Decameter scale irregularities in the polar ionosphere
From the Sun to the Earth’s upper atmosphere, particles and energy are trans- ported through several key processes. Many of these we know well, and some we are still learning about. In this thesis we will study one of the last processes the energy takes part in before dissipating in the upper atmosp...
| Main Author: | |
|---|---|
| Format: | Master Thesis |
| Language: | English |
| Published: |
2019
|
| Subjects: | |
| Online Access: | http://hdl.handle.net/10852/71421 http://urn.nb.no/URN:NBN:no-74548 |
| Summary: | From the Sun to the Earth’s upper atmosphere, particles and energy are trans- ported through several key processes. Many of these we know well, and some we are still learning about. In this thesis we will study one of the last processes the energy takes part in before dissipating in the upper atmosphere, namely the production of deca-meter scale irregularities in the high latitude ionosphere. We make use of NorSat-1, the Longyearbyen SuperDARN radar and ground- based magnetometers and All-Sky Camera to conduct a case study on the differ- ence in ionospheric conditions and structures between a period of low backscat- ter and one with significant backscatter. The SuperDARN backscattered signal comes from regions where the emit- ted, and later refracted, signal hits the geomagnetic field lines in the ionosphere perpendicularly. The amount of backscattered signal can vary significantly from one day to the next, even though the general conditions in the ionosphere should be similar for the two periods. The structure of the plasma being hit by the signal has been shown to be important, and to see this and build on the knowl- edge we need accurate, small scale measurements of the electron density in the ionosphere. NorSat-1’s m-NLP instrument is capable of sampling the density at 1 kHz sampling frequency and will give us down to decameter scale measure- ments of the irregularities. Combining this with the SuperDARN radar network we explore the differences between one period of minimal backscatter and one with significant backscatter. Through Fourier analysis we find that NorSat-1 encountered more structures of all measurable scale sizes during a pass through backscatter, as compared to a pass through the same location with no backscat- ter. This is found as evidence for the energy cascade model stating that energy is transported through decreasingly sized structures in turbulent flows. In relation to this we use results from previous studies on the matter to discuss the role of the KH and GD instabilities in the production of deca-meter scale irregularities in the polar ionoshpere. More research on this subject is encouraged, as a statistical analysis is necessary for any strong conclusion to be made. |
|---|