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

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−1. This result demonstrates a new possibility of studying chromospheric flows by time–distance analysis. Subject headings: Sun: chromosphere — Sun: faculae, plages — Sun: helioseismology