Krystyna Mylostna
The present poster is about the radio emissions of lightning in the atmospheres of Saturn and Uranus. These planets have such incredibly dynamic atmospheres that they are suitable objects for studying extraterrestrial lightning by means of low-frequency ground based radio telescopes, such as UTR-2. The major goal of the study was to find the characteristics of the radio emission of lightning in the atmosphere of Saturn. We studied a range of data to resolve the problem: from the knowledge about lightning on Earth to existing space and ground-based data about lightning of extraterrestrial origin. We also used some theoretical hypotheses to be checked during our study. For several years a group of Ukrainian scientists have carried out the detection and identification of electrostatic discharges on Saturn,which are Saturnian lightning, in the records made by the radio telescope UTR-2 in a wide range of time scales. The results of Saturn lightning investigations provide a high resolution time profile and radio-frequency spectrum of the lightning signals. Our next goals are to study Saturn lightning radio emission propagation effects and parameters of its complex structure with higher temporal resolution simultaneously with new attempts to register Uranian lightning.
Research of low frequency radio emission associated with lightning or electrostatic discharges (ED) from the ground can supply instantaneous broadband observations which are suitable for high temporal resolution analysis of Saturn electrostatic discharges (SED) time profile and radio spectrum. Even though the ground-based observations meet some limitations, such as broadband interference of different nature and an influence of the ionosphere of the Earth, the latest successful SED’s study have proved the capability of radio telescopes along with approved data processing methods to fulfil the task of investigation of ED. After unsuccessful observational sessions in 2015-2016, we concluded that ‘blind observations’ in radio range are comparatively much less effective than the combined with the optical or infrared ones .
Using optical or infrared data as a trigger, the observations of Saturn or Uranus by the UTR-2 radio telescope can be started as soon as the next day. Therefore, the PVOL and the ALPO-Japan websites are monitored on the regular basis.
Ground-based Astronomy achievements of the observations of Saturn and Uranus observations are:
Resolution of the microstructure of lightning discharges;
First estimations of SED energy;
The discovery of a broadening of an otherwise sharp pulse when a discharge is observed over a finite bandwidth, that is explained by the effects of travel of the radio signal through the heliosphere between the planet and the Earth and quantified by dispersion measure (DM) .
The first measurements of average signal's dispersion delay
Due to the fact that the records were made in a waveform mode of the receiver, there were obtained the first data with temporal resolution of 15 ns, the SED temporal structures were analysed with resolution down to 32 mks.
One can calculate DM, which represents integrated column density of free electrons on the way between an observer and the lightning source, by knowing the time of the signal’s delay between the minimum and maximum frequencies recorded. We determined average signal's dispersion delay to 43×10-6 and 48×10-6 pc cm-3 with a standard deviation 5*10-6 and 5*10-6 pc/cm3, respectively [1]. In this case the lightning signals serve as a probe of the heliosphere between the Earth and the planet.
On the other hand, we were targeting Uranus as a planet with lightning, which were called Uranus Electrostatic discharges (UED). As, to the date, these signals occur on the planet that is 2,9 billion kilometres far, which is more than 2 times further than Saturn, we are not hoping to resolve the fine temporal structure of those signals, but rather aiming to register them for the first time by ground-based means.
Our next goals are to study the variations of DM on the path of SED propagation and, further, estimate characteristics of the medium, as well as to obtain the parameters of SED’s complex structure with higher temporal resolution and conduct a statistical analysis on a bigger data set. The last aim of the project is to continue to attempt at registering UED.