Decoding the Northern Lights
- 20 Oct 2022
- Start time
- 7:00 PM
- The Yorkshire Museum
- Dr Maria Walach, University of Lancaster
“Decoding the Northern Lights”
Dr Maria Walach, University of Lancaster, FRAS
“99% of the visible universe is made up of plasma, the fourth state of matter. Plasma is generated when gases are energised. This process constantly happens in Earth’s atmosphere and it means plasma is abundant in geospace, the part of space which is engulfed by Earth’s magnetic field. When plasma is accelerated along the magnetic field and interacts with the atmosphere, one of the most impressive and well-known natural light shows on Earth is generated: the aurora.
In this talk I will explain how the aurora is generated and how we measure and study it. The dynamics in the auroral intensity and locations can tell us a lot about geospace and whilst it is beautiful, the electric fields generated by the moving plasma have consequences for our modern lives.”
This lecture will be held in the Tempest Anderson Lecture Theatre in the Yorkshire Museum, York at 7pm.
Dr Walach won the prestigious British Association lecture prize in Mathematics and Physics in 2022. She now studies how the ionosphere moves and on what timescales it responds to events within the magnetosphere and in space. Her lecture to the YPS first introduced the phenomena of plasma and of solar wind, and then focussed on the Northern Lights, or Aurora Borealis, which are an effect of the solar wind.
The solar wind is a continual stream, mainly of protons and electrons in a plasma state, ejected from the sun’s corona at 250 to 500 miles per second. Plasma is the fourth state of matter, formed when a gas is given sufficient energy to free some electrons from atoms or molecules and to allow charged ions and electrons to coexist – critically, it responds to magnetic fields. Plasma can also be created by lightning, as well as by other high energy sources. Although not abundant on earth, apart from in the magnetosphere, plasma makes up 99% of the visible universe – including the sun.
Most of the solar wind reaching the earth is deflected by the magnetosphere, but some of the more highly charged plasma breaks through, and accelerates along the magnetic lines of force until it reacts with gases in the outer atmosphere – particularly above the polar regions. This generates the aurora, one of the most impressive and well-known natural light shows on Earth, concentrated at about 80 degrees of latitude. The aurora moves around, is very dynamic, encircles the earth mostly in the polar regions, and shows different colours and varying brightness over time but also depending on whether the ‘day’ or ‘night’ side of the earth is being observed.
The northern lights most often occur at altitudes of 100 to 300 km in the atmosphere, but can sometimes occur at altitudes of up to 600 km. With increasing altitude, colours change from pink (due to interactions with nitrogen), to green (oxygen), to blue (nitrogen) to red (oxygen). Latitude also has an effect – in the UK there is a preponderance of blues and greens, changing to reds further north. Satellite images combined with doppler radar from earth show whether the plasma is moving upwards or downwards. Unsurprisingly, the frequency and intensity of aurora are impacted by the eleven-year solar cycle. The aurora phenomenon may be produced by different mechanisms, as evidenced by earth’s Northern and Southern auroras being somewhat different, and by auroras being detected on other planets that have very different atmospheres and magnetic fields than earth.
Other effects of the plasma include geomagnetic storms, which can impact communication systems and can burn out electrical transformers. They are now being predicted by ‘whole atmosphere’ models, which include the highly interactive effects of ocean currents, surface wind, and different levels of the atmosphere including the ionosphere. Although geomagnetic storms are impacted by surface weather, the reverse is not generally true.
The lecture was illustrated with many stunning photographs and video clips, many taken from satellites and manned spacecraft, that demonstrated the size, varying colours, and dynamic nature of the aurora. Many images taken from space measure ultraviolet light and capture different parts of the spectrum than those seen from earth. The lecture generated many technical questions from the enthusiastic audience.