Using satellite data to understand the influence of marine biogenic activity on high latitude clouds and climate

该项目旨在利用卫星数据推进我们对生物海洋活动如何影响偏远高纬度地区云和气候的理解。在我们对未来气候变化的预测中，作为形成云滴和冰的种子的气溶胶颗粒的影响是最大的不确定性。对于用作确定人为气溶胶影响基线的前工业化时期尤其如此。在前工业化时期，自然气溶胶源占主导地位，因此非常需要了解它们，以便作出准确的气候预测。有充分的证据表明，海洋中的浮游植物对偏远地区的气溶胶和云滴数浓度（CDNC）有很强的影响，这反过来又影响了太阳能量云反射回太空的多少。但是，所涉及的过程的许多细节需要澄清。最近的卫星研究表明，最新的地球系统气候模式（用于即将到来的CMIP6气候评估）严重低估了高纬度地区的CDNC，指出生物气溶胶的外来来源可能与海冰的存在和/或融化有关。我们对高纬度云层中决定冰形成的因素的了解甚至更加不确定，但也对云反射率和气候模型预测具有重要意义。我们缺乏知识的部分原因是无法进入南极、南大洋和北极等偏远地区。因此，卫星仪器是研究这些地区的理想方法。该项目的目的如下：1)利用野外活动数据验证CDNC和云冰川的最新检索结果：目前使用太阳反射光的CDNC和冰浓度检索存在不确定性，并且需要确定卫星观测到的南极洲周围的高CDNC值是否是由于检索偏差造成的。2)利用卫星数据确定导致南极洲和其他高纬度地区附近的高CDNC值的因素，并确定高纬度云的冰川化程度和潜在原因：将使用卫星检索的CDNC、冰浓度、云相（液体或冰）和其他云特性，以及海冰覆盖和浮游植物活动标志。这将需要对大量数据进行分析，并有机会使用机器学习技术来确定CDNC/云冰川与潜在致病因素之间的相关性。3)利用卫星数据在最新的英国气象局地球系统气候模式（UKESM1）中测试和改进高纬度气溶胶、CDNC、冰过程和云的表示：模式评估将涉及对UKESM1模式的数百万个变体的分析，这些变体采样了不确定的参数组合。目的是利用卫星数据确定合理的模式变体，减少生物成因气溶胶形成机制的不确定性。这将需要使用超级计算设备和“大数据”处理技术。英国南极调查局是这项工作的一个项目合作伙伴，将在收集和分析高纬度数据方面带来丰富的经验，并将提供与过去和即将进行的实地活动的数据一起工作的机会，并可能有机会参加即将进行的南极活动。英国气象局的合作伙伴将提供最先进的UKESM1地球系统模型和超级计算设施，并有机会帮助开发下一代气候模型。

This project aims to use satellite data to advance our understanding of how biogenic marine activity affects clouds and climate in remote high latitude regions.The influence of aerosol particles that act as seeds to form cloud droplets and ice represents the largest uncertainty in our predictions of future climate change. This is particularly true for the pre-industrial period that is used as a baseline for determining the influence of anthropogenic aerosol. In the pre-industrial period natural aerosol sources dominated and so there is a great need to understand them in order to make accurate climate predictions.There is good evidence that phytoplankton in the oceans strongly influence aerosols and cloud drop number concentrations (CDNC) in remote regions, which in turn affects how much of the Sun's energy clouds reflect back to space. However, many of the details of the processes involved need to be clarified. Recent satellite studies suggest that the latest Earth System climate models (as used for the upcoming CMIP6 climate assessment) severely underestimate CDNC at high latitudes pointing towards exotic sources of biogenic aerosol potentially related to the presence and/or the melt of sea-ice. Our knowledge of what determines ice formation in high-latitude clouds is even more uncertain, but yet also has important implications for cloud reflectivity and climate model predictions. Our lack of knowledge partly stems from the inaccessibility of remote locations such as Antarctica, the Southern Ocean and the Arctic. Satellite instruments thus represent an ideal way to study these regions. The aims of the project are as follows :-1) Validate the latest retrievals of CDNC and cloud glaciation using field campaign data: There is uncertainty in current CDNC and ice concentration retrievals that use reflected light from the Sun and a need to determine whether the high CDNC values around Antarctica observed by satellite are due to retrieval biases.2) Use satellite data to determine the factors that lead to high CDNC values near Antarctica and other high latitude regions, and to determine the degree and potentially the causes of glaciation of high latitude clouds: Satellite retrievals of CDNC, ice concentrations, cloud phase (liquid or ice) and other cloud properties, as well as retrievals of sea-ice coverage and markers of phytoplankton activity, will be used. This will require the analysis of vast amounts of data with the opportunity to use machine learning techniques to determine correlations between CDNC/cloud glaciation and potential causative factors.3) Use the satellite data to test and improve the representation of high latitude aerosols, CDNC, ice processes and clouds in the latest Met Office Earth system climate model (the UKESM1) : The model evaluation will involve the analysis of millions of variants of the UKESM1 model that sample uncertain parameter combinations. The aim is to use the satellite data to identify plausible model variants and reduce uncertainty in biogenic aerosol formation mechanisms. This will require the use of supercomputing facilities and processing techniques for "big data".The British Antarctic Survey is one project partner for this work and will bring great experience in collecting and analysing high latitude data, and will provide the opportunity to work with data from past and upcoming field campaigns, and potentially the chance to take part in an upcoming Antarctic campaign. Met Office partners will provide access to the latest cutting edge UKESM1 earth system model and supercomputing facilities with the opportunity to help develop the next generation of climate models.