Possible evidence of long-term oscillations in the solar atmosphere

We have obtained the temporal correlation function, Q(t), from time sequenc es of Ca II K filtergrams and Dopplergrams from Antarctica, Taiwan Oscillat ion Network (TON) and Solar and Heliospheric Observatory (SOHO). Q(t) gives the time evolution of the pattern under examination, supergranulation in t his case. It has been round that Q(t) shows oscillatory signals of both 5-m in and long-term periods. The 5-min oscillations are suppressed by averagin g the images over 10 min. An exponential decay curve which represents the l ifetime trend of supergranules. is fitted to Q(t) and subtracted out. The Q (t) residuals thus obtained contain the oscillatory component and are then subjected to a periodogram analysis. Significant periodicities in the range of 1.4-10 hours have been noted. The causes of these oscillations are not fully known at present, but the instrumental and atmospheric factors can be ruled our, pointing to solar origin. Various possibilities are discussed. Some of the observed periodicities may be considered as probable candidates for long-term oscillations in the Sun, such as the elusive gravity modes.