Does magnetic reconnection have a characteristic scale in space and time?

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The Earth is continually enveloped by the expanding atmosphere of the Sun (known as the solar wind) that carries with it charged particles (plasma) and the Sun's magnetic field. The Earth's own magnetic field, extending into space, protects us from this solar wind, forming a cavity known as the magnetosphere. A process known as magnetic reconnection allows the Sun's magnetic field to connect to that of the Earth leading to the transfer of particles and energy from the solar wind into the magnetosphere. Some of these particles may travel along the Earth's magnetic field lines and strike the atmosphere, causing it to give off light in displays known as the aurora (commonly known as the northern lights). In fact, magnetic reconnection is the most significant transport process in the Earth's magnetosphere. There is also compelling observational evidence that magnetic reconnection processes take place in the Sun's atmosphere near its surface (the solar corona) and magnetic reconnection may be important for understanding the formation of stars, the origin of cosmic rays (high energy particles coming from space), accretion disks (found around stars, galaxies and black holes), and the generation of magnetic fields in planets, stars and galaxies. Closer to home, understanding and controlling magnetic reconnection is vital in the development of nuclear fusion reactors. Whilst there is a basic understanding of the magnetic reconnection process, exactly how, where, and when it occurs is still not understood. Recent observations of plasma flows and electric currents in the magnetosphere and of brightenings in the aurora, have provided evidence of scale-free behaviour i.e. that fluctuations in these quantities do not have a typical size and are seen across a wide range of sizes. This behaviour is typical of fractals and is often seen in nature such as in the shape of coastlines and the size of snow avalanches. These scale-free observations have, in turn, promoted the idea that magnetic reconnection is itself scale-free. However, there is no direct evidence for this and it is contrary to the traditional understanding of the magnetic reconnection process. Researchers at the British Antarctic Survey have developed a new technique to remotely sense magnetic reconnection in the magnetosphere using a combination of observations made from spacecraft and on the ground with auroral imagers and a radar network known as SuperDARN(the Super Dual Auroral Radar Network). We will use this technique to characterise statistically the structure of magnetic reconnection in both space and time over a wide range of scales. By doing this we will test the hypothesis that magnetic reconnection is scale-free and provide a constraint for new multi-scale magnetic reconnection models.