Ocean-atmosphere influences on tropical Pacific cloud feedbacks

云反馈，特别是热带高压云的反馈，是对平衡气候敏感性(即二氧化碳倍增导致的全球气温升高)最不确定的贡献1，2.东热带太平洋地区的云在气候模式的云反馈中表现出一些最大的传播。需要把重点放在该区域云辐射效应的驱动因素上，以便更好地了解对云反馈的控制。厄尔尼诺南方涛动是太平洋海洋和大气大规模耦合的典型；这种耦合必须在云反馈驱动因素方面加以考虑。然而，辐射效应直接源于云的分布和微物理性质。这里提出的项目将利用地球观测、现有的现场运动数据和再分析数据来描述小尺度和大尺度的海洋-大气对太平洋云辐射效应的影响，然后将其与该地区的全球模式可变性联系起来。正在进行的NERC计划CloudSense旨在减少气候敏感性的不确定性。该计划的两个项目DCMEX和Circulates正在研究微物理、气溶胶和大范围环流对云反馈的影响。但两者都没有把重点放在赤道太平洋的海洋-大气相互作用上。这些项目可以指导和借鉴这里提出的PHD研究。目标/方法/数据集在先前分析的基础上，在热带太平洋云的卫星(GOES/CERES)观测中，云的特征可变性及其辐射效应3.探索观测到的海-气相互作用变量(如SST、海洋热含量可变性、近地表空气温度和湿度、风速、Walker/Hadley环流强度、云基温或气溶胶浓度)对太平洋云可变性的潜在重要性。这项工作将首先将影响云的“输入”变量和“输出”云变量分解为主成分，并使用多元线性回归将输入和输出关联起来。如果有必要解决科学问题，我们将发展到更复杂的技术，如自动编码器，它能够通过使用非线性关系更好地表示变化，但保留少量特征以便于解释。这种经验方法将进一步发展“云控制因素”方法4，该方法迄今尚未包括对海洋相互作用和重要的云微物理过程的关注。关键数据集包括MODIS/CALIPSO卫星数据、HadISST、英国气象局EN4和TOGA-COARE/CEPEX太平洋实地活动5、6、7.将已确定的重要变量(包括它们的相互作用)应用于全球模式理解。评估变量在全球气候模式中的表现，以及变量是否可以解释太平洋云反馈中的大模式扩散，或者不同的变量在模式中是否重要。

Cloud feedback, particularly resulting from tropical high cloud, is the most uncertain contribution to equilibrium climate sensitivity (i.e. global temperature rise from doubling of CO2)1,2. Clouds in the eastern tropical Pacific region exhibit some of the largest spread in cloud feedback across climate models. A focus on drivers of cloud radiative effects in the region is needed in order to better understand controls on cloud feedback.The El Nino Southern Oscillation typifies the large-scale coupling of ocean and atmosphere in the Pacific; a coupling that must be considered in relation to drivers of cloud feedback. However, radiative effects stem directly from the distribution and microphysical properties of clouds. The project proposed here will use Earth observations, existing in-situ campaign data and reanalysis data to characterise the small and large-scale ocean-atmosphere influences on the Pacific cloud radiative effect, and then relate this to global model variability in the region.An ongoing NERC programme, CloudSense, aims to reduce uncertainty in climate sensitivity. Two of the programme's projects, DCMEX and CIRCULATES, are between them studying the effects of microphysics, aerosol and large-scale circulation on cloud feedback. But neither has focused on the ocean-atmosphere interaction in the equatorial Pacific. These projects can guide, as well as learn from, the PhD research proposed here.Objectives / Methods / DatasetsCharacterise variability in clouds and their radiative effect in satellite (GOES/CERES) observations of tropical Pacific cloud, building on previous analysis3.Explore the potential importance to Pacific cloud variability of observed ocean-atmosphere interaction variables (e.g SST, ocean heat content variability, near surface air temperature and humidity, wind speed, strength of Walker/Hadley circulations, cloud base temperature, or aerosol concentration). The work will begin by decomposing "input" variables that influence cloud and "output" cloud variables into principal components and associating inputs and outputs using multiple linear regression. If it is necessary to address the scientific questions, we will progress to more sophisticated techniques, such as an autoencoder, that are better able to represent variance by using nonlinear relationships but retain a small number of features for ease of interpretability.This empirical approach will further develop the "cloud-controlling factors" approach4, which so far has not included a focus on ocean interactions and important cloud microphysical processes. Key datasets include MODIS/CALIPSO satellite data, HadISST, UK Met Office EN4, and TOGA-COARE/CEPEX Pacific field campaigns5,6,7.Apply identified important variables (including their interactions) to global model understanding. Assess the representation of variables in global climate models and whether the variables can explain the large model spread in Pacific cloud feedback, or whether different variables are important in the models.