What Causes the Inter-Solar-Cycle Variation of Total Solar Irradiance?

Abstract

The Physikalisch Meteorologisches Observatorium Davos total solar irradiance (TSI), Active Cavity Radiometer Irradiance Monitoring TSI, and Royal Meteorological Institute of Belgium TSI are three typical TSI composites. Magnetic Plage Strength Index (MPSI) and Mount Wilson Sunspot Index (MWSI) should indicate the weak and strong magnetic field activity on the solar full disk, respectively. Cross-correlation (CC) analysis of MWSI with three TSI composites shows that TSI should be weakly correlated with MWSI, and not be in phase with MWSI at timescales of solar cycles. The wavelet coherence (WTC) and partial wavelet coherence (PWC) of TSI with MWSI indicate that the inter-solar-cycle variation of TSI is also not related to solar strong magnetic field activity, which is represented by MWSI. However, CC analysis of MPSI with three TSI composites indicates that TSI should be moderately correlated and accurately in phase with MPSI at timescales of solar cycles, and that the statisticalsignificancetest indicates that the correlation coefficient of three TSI composites with MPSI is statistically significantly higher than that of three TSI composites with MWSI. Furthermore, the cross wavelet transform (XWT) and WTC of TSI with MPSI show that the TSI is highly related and actually in phase with MPSI at a timescale of a solar cycle as well. Consequently, the CC analysis, XWT, and WTC indicate that the solar weak magnetic activity on the full disk, which is represented by MPSI, dominates the inter-solar-cycle variation of TSI.

Revisiting the Question: The Cause of the Solar Cycle Variation of Total Solar Irradiance

“…Moreover, the long-term part of the Mg II index shows the small magnetic features contribution to the intensification of TSI [9,12]. Consequently, our finding validates that the solar cycle variation of TSI is dominated by the small magnetic features on the solar full disk, which somewhat coincides with early studies [12,14,15]. It is known that the small-scale magnetic elements, which populate (and form) the faculae in active regions and quiet Sun network/internetwork [57][58][59], are bright and raise the energy transportation from the solar interior toward the solar surface, since the darkness is overcome by the lateral heating in the small-scale magnetic concentrations [4,53,[60][61][62].…”

“…The TSI was first measured by radiometer on board satellites in October 1978, and space-based measurements have continued for more than 40 years. The satellite measurements near Earth show that the TSI varies at all of the timescales it is measured; that is, it varies from solar minimum to maximum, and from one cycle to the next [6][7][8][9][10][11][12][13][14][15][16]. It is generally accepted that the variations of TSI on timescales of minutes to hours are mainly related to granulation, mesogranulation, and supergranulation [17], and the variations in TSI on timescales of a few days to weeks are dominated by the evolution of magnetic features on the solar surface [12,17,18].…”

“…Fröhlich [9] advised that the solar cycle variation of TSI is probably due to a change of the global temperature of the Sun modulated by the strength of activity but not modulated by the surface magnetism as the solar cycle modulation. Xiang and Kong [15] investigated the relation between TSI and magnetic fields and found that the weak magnetic activity seen on the solar full disk dominates the solar cycle variation of TSI. This result is the same as the finding in Li et al [22], in which the conclusion is based on the phase relations between TSI and Mg II core-to-wing ratio.…”

Systematic regularity of solar coronal rotation during the time interval 1939–2019

“…One of its extension, the cross-wavelet transform (CWT), can be applied to determine the relative phase difference between the two time series (Grinsted et al 2004). This technique has been successful used in a broad range of research aspects of solar physics fields, such as Xiang & Kong (2015), Roberts et al (2017), Xu et al (2017), Gil & Mursula (2018), Keys et al (2018), and so on.…”

Multi-scale Oscillation Modes and Secular Trend Analysis of Astronomical Historic Archives

“…Sunspots are the dark parts those are cooler (around 4500 K) than the surrounding area in the photosphere of the Sun, and they are as large as 5000 miles in diameter [9]. Solar magnetic fields are formed below the surface atmosphere and extend put into the corona which owns high temperature.…”