Deriving Large Coronal Magnetic Loop Parameters Using LOFAR J burst Observations

Abstract

Large coronal loops around one solar radius in altitude are an important connection between the solar wind and the low solar corona. However, their plasma properties are ill-defined as standard X-ray and UV techniques are not suited to these low-density environments. Diagnostics from type J solar radio bursts at frequencies above 10 MHz are ideally suited to understand these coronal loops. Despite this, J bursts are less frequently studied than their type-III cousins, in part because the curvature of the coronal loop makes them unsuited for using standard coronal density models. We used LOw −F requency −ARray (LOFAR) and P arker Solar P robe (PSP) solar radio dynamic spectrum to identify 27 type-III bursts and 27 J bursts during a solar radio noise storm observed on 10 April 2019. We found that their exciter velocities were similar, implying a common acceleration region that injects electrons along open and closed magnetic structures. We describe a novel technique to estimate the density model in coronal loops from J burst dynamic spectra, finding typical loop apex altitudes around 1.3 solar radius. At this altitude, the average scale heights were 0.36 solar radius, the average temperature was around 1 MK, the average pressure was 0.7 mdyn cm−2 , and the average minimum magnetic field strength was 0.13 G. We discuss how these parameters compare with much smaller coronal loops.