Cloud and haze properties from Pioneer Venus polarimetry
Cloud and haze properties from Pioneer Venus polarimetry
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Pioneer Venus 偏振测量的云雾特性
DOI：
10.1029/ja085ia13p08129
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发表时间：
1980
影响因子：
--
通讯作者：
L. Travis
中科院分区：
文献类型：
--
作者：
K. Kawabata;D. Coffeen;J. Hansen;W. Lane;M. Sato;L. Travis
对先锋金星轨道飞行器云光偏振计实验获得的线偏振数据的分析表明，低纬度和中纬度地区的可见云主要由半径为 1 µm 的 H2SO4 液滴组成，这是之前通过地球观测得出的结论。混合在主要可见云层内部并延伸到其上方的是大量亚微米级颗粒的雾霾。这些雾霾颗粒在λ≃550 nm处的折射率为1.45±0.04，有效半径为0.23±0.04 µm，有效方差为0.18±0.1的尺寸分布。纬度约 55° 的极地明亮区域的偏振几乎完全是由这种亚微米雾霾产生的。已发现亚微米雾霾表现出较大的空间和时间变化。 1979 年 1 月，极地区域 λ=365 nm 处的雾霾垂直光学厚度为 τh ∼0.8，高于 l-μm 颗粒的主云。相比之下，低纬度主云上方雾霾的光学厚度通常小 1 个数量级，τh ∼0.06，但云内混合的雾霾贡献了 λ=365 nm 处单位体积总散射截面的 ∼18%。最近的观测表明，雾霾在数百天的时间尺度上发生了重大变化（例如，1979年10月极冠雾霾的光学厚度比1979年1月小2-3倍）。低纬度地区存在显着的昼夜变化，早晨明界线附近的雾霾量比中午子午线附近的雾霾量更大。在先锋金星任务扩展期间，将监测雾霾的全球分布，以便分析长期尺度变化以及与从云顶紫外线图像推断出的大气动力学特征的相关性。
Analysis of linear polarization data obtained by the Pioneer Venus Orbiter Cloud Photopolarimeter experiment indicates that the visible clouds at low and mid-latitudes are composed predominantly of 1 µm radius H2SO4 droplets, an identification made previously by using earth-based observations. Mixed within and extending above this main visible cloud is an extensive haze of submicron-sized particles. These haze particles have a refractive index of 1.45±0.04 at λ ≃550 nm, an effective radius of 0.23±0.04 µm, and a size distribution with an effective variance of 0.18±0.1. The polarization of the bright regions poleward of about 55° latitude is produced almost entirely by this submicron haze. The submicron haze has been found to exhibit large spatial and temporal variations. In January 1979 the haze vertical optical thickness in the polar region at λ=365 nm was τh ∼0.8 above the main cloud of l-µm particles. By comparison, the optical thickness of the haze above the main cloud at low latitudes was typically 1 order of magnitude smaller, τh ∼0.06, however haze mixed within the cloud contributed ∼18% of the total scattering cross section per unit volume at λ=365 nm. More recent observations indicate that there are major changes of the haze on time scales of hundreds of days (e.g., the optical thickness of the polar cap haze is smaller by a factor of 2–3 in October 1979 than in January 1979). Substantial diurnal variations exist at low latitudes, with a greater amount of haze near the morning terminator than near the noon meridian. The global distribution of haze will be monitored during the extended Pioneer Venus mission to permit analysis of long time scale variations as well as correlation with characteristics of the atmospheric dynamics deduced from ultraviolet images of the cloud tops.