Variations of the solar granulation motions with height using the GOLF/SoHO experiment

摘要

Below 1 mHz, the power spectrum of helioseismic velocity measurements isdominated by the spectrum of convective motions (granulation andsupergranulation) making it difficult to detect the low-order acoustic modesand the gravity modes. We want to better understand the behavior of solargranulation as a function of the observing height in the solar atmosphere andwith magnetic activity during solar cycle 23. We analyze the Power SpectralDensity (PSD) of eleven years of GOLF/SOHO velocity-time series using aHarvey-type model to characterize the properties of the convective motions inthe solar oscillation power spectrum. We study then the evolution of thegranulation with the altitude in the solar atmosphere and with the solaractivity. First, we show that the traditional use of a lorentzian profile tofit the envelope of the p modes is not well suitable for GOLF data. Indeed, toproperly model the solar spectrum, we need a second lorentzian profile. Second,we show that the granulation clearly evolves with the height in the photospherebut does not present any significant variation with the activity cycle.