Helioseismic Signature of Chromospheric Downflows in Acoustic Travel-Time Measurements from Hinode
arXiv:0903.1323 · doi:10.1088/0004-637X/694/2/L115
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.
arXiv comment9 pages, 4 figures, accepted for publication in ApJL
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- Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements
- Properties of Sequential Chromospheric Brightenings and Associated Flare Ribbons