Possible solar modulation of the ENSO cycle

Previous studies suggested that solar activity may influence the El Nino/ Southern Oscillation (ENSO) cycle, such as in the modulation of the amplitude of the Tropospheric Biennial Oscillation (TBO). This study shows that the difference of the TBO due to the solar cycle is, in fact, derived from a difference in the association of the Indian Ocean sea-surface temperatures (SSTs) with the Pacific Ocean SSTs. High SSTs appear in the Indian Ocean following a warming in the Pacific Ocean during low solar activity (LS) from summer to winter. However, such a relationship is absent during high solar activity (HS). This difference in SSTs is related to the distribution of convective activity over the equator. Convective activity is more localized over the Pacific sector during HS, but more zonal and extending over the Indian Ocean during LS. Differences are also found in the vertical velocity in the troposphere. Up-welling over a warm SST region is connected to the stratosphere during LS, but limited within the troposphere during HS.A possible mechanism suggested from this study is that the solar influence in the equatorial troposphere does not arise from a change in the ocean temperature, but originates from the equatorial stratosphere through changes in the meridional circulation. This circulation modulates the vertical extent of convective activity as well as the horizontal distribution along the equator.