Upper atmosphere phenomena like northern lights are best studied in polar regions. Aurora is highly spectacular to watch. Shower of solar particles make aurora flicker and interfere with the navigation and communication equipment.

June Lunde from the Andøya Rocket Range has recently defended her PhD thesis on "Particle Precipitation: Selected Effects on Ionospheric Phenomena" at the University of Tromsø.

The motivation behind her thesis wasto study particle precipitation from the Sun into the Earth’s upper atmosphere and its effects on selected ionospheric phenomena. Particles from the solar wind can enter the Earth's magnetosphere through magnetic merging, either at the sub-solar point, or at higher latitudes, depending on the configuration of the interplanetary magnetic field. This interaction can be studied from the ground in Svalbard, due to its fortunate location beneath the magnetospheric cusp region on the dayside, and its location inside the polar cap during night-time.

It has been studied how these precipitating particles influence aurora and ion-acoustic waves in the ionized part of the atmosphere. The studies have been conducted using various methods, including extracting data from databases, running different experiments and building new instrumentation. The latter was a radiation detector for measuring Bremsstrahlung X-rays. The main instrument used for this study has been the EISCAT (European Incoherent SCATtering) radar located at Svalbard, together with various other ground based instruments such as photometers, riometers and magnetometers. In addition, particle instruments onboard satellites have been used as well as an X-ray instrument mounted on a balloon launched from Longyearbyen. Primarily, it is the effect of particle precipitation on large ion-acoustic waves that has been studied. These waves can be observed by advanced radar facilities, both from Svalbard and Tromsø (EISCAT), in the form of spectra known as natural enhanced ion acoustic lines (NEIALs). Furthermore, in this work, the infrared atomic oxygen emission line (844.6 nm) has been introduced as a new possible method to detect NEIALs in optical data.

It has been found that the most energetic particle precipitation causes ion-acoustic waves which mainly propagate downward; while the less energetic part of the particle precipitation is related to ion-acoustic waves which propagate upward.

Large ion-acoustic waves have been discovered during night-time at very high latitudes, where they were not expected to occur. Previously these phenomena had been observed only during daytime.

It was also found that particle precipitation causes flickering aurora, hence intensity variation and the apparent motion of flickering spots in the aurora have been also studied.

Finally, precipitating particles typically consists of electrons and ions, and in this study, an example is given on of how the merging of the Earth’s and Sun’s magnetic fields guide the precipitation.
 

Source and Contact: June Lunde, Andøya Rocket Range (tel. 761 44 448; june@rocketrange.no)

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June Lunde, ARR.

Aurora Borealis (photo: Jeff Holmes)

EISCAT 42 m antenna (photo: June Lunde)