Turbulent Exchange: Aerosols, Bubbles And Gases

现在有一种共识，即全球气候正在发生变化，这是对大气中温室气体浓度增加的反应。这些气体有天然的和人为的来源和汇。对于二氧化碳来说，最大的碳汇是海洋，它吸收了化石燃料燃烧产生的30%到50%的二氧化碳。大气和海洋之间气体交换的方向取决于空气和水之间气体浓度的差异，以及一些改变交换速率的物理过程。这些过程中最重要的是靠近地表的空气和水的湍流混合。这随着风速的增加而增加，但由于其他因素，如波浪状态和海洋和大气近表层的热力学稳定性，这种关系变得复杂。在高风速下，波浪破碎会产生气泡，将空气混合到水柱中。气泡的存在增加了气体交换的速率，但是这一过程的详细性质还没有被完全理解，而且对于描述气体传递速率的方程式的确切形式也存在着相当大的分歧。这在很大程度上是由于缺乏足够详细的测量。波浪破碎和气泡也与海洋喷雾气溶胶颗粒的形成密切相关，这些颗粒对云凝结核很重要。气溶胶是由海面上的气泡破裂产生的。气溶胶形成的速率通常表示为海面上白浪分数的函数，但产生速率的不确定性约为10倍。这表明，白浪分数本身并不能控制产量，但破碎波浪产生的气泡大小和数量等因素可能会随着波浪大小或陡峭度等其他因素而变化。该项目是英国对美国研究巡航的贡献，旨在研究波浪破碎和气泡过程对空气-海洋气体交换的影响。我们将测量白头分数、波浪状态、波浪破碎统计数据和破碎波下的气泡特性。测量将由一个11米高的桅杆浮标进行，浮标配有波浪线，以高空间分辨率测量局部波高，一个气泡相机，用于测量靠近水面的大气泡，以及两个声学谐振器，用于测量水面以下深处的小气泡。另外，“乘波号”还将部署一个独立的浮标，对波浪谱进行长期和独立的测量。在船上，我们将通过涡流相关技术直接测量气溶胶通量，同时测量热量、水蒸气、二氧化碳和动量。我们来自美国国家海洋和大气管理局和夏威夷大学的合作伙伴将测量几种不同气体的通量：二氧化碳、一氧化碳和DMS。气体通量、白头和气泡特性的联合测量将允许根据各种现有参数化直接评估气泡对通量的影响。

There is now a consensus that global climate is changing in response to increasing atmospheric concentrations of greenhouse gases. These gases have natural as well as man-made sources and sinks. For carbon dioxide the largest sink is the ocean, which absorbs between 30% and 50% of the CO2 generated by the burning of fossil fuel. The direction of the exchange of gases between atmosphere and ocean depends on the difference in gas concentration between the air and water, and on a number of physical processes that modify the rate of the exchange. The most important of these processes is turbulent mixing in both the air and water close to the surface. This increases with wind speed, but the relationship is complicated by other factors such as the waves state and the thermodynamic stability of the near-surface layers of both ocean and atmosphere. At high wind speeds wave breaking generates bubbles, mixing air down into the water column. The presence of bubbles increases the rate of gas exchange, but the detailed nature of the process is not fully understood and there is considerable disagreement about the exact form of the equations that describe the rate of gas transfer. This is largely a result of a lack of sufficiently detailed measurements.Wave breaking and bubbles are also closely linked to the formation of sea-spray aerosol particles - these are important as cloud condensation nuclei. Aerosols are generated by the bursting of bubbles at the sea surface. The rate of aerosolformation is often expressed as a function of whitecap fractions on the sea surface, but there is an uncertainty of about a factor of 10 in the production rate. This suggests that whitecap fraction alone does not control the production rate, but thatfactors such as the size and number of bubbles produced by breaking waves may vary with other factors such as size or steepness of the wave.This project is a UK contribution to a US research cruise that aims to examine the impact of wave breaking and bubble processes on air-sea gas exchange. We will measure whitecap fraction, wave state, wave breaking statistics, and bubbleproperties beneath breaking waves. Measurements will be made from an 11-m spar buoy equipped with wave wires to measure the local wave height at high spatial resolution, a bubble camera to measure large bubbles near the surface, and2 acoustical resonators to measure smaller bubbles deeper below the surface. A separate Waverider buoy will also be deployed to make longer term and independent measurements of the wave spectra. On the ship we will make direct measurements of aerosol fluxes via the eddy covariance technique, along with those of heat, water vapour, CO2, and momentum. Our partners from NOAA and the University of Hawi'i will measure fluxes of several different gases: CO2, CO, and DMS. The joint measurements of gas fluxes, and whitecap and bubble properties will allow the influence of bubbles on the flux to be evaluated directly against a variety of existing parameterizations.