The role of air-sea interactions in sub-seasonal variability

这项研究旨在了解海气相互作用控制高影响极端天气发展和加剧的机制，并提高数值模式模拟这些机制的能力。天气和气候的每日和每月区域变化通过影响农业、水文和基础设施来影响人们的生活和生计。这些次季节变化是由高影响现象控制的，包括热带气旋；造成干旱和热浪的“阻塞”高压系统；以及引起季风降雨活跃和抑制的广泛、有组织的热带雷暴活动增强或减少的区域。对现场和卫星观测的分析表明，大气和海面之间的能量和水汽转移影响这些现象的位置和强度。这些转移导致海面温度(SST)的短暂(1-2周)变化，这可能会影响大气；例如，热带雷暴倾向于更温暖的水域。然而，仅凭观测是不可能区分强迫和反应的，这妨碍了对海-气反馈如何影响亚季节现象的理解。许多短期和中期(1-14天)预报只使用大气的数值模式，而忽略了潜在的关键的海-气相互作用。代表这些相互作用的大气-海洋耦合模式被用于季节到年代际预报和气候变化预测，但往往难以模拟亚季节变化。这些缺陷限制了对区域天气和极端天气的预测，造成了区域气候变化预测的不确定性，并阻止了科学家使用这些模型来理解海气反馈。这些缺陷将通过一个大气模型和一个简化的海洋模型组成的新的建模框架来解决，该框架改进了模拟的短期SST变化；最小化了模型平均气候中抑制高影响现象模拟的误差；并允许仅在全球某些地区或在一年中的特定时间模拟海-气反馈，以帮助理解这些反馈如何影响高影响现象。该框架将与英国气象局、欧洲中期天气预报中心和大气过程多尺度建模中心(美国)的模式一起使用。使用在模拟高影响现象方面有很大不同的模式，可以更彻底地检验关于海-气相互作用影响的假设。这一框架使模拟的海-气相互作用对高影响现象的影响与平均气候模拟中的误差的影响更清晰地分开。以前的研究将这些影响合并在一起，造成了关于海-气相互作用在亚季节变化中所起作用的不确定性。在这一框架下，不同的模型在高影响现象对海-气相互作用的反应方式上的差异将仅仅是由于大气模型的公式的不同造成的。这将启发实验改变这些公式，并调查关键大气过程的表示，如大气湿度和降水之间的关系，如何影响对高影响现象的模拟。对过去高影响现象的重新预测将允许对模拟和观测进行近距离比较，并允许进行实验以测试个别过程的影响。将模拟的平均气候中的模型误差引入特定地区或一年中的某些时间的实验，将确定那些最能抑制亚季节变化的误差。这一研究金将增进对海-气相互作用及其在亚季节变化中的作用、天气和气候周-月变化预测以及区域气候变化预测的了解。

This fellowship aims to understand the mechanisms by which air-sea interactions control the development and intensification of high-impact weather extremes, and to improve the ability of numerical models to simulate those mechanisms.Daily-monthly regional variations in weather and climate influence lives and livelihoods by affecting agriculture, hydrology and infrastructure. These sub-seasonal variations are controlled by high-impact phenomena including tropical cyclones; "blocking" high-pressure systems that cause droughts and heatwaves; and broad, organised areas of enhanced or reduced tropical thunderstorm activity that cause active and suppressed periods of monsoon rainfall.Analysis of field and satellite observations has suggested that transfers of energy and moisture between the atmosphere and the sea surface influence the location and intensity of these phenomena. These transfers result in short-lived (1-2 weeks) changes to sea-surface temperatures (SSTs), which can influence the atmosphere; tropical thunderstorms tend to favour warmer waters, for example. It is not possible to distinguish forcing from response using observations alone, however, preventing understanding of how air-sea feedbacks influence sub-seasonal phenomena. Many short- and medium-range (1-14 days) forecasts use numerical models of only the atmosphere, neglecting potentially critical air-sea interactions. Atmosphere-ocean coupled models that represent these interactions are used for seasonal-to-decadal forecasts and climate-change projections, but often struggle to simulate sub-seasonal variability. These failings limit predictions of regional weather and extremes, create uncertainty in regional climate-change projections and prevent scientists from using these models to understand air-sea feedbacks.These failings will be addressed through a novel modelling framework of an atmospheric model coupled to a simplified ocean model, which improves simulated short-lived SST variations; minimises errors in the model's mean climate that inhibit the simulation of high-impact phenomena; and allows air-sea feedbacks to be simulated in only certain regions of the globe or at certain times of year, to aid understanding of how these feedbacks influence high-impact phenomena. The framework will used with models from the Met Office, the European Centre for Medium-range Weather Forecasts and the Center for Multiscale Modelling of Atmospheric Processes (U.S.). Using models that differ considerably in their simulated high-impact phenomena permits more thorough testing of hypotheses about the impacts of air-sea interactions.This framework allows the simulated effects of air-sea interactions on high-impact phenomena to be more cleanly separated from the effect of errors in the simulation of the mean climate. Previous studies have conflated these effects, creating uncertainty about the role of air-sea interactions in sub-seasonal variability. In this framework, variations among models in how high-impact phenomena respond to air-sea interactions will be caused only by variations in the formulations of the atmospheric models. This will inspire experiments to alter these formulations and investigate how the representation of key atmospheric processes, such as the relationship between atmospheric moisture and precipitation, affects the simulation of high-impact phenomena. Re-forecasts of past high-impact phenomena will allow close comparisons of simulations and observations and permit experiments that test the effects of individual processes. Experiments in which model errors in the simulated mean climate are introduced in particular regions, or times of year, will identify those errors that most inhibit sub-seasonal variability. This fellowship will improve understanding of air-sea interactions and their role in sub-seasonal variability, predictions of weekly-monthly variations in weather and climate, and regional projections of climate change.