Deriving Large Coronal Magnetic Loop Parameters Using LOFAR J burst Observations
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Date
2022-12-05
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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.