On Active Region Emergence Precursors

Abstract

I present intriguing results from a systematic look at possible indicators of active region emergence precursors using both acoustic power mapping and time distance travel time anomalies. I analyzed a set of active regions that have emerged at low latitudes and close to the central meridian, and were observed with HMI. Such regions, since they emerged near disk center, could be tracked for days before and after their emergence. Data cubes of tracked surface observable were analyzed, using time-series of various length, using HMI’s intensity, velocity and magnetic field data. While each active region displays its own particularities, this systematic approach allowed me to pick some interesting statistical properties that will be summarized. Using different time-series length allowed me to investigate the trade-off between precision and resolution, whether temporal or spatial. It also revealed to which extent one sees a tight correlation between various metric of surface activity and its effect of the measured acoustic signal, whether seen in raw of filtered power map or travel time anomalies.