UV spectra, bombs, and the solar atmosphere

TL;DR

This paper reanalyzes IRIS UV data on solar plasma bombs, concluding they originate in the chromosphere and are more consistent with Alfvénic turbulence than reconnection jets.

Contribution

It provides an independent analysis of IRIS data, clarifying the plasma origin and nature of solar bombs, challenging previous interpretations of their pressure and temperature.

Findings

Bomb plasma originates in the low-mid chromosphere or above.

Plasma pressures before explosion are between 80 and 800 dyne/cm^2.

Spectral data aligns more with Alfvénic turbulence than reconnection jets.

Abstract

A recent analysis of UV data from the Interface Region Imaging Spectrograph {\em IRIS} reports plasma "bombs" with temperatures near \hot{} within the solar photosphere. This is a curious result, firstly because most bomb plasma pressures $p$ (the largest reported case exceeds $10^3$ dyn~cm$^{-2}$) fall well below photospheric pressures ($> 7\times10^3$), and secondly, UV radiation cannot easily escape from the photosphere. In the present paper the {\em IRIS} data is independently analyzed. I find that the bombs arise from plasma originally at pressures between $\lta80$ and 800 dyne~cm$^{-2}$ before explosion, i.e. between $\lta850$ and 550 km above $\tau_{500}=1$. This places the phenomenon's origin in the low-mid chromosphere or above. I suggest that bomb spectra are more compatible with Alfv\'enic turbulence than with bi-directional reconnection jets.