Southern Ocean Seaspray Aerosol Flux Experiment

大气气溶胶/大小从1纳米到100微米不等的小颗粒/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内辐射平衡的直接影响——它们可以反射入射的太阳辐射，从而作为气候的冷却因素；它们通过与云的相互作用产生间接影响，在那里它们充当凝结核，使云滴在其上形成。在开阔的海洋上，气溶胶最重要的来源是海浪；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；温度、湿度或海洋边界层深度的相对微小变化，或气溶胶作为凝结核的可用性的相对微小变化，都会对云的空间范围、寿命和反射率产生重大影响。在气候模式中，任何这些因子的表示出现小的误差都可能导致对未来气候的预测出现大的误差。关于海上喷雾气溶胶产生的最佳可用参数化具有大约10倍的散射。这些海雾源函数几乎都是间接地从在几分钟到几小时的周期内平均气溶胶大小谱的测量中得出的；气溶胶的通量是从平均浓度随时间的变化和关于产生和去除过程平衡的假设中推断出来的。另一种方法是尝试扩大实验室测量单个气泡羽流（或称白浪）中气泡破裂产生的气溶胶的规模，使其达到野外一系列风况下的平均白浪覆盖范围。测量通量最可靠的方法是通过涡动相关方差技术，该技术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既能够快速测量气溶胶浓度，以进行涡动相关通量估计，又足够小，可以定位在声波风速仪附近，而不会造成不可接受的大气流畸变。2006年和2007年在一艘科考船的前桅上进行的测量表明，CLASP坚固耐用，能够在无人看管的情况下长时间运行。这里提出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，该浮标由佛罗里达州迈阿密大学开发，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：仪器可以放置在靠近水面（~6米）的位置，同时由于浮标的波浪跟随性能，可以保持安全，不被海浪浸没。在为期4周的部署中，将获得各种条件下海洋喷雾气溶胶湍流通量的测量数据，以及风应力、热量、湿度和风力驱动波场的细节。这些结果将有助于开发新的和改进的用于气候模式的海雾气溶胶产生的参数化，从而提高对未来气候预测的保真度。

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.