Vertical cloud structure of Uranus from UKIRT/UIST observations and changes seen during Uranus' northern spring equinox from 2006 to 2008
Vertical cloud structure of Uranus from UKIRT/UIST observations and changes seen during Uranus' northern spring equinox from 2006 to 2008
复制标题
UKIRT/UIST 观测得出的天王星垂直云结构以及 2006 年至 2008 年天王星北春分点期间的变化
DOI：
10.1016/j.icarus.2009.05.003
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发表时间：
2009
期刊：
影响因子：
3.2
通讯作者：
Irwin P
中科院分区：
文献类型：
--
作者：
Irwin P
利用联合王国红外线望远镜Uist仪器在2006年、2007年和2008年对天王星进行的长缝光谱观测，监测了2007年12月天王星北半球春分期间天王星垂直和纬度云结构的变化。对沿天王星中心子午线狭缝观测到的长J(1.17-1.31μm)和H(1.45-1.65μm)波段的反射光谱，用最优估计反演模式进行了拟合，确定了较宽纬度范围内0.1~6-8bar的垂直云廓线。多个光谱波段的背景图像被用来区分一般的纬向云结构变化和经过的离散云。从2006年到2007年，气压在2到6-8bar之间的深云反射在所有纬度都有所增加，尽管通过外推Irwin等人的甲烷系数，绝对气压水平存在一些系统性的不确定性。(Irwin，P.G.J.，Sromovsky，L.A.，Strong，E.K.，Sihra，K.，Teanby，N.A.，Bowles，N.，Calutt，S.B.，Remedios，J.J.[2006]Icarus，181,309-319)，如Tomasko等人所指出的。以及Karkoschka和Tomasko(Tomasko，M.G.，Bezard，B.，Doose，L.，Engel，S.，Karkoschka，E.空间科学，56,624-647；Karkoschka，E.，Tomasko，M.[2009]Icarus)。然而，从2007年到2008年，这些云在整个南半球和南北中纬度(30°N，S)的反射减弱。因此，与中纬度相比，位于45°S的南极圈亮度减弱，位于45°N的类似圈变得更加突出(例如Rages，K.A.，Hammel，H.B.，Sromovsky，L.[2007]Bull)。上午好。阿斯特龙。Sromovsky，L.A.，Fry，P.M.，Ahue，W.M.，Hammel，H.B.，de Pater，I.，Rages，K.A.，Showalt，M.R.，van Dam，M.A.[2008]美国科学院/行星科学部会议摘要第40卷，第488-489页；Sromovsky，L.A.，Ahue，W.K.M.，Fry，P.M.，Hammel，H.B.，De Pater，I.，Ranges，K.A.，Showalt，M.R.[2009]Icarus)，来自中纬度地区的反射率下降在赤道留下了明显更明亮的云带(例如Sromovsky，L.A.，Fry，PM[2007]Icarus，192,527-557；Karkoschka，E.，Tomasko，M.[2009]Icarus)。短短两年内发生的如此巨大的云层变化表明，天王星大气的循环比人们通常认为的要活跃和/或高效得多。2到6-8bar之间的主要观测云层的组成尚不清楚，但在1.2-1.3bar没有预期的甲烷云(Lindal，G.F.，Lyons，J.R.，Sweetnam，D.N.，Eshleman，V.R.，Hinson，D.P.[1987]J.地球物理。研究，92,14987-15001)是引人注目的(如先前指出的，斯罗莫夫斯基，洛杉矶，欧文，P.G.J.，弗莱，下午[2006年]伊卡洛斯，1825777593；斯罗莫夫斯基，洛杉矶，弗莱，下午[2007年]伊卡洛斯，192527557；斯罗莫夫斯基，洛杉矶，弗莱，下午[2008年]伊卡洛斯，1932252266；Karkoschka，E.，Tomasko，M.[2009]Icarus)，并提出云粒子可能与纯凝聚物有很大不同，可能与从上方滴落的平流层雾霾粒子有关，或者如Karkoschka和Tomasko(Karkoschka，E.，Tomasko，M.[2009]Icarus)所述，对流层雾霾是在甲烷凝结水平附近产生的，然后向下滴落到深气压。对反演的云结构也进行了测试，以确定不同的甲烷摩尔分数假设，卡科施卡和托马斯科(Karkoschka，E.，Tomasko，M.[2009]Icarus)发现的甲烷摩尔分数的变化可能从极地地区的∼1-2%到45°N，S赤道方向的4%。我们发现，这种变化不会影响…
Long-slit spectroscopy observations of Uranus by the United Kingdom Infrared Telescope UIST instrument in 2006, 2007 and 2008 have been used to monitor the change in Uranus’ vertical and latitudinal cloud structure through the planet’s northern spring equinox in December 2007. The observed reflectance spectra in the Long J (1.17–1.31μm) and H (1.45–1.65μm) bands, obtained with the slit aligned along Uranus’ central meridian, have been fitted with an optimal estimation retrieval model to determine the vertical cloud profile from 0.1 to 6–8bar over a wide range of latitudes. Context images in a number of spectral bands were used to discriminate general zonal cloud structural changes from passing discrete clouds. From 2006 to 2007 reflection from deep clouds at pressures between 2 and 6–8bar increased at all latitudes, although there is some systematic uncertainty in the absolute pressure levels resulting from extrapolating the methane coefficients of Irwin et al. (Irwin, P.G.J., Sromovsky, L.A., Strong, E.K., Sihra, K., Teanby, N.A., Bowles, N., Calcutt, S.B., Remedios, J.J. [2006] Icarus, 181, 309–319) at pressures greater than 1bar, as noted by Tomasko et al. and Karkoschka and Tomasko (Tomasko, M.G., Bezard, B., Doose, L., Engel, S., Karkoschka, E. [2008] Planet. Space Sci., 56, 624–647; Karkoschka, E., Tomasko, M. [2009] Icarus). However, from 2007 to 2008 reflection from these clouds throughout the southern hemisphere and from both northern and southern mid-latitudes (30° N,S) diminished. As a result, the southern polar collar at 45°S has diminished in brightness relative to mid-latitudes, a similar collar at 45°N has become more prominent (e.g. Rages, K.A., Hammel, H.B., Sromovsky, L. [2007] Bull. Am. Astron. Soc., 39, 425; Sromovsky, L.A., Fry, P.M., Ahue, W.M., Hammel, H.B., de Pater, I., Rages, K.A., Showalter, M.R., van Dam, M.A. [2008] vol. 40 of AAS/Division for Planetary Sciences Meeting Abstracts, pp. 488–489; Sromovsky, L.A., Ahue, W.K.M., Fry, P.M., Hammel, H.B., de Pater, I., Rages, K.A., Showalter, M.R. [2009] Icarus), and the lowering reflectivity from mid-latitudes has left a noticeable brighter cloud zone at the equator (e.g. Sromovsky, L.A., Fry, P.M. [2007] Icarus, 192, 527–557;Karkoschka, E., Tomasko, M. [2009] Icarus). For such substantial cloud changes to have occurred in just two years suggests that the circulation of Uranus’ atmosphere is much more vigorous and/or efficient than is commonly thought. The composition of the main observed cloud decks between 2 and 6–8bar is unclear, but the absence of the expected methane cloud at 1.2–1.3bar (Lindal, G.F., Lyons, J.R., Sweetnam, D.N., Eshleman, V.R., Hinson, D.P. [1987] J. Geophys. Res., 92, 14987–15001) is striking (as previously noted by, among others, Sromovsky, L.A., Irwin, P.G.J., Fry, P.M. [2006] Icarus, 182, 577–593; Sromovsky, L.A., Fry, P.M. [2007] Icarus, 192, 527–557; Sromovsky, L.A., Fry, P.M. [2008] Icarus, 193, 252-266; Karkoschka, E., Tomasko, M. [2009] Icarus) and suggests that cloud particles may be considerably different from pure condensates and may be linked with stratospheric haze particles drizzling down from above, or that tropospheric hazes are generated near the methane condensation level and then drizzle down to deep pressures as suggested by Karkoschka and Tomasko (Karkoschka, E., Tomasko, M. [2009] Icarus). The retrieved cloud structures were also tested for different assumptions of the deep methane mole fraction, which Karkoschka and Tomasko (Karkoschka, E., Tomasko, M. [2009] Icarus) find may vary from ∼1–2% in polar regions to perhaps as much as 4% equatorwards of 45°N,S. We found that such variations did not …