Mem. S.A.It. Vol. 84, 351 c  SAIt 2013 Memorie della F. Giannattasio 1 , M. Stangalini 1,2 , D. Del Moro 1 , F. Berrilli 1 1 Dipartimento di Fisica, Universit` a di Roma ”Tor Vergata”, Via della Ricerca Scientifica,1 00133 Rome, Italy, e-mail: Fabio.Giannattasio@roma2.infn.it 2 Max Planck Institute for Solar System Research, Max-Planck-Str. 2 37191 Katlenburg- Lindau, Germany Abstract. Since their discovery, velocity oscillations in the lower solar atmosphere have been observed to interact with magnetic fields. The nature of this interaction, and the mech- anisms that channel the energy to the upper layers, represent a crucial issue for the corona heating. In this work, we use SDO dopplergrams and magnetograms of 12 bipolar active regions (βARs) to study the relation between velocity oscillation amplitude and magnetic field. We find that the velocity oscillation amplitude depends not only on the magnetic field strength, but also on its polarity. Key words. Sun:activity – Sun: oscillations 1. Introduction The interaction between acoustic waves and magnetic fields generates MHD modes, which are able to channel and carry energy to the upper atmosphere. For this reason, this inter- action may play an important role for solar corona heating. The first evidence of velocity oscillation dependence on the magnetic field was pro- vided by the works of Leighton et al. (1962); Woods & Cram (1981); Lites et al. (1982). They reported an amplitude reduction in the five-minute band by a factor 2 − 3 within ARs. Such a behavior was also found in smaller magnetic field concentrations (e.g. Roberts & Webb 1978; Spruit 1981). Several mechanisms may explain the ob- servations (Hindman et al. 1997): the intrin- Send offprint requests to: F. Giannattasio sic power inhibition due to local convection suppression; partial p-mode absorption (Braun et al. 1987; Bogdan et al. 1993; Cally 1995); opacity effects; and the alteration of the p- mode eigenfunctions at the hands of the mag- netic field (Jain et al. 1996; Hindman et al. 1997). From an observational point of view, it is natural to find a more evident amplitude re- duction within ARs, where the strongest and largest scale magnetic fields are found. Among them, bipolar active regions (βARs) show pe- culiar morphological and physical asymme- tries (e.g. Balthasar & Woehl 1980; Ternullo, M. et al. 1981; Zwaan 1985; van Driel- Gesztelyi & Petrovay 1991; Fan et al. 1993). In this work we investigate the velocity os- cillation amplitude reduction by the magnetic field. We conclude that such a reduction does