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

TL;DR

This study analyzes eleven years of GOLF/SoHO data to understand how solar granulation motions vary with height in the atmosphere and during the solar cycle, revealing height-dependent behavior but stability across activity levels.

Contribution

It introduces a refined model for the solar spectrum using two Lorentzian profiles and characterizes the evolution of granulation with height and activity.

Findings

Granulation evolves with height in the solar atmosphere.

A second Lorentzian profile is needed to model the spectrum accurately.

Granulation shows no significant variation with solar activity cycle.

Abstract

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