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A study on the diurnal variation of low cloud microphysical properties

低云微物理性质日变化研究

基本信息

批准号：
16340143
负责人：
HAYASAKA Tadahiro
金额：
$ 7.3万
依托单位：
Research Institute for Humanity and Nature
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

The cloud is one of the most important factors controlling the Earth's climate change. The low level cloud has a large reflectance and is affected by anthropogenic aerosols, that is, the indirect effect. However, the basic properties of low cloud is not sufficiently investigated. The intent of the present study is to investigate the mechanism of diurnal variation of low cloud microphysical properties. We used satellite data such as GOES and NOAA/AVHRR.The stratiform low clouds off the coast of California were investigated by using GOES data. The reflection property of the cloud was used to estimate optical thickness and effective particle radius of cloud. It is found that cloud optical thickness decreased from morning to afternoon while effective particle radius increased during the same period and then decreased. The variation of optical thickness may ascribed to heating due to absorption of solar radiation. On the other hand, effective particle radius might change as a result of condensation, evaporation, coagulation, and gravitational fall out. It should be noted that the properties observed here is limited to cloud top because we used the reflected solar radiation in visible and near infrared spectral region.In addition, NOAA/AVHRR data were used. The NOAA is polar orbital satellite, but diurnal variation can be observed because the orbit of NOAA satellite drifts and then equator overpass time slightly delay. It is also shown from the analysis of NOAA/AVHRR data that effective particle radius of low cloud decreased from noon to evening. This is consistent with the result obtained from the above GOES data analysis and ground based measurements with microwave radiometer and pyranometer carried out by other research group.There are several different mechanisms of cloud forming, maintaining and disappearing, so that we need further studies involving satellite remote sensing, ground based observation, and meso-scale modeling with cloud microphysical processes.

云是控制地球气候变化的最重要因素之一。低空云反射率大，受人为气溶胶影响，即间接效应。然而，对低云的基本性质研究并不充分。本研究的目的是探讨低云微物理性质的日变化机制。我们使用了GOES和NOAA/AVHRR等卫星数据。利用GOES资料对加利福尼亚近海的层状低云进行了研究。利用云的反射特性估计云的光学厚度和有效粒子半径。从上午到下午，云光学厚度减小，有效粒子半径先增大后减小。光学厚度的变化可归因于吸收太阳辐射引起的加热。另一方面，有效粒子半径可能由于冷凝、蒸发、凝聚和重力落落而发生变化。值得注意的是，由于我们使用的是可见光和近红外光谱区域的反射太阳辐射，因此这里观测到的性质仅限于云顶。此外，还使用了NOAA/AVHRR数据。NOAA为极轨卫星，由于轨道漂移，赤道交点时间略有延迟，因此可以观测到日变化。对NOAA/AVHRR资料的分析也表明，低云有效粒子半径从中午到傍晚逐渐减小。这与上述GOES数据分析和其他研究组使用微波辐射计和热辐射计进行的地面测量结果一致。云的形成、维持和消失有多种不同的机制，因此我们需要进一步研究包括卫星遥感、地面观测和云微物理过程的中尺度模拟。