High Wind Air-Sea Exchanges (HiWASE)

这项建议是英国对国际表层海洋-低层大气研究项目的贡献的一部分，该项目旨在提高我们对海洋和大气相互作用方式的理解，重点是影响世界气候的相互作用。一种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大气-海洋气体交换，因为它决定了大气中微量气体的数量，从而决定了导致我们气候变化的“温室效应”的规模。交换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，以及有多少海浪正在破裂形成“白马”。为了解决这些不同的影响，我们需要大量的测量，因此我们计划在一艘在海上花费大量时间的船只上安装自动测量系统，该区域的空气和海洋气体浓度往往存在很大差异。合适的自动化系统已被证明适用于二氧化碳(CO2)，因此我们将测量这种气体的交换，并通过我们对其他气体不同物理和化学性质的了解，使用我们的结果来估计其他气体的转移。我们将在三年内保持测量，以便对各种不同的风况和海况进行采样。我们尤其希望在高风速下获得测量结果，因为那时的交易所要大得多。例如，二氧化碳的交换可能会随着风速的平方而变化(或者可能是立方的--我们还不知道)，这意味着在每小时42英里的风速下，二氧化碳的交换比在每小时14英里的风速下的交换要大9倍(或者27倍)。尽管风暴和飓风等其他高风速事件的持续时间相对较短，但可以看出，它们可能是造成海气交换的一大部分原因，特别是在暴风雨肆虐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、但目前还没有解决的谜题。在开阔的海洋上进行测量是困难的。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，并且必须准确地测量船舶的运动，并从风速和湍流数据中删除。这艘船干扰流向传感器的气流，导致测量的风速与真实风速相比偏高或偏低。这种“流量失真”还可能在交易所本身的衡量中造成非常大的偏差。这些困难解释了为什么在高风速时缺乏数据(超过每小时30英里的风速没有数据)，也解释了从一个实验和另一个实验结果之间发现的一些差异。对交易所本身的测量并不是所需的全部，因为为了了解交易所的原因，还需要测量许多其他变量。例如，许多属性的海气交换被认为取决于海浪的行为、海浪对风的方向、海浪破碎和白浪的数量、海洋表面和大气之间的温差，以及风速。这些必须与交易所同时进行衡量，以便发现它们之间的关系。一旦了解了这些关系，就有可能计算交换，而不是直接测量它们，例如使用从卫星数据获得的风速和海浪信息。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，从而改善对气候变化的预测。

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.