GeoLog

Aurora

Imaggeo on Mondays: How do Earth’s Northern Lights form?

Imaggeo on Mondays: How do Earth’s Northern Lights form?

Aurora Borealis, which means Northern Lights are caused by electrically charged particles from the sun, which enter the Earth’s atmosphere and collide with gases such as oxygen and nitrogen. When the charged particles are blown towards the Earth by the solar wind, they are largely deflected by the Earth’s magnetic field. However, the Earth’s magnetic field is weaker at the poles and therefore some particles enter the Earth’s atmosphere and collide with gas particles. It has been found that in most instances northern and southern auroras are mirror-like images that occur at the same time, with similar shapes and colours.

Auroras can appear in many vivid colours, although green is the most common. Auroras can also appear in many forms, from small patches of light that appear out of nowhere to streamers, arcs, rippling curtains or shooting rays that light up the sky with an incredible glow. Ny Ålesund, Svalbard constitutes an ideal platform for observing and investigating Aurora Borealis thanks to the scarcity of anthropogenic light sources and the dark polar night sky.

This photo was kindly provided by Gregory Tran, who is going to be the AWIPEV Station Leader for the Overwintering period 2019-2020.

Description by Konstantina Nakoudi, as it first appeared on imaggeo.egu.eu

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Magnetic interaction

Imaggeo on Mondays: Magnetic interaction

Space weather is a ubiquitous, but little known, natural hazard. Though not as tangible as a volcanic eruption, storm or tsunami wave, space weather has the potenital to cause huge economic losses across the globe. In Europe alone, the interaction of solar wind with our planet’s magnetosphere, ionosphere and thermosphere, could lead to disrutions to space-based telecommunications, broadcasting, weather services and navigation, as well as distributions of power and terrestrial communications.

The Sun’s magnetic field drives all solar activity, from coronal mass ejections (CMEs), to high-speed solar wind, and solar energetic particles. While not all solar activity impacts the Earth, when it does, it can cause a geomagnetic storm. The Earth’s magnetic field creates, the magnetosphere which protects us from most of the particles the Sun emits. But when a “CME or high-speed stream arrives at Earth it buffets the magnetosphere. If the arriving solar magnetic field is directed southward it interacts strongly with the oppositely oriented magnetic field of the Earth. The Earth’s magnetic field is then peeled open like an onion, allowing energetic solar wind particles to stream down the field lines to hit the atmosphere over the poles,” explains NASA.

Aurorae are the most visible effect of the sun’s activity on the Earth’s atmosphere. They usually occur 80 to 300 km above the Earth’s surface, but can extend laterally for thousands of kilometers. They most commonly occur at the Earth’s poles, meaning only those at very northern, or southern, latitudes get the chance to see them (at least regularly). However, they are a reminder of the Sun’snpower and the threat posed by space weather.

To bring aurora to those who haven’t seen them before, and raise awarness about space weather at the same time, Jean Lilensten, director of research at l’Institut de planétologie et d’astrophysique de Grenoble (IPAG) in France, created the Planeterrella; an experiment which includes two spheres, one acting as the Earth and the other acting as the Sun. It allows for auroral displays, and demonstrations of other phenomena which ocurr in the space environment, to be brought into classrooms and public outreach events.

Today’s featured image shows the Planeterrella and several space phenomena. The violet colors on the big sphere ( the “star” ) are due to N2+ (a nitrogen cation), while the redish light on the little one is due to nitrogen. Both colours are seen in actual aurorae on Earth. The red “bow” in the middle, between the two spheres, is a bow shock similar to the magnetopause between Earth and the Sun (of course not to scale). Finally, a direct magnetic reconnection between the two spheres can be seen at the bottom.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

Geosciences column: Making aurora photos taken by ISS astronauts useful for research

Geosciences column: Making aurora photos taken by ISS astronauts useful for research

It’s a clear night, much like any other, except that billions of kilometers away the Sun has gone into overdrive and (hours earlier) hurled a mass of charged particles, including protons, electrons and atoms towards the Earth.  As the electrons slam into the upper reaches of the atmosphere, the night sky explodes into a spectacular display of dancing lights: aurora.

Aurora remain shrouded in mystery, even to the scientists who’ve dedicate their lives to studying them. Photographs provide an invaluable source of data which can help understand the science behind them. But, for aurora images to be of scientific value researchers need to know when they were taken and, more importantly, where.

You’ve got to be in the right place at the right time to catch a glimpse of the elusive phenomenon. In the Northern Hemisphere, aurora season peaks in autumn through to winter. Geographically, the best chance of seeing them is at latitudes between 65 and 72 degrees – think the Nordic countries.

That is unless you are an astronaut on the International Space Station (ISS), in which case, you’ve got the best seat in the house!

The orbit of the ISS means it skims past the point at which aurora intensity is at its peak, which also happens to be the point at which they look their most spectacular. Its orbital speed means it can get an almost global-scale snapshot of an aurora, passing over the dancing lights in just under 5 minutes.

Not as much is known about Aurora Australis (those which occur in the southern hemisphere) as we do about the Northern Lights (visible in the northern hemisphere), because there are far less ground-based auroral imagers south of the equator. The ISS orbit means that astronauts photograph Aurora Australis almost as frequently as Aurora Borealis, helping to fill the gap.

Testament to the privileged viewpoint is the hoard of photographs ISS astronauts have amassed over time – perfect for scientists who study aurora to use in their research.

Time-lapse shot from the International Space Station, showing both the Aurora Borealis and Aurora Australis phenomena. Credit: NASA

Except that, until recently, the ISS photographs were of little scientific value because they aren’t georeferenced. The images are captured by astronauts in their spare time using commercial digital single lenses reflector cameras (DSLRs), which can’t pinpoint the location at which the photographs were taken – they were never intended to be used in research.

Now, researchers at the European Space Agency (ESA) have developed a method which overcomes the problem. By mapping the stars captured in each of the photographs and the timestamp on the image (as determined by the camera used to take the photograph), the team are now able to geolocated the images, giving them accurate orientation, scale and timestamp information.

Despite the success, it’s not a straightforward thing to do. One of the main problems is that the timestamps aren’t always accurate. Internal clocks in DSLRs have a tendency to drift. Over the period of a week they can be out by as much as a minute, making it difficult to establish the location of the ISS when the image was captured. This has implications when creating the star map, as the location of the station is used as a starting point.

To resolve the issue, aurora images which also include city lights can be aligned to geographical maps using reference city markers to get a timestamps accurate to within one second or less. In the absence of city lights, images which also capture the Earth’s horizon are aligned with its expected position instead. The correction works best if both city lights and the horizon can be used.

Errors are also introduced when the star maps can’t be fully resolved (due to the original image being noisy, for example) and because the method assumes that auroras originate from a single height, which isn’t true either.

detailed comparison between the ISS image plotted in Fig. 11 (b) and the contemporaneous image acquired by the SNKQ THEMIS ASI (a) . The original ISS image is plotted in (c) . Red and blue symbols trace the locations of the j shaped arc and northern edge of the main auroral arc, respectively, derived from their locations in the THEMIS image. The features are marked with the same coloured arrows in (c) . The magenta arrows point out a vertical feature projected very differently in (a) and (b) .

A detailed comparison between an ISS image of aurora (a) plotted and (b) the contemporaneous image acquired by the SNK THEMIS ASI [ground-based]. The original ISS image (a) is plotted in (c). For more detail see Riechert, et al., 2016.

Comparing images of an aurora on 4 February 2012, captured both by the ISS crew and a ground-based instrument, has allowed the researchers to test the accuracy of their method. Overall, the results show good agreement, but highlight that the projection of the ISS images has to be taken into account when interpreting the results.

Now, a trove of thousands of Aurora Borealis and Australis photographs can be used by researchers to decipher the secrets of one the planet Earth’s most awe-inspiring phenomenon.

By Laura Roberts Artal, EGU Communications Officer

 

References:

Riechert, M., Walsh, A. P., Gerst, A., and Taylor, M. G. G. T.: Automatic georeferencing of astronaut auroral photography, Geosci. Instrum. Method. Data Syst., 5, 289-304, doi:10.5194/gi-5-289-2016, 2016.

Automatic georeferencing of astronaut auroral photography: http://www.cosmos.esa.int/web/arrrgh

The research was accomplished using only free and open-source software. All the images processed to date are made freely available at htttp://cosmos.esa.int/arrgh, as is the software needed to produce them.

Imaggeo on Mondays: A single beam in the dancing night lights

Laser and auroras. (Credit: Matias Takala distributed via imaggeo.egu.eu)

Laser and auroras. (Credit: Matias Takala distributed via imaggeo.egu.eu)

Research takes Earth scientists to the four corners of globe. So, if you happen to have a keen interest in photography and find yourself doing research at high latitudes, chances are you’ll get lucky and photograph the dancing night lights: aurora (or northern lights), arguably one of the planet’s most breath taking natural phenomenon. That is exactly the position Matias Takala, a researcher at the Finnish Meteorological Institute (FMI), was in when he was able to take this incredible photograph of the swirling aurora and a single beam of green penetrating the Finnish night sky.

The green beam is emitted by Lidar (the Mobile Aerosol Raman Lidar, MARL, to be more precise). This lidar system is designed to measure tropospheric and stratospheric aerosol profiles (backscatter, size distribution, mass), tropospheric water vapour and clouds, with the ability to distinguish between particulates such as dust, ash, and smoke from biomass burning. The system is based at the Arctic Research Centre (ARC) at Sodankylä. Because environmental change is most pronounced in the Polar Regions, the location is ideal to study the effects of a warming climate as a result of environmental changes brought about by the activities of humans.

The high latitude position of the research station means it is also ideally located to contribute to the continuous monitoring of ionospheric activity. Think of the ionosphere as a ring, 85 km to 600 km above the Earth’s surface, of electrons, electrically charged atoms and molecules that surround the Planet. It is here that aurora are generated as incoming charged particles from solar wind collide with the electrons and atoms of gas in the ionosphere. A network of FMI auroral cameras and magnetometers continually survey the sky to provide space weather services, including alerts for when the best auroral displays are likely.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.