PHASE AND GAIN RELATIONS BETWEEN LOW-DEGREE INTENSITY AND VELOCITY ACOUSTIC MODES DURING THE SOLAR ACTIVITY CYCLE

摘要

Phase and gain relations between low-degree acoustic modes measured as intensity and velocity fluctuations have been carried out using various instruments and techniques. The helioseismic instrument aboard the Solar and Heliospheric Observatory (SOHO) satellite provides an opportunity to observe solar oscillations in intensity and velocity under the unique conditions of the quiet environment of this well-run platform. Simultaneous measurements of intensity and velocity oscillations provide information on nonadiabatic effects in the radiatively cooled solar atmosphere and the interaction with the underlying solar background. The thermodynamical properties of the atmosphere cause a phase shift between intensity and velocity of -90° (downward positive) in the case of an adiabatic atmosphere. With simultaneous velocity (SOHO Global Oscillations at Low Frequencies [GOLF]) and intensity (SOHO Variability of Irradiance and Gravity Oscillations [VIRGO]) observations, the Ⅰ-Ⅴ phase differences of the low-degree acoustic modes have been computed with high accuracy (Jimenez in 1999), and the influence of the background has been found, which produces a degree dependence on the measured Ⅰ-Ⅴ phase differences. After a correction for the background influence, the Ⅰ-Ⅴ phase differences did not show an exactly adiabatic behavior, but were close to it; the best agreement was found from models including turbulent pressure associated with convection and fluctuations of the superadiabatic temperature gradients. The observations of Jimenez were taken during the minimum of the solar activity cycle (1996). That work is extended here with VIRGO sunphotometer and GOLF observations from 1996 to 2001 (from minimum to maximum solar activity) to study the Ⅰ-Ⅴ phase differences and gains between low-degree acoustic modes by looking for changes, or otherwise, with solar magnetic activity.