Classification of spectral fine structures of Saturn kilometric radiation

0559427 - ÚFA 2023 RIV DE eng J - Článek v odborném periodiku
Fischer, G. - Taubenschuss, Ulrich - Píša, David
Classification of spectral fine structures of Saturn kilometric radiation.
Annales Geophysicae. Roč. 40, č. 4 (2022), s. 485-501. ISSN 0992-7689. E-ISSN 1432-0576
Grant CEP: GA ČR(CZ) GF20-06802L
Institucionální podpora: RVO:68378289
Klíčová slova: cyclotron maser * radio * band * generation * model
Obor OECD: Astronomy (including astrophysics,space science)
Impakt faktor: 1.9, rok: 2022
Způsob publikování: Open access
https://angeo.copernicus.org/articles/40/485/2022/

The spectral fine structures of Saturn kilometric radiation (SKR) are best investigated with the wideband receiver (WBR) of Cassini's Radio and Plasma Wave Science (RPWS) instrument, with which measured radio fluxes can be displayed in time-frequency spectra with resolutions of 125 ms and similar to 0.1 kHz. We introduce seven different classes of SKR fine structures ranging from dots (one class for 0-dimensional objects) over lines (four classes of 1-dimensional objects being horizontal, vertical, or with negative or positive slope) to areal features (one class for 2-dimensional objects). Additionally, we define a seventh class containing special structures named according to their appearance in time-frequency spectra. These special features are named rain, striations, worms, and caterpillar and the latter two have never been described in the literature so far. Using this newly defined classification scheme, we classify features in spectra at low frequencies in the baseband of the 80 kHz WBR and at medium frequencies around 325 kHz. A statistic of the occurrence of various classes and sub-classes shows some notable characteristics: lines with a positive slope are much more common at medium frequencies than at low frequencies and vertical lines are almost absent at low frequencies. The particular fine structure of striations (group of narrowbanded lines with predominantly negative slopes) is quite common below 80 kHz but less common near 325 kHz. At these medium frequencies, the lines rather look like interrupted striations which we term with the name “rain”. We also find rare instances of striations with a positive slope and rare instances of absorption signatures within areal features. The newly introduced sub-classes of worms (lines oscillating in frequency) and caterpillars occur almost exclusively below 80 kHz. Caterpillars have a typical bandwidth of similar to 10 kHz, a constant frequency below similar to 40 kHz for several hours and they are mostly observed beyond distances of 10 Saturn radii. We discuss the implications of our findings in view of the many theories about spectral fine structures of auroral radio emissions.
Trvalý link: https://hdl.handle.net/11104/0332742