在天气预报中应用机器学习
原文發表于 2017年7月21日 ,是由英國氣象信息部門(Met Office Informatics Lab, UK)發表的。
Authors list :Rachel Prudden, Niall Robinson, Alberto Arribas , Charles Ewen
In the 1950s, there was a revolution in weather forecasting. Advances in technology made it possible to simulate the atmosphere using dynamical models, quickly and accurately enough to be used for operational forecasts. Dynamical models are now a central part of weather forecasting. Starting from basic physical laws, they make it possible to predict events such as storms before they have even begun to form.
二十世紀五十年代,天氣預報有了革命性的變化。技術進步使我們可以使用模式來模擬大氣運動,這種方法在預報業務中是快速而準確的。模式直到現在仍是天氣預報的核心。通過基本的物理學原理,模式可以在暴風雨形成之前便做出預測。
A crucial challenge in the coming decade will be the integration of direct physical simulations on the one hand, and data-driven approaches on the other. Such a hybrid approach holds many opportunities for weather forecasting, as well as countless other fields.
未來十年的一個關鍵挑戰將是直接物理模擬與數據驅動方式融合應用。這種混合方式為天氣預報以及無數其他領域帶來許多機會(可能性)。
From model to outcomes 從模式到結果
- Localisation and super-resolution (downscaling) 局地和超高分辨率(降尺度)
- Links to the real world 與其他領域結合
Operational weather models are usually run at a resolution of between 1km and 10km, that is, everything within the same square kilometer is represented by a single grid cell. This resolution is fine enough to capture a wide range of phenomena, but will obviously be unable to capture very localised details.
目前業務運行的天氣模式的空間分辨率在1公里和10公里之間,這意味著在這個分辨率網格內只有一個值。這個分辨率對于一個大尺度的天氣現象是夠用的,但是對于一些局地性的天氣卻是不夠的。
It may be possible to perform this kind of localisation using models trained on historical data, providing a mapping between the large-scale predictions of the simulation and the small-scale effects. This is an area of active research which could make forecasts more useful for day-to-day activities.
可以嘗試使用歷史數據訓練的模型(機器學習的方法)來預測局地效應,之后建立一個大尺度模型預測與小規模效應之間的映射關系。此類研究現在非常活躍,有助于提升天氣預測對日常活動的價值。
As well as predicting weather at finer scales, similar techniques could help to link weather forecasts with their broader impacts. Many things are affected by the weather, either directly or indirectly; these include traffic, hayfever, flight delays, and hospital admissions. While some effects may not be easy to simulate, using data-driven models could help to provide advance warning of significant impacts.
除了在更細微的尺度上預測天氣,類似的技術可以幫助將天氣預報與更廣泛的領域聯系起來。許多事情直接或間接地受到天氣的影響,包括交通、花粉過敏、飛行延誤和住院率,這些事情不容易通過模型來推理,但可以使用數據驅動的模型來預測進而提供預警。
Emulation
- Faster components (emulation) 局部加速
- Hybrid models 混合模式
Once a machine learning model has been trained, it is often much faster to run than a full simulation. This is the motivation for a technique called model emulation. The idea is to build a fast statistical model which closely approximates a far more expensive simulation. Emulators are already being applied to problems such as climate sensitivity. An area of current interest is using the same tools to speed up some components of the weather model.
機器學習模型一旦被建立,通常是要比完整的數值模擬工程要快。可以使用一種模式仿真(model emulation)的方法,建立一個非常接近于數值模式的統計學模型,這種方法已經應用于氣候敏感性研究。現在比較熱的領域是使用機器學習工具加速天氣模式的部分 組件。
There are some aspects of weather prediction which require a full physical simulation; this is what lets you predict unseen events with confidence. Other places this is not possible or even justified, and a statistical approximation may be the best you can do. This second case is where emulation can be useful in operational forecasting.
天氣預測中的一些場景是需要通過大氣物理模式來實現,但有些場景使用模式卻是不可能或不合理的,這些場景下使用統計學趨近是最好的選擇,模式仿真(model emulation)在預報業務中會有效果。
Beyond emulators, there is broader potential for hybrid models with both learned and simulated components. Such models would combine data-driven and physically-driven approaches. For example, it may be possible to adapt statistical components of the model to the local terrain, based on previous observations.
除了模式仿真(model emulation),建立融合機器學習與數值模擬的混合模式也是非常有潛力的。這種混合模型可以融合數據驅動和物理驅動兩種方法。比如,在局地地形對天氣影響方面,可以基于前期觀測的結果訓練模型,融合到數值模式中。
Descriptive learning 描述學習
- Finding features 特征識別
- Exploring and summarising 信息匯總
An area where machine learning has made dramatic progress is feature detection. You can see examples of this in apps which not only detect your face, but add glasses and a moustache in real-time.
機器學習取得了顯著進步的一個領域是特征檢測。一些基于機器學習的應用程序不僅可以檢測到您的臉部,還可以實時在臉上添加眼鏡和胡子。
There is currently a lot of interest in applying similar methods to hazard detection, especially to storm tracking. Trained experts are able to recognise storms and trace their paths from weather imagery; in principle there is no reason an algorithm could not learn to do the same.
目前有很多研究在使用類似的方法做災害監測,特別是風暴跟蹤。訓練有素的專家能夠識別風暴,并從天氣圖像中追蹤路徑,理論上算法也可以做得到。
Another application could address the challenges posed by data volume and complexity when dealing with data from physical simulations. The fields output by such models are highly multidimensional; making sense of them is a complex task, requiring many “screens” of information. An algorithm which could summarise the salient features and bring them to the forecaster’s attention would help streamline this task.
預報員在使用觀測數據和數值預報結果時,需要處理大量的多維度的數據,理解這些數據是一項復雜的工作,經常需要切換多個屏幕來查閱信息。通過算法可以自動識別這些數據中的關鍵信息,然后匯總到預報員的桌面,從而簡化這項工作。
Summary 總結
Exploring combinations of machine learning and numerical simulation is an area of great interest and promise for the Met Office. Not only does it offer an advance in scientific capability, but the challenges arising from the attempt could drive new research in the field of machine learning. This article has given an outline of a few research directions within meteorology, but a similar story holds across a range of scientific disciplines.
探索機器學習和數值模擬的組合是 Met Office 非常感興趣且抱有期望的領域。它不僅促進了預報能力的進步,而且可能會推動機器學習領域的新研究。本文概述了氣象學中的一些研究方向,在其他科學學科中,機器學習的應用的方向與本文所述類似。
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