Nighttime cirrus detection using Atmospheric Infrared Sounder window channels and total column water vapor
Nighttime cirrus detection using Atmospheric Infrared Sounder window channels and total column water vapor
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使用大气红外探测器窗口通道和总柱水蒸气检测夜间卷云
DOI：
10.1029/2004jd005430
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发表时间：
2005
影响因子：
--
通讯作者：
L. Strow
中科院分区：
文献类型：
--
作者：
B. Kahn;K. Liou;Sung;E. Fishbein;S. Desouza;A. Eldering;E. Fetzer;S. Hannon;L. Strow
[1]提出了一种利用3.8m和10.4μm红外窗口亮度温差和总柱可降水量测量夜间卷云的方法。这项技术被应用于EOS-AQUA上的大气红外探测仪(AIRS)和先进微波探测仪A(AMSU-A)仪器套件，其中DBT是根据精心选择的AIRS窗口通道确定的，而PW则是通过AIRS和AMSU-A水汽的协同反演得出的。对于特定的PW值，模拟和观测的DBT不是恒定的；几个物理因素影响DBT，包括温度和相对湿度分布、表面发射率、仪器噪声和皮肤/近地表空气温差的变化。我们使用8350无线电探空仪在真实的PWS范围内模拟晴空DBT，这些探空仪具有不同的温度和相对湿度分布。一旦确定了晴空DBT中的散射，就得到了多云和不确定天空条件之间的阈值。对光学薄卷云的模拟表明，该技术对热带和副热带海洋上10μm窗口(0.1-0.15或更大)的卷云光学厚度最敏感，那里的地表发射率和皮肤/近地表气温对红外辐射的影响最小。目前这种方法一般只适用于海洋地区，特别是热带和亚热带地区。对薄卷云和其他云类型的探测通过了位于热带西太平洋马努斯岛的大气辐射测量(ARM)计划现场对符合EOS-AQUA立交桥的观测验证。尽管这项工作的重点是在夜间探测薄薄的卷云，但这项技术对宽阔的云层形态很敏感。云探测技术在82-84%的时间内与ARM探测到的云一致，包括薄卷云以及其他类型的云。与ARM点测量相比，AIRS足迹尺度的异质性、覆盖在低层水云上的卷云、中层云中可能的混合相微物理以及深对流塔上方冷BT场景的显著IR通道噪声很好地解释了大多数分歧。
[1] A method of cirrus detection at nighttime is presented that utilizes 3.8 and 10.4 μm infrared (IR) window brightness temperature differences (dBT) and total column precipitable water (PW) measurements. This technique is applied to the Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit A (AMSU-A) instrument suite on board EOS-Aqua, where dBT is determined from sets of carefully selected AIRS window channels, while PW is derived from the synergistic AIRS and AMSU-A water vapor retrievals. Simulated and observed dBT for a particular value of PW are not constant; several physical factors impact dBT, including the variability in temperature and relative humidity profiles, surface emissivity, instrument noise, and skin/near-surface air temperature differences. We simulate clear-sky dBT over a realistic range of PWs using 8350 radiosondes that have varying temperature and relative humidity profiles. Thresholds between cloudy and uncertain sky conditions are derived once the scatter in the clear-sky dBT is determined. Simulations of optically thin cirrus indicate that this technique is most sensitive to cirrus optical depth in the 10 μm window of 0.1–0.15 or greater over the tropical and subtropical oceans, where surface emissivity and skin/near-surface air temperature impacts on the IR radiances are minimal. The method at present is generally valid over oceanic regions only, specifically, the tropics and subtropics. The detection of thin cirrus, and other cloud types, is validated using observations at the Atmospheric Radiation Measurement (ARM) program site located at Manus Island in the tropical western Pacific for 89 coincident EOS-Aqua overpasses. Even though the emphasis of this work is on the detection of thin cirrus at nighttime, this technique is sensitive to a broad cloud morphology. The cloud detection technique agrees with ARM-detected clouds 82–84% of the time, which include thin cirrus, as well as other cloud types. Most of the disagreements are well explained by AIRS footprint-scale heterogeneity compared to ARM point measurements, cirrus overlying lower-layer water clouds, possible mixed phase microphysics in midlevel clouds, and significant IR channel noise for cold BT scenes over deep convective towers.