The Observations of p -Modes/s-Modes conversion in the Magnetic Field and Absorption of p-Mode by the Sunspot

We decomposed the oscillations inside the annular region surrounding a spot (excluding the spot itself) into the incoming waves(propagate towards the spot)and the outgoing waves(away from the spot)under a cylindrical coordinate system.We make the same decomposition for the oscillations in the annular region surrounding the spotless area.The incoming waves in the region surrounding the spot can be considered as ones,which propagate inside the medium magnetized by the spot flux tube (the magnetic fields in the medium are basically the horizontal)and the incoming waves in the spotless region are considered as the waves propagating inside the non-magnetic medium.By comparing the distributions of the power with the frequency for the two kinds of waves in fixed wave-numbers,it can be found that the frequences,at which the ridges of mode are placed,have been reduced systematically for different radial order n of the mode in the magnetic field,and the power of the waves in the magnetic feild has been reduced as well.The reduced power of the wave is up to 30%of that in the non-magnetic medium.Also,comparing the variations of the power vs.wave-number in the fixed frequency for the two waves,we found that the wave-numbers,in the which the ridges of the mode in magnetic field are placed,have been shifted onto the direction of higher wave-number with respect to the fundamental and p -modes of n=1,2,3 and that the wave-number shifts are increased with the frquency.However,the power depression is modiifed by the frequency,i.e.the acoustic waves suffer some absorption at some limited zones of the frequency.These observations indicate that the mode coupling (or mixing) of p -mode with the corresponding magnetoacoustic-gravity (MAG) waves is generated in the magnetic feild.The generation of the mode mixing supports the explanation that the mode conversion is probably as the prime mechanism for the absorption of p -mode by the sunspot.In addition,the converted MAG waves are absorbed further when they propagate into the spot flux tube(in which the magnetic fields are basically the vertical).The power absorbed is up to 20% of the (residual)power of the waves.No further conversion inside the tube are observed.