Spatio-Temporal Comparisons of the Hydrogen-Alpha Line Width and ALMA 3 mm Brightness Temperature in the Weak Solar Network

TL;DR

This study compares the spatial and temporal behavior of H-alpha line width and ALMA 3mm brightness temperature in the solar chromosphere, revealing a correlation with different slopes for hot and cool regions and explaining the absence of p-modes in ALMA data.

Contribution

It demonstrates the correlation between H-alpha line width and ALMA 3mm brightness temperature, and explains the absence of p-modes in ALMA observations due to spectral windowing effects.

Findings

Correlation between H-alpha line width and 3mm brightness temperature confirmed.

Different slopes for hot and cool regions in the diagnostics.

Absence of p-modes in ALMA data explained by spectral windowing.

Abstract

The strongest known correspondence between ALMA 3mm emission and other solar observations is between the H-alpha line width and 3 mm brightness temperature, while the typical 3-5min p-mode oscillations found in many chromospheric diagnostics are often lacking from ALMA Band 3 and 6 observations. We study these issues using a publicly available data set of weak network flux near disk center at time SOL2017-03-17T15:42-16:45 that includes IBIS H-alpha and ALMA 3 mm data series. We confirm the correlation between the H-alpha line width and the 3 mm temperature, but find a different slope between the two diagnostics for hot versus cool regions, both of which are steeper than previous reports. The origin of the two slopes is unknown, but does hold for the duration of the observations. Spatially averaged power spectra of the IBIS data do show p-mode oscillations while the ALMA data do not. However, removing IBIS data at times corresponding to the ALMA calibration windows makes the averaged power spectra for the two data series nearly identical. Spatial maps of the power integrated over p-mode frequency bands agree well between the two data series and show the typical pattern of magnetic shadows and halos found in many chromospheric diagnostics. We therefore argue that the lack of observed p-modes in the ALMA data may be predominantly due to spectral windowing induced by the timing and duration of the calibration observations.