Global water vapor distributions in the stratosphere and upper troposphere derived from 5.5 years of SAGE II observations (1986–1991)
Global water vapor distributions in the stratosphere and upper troposphere derived from 5.5 years of SAGE II observations (1986–1991)
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来自 5.5 年 SAGE II 观测（1986-1991）的平流层和对流层上层的全球水汽分布
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发表时间：
1997
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影响因子：
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通讯作者：
W. Chu
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作者：
E. Chiou;M. McCormick;W. Chu
平流层和对流层上层水蒸气的全球分布是根据地球辐射预算卫星（ERBS）上的平流层气溶胶和气体实验 II（SAGE II）约 5.5 年（1986 年 1 月至 1991 年 5 月）的观测得出的。表格中包括季节性纬向平均水汽混合比（体积百万分之一），垂直分辨率为 1 公里，高度范围为 6 至 40 公里。之前的研究[McCormick et al., 1993]基于3年的观测，确定了几个气候特征，本次研究已经证实：（1）在所有纬度带都存在水汽最少的区域（湿顶）； (2) 对流层顶和湿层顶之间的距离从低纬度的1公里增加到高纬度的4公里； (3) 在 20 公里至 40 公里之间的固定高度上，所有季节都出现向极地的正梯度。 20 km处水汽混合比的纬度变化具有对称分布特征，最小出现在赤道处。然而，25 公里和 30 公里处的相应变化表明最小值向夏半球移动。两半球0°~20°和20°~40°纬度区域的湿顶季节变化表明，从12月、1月、2月到3月、4月、5月，海拔高度和最低水汽混合比值基本保持不变。 9月、10月和11月期间，在整个低纬度和中纬度地区，湿顶减弱，最低水汽区域向更广泛的海拔范围扩散。对于对流层上层，300 mbar 下的晴空相对湿度显示出 5-60% 的典型范围，这与之前基于 Meteosat 6.3 μm 测量的结果一致。此外，SAGE II 观测的独特能力为我们提供了前所未有的对流层上层垂直分辨湿度信息。例如，300 至 100 mbar 层的积分柱水蒸气含量范围为 0.002 至 0.01 g/cm2，在热带地区纵向变化较大。发现东半球 500 至 100 mbar 的综合柱水蒸气含量明显大于西半球。从冬季到夏季，高纬度地区相应的综合水汽含量增加了6倍（0.02克/厘米2与0.13克/厘米2相比）。
Global distributions of water vapor in the stratosphere and upper troposphere are presented on the basis of ∼5.5 years (January 1986 to May 1991) of observations from the Stratospheric Aerosol and Gas Experiment II (SAGE II) aboard the Earth Radiation Budget Satellite (ERBS). Tabulations are included for seasonal zonal mean water vapor mixing ratios (in parts per million by volume) with 1-km vertical resolution and an altitude range from 6 to 40 km. Several climatological features identified in a previous study [McCormick et al., 1993], based on 3 years of observations, have been confirmed by this study: (1) the existence of a region of minimum water vapor (the hygropause) at all latitude bands; (2) the increase in the distance between the tropopause and the hygropause from 1 km at low latitudes to 4 km at high latitudes; and (3) the appearance of a positive poleward gradient throughout all seasons for fixed altitudes between 20 km and 40 km. The latitudinal variation of water vapor mixing ratio at 20 km is characterized by a symmetric pattern with a minimum occurring at the equator. However, the corresponding variations at 25 and 30 km indicate a shift of the minimum toward the summer hemisphere. For the latitude zones 0°–20° and 20°–40° in both hemispheres, the seasonal variations of the hygropause reveal that the altitude as well as the value of the minimum water vapor mixing ratio remain essentially unchanged from December, January, and February to March, April, and May. During September, October, and November the weakening of the hygropause and the spreading of the region of minimum water vapor to a wider altitude range are identified throughout these low-latitude and midlatitude zones. For the upper troposphere the clear-sky relative humidities at 300 mbar show a typical range of 5–60%, which is consistent with previous findings based on Meteosat 6.3 μm measurements. In addition, the unique capability of SAGE II observations has provided us with unprecedented vertically resolved moisture information for the upper troposphere. For example, the integrated column water vapor content for the 300- to 100-mbar layer ranges from 0.002 to 0.01 g/cm2 with larger longitudinal variability in the tropics. The integrated column water vapor content from 500 to 100 mbar is found to be significantly larger in the eastern hemisphere than in the western hemisphere. The corresponding integrated water vapor content at high latitudes increases by a factor of 6 from winter to summer (0.02 g/cm2 compared with 0.13 g/cm2).