Space and Time Analysis of the Solar Photospheric Dynamics at Moderate-ℓ Values

Abstract

A space-time analysis of 36 days' worth of full-disk intensity and velocity images, obtained by the Global Oscillation Network Group, is used to produce a high-resolution ℓ-ν phase-difference spectrum for the spectral range (4≤ℓ≤2000, 0≤ν≤8.3 mHz). This is the first time a phase-difference spectrum has been produced for intermediate-ℓ values. The phase differences on the p-mode ridges are found to linearly increase from ~65° at 2 mHz up to ~95° at 4.7 mHz. Only near 3.9 mHz are the differences close to 90°, the theoretically expected phase for adiabatic evanescent waves. The phases between the ridges exhibit a steplike behavior in frequency with negative values at low frequency and positive values (greater than 90°) at high frequency. The negative phase values are consistent with the extension to low- and moderate-ℓ values of the plateau-interridge regime discovered by Deubner et al. in 1990. However, positive phase values, which represent higher phase for the solar background than for the acoustic modes, were not expected. An understanding of this observed phase-difference behavior will improve our knowledge of the nature of the solar background and its interaction with the acoustic p-modes.