Description: This paper uses the sunspot number (SSN) index and the El Niño modoki index (EMI) to examine the possible modulation of El Niño Modoki events by variations in solar activity. A significant positive correlation was found between SSN and EMI with a lag of two years, and both SSN and EMI have an obvious period of about 11–12 years. The evolution of El Niño Modoki events was investigated using composite analysis. There was a clear evolution of El Niño Modoki events in the three years after the solar peak year. An ocean mixed layer heat budget diagnostic method is used to investigate the contributor to the anomalous patterns in the three years after the solar peak. The atmosphere radiation fluxes are confirmed as the major contributor to the warming response in the central tropical Pacific. Two possible mechanisms are proposed, one is the direct mechanism that the solar radiation warms up the tropical pacific with a geographical difference, due to the cloud distribution. The warming response in the central Pacific is amplified by the coupled positive feedback between the ocean and atmosphere with 1–2 years lag. Another possible way can be described as follows: the solar heating effect propagating from the upper atmosphere modulates the strength and variation of atmospheric anomaly at high and mid-latitudes in the northern hemisphere winter, which results in an anomalous subtropical cyclone over the northeastern Pacific in the winter seasons following the solar peak years. The anomalous cyclone reduces the cloud cover over the northeastern Pacific and enhances the local input of solar radiation. As a result, a positive sea surface temperature (SST) anomaly occurs over the northeastern Pacific and extends towards the central tropical Pacific along the path of anomalous southwesterly winds, which may trigger an El Niño Modoki event in the following years.

Description: Solar radiation is a forcing of the climate system with a quasi-11-year period. As a quasi-period forcing, the influence of the phase of the solar cycle on the ocean system is an interesting topic of study. In this paper, the authors investigate a particular feature, the ocean heat content (OHC) anomaly, in different phases of the total solar irradiance (TSI) cycle. The results show that almostopposite spatial patterns appear in the tropical Pacific during the ascending and declining phases of the TSI cycle. Further analysis reveals the presence of the quasi-decadal (~11-year) solar signal in the SST, OHC and surface zonal wind anomaly field over the tropical Pacific with a high level of statistical confidence (〉95%). It is noted that the maximum centers of the ocean temperature anomaly are trapped in the upper ocean above the main pycnocline, in which the variations of OHC are related closely with zonal wind and ocean currents.

Description: The equatorial Pacific response to 11-year solar cycle is assessed in observation and ensemble historical-Nat simulations from the Coupled Model Intercomparison Project, Phase 5 (CMIP5). We find the central equatorial Pacific is sensitive to the solar forcing. A significant positive correlation is found between observed sea surface temperature (SST) anomaly and sunspot number (SSN) index with a lag of 2 years in the central Pacific. The 11-year solar signal particularly exits in the SST and zonal wind anomalies from spectrum analysis. Based on composite analysis, a warming response appears in the central Pacific with lagging the solar cycle by 1-2 years in observation, and 2-3 years in simulation results. Associated with the ocean temperature anomaly, an anomalous twin Walker circulation cells arise in the equatorial Pacific with their updraft branch centered over the central equatorial Pacific, which is significantly both in observation and simulation. Mixed layer heat budget analysis shows that the atmosphere radiation fluxes modulated by the amounts of cloud cover are responsible for the warming response pattern in the central Pacific. There is a significant positive correlation between the meridional gradient of cloud cover (Δα, Subtropics-Tropic) and zonal SST gradient (ΔT, east-west) in the equatorial Pacific. The warming response in the central equatorial Pacific is amplified by the coupled atmosphere and ocean processes. On the one hand, owing to the zonal SST gradient decreasing in the western and central Pacific but increasing in the eastern and central Pacific, anomalous zonal wind convergence appears in the central Pacific in the three years following the solar peak. The ocean heat transport effect is negative in the central equatorial Pacific, more warm water accumulates locally. On the other hand, anomalous ascending motion over the central Pacific increases the high cloud amount and lets more shortwave radiation come into surface, which combined with the longwave radiation trapping, also amplifies the warming response in the central Pacific.

Description: A delayed response to the solar variability has been found in the tropical Pacific that resembles the pattern of El Nino Modoki, it also been noted that this response connects to the atmosphere circulation anomalies over mid-high latitude. Here we use the multiple reanalysis data to detect the indirect route of solar activity modulation on tropical Pacific SST anomalies through the atmosphere anomalies at mid-high latitude. The results suggest that high solar activity enhances the atmosphere-to-ocean forcing from the higher extratropical Arctic Oscillation (AO)-like atmospheric anomalies to the El Niño Modoki-like SST anomalies in the tropical Pacific one year later. During high solar activity years, a meridional dipole pattern of wintertime sea level pressure anomalies over the North Atlantic and America can trigger an El Niño Modoki-like SST warming in the tropical Pacific during the following seasons and the next year. However, during low solar activity years the AO-like pattern is weak and hence the El Niño Modoki-like SST response disappears in the tropical Pacific