氦丰度)和我们的反演算法的性质而引起的不确定性被量化。在1mbar附近的平流层温度显示北极和南极之间的25-30K温差。这种不对称性随着深度的增加而变得不那么明显，因为大气响应的辐射时间常数在更深的气压水平下增加。当气压大于100mbar时，与纬向风有关的半球对称的小尺度温度结构被叠加到温度不对称上。100-400mbar范围内的对氢含量大于对南半球和北半球部分地区的平衡预测，而在极地低于40度的平衡预测。150-300mbar之间的温度膝部夏季半球大于冬季，赤道较小且较高，赤道带较深且较大，两极较小。对流层雾霾的太阳加热被认为是这种效应的一种可能机制；南半球垂直氢气转化效率的增加与夏半球更大气溶胶的存在是一致的，我们证明这与以前对土星对流层气溶胶分布的研究定性一致。(C)2007 Elsevier Inc.保留所有权利。
Thermal infrared spectra of Saturn from 10-1400 cm(-1) at 15 cm(-1) spectral resolution and a spatial resolution of 1 degrees-2 degrees latitude have been obtained by the Cassini Composite Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space Sci. Rev. 115, 169-297]. Many thousands of spectra, acquired over eighteen-months of observations, are analysed using an optimal estimation retrieval code [Irwin, P.G.J., Parrish, P., Fouchet, T., Calcutt, S.B., Taylor, F.W., Simon-Miller, A.A., Nixon, C.A., 2004. Icarus 172, 37-49] to retrieve the temperature structure and para-hydrogen distribution over Saturn's northern (winter) and Southern (summer) hemispheres. The vertical temperature structure is analysed in detail to study seasonal asymmetries in the tropopause height (65-90 mbar), the location of the radiative-comective boundary (350-500 mbar), and the variation with latitude of a temperature knee (between 150 and 300 mbar) which was first observed in inversions of Voyager/IRIS spectra [Hanel, R., and 15 colleagues, 1981. Science 212, 192-200; Hanel, R., Conrath, B., Flasar, F.M., Kunde, V., Maguire, W., Pearl, J.C., Pirraglia, J., Samuelson, R., Cruikshank, D.P., Gautier, D., Gierasch, P.J., Horn, L., Ponnamperuma, C., 1982. Science 215, 544-548]. Uncertainties due to both the modelling of spectral absorptions (collision-induced absorption coefficients, tropospheric hazes, helium abundance) and the nature of our retrieval algorithm are quantified.Temperatures in the stratosphere near 1 mbar show a 25-30 K temperature difference between the north pole and south pole. This asymmetry becomes less pronounced with depth as the radiative time constant for the atmospheric response increases at deeper pressure levels. Hemispherically-symmetric small-scale temperature structures associated with zonal winds are superimposed onto the temperature asymmetry for pressures greater than 100 mbar. The para-hydro.-en fraction in the 100-400 mbar range is greater than equilibrium predictions for the southern hemisphere and parts of the northern hemisphere, and less than equilibrium predictions polewards of 40 degrees N.The temperature knee between 150-300 mbar is larger in the summer hemisphere than in the winter, smaller and higher at the equator, deeper and larger in the equatorial belts and small at the poles. Solar heating on tropospheric haze is proposed as a possible mechanism for this effect; the increased efficiency of ortho- to pora-hydrogen conversion in the southern hemisphere is consistent with the presence of larger aerosols in the Summer hemisphere, which we demonstrate to be qualitatively consistent with previous studies of Saturn's tropospheric aerosol distribution. (C) 2007 Elsevier Inc. All rights reserved.