Low-frequency modulations in the solar microwave radiation as a possible indicator of inductive interaction of coronal magnetic loops

¹ Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, 8042 Graz, Austria e-mail: [maxim.khodachenko;rucker]@oeaw.ac.at
² Institute of Applied Physics, Russian Academy of Sciences, Ulyanov str. 46, 603950 Nizhny Novgorod, Russia e-mail: za130@appl.sci-nnov.ru
³ Lobachevsky State University, Gagarin av. 23, 603950 Nizhny Novgorod, Russia e-mail: kiag2@uic.nnov.ru
⁴ Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland

Received: 10 September 2004
Accepted: 30 November 2004

Abstract

Low-frequency (LF) modulations of 37 GHz microwave radiation during solar flares, recorded at the Metsähovi Radio Observatory, are considered. A fast Fourier transformation with a sliding window is used to obtain the dynamic spectra of the LF pulsations. We pay attention to the LF dynamic spectra having a specific multi-track structure, which is supposed to be an indication of a complex multi-loop composition of a flaring region. Application of the equivalent electric circuit models of the loops including the effects of electromagnetic inductive interaction in groups of slowly growing current-carrying magnetic loops allows us to explain and reproduce the main dynamical features of the observed LF modulation dynamic spectra. Each loop is considered as an equivalent electric circuit with variable parameters (resistance, capacitance and inductive coefficients) which depend on shape, scale, position of the loop with respect to other loops, as well as on the plasma parameters and value of the total longitudinal current in the magnetic tube.