Southern Ocean Seaspray Aerosol Flux Experiment

大气气溶胶/小颗粒的尺寸从1纳米到100微米/在与全球气候有关的许多重要过程中发挥着重要作用。特别值得注意的是它们对大气层内辐射平衡的直接影响--它们既可以反射到来的太阳辐射，因此也可以作为气候的冷却因素，还可以通过它们与云的相互作用产生间接影响，在那里它们充当云滴形成的凝结核。在公海上空，气溶胶最重要的单一来源是海雾；海盐气溶胶是太阳辐射的主要散射者，也是海洋层积云凝结核的主要来源。海洋层积云是气候模型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，或用作凝结核的气溶胶的相对较小的变化，可以对云的空间范围、寿命和反射率产生重大影响。在气候模型中表示这些因素中的任何一个的小错误都可能导致对未来气候的预测出现重大错误。海雾气溶胶生成的最佳可用参数的离散度约为10倍。这些海雾源函数几乎都是通过测量平均气溶胶尺寸谱间接得出的，这些平均尺寸谱在几分钟到几小时的时间内平均；气溶胶通量是根据平均浓度随时间的变化和关于生成和去除过程的平衡的假设推断出来的。另一种方法是尝试将实验室测量的单个气泡羽流中破裂的气泡所产生的气溶胶扩大到野外各种风条件下的平均白云覆盖率。最可靠的测量通量的方法是通过涡旋协方差技术，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。利兹大学设计和制造的一种新仪器/CLAP既能够足够快地测量气溶胶浓度，以便进行涡流协方差通量估计，又足够小，可以定位在接近音速风速计的位置，而不会造成不可接受的大流量失真。在2006年和2007年的巡航中，对一艘科考船前部进行的测量表明，卡箍是坚固的，能够在无人值守的情况下长时间运行。这里提出的项目将在佛罗里达迈阿密大学开发的新的极端海气相互作用(EASI)浮标上安装两个扣件，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海面(~6米)的地方，同时由于浮标的追波性能，可以保持安全，不会被波浪浸没。在为期4周的部署期间，将在广泛的条件下测量海雾气溶胶的湍流通量，以及风应力、热量、湿度和风致波浪场的细节。这些结果将有助于开发新的和改进的海雾气溶胶生产参数，用于气候模型，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.