The meridional phosphine distribution in Saturn's upper troposphere from Cassini/CIRS observations
The meridional phosphine distribution in Saturn's upper troposphere from Cassini/CIRS observations
复制标题
DOI：
10.1016/j.icarus.2006.10.029
复制
发表时间：
2007-05
期刊：
影响因子：
3.2
通讯作者：
L. Fletcher;P. Irwin;N. Teanby;G. Orton;P. Parrish;S. Calcutt;N. Bowles;R. Kok;C. Howett;F. Taylor
中科院分区：
文献类型：
--
作者：
L. Fletcher;P. Irwin;N. Teanby;G. Orton;P. Parrish;S. Calcutt;N. Bowles;R. Kok;C. Howett;F. Taylor
卡西尼复合红外光谱仪（CIRS）已被用来推导出土星对流层上部温度和磷化氢（PH 3）丰度的垂直和纬向变化。PH 3对测量的热红外辐射有显著的影响，在2004年5月至2005年9月期间，CIRS记录了数千个远红外（10-600 cm−1）和中红外（600-1400 cm−1）光谱，覆盖南半球的不同纬度。低光谱分辨率（15 cm−1）数据已被用于将对流层的温度结构限制在100和500 mbar之间。磷化氢和氨的垂直分布是从最高光谱分辨率（0.5 cm−1）的远红外光谱中检索出来的，而较低分辨率（2.5 cm−1）的中红外数据则用于绘制250-500 mbar范围内磷化氢丰度的纬向变化。在250毫巴的水平上，温度变化与土星大气中的逆行和逆行喷流具有相同的尺度[Porco，C.C.，和34位同事，2005年。Science 307，1243-1247]。在250毫巴的PH 3丰度被发现是增强在赤道相比，中纬度地区。在中纬度地区，我们看到温度和PH 3丰度之间的反相关性在250毫巴，磷化氢在45° S增强，在25和55° S耗尽。垂直分布在60-65° S极区有明显的差异，在500毫巴时PH 3含量减少，但与中纬度地区相比，PH 3含量随高度下降的速度较慢。这种变化类似于在可见光和近红外线观测到的云和气溶胶参数的变化，可能表明极地纬度对流层空气的沉降，加上太阳光穿透深度的减少，降低了极地地区PH 3光解的速率。
The Cassini Composite Infrared Spectrometer (CIRS) has been used to derive the vertical and meridional variation of temperature and phosphine (PH3) abundance in Saturn's upper troposphere. PH3has a significant effect on the measured radiances in the thermal infrared and between May 2004 and September 2005 CIRS recorded thousands of spectra in both the far (10–600 cm−1) and mid (600–1400 cm−1) infrared, at a variety of latitudes covering the southern hemisphere. Low spectral resolution (15 cm−1) data has been used to constrain the temperature structure of the troposphere between 100 and 500 mbar. The vertical distributions of phosphine and ammonia were retrieved from far-infrared spectra at the highest spectral resolution (0.5 cm−1), and lower resolution (2.5 cm−1) mid-infrared data were used to map the meridional variation in the abundance of phosphine in the 250–500 mbar range. Temperature variations at the 250 mbar level are shown to occur on the same scale as the prograde and retrograde jets in Saturn's atmosphere [Porco, C.C., and 34 colleagues, 2005. Science 307, 1243–1247]. The PH3abundance at 250 mbar is found to be enhanced at the equator when compared with mid-latitudes. At mid latitudes we see anti-correlation between temperature and PH3abundance at 250 mbar, phosphine being enhanced at 45° S and depleted at 25 and 55° S. The vertical distribution is markedly different polewards of 60–65° S, with depleted PH3at 500 mbar but a slower decline in abundance with altitude when compared with the mid-latitudes. This variation is similar to the variations of cloud and aerosol parameters observed in the visible and near infrared, and may indicate the subsidence of tropospheric air at polar latitudes, coupled with a diminished sunlight penetration depth reducing the rate of PH3photolysis in the polar region.