Ice formation in clouds and the implications for climate

该项目将天气尺度和气候模拟与卫星数据相结合，以了解云中冰的形成及其对未来气候的影响。气候模型在描述云中冰和过冷水滴的混合物方面非常差。因此，模型在模拟的冰和水的数量上存在巨大差异，对于许多模型来说，与卫星观测的一致性非常差。云中冰晶的形成降低了云的反射率，甚至可以通过强降水完全清除云中的水分，导致云层覆盖率大幅下降。模型预测的范围很大，部分原因是模型中对与冰有关的过程的表示不充分(有时是非物理的)，大多数模型甚至忽略了触发冰形成的粒子-冰核粒子(INP)的任何表示。冰的形成是确定云反馈的大小(未来气候中云性质的变化可能在多大程度上改变气候)的关键过程。因此，它代表了气候预测中的一个主要不确定性。决定混合相云反馈强度的两个关键因素是当今云中的冰量，以及这种冰量对气温升高或气象条件其他变化的反应。该项目将使用卫星观测来了解并限制英国地球系统模型(UKESM)中的这些因素。

This project combines weather-scale and climate modelling with satellite data to understand ice formation in clouds and the effect on future climate.Climate models are very poor at representing the mixture of ice and supercooled water drops in clouds. Models therefore diverge dramatically in the amounts of ice and water that they simulate and the agreement with satellite observations is extremely poor for many models. The formation of ice crystals in a cloud reduces cloud reflectivity and can even result in the complete removal of cloud water through strong precipitation, leading to substantial reductions in cloud coverage. The huge range of model predictions is partly due to inadequate (and sometimes non-physical) representations of ice-related processes in models, with most models even neglecting any representation of the particles that trigger ice formation - ice-nucleating particles (INPs).Ice formation is a critical process in determining the magnitude of cloud feedbacks (how much a change in cloud properties in a future climate could alter the climate). It therefore represents a major uncertainty in climate projections. Two key factors determining the strength of the feedback for mixed-phase clouds are the amount of ice in present-day clouds and the response of this ice content to increases in temperature or other alterations in the meteorological conditions. This project will use satellite observations to understand and then constrain these factors in the UK Earth System Model (UKESM).