Coronal electron density distributions estimated from CMEs, DH type II radio bursts, and polarized brightness measurements

Abstract

We determine coronal electron density distributions (CEDDs) by analyzing decahectometric (DH) type II observations under two assumptions. DH type II bursts are generated by either (1) shocks at the leading edges of coronal mass ejections (CMEs) or (2) CME shock‐streamer interactions. Among 399 Wind/WAVES type II bursts (from 1997 to 2012) associated with SOHO/LASCO (Large Angle Spectroscopic COronagraph) CMEs, we select 11 limb events whose fundamental and second harmonic emission lanes are well identified. We determine the lowest frequencies of fundamental emission lanes and the heights of leading edges of their associated CMEs. We also determine the heights of CME shock‐streamer interaction regions. The CEDDs are estimated by minimizing the root‐mean‐square error between the heights from the CME leading edges (or CME shock‐streamer interaction regions) and DH type II bursts. We also estimate CEDDs of seven events using polarized brightness (pB) measurements. We find the following results. Under the first assumption, the average of estimated CEDDs from 3 to 20 Rs is about 5‐fold Saito's model (NSaito(r)). Under the second assumption, the average of estimated CEDDs from 3 to 10 Rs is 1.5‐fold NSaito(r). While the CEDDs obtained from pB measurements are significantly smaller than those based on the first assumption and CME flank regions without streamers, they are well consistent with those on the second assumption. Our results show that not only about 1‐fold NSaito(r) is a proper CEDD for analyzing DH type II bursts but also CME shock‐streamer interactions could be a plausible origin for generating DH type II bursts.

Variation in Coronal Activity from Solar Cycle 24 Minimum to Maximum Using Three-Dimensional Reconstructions of the Coronal Electron Density from STEREO/COR1

“…This suggests that our SSPA 3D coronal density models reconstructed for 100 CRs (with a cadence of about two weeks) may be used for the interpretation of radio bursts (such as type II and moving type IV produced by CMEs) as observed from the Earth direction (e.g. Cho et al, 2007;Ramesh et al, 2013;Shen et al, 2013;Sasikumar Raja et al, 2014;Hariharan et al, 2016;Lee et al, 2016), in particular, when LASCO/C2 pB data are not available. We estimate the total mass (or electron content) contained in the coronal region observed with COR1 and its evolution with solar cycle.…”

Can We Detect Coronal Mass Ejections through Asymmetries of Sun-as-a-star Extreme-ultraviolet Spectral Line Profiles?

“…the height variation of the electron density in the CME structure. A comparison with observations of electron densities in CMEs has shown very similar behavior to our derivations (e.g.,Lee et al 2016). …”