High Wind Air-Sea Exchanges (HiWASE)

该提案是英国对国际表层海洋-低层大气研究项目的一部分贡献，该项目旨在提高我们对海洋和大气相互作用方式的理解，重点关注影响世界气候的相互作用。一个鲜为人知的相互作用是大气和海洋之间气体交换的方式。我们需要能够预测不同条件下的海气交换，因为它决定了大气中微量气体的数量，从而决定了导致气候变化的“温室效应”的大小。交换速率取决于与大气相比地表水中气体的浓度，也取决于环境因素，如风速、海浪的大小，以及形成“白马”的海浪数量。为了解决这些不同的影响，我们需要进行大量的测量，因此我们计划将自动测量系统安装在一艘船上，这艘船会在一个空气和海洋气体浓度经常存在巨大差异的地区航行很长时间。合适的自动化系统已被证明对二氧化碳（CO2）有效，因此我们将测量该气体的交换，并利用我们的结果通过我们对其他气体不同物理和化学性质的了解来估计它们的转移。我们将保持三年的测量，以便对各种不同的风和海况进行采样。我们特别想获得在高风速下的测量，因为那时的交换要大得多。例如，二氧化碳的交换可能会随着风速的平方（或者可能是立方——我们还不知道）而变化，这意味着42英里每小时风速下的二氧化碳交换是14英里每小时风速下的9倍（或者可能是27倍）。虽然风暴和其他高风速事件（如飓风）的持续时间相对较短，但可以看出，它们可能是很大一部分海气交换的原因，特别是在多风暴的北大西洋和南大洋。因此，对高风速下的交换的理解是一个重要的，但目前尚不清楚的谜团。在公海上进行测量是很困难的。为了在深水和恶劣天气条件下可靠地获取数据，这些仪器必须安装在船上，并且必须精确测量船舶的运动，并从风速和湍流数据中去除。船舶干扰空气流向传感器，导致测量风速与真实风速相比偏高或偏低。这种“流量扭曲”也会在测量交换本身时造成很大的偏差。这些困难解释了在高风速下（超过30英里/小时的风速没有数据）获得的数据的缺乏，以及在一个实验和另一个实验的结果之间发现的一些差异。对交换本身的测量并不是所需要的全部，因为为了理解交换的原因，还需要测量许多其他变量。例如，许多特性的海气交换被认为取决于海浪的行为，巨浪对风的方向，海浪破碎和白浪的数量以及海洋表面和大气之间的温差，此外还有风速。这些必须在交换的同时进行测量，这样才能发现它们之间的关系。一旦了解了这种关系，就有可能计算出这种交换，而不必直接测量它们，例如使用从卫星数据中获得的风速和波浪信息。这些关系还将用于气候模型，以改进它们模拟海洋和大气之间相互作用的方式，从而改进气候变化预测。

This proposal is part of the UK's contribution to the international Surface Ocean-Lower Atmosphere Studies project which aims to improve our understanding of the way the ocean and atmosphere interact, with emphasis on the interactions which affect the world's climate. One poorly understood interaction is the way gases are exchanged between the atmosphere and ocean. We need to be able to predict the air-sea gas exchange under varying conditions because it determines the amount of trace gases in the atmosphere, and hence the size of the 'greenhouse effect' which is causing our climate to change. The rate of exchange depends on the concentration of the gas in the surface water compared to the atmosphere and also on environmental factors such as wind speed, the size of the ocean waves, and how many waves are breaking to form 'white horses'. To untangle these different effects we need a lot of measurements and therefore we plan to put automatic measuring systems on a ship which spends a lot of time at sea in an area where there are often large differences in the air and sea gas concentrations. Suitable automatic systems have been shown to work for carbon dioxide (CO2) so we will measure the exchange of that gas and use our results to estimate the transfers of other gases through our knowledge of their different physical and chemical properties. We will maintain the measurements for a three year period in order to sample a wide range of different wind and sea conditions. We particularly want to obtain measurements at high wind speeds since the exchanges are much larger then. For example, the exchange of CO2 may vary with wind speed squared (or perhaps cubed - we don't yet know) which would mean that the exchange of CO2 during wind speeds of 42 miles per hour is nine (or perhaps twenty seven) times greater than the exchange at wind speeds of 14 mph. Although storms and other high wind speed events such as hurricanes are relatively short lived it can be seen that they may be responsible for a large fraction of the air-sea exchanges, particularly in the stormy North Atlantic and Southern Ocean. An understanding of the exchanges under high wind speeds is therefore an important, but presently missing, piece of the puzzle. Making measurements over the open ocean is difficult. To reliably obtain data in deep water and bad weather conditions the instruments must be mounted on a ship and the ship's motion has to be accurately measured and removed from the wind speed and turbulence data. The ship disturbs the flow of air to the sensors causing the measured wind speed to be biased high or low compared to the true wind speed. This 'flow distortion' can also cause very large biases in the measurement of the exchanges themselves. These difficulties explain the lack of data obtained during high wind speeds (there are none for winds over 30 mph) and also some of the differences found between the results from one experiment and another. Measurements of the exchanges themselves is not all that is required, since, in order to understand the causes of the exchanges, many other variables need to be measured as well. For example, the air-sea exchanges of many properties are thought to depend on the behaviour of the waves, the direction of the swell waves to the wind, the amount of wave breaking and whitecapping and the difference in temperature between the ocean surface and the atmosphere, in addition to the wind speed. These have to measured at the same time as the exchanges so that the relationships between them can be discovered. Once the relationships are understood it will be possible to calculate the exchanges, rather than having to measure them directly, using wind speed and wave information available from satellite data for example. The relationships will also be used in climate models to improve the way they simulate the interactions between the ocean and atmosphere, and thus improve climate change predictions.