Precursor like Signatures in Flaring Active Regions

High frequency acoustic waves are ubiquitous in the atmosphere of the Sun. Low frequency acoustic waves are expected to escape into the atmosphere during or prior to magnetic reconnection events, prior to solar flares, owing to their sensitivity to the angle of the magnetic field lines along which they propagate, and to the acoustic cutoff frequency. Waves with frequencies higher than the quiet-Sun acoustic cutoff frequency are affected by the plasma beta surface in that they may get mode-converted and/or get reflected and refracted. If some of these waves can be detected prior to flares, then they may be used as for predicting the flares. This is essential for early precautionary measures for astronauts and satellites in space that are often affected by proton fluxes and solar energetic particles coming from flares.

We use MOTH (Magneto-Optical filters at Two Heights) data and perform phase-difference analysis on solar flaring and non-flaring active regions. The data was obtained in Jan 2003 at the South Pole Station in Antarctica and contains Dopplergrams obtained at two heights above the solar photosphere, one in Na D2 line and the other at the KI line. The data appropriately consists of periods of flaring and non-flaring regions. We create maps of travel-times of the acoustic waves to show how they change prior to, during and after the flares. We have performed the analysis on data from three observing runs from Jan 2003. Two of these runs contain one or two flares towards the ends of the observing runs and one of them contain regions producing many flares. We observe negative travel times prior to flares in regions producing a few flares, and a large variance in the travel-times prior to flares from the regions producing many flares. We will present the results from all these runs, the third of which would act as a semi-test data as the data was processed differently but was obtained from the same instrument as the other runs.