能夠提前24小時預測大型太陽風暴的新工具

　　中國科技網6月10日報道（張微 編譯）能夠影響GPS和電網技術的，來自太陽的大型磁暴，可能很快就會提前24小時得到預報。

　　日冕物質拋射(CME)是從太陽中噴發出的氣體和磁性物質，有可能破壞衛星和地面技術，干擾無線電傳輸，導致變壓器泄露和停電。

　　這些拋射物質能夠引發GPS技術的諸多問題，而GPS技術在包括汽車到油輪到拖拉機的各種交通工具上有著廣泛的應用。例如，它們可以影響飛機系統在著陸時精確判斷飛機與地面距離的能力，導致飛機長達一個小時沒法著陸。

　　但是，并不是從太陽到地球的每種拋射物質都能對地球造成這么多的干擾;這種力量取決于拋射物質中的磁場方向。目前，衛星只能在拋射物質接近地球的時候，才能明確地辨識出日冕物質拋射的磁場方向，發出一個30-60分鐘的通知。這點時間不足以減輕對電網和GPS操作系統的影響。

　　現在，一個新的測量和建模工具可以提前24小時通知對地球有害的拋射物質到達地球的時間。倫敦帝國理工學院的校友和客座研究員，同時也是美國宇航局戈達德太空飛行中心的一位太空科學家尼爾 薩瓦尼博士領導的研究團隊開發了這項技術，研究成果發表在今天出版的《Space Weather》期刊上。

　　“當越來越多的技術融合和集成在一起的時候，太空天氣事件的干擾就會越來越多地影響我們的日常生活，”薩瓦尼博士說。“打破24小時預測瓶頸對于有效處理潛在的問題非常重要。”

　　日冕物質拋射的磁場方向取決于兩件事情：它們從太陽噴發出來的最初形態，以及它們奔向地球過程中的演變。日冕物質拋射來自于太陽表面的兩個區域，在拋射向太空和太陽表面之間形成一個牛角包狀的一團日冕物質。

　　隨著日冕物質的移動，里面的磁場方向也在發生改變。如果其中一個磁場與地球磁場的方向相同，那么兩個磁場就會連接，“打開一扇門”讓這些物質到達地球并引起地磁風暴。

　　此前，預測依賴于測量初始CME的爆發，但是對于CME爆發和日冕物質到達地球過程中的情況沒有有效地建模。這項新技術仔細調查了日冕物質來自太陽的具體位置，利用一系列的觀測來追蹤和建模日冕物質的演變。

　　薩瓦尼博士和他的同事根據之前的八次日冕物質拋射情況，對該模型進行了測試，結果顯示，對于改善目前影響地球的太陽風暴預測系統帶來了巨大希望。如果美國宇航局支持進行進一步的測試，那么這個系統將很快在美國國家海洋和大氣管理局以及英國氣象局的地磁風暴預測中得到應用。

　　New tool could predict large solar storms more than 24 hours in advance

　　Large magnetic storms from the Sun, which affect technologies such as GPS and utility grids, could soon be predicted more than 24 hours in advance.

　　Coronal mass ejections (CMEs) are eruptions of gas and magnetised material from the Sun that have the potential to wreak havoc on satellites and Earth-bound technologies, disrupting radio transmissions and causing transformer blowouts and blackouts.

　　These mass ejections can cause problems with GPS technology - used by all kinds of vehicles, from cars to oil tankers to tractors. For example, they can affect the ability of aircraft systems to judge precisely a plane\'s distance from the ground for landing, leading to planes being unable to land for up to an hour.

　　However, not every mass ejection from the Sun that travels past the Earth causes this much disturbance; the power depends on the orientation of magnetic fields within the mass ejection. Currently, satellites can only tell the orientation of a mass ejection\'s magnetic field with any certainty when it is relatively close to the Earth, giving just 30-60 minutes\' notice. This is not enough time to mitigate the impacts on utility grids and systems operating on GPS.

　　Now, a new measurement and modelling tool could give more than 24 hours\' notice of mass ejections that could be harmful to systems on Earth. Details of the technique, developed by a team led by Dr Neel Savani, an alumnus and Visiting Researcher at Imperial College London and a space scientist at NASA\'s Goddard Space Flight Center, were published today in a paper in Space Weather.

　　"As we become more entwined with technology, disruption from large space weather events affects our daily lives more and more," said Dr Savani. "Breaking through that 24 hour barrier to prediction is crucial for dealing efficiently with any potential problems before they arise."

　　The orientations of magnetic fields within coronal mass ejections depend on two things: their initial form as they are erupted from the Sun, and their evolution as they travel towards Earth. Mass ejections originate from two points on the Sun\'s surface, forming a croissant-shaped cloud in between that discharges into space.

     This cloud is full of twisted magnetic fields that shift as they travel. If one of these magnetic fields meets the Earth\'s magnetic field at a certain orientation, the two will connect, \'opening a door\' that allows material to enter and cause a geomagnetic storm.

　　Previously, predictions had relied on measuring the initial CME eruption, but were not efficient modelling what happened between this and the cloud\'s arrival at Earth. The new technique takes a closer look at where mass ejections originate from on the Sun and makes use of a range of observatories to track and model the evolution of the cloud.

　　Dr Savani and colleagues have tested the model on eight previous mass ejections, with the results showing great promise at improving the current forecasting system for large Earth-directed Solar storms. If further testing at NASA supports these initial results, the system could soon be used by NOAA in the US and the Met Office in the UK for geomagnetic storm predictions.