Top image: Northern lights over the Kjell Henriksen Observatory outside Longyearbyen. Photo: Njål Gulbrandsen/UNIS.
UNIS PhD candidate Fasil Tesema has studied the pulsating aurora – a low emission aurora. It is caused by high energy electrons which can reach deep into the atmosphere and can deplete ozone. This significant ozone loss suggests that pulsating aurora may alter the temperature and winds in the upper atmosphere. Tesema will defend his PhD thesis on 17 June 2021.
11 June 2021
Press release from the University Centre in Svalbard (UNIS) and the University of Bergen
A geomagnetic field, which protects the Earth’s atmosphere from solar wind particles, is not a perfect shield. A proof of its glitches is the magnificent display of aurora in the polar region. Broadly, aurorae can be divided into two categories: Discrete and diffuse types. Discrete aurora has high brightness and distinctive structures like spirals, curls, and folds, which we usually observe around midnight. The diffuse aurora has low intensity and less structure, covering a wide area of the sky mainly after midnight. It is also common to observe auroral features blinking on and off within the diffuse aurora. This is called pulsating aurora.
Pulsating aurora is caused by high-energy electrons with enough energy to reach below 100 km, sometimes down to even 70 km in the atmosphere. These energetic electrons initiate chemical reaction which produces NOx and HOx gasses (NOx=N, NO, NO2, and HOx= H, OH, HO2), which can participate in a catalytic reaction and deplete ozone. During wintertime, NOx gases can be transported deep into the atmosphere. Ozone is a vital component of the Earth’s atmosphere due to the absorption of UV light from the Sun and it can emit infrared radiation. It regulates the heating and cooling of the atmosphere. A reduction in ozone can therefore affect temperature and winds in the upper atmosphereand possibly contribute to climate variability. Thus, pulsating aurora electrons are vital in the chemistry and dynamics above 50 km.
By the use of multiple satellite measurements, ground based observations, and an atmospheric model this dissertation characterizes the spatial scale of the pulsating aurora, the ionization level, and the chemical impact of pulsating aurora electrons
This study shows that the energy of pulsating aurora electrons typically varies between 10 and 200 keV. The patchy pulsating aurora, which usually covers a large area and is common in the morning, has the most substantial effects below 100 km. The energy can significantly deplete ozone in the upper atmosphere. At an altitude around 80 km, the immediate effect was up to 70% reduction of the ozone. This significant ozone loss suggests that pulsating aurora may also alter the temperature and winds in the upper atmosphere, which could also be connected to the dynamics on a global scale. The study also shows that different pulsating aurora types are associated with varying energies of electrons.
PhD candidate Fasil Tesema will defend his thesis “Energetic electron precipitation of pulsating aurorae and their mesospheric effects” on 17 June 2021 at 15:15 on Zoom at the University of Bergen.
About the candidate
Fasil Tesema is from Gondar in Ethiopia and took his MSc in space physics at Bahir Dar University in Ethiopia.
He started his PhD study in 2018 at the Arctic Geophysics Department at UNIS in collaboration with the Birkeland Centre for Space Science at the University of Bergen.
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