The 27-day rotational variations in total solar irradiance observations: From SORCE/TIM, ACRIMSAT/ACRIM III, and SOHO/VIRGO

Abstract

During the last decade, observations from SORCE (Solar Radiation and Climate Experiment)/TIM (Total Irradiance Monitor), ACRIMSAT (Active Cavity Radiometer Irradiance Monitor Satellite)/ACRIM III, and SOHO (Solar and Heliospheric Observatory)/VIRGO (Variability of IRradiance and Gravity Oscillations Sun PhotoMeter) provided Total Solar Irradiance (TSI) measurements with unprecedented accuracy and stability to determine the amount of solar irradiance reaching the top of the atmosphere and how solar irradiance varies on different time scales. These three independent measurements are analyzed using the EEMD (Ensemble Empirical Mode Decomposition) method to characterize the phase and amplitude of the 27-day solar rotational variation in TSI. The mode decomposition clearly identifies a 27-day solar rotational signature on TSI measurements. The rotational variations of TSI from the three independent observations are generally consistent with each other, despite different mean TSI values. During the declining phase of solar cycle 23, the amplitude of TSI 27-day variations is as high as 0.8 W/m² (~0.05%), while during the rising phase of solar cycle 24, the amplitude is up to 0.4 W/m² (~0.04%). During the minimum phase (2008–2009), the amplitude of the rotational mode is only ~0.1 W/m². The correlation of this rotational mode between TIM and ACRIM III is ~0.92 and the slope of the local peak values is ~0.98. The correlation between TIM and VIRGO is ~0.96 and the slope of the local peak values is ~0.98, very similar to the slope with ACRIM III.