A type III radio burst automatic analysis system and statistic results for a half solar-cycle with the Nan\c{c}ay Decameter Array data

TL;DR

This paper presents an automated system for detecting and analyzing solar type III radio bursts using Nancay Decameter Array data, providing statistical insights into burst characteristics over half a solar cycle.

Contribution

The study introduces a novel automatic analysis system employing computer vision techniques to detect and analyze type III radio bursts from dynamic spectra.

Findings

Median frequency drift rate is about 6.94 MHz/s for detected bursts.

Frequency drift rate follows a power-law dependence on frequency.

Average exciter speed is approximately 0.2c, with no significant cycle dependence.

Abstract

We design an event recognition-analysis system that can automatically detect solar type III radio burst and can mine information of the burst from the dynamic spectra observed by Nancay Decameter Array (NDA). We investigate the frequency drift rate of type III bursts and the speed of electron beams responsible for the generation of the bursts. Several computer vision methods are used in this automatic analysis system. The Hough transform is performed to recognize the line segment associated with type III bursts in the dynamic spectra. A modified active contour model is used to track the backbone of the burst and estimate the frequency drift rate at different frequency channels. We run this system on the NDA data from 2012 to 2017, and give a statistical survey of the event number distribution, the starting and stopping frequencies of bursts, the frequency dependence of the drift rate, and the exciter speed using three corona density models. The median value of the average frequency drift rates is about 6.94MHz/s for 1389 simple well-isolated type III bursts detected in the frequency range 10--80 MHz of NDA observation. The frequency drift rate changes with frequency as $df/dt = -0.0672 f^{1.23}$ from a least-squares fitting. The average exciter speed is about 0.2c based the density models. We do not find any significant dependence of the drift rate and the exciter speed on the solar activity cycle.