Helioseismic Signature of Chromospheric Downflows in Acoustic Travel-Time Measurements from Hinode

TL;DR

This study uses helioseismology to detect chromospheric downflows in emerging-flux regions, revealing travel-time anomalies in chromospheric data that suggest downflows below 10 km/s, demonstrating a new method for studying chromospheric flows.

Contribution

It introduces a novel application of time-distance helioseismology to detect chromospheric downflows using Hinode data, highlighting a new approach for chromospheric flow analysis.

Findings

Detected travel-time anomalies indicating downflows in chromospheric regions.

Downflow speeds estimated below 10 km/s.

Chromospheric flows can be studied via time-distance helioseismology.

Abstract

We report on a signature of chromospheric downflows in two emerging-flux regions detected by time-distance helioseismology analysis. We use both chromospheric intensity oscillation data in the Ca II H line and photospheric Dopplergrams in the Fe I 557.6nm line obtained by Hinode/SOT for our analyses. By cross-correlating the Ca II oscillation signals, we have detected a travel-time anomaly in the plage regions; outward travel times are shorter than inward travel times by 0.5-1 minute. However, such an anomaly is absent in the Fe I data. These results can be interpreted as evidence of downflows in the lower chromosphere. The downflow speed is estimated to be below 10 km/s. This result demonstrates a new possibility of studying chromospheric flows by time-distance analysis.