The causality from solar irradiation to ocean heat content detected via multi-scale Liang-Kleeman information flow

Solar irradiation is the primary driving force for the Earth's climate system. However, we are still short of powerful tools to study the variability of the Earth's climate due to the solar activity. Here we apply the Liang-Kleeman information flow to quantify the causality from Total Solar Irradiance (TSI) to the global ocean heat content anomaly (OHCA). It reveals that the information flow from TSI to OHCA varies in both time and space. We adapt the method into a multi-scale version which describes the variation of information flow on different timescales. In different ocean basins, the significant information flow from TSI to OHCA varies on different timescales, which could be several decades, much longer than the timescale of the correlation revealed by wavelet coherence. Then we calculate the information flow from TSI to the first three expansion coefficients of the OHCA Empirical Orthogonal Functions. The results indicate that TSI is a part cause of the El Niño-Southern Oscillation (ENSO) and global warming, especially in the 1970s. In the recent 40 years, the contribution of TSI to the variation of the OHCA becomes less significant probably due to the increasing influence of human activity on the climate system.