CEDAR: Polar Mesospheric Cloud Research Using the Sondrestrom, Greenland Lidar

CEDAR：使用格陵兰岛 Sondrestrom 激光雷达进行极地中层云研究

• 批准号: 0437178
• 负责人: Weilin Pan
• 金额: $ 26.98万
• 依托单位: SRI International
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-01-01 至 2008-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0437178&HistoricalAwards=false
• 关键词: CEDAR; Polar; Mesospheric; Cloud; Research

The investigators will study the aspherical nature of polar mesospheric cloud (PMC) particles and the interaction of PMC particles with the mesospheric sodium layer. The shape of PMC particles affects the growth-sedimentation-sublimation cycle associated with visible cloud formation. For example, the fall rate of a PMC particle depends on its shape as well as its size; an aspherical particle experiences different aerodynamic forces that could cause it to reside longer in the supersaturation region and thus could enhance its growth. The aspherical nature of PMCs can affect the characterization of PMC particle size distributions and the interpretation of PMC microphysics. Lastly, the presence of PMCs may affect sodium concentrations and the greater surface area-to-volume ratio of an aspherical particle may enhance the interaction of PMC particles with the mesospheric sodium species. Owing to the submicron size of PMC particles and the visible wavelengths used to probe them, Mie-Rayleigh scattering theory has predominantly been applied to study PMCs. However, these studies have assumed that the PMC particles are spherical -- a fundamental assumption with little experimental support. An aspherical particle causes incident linearly polarized light to depolarize when scattered. Lidar observations have shown nonzero PMC depolarization ratios in lidar measurements from Norway. Recently the Sondrestrom, Greenland, lidar system has also measured nonzero depolarization ratios at visible wavelengths. The results indicated that PMC particles can at times be aspherical. The goal of this research is to evaluate the aspherical nature of PMCs at Sondrestrom. Another new and emerging research area is the study of the interaction of PMCs with the mesospheric metal species. Sondrestrom sodium and Rayleigh lidar measurements have indicated a reduction in sodium density at the lower boundary of the sodium layer when PMCs are present. These new observations suggest a connection between PMCs and sodium that involves either heterogeneous chemistry in the presence of ice or the physical uptake of sodium onto existing ice particles. The investigators will study seasonal changes of sodium at high latitudes, including the effect of ice on the sodium distribution, by using a seven-year database of Sondrestrom lidar measurements and by using a sodium chemistry model. The research plan includes an analysis of PMC depolarization measurements made by the Sondrestrom lidar in the summers of 2003, 2004, and 2005 to address the question about the aspherical nature of the PMCs. The investigators will develop a model based on aspherical particle scattering to address the question of PMC shape and size. In addition, six years of coincident PMC and sodium density measurements will be compiled and the relationship of PMC occurrence to sodium density depletion will be detailed. In addition, new observations from 1064 nm PMC backscatter measurements in the summers of 2005 and 2006 will be used. The combination of 532 nm and 1064 nm backscatter measurements, with depolarization measurements at 532 nm, will be used to better constrain the PMC model and improve the shape and size parameter estimates. The seasonal variability in the sodium layer observed with the lidar will be used to test sodium chemistry models. The PMC depolarization measurements since 2003 and the modeling effort will provide a reasonable database that will be used to characterize basic PMC properties. PMCs are believed to be an indicator of global change. Thus, it is important to understand the physical and chemical mechanisms by which they are formed.

研究人员将研究极地中间层云（PMC）粒子的非球形性质以及PMC粒子与中间层钠层的相互作用。PMC颗粒的形状影响与可见云形成相关的生长-沉积-升华循环。例如，PMC颗粒的下落速率取决于它的形状和大小；非球面粒子经历不同的空气动力，这可能导致它在过饱和区域停留更长时间，从而可以促进它的生长。PMC的非球形性质会影响PMC粒度分布的表征和PMC微物理的解释。最后，PMC的存在可能会影响钠浓度，非球形颗粒的较大表面积与体积比可能会增强PMC颗粒与中间层钠物质的相互作用。由于PMC粒子的亚微米大小和用于探测它们的可见波长，Mie-Rayleigh散射理论主要应用于PMC的研究。然而，这些研究都假设PMC粒子是球形的——这是一个基本的假设，几乎没有实验支持。非球面粒子使入射的线偏振光在散射时去极化。在挪威的激光雷达测量中，激光雷达观测显示PMC退极化比非零。最近，格陵兰岛Sondrestrom的激光雷达系统也测量了可见光波长的非零去极化比。结果表明，PMC颗粒有时是非球形的。本研究的目的是评估Sondrestrom的pmc的非球面性质。另一个新兴的研究领域是pmc与中间层金属物质相互作用的研究。Sondrestrom钠和Rayleigh激光雷达测量表明，当pmc存在时，钠层下边界的钠密度降低。这些新的观察结果表明，pmc和钠之间存在联系，可能涉及冰存在时的非均相化学反应，也可能涉及钠在现有冰粒上的物理吸收。研究人员将利用Sondrestrom激光雷达7年测量数据和钠化学模型，研究高纬度地区钠的季节性变化，包括冰对钠分布的影响。该研究计划包括对Sondrestrom激光雷达在2003年、2004年和2005年夏季所做的PMC去极化测量进行分析，以解决PMC非球面性质的问题。研究人员将开发一个基于非球面粒子散射的模型来解决PMC形状和大小的问题。此外，还将编制6年的PMC和钠密度测量数据，详细分析PMC的发生与钠密度损耗的关系。此外，将使用2005年和2006年夏季1064 nm PMC背向散射测量的新观测结果。结合532 nm和1064 nm的后向散射测量，以及532 nm的退极化测量，将更好地约束PMC模型，并改进形状和尺寸参数估计。激光雷达观测到的钠层的季节性变化将用于测试钠化学模型。自2003年以来的PMC去极化测量和建模工作将提供一个合理的数据库，用于表征PMC的基本特性。pmc被认为是全球变化的一个指标。因此，了解它们形成的物理和化学机制是很重要的。