The mysterious Jets, Sprites and Elves

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Danish/Norwegian Instruments at the International Space Station May Unveil the Mysteries.


Jets, Sprites and Elves are phenomena that occur above the clouds with thunder and lightning conditions on Earth. Unknown and invisible for most of us, but visible from high flying airplanes and from manned spacecrafts. However, what are these phenomena?

Many scientists have wondered and sought answers to these questions ever since the first observations. Some of the questions may be answered through a Danish/Norwegian instrument package outside the International Space Station. The visibility is relatively well documented through pictures taken by the Danish Astronaut, Andreas Mogensen, from the Space Station during his stay at ISS in September 2015, but the pictures do not unveil the physical background for the phenomena.

During the ASIM mission, Andreas Mogensen, who has been seconded to NASA, acted as lead Capcom at the control centre in Houston. Here, shortly after launch, he communicated with the astronauts aboard ISS as they prepared to grab the Dragon transport vehicle, where the observatory is located, using a 17-metre-long robot arm.

ASIM outside the European laboratry at ISS. Illustration: ESA

The instrument package had been placed outside the European scientific module, Columbus. With scientific participation from DTU Space, Denmark and University of Bergen, Norway, the instruments will possibly help to understand physics phenomena connected to the interaction between the Earth’s atmosphere and space.

Launched on of the second day of April, it takes nearly two weeks before the instruments are mounted at the right place and the commissioning time can start. The test phase can take several more weeks, so the first scientific measurements may be carried out around turn of the month May/June, at the earliest.


The project is a relatively long-term project; the team has been working with the project for more than fourteen years and now look forward to an important milestone – the first measurements. Immediately after the first measurements are received, the scientific analysis will start. At last, the data will hopefully provide the scientists with an understanding of what happens above the clouds with thunder and lightning on Earth.



Atmosphere-Space Interactions Monitor (ASIM) consists of two main instruments for measuring light and X-ray radiation from thunderstorms.

  • X-ray detector called MXGS (Modular X- and Gamma-ray Sensor).
  • Modular Multi-spectral Imaging Array (MMIA)—consists of two cameras and three photometers that detect flashes of light at different wavelengths.

ASIM is being carried out under the auspices of the European Space Agency, ESA. The ASIM project falls under DTU Space, which is responsible for scientific management and one of the instrument development. The Danish technology company Terma A/S has overall technical responsibility for the observatory, while the Danish Meteorological Institute is participating in the scientific interpretation of the data.

The University of Bergen is involved in the miniature X-ray and gamma sensor (MXGS), which will be optimized to detect occurrence frequency of TGFs and obtain spectral characteristics at the highest time resolution as possible. Due to the absorption and Comptong scattering of X-rays on their way out of the atmosphere it is possible to infer the peak production altitude from the X-ray spectra. This is crucial to understand the production mechanism of TGFs.




(Emission of Light and Very Low Frequency perturbations due to Electromagnetic Pulse Sources) often appear as a dim, flattened, expanding glow around 400 km in diameter that lasts for, typically, just one millisecond. They occur in the ionosphere 100 km above the ground over thunderstorms. Their colour was a puzzle for some time but is now believed to be a red hue. ELVES were first recorded on another shuttle mission, this time recorded off French Guiana on October 7, 1990.


Sprites are large-scale electrical discharges which occur high above a thunderstorm cloud, or cumulonimbus, giving rise to a quite varied range of visual shapes. They are triggered by the discharges of positive lightning between the thundercloud and the ground. The phenomena were named after the mischievous sprite, is an acronym for Stratospheric/mesospheric Perturbations Resulting from Intense Thunderstorm Electrification. They normally are coloured reddish-orange or greenish-blue, with hanging tendrils below and arcing branches above. They can also be preceded by a reddish halo. They often occur in clusters, lying 50 kilometres to 90 kilometres above the Earth’s surface. Sprites have since been witnessed thousands of times. Sprites have been held responsible for otherwise unexplained accidents involving high altitude vehicular operations above thunderstorms.


Although jets are considered to be a type of upper-atmospheric lightning, it has been found that they are components of tropospheric lightning and a type of cloud-to-air discharge that initiates within a thunderstorm and travel upwards. In contrast, other types of TLEs are not electrically connected with tropospheric lightning– despite being triggered by it. The two main types of jets are blue jets and gigantic jets. Blue starters are considered to be a weaker form of blue jets.


Featured image: Thunderstorm seen from ISS. Photo credit: ESA.