Southern Ocean Seaspray Aerosol Flux Experiment

南大洋海喷雾气溶胶通量实验

• 批准号: NE/F00950X/1
• 负责人: Ian Brooks
• 金额: $ 5.58万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF00950X%2F1
• 关键词: Southern; Ocean; Seaspray; Aerosol; Flux

Atmospheric aerosol / small particles with sizes ranging from 1nanometre up to 100s of micrometres / play a significant role in many important processes related to global climate. Of particular note are their direct effect on the radiation balance within the atmosphere - where they can act both to reflect incoming solar radiation, and hence as a cooling factor on climate / and their indirect effect via their interactions with clouds, where they act as condensation nuclei for cloud droplets to form on. Over the open oceans the single most important source of aerosol is sea spray; sea salt aerosol are the major scatterer of solar radiation, and a major source of condensation nuclei for marine stratocumulus clouds. Marine stratocumulus are one of the largest sources of uncertainty in climate models due to their great sensitivity to environmental conditions; relatively small changes in the temperature, humidity, or depth of the marine boundary layer, or of the availability of aerosol to act as condensation nuclei, can have a significant impact on the spatial extent, lifetime, and reflectivity of the clouds. Small errors in the representation of any of these factors within climate models can result in major errors in the prediction of future climate. The best available parameterizations of the generation of sea spray aerosols have a scatter of about a factor of 10. These sea-spray source functions are almost all derived indirectly from measurements of the mean aerosol size spectra averaged over periods of the order of minutes to hours; the flux of aerosol being inferred from the change in mean concentration over time and assumptions about the balance of generation and remocal processes. An alternative approach has been to try to scale up laboratory measurements of the aerosol generated by bursting bubbles within a single bubble plume, or whitecap, to the average whitecap coverage under a range of wind conditions in the field. The most robust method of measuring the flux is via the eddy covariance technique, in which the high frequency fluctuations of the vertical wind component and aerosol concentration are measured and the flux estimated from their correlation over time. Until recently the instrumentation required to make such measurements did not exist. A new instrument / CLASP - designed and built at Leeds has both the capability to measure aerosol concentrations fast enough for eddy covariance flux estimates to be made, and be small enough to locate close to a sonic anemometer without causing an unacceptably large flow distortion. Measurements made on the foremast of a research ship during cruises in 2006 and 2007 have shown CLASP to be robust and capable of operating unattended for extended periods. The project proposed here will install two CLASP units on a new Extreme Air-Sea Interaction (EASI) buoy, developed by the University of Miami, Florida, for a measurement campaign in the Southern Ocean. The EASI buoy is an ideal platform for making such measurements: the instrumentation can be sited close to the surface (~6 m), while remaining safe from immersion by waves due to the wave-following performance of the buoy. During a 4-week deployment, measurements of the turbulent flux of sea spray aerosol will be obtained under a wide range of conditions, along with those of wind stress, heat, moisture, and details of the wind-driven wave field. The results will help to develop new and improved parameterizations of sea-spray aerosol production for use in climate models, and thus improve the fidelity of predictions of future climate.

大气气溶胶/尺寸从1纳米到100微米的小颗粒/在与全球气候有关的许多重要过程中起着重要作用。特别值得注意的是它们对大气层内辐射平衡的直接影响-在大气层中，它们可以反射入射的太阳辐射，从而成为气候的一个冷却因素;它们还通过与云的相互作用产生间接影响，在云中，它们充当云滴形成的凝结核。海盐气溶胶是太阳辐射的主要散射体，也是海洋层积云凝结核的主要来源。海洋层积云是气候模式中最大的不确定性来源之一，因为它们对环境条件非常敏感;海洋边界层的温度、湿度或深度，或气溶胶作为凝结核的可用性的相对较小的变化，都可能对云的空间范围、寿命和反射率产生重大影响。在气候模式中，这些因素中任何一个的表现出现微小误差，都可能导致未来气候预测出现重大误差。最好的可用参数化的代海喷雾气溶胶有一个分散的约10倍。这些海喷雾源函数几乎都是间接来自平均气溶胶粒径谱的测量平均在几分钟到几小时的顺序期间;气溶胶的通量被推断出的平均浓度随时间的变化和假设的生成和remocal过程的平衡。另一种方法是尝试将单个气泡羽流（或白顶）内气泡破裂产生的气溶胶的实验室测量值扩大到实地一系列风力条件下的平均白顶覆盖范围。最可靠的通量测量方法是通过涡度协方差技术，其中测量垂直风分量和气溶胶浓度的高频波动，并根据它们随时间的相关性估计通量。直到最近，进行这种测量所需的仪器还不存在。在利兹设计和建造的一种新仪器/ CLASP既有能力快速测量气溶胶浓度，以便进行涡动协方差通量估计，又有能力足够小，以便靠近音速风速计，而不会造成不可接受的大流量失真。在2006年和2007年巡航期间对一艘研究船的前桅进行的测量表明，CLASP是坚固的，能够长时间无人值守。这里提议的项目将在一个新的极端海气相互作用（EASI）浮标上安装两个CLASP装置，该浮标由佛罗里达的迈阿密大学开发，用于南大洋的测量活动。EASI浮标是进行此类测量的理想平台：仪器可以靠近水面（约6 m）放置，同时由于浮标的波浪跟踪性能，可以安全地防止波浪浸没。在为期4周的部署期间，将在广泛的条件下获得海雾气溶胶湍流通量的测量结果，沿着获得风应力、热量、湿度以及风驱动波场的详细情况。研究结果将有助于开发新的和改进的参数化海洋喷雾气溶胶生产用于气候模型，从而提高未来气候预测的保真度。