Solar cycle modulation of the connection between boreal winter ENSO and following summer South Asia high

Abstract

In this study, the solar cycle modulation of the connection between boreal winter El Niño-South Oscillation (ENSO) and following summer South Asia High (SAH) are revealed. For El Niño accompanied by low solar cycle (EL & LS) or La Niña accompanied by low solar cycle (LA & LS), the boreal winter ENSO prominently affects the following summer's SAH variation. The SAH is enhanced (weakened) and expanded (narrowed) in the meridional and zonal directions in the EL & LS (LA & LS) phase. The composite difference in the SAH between El Niño and La Niña events is obviously stronger in the low solar cycle phase. In low solar cycle phase, El Niño signal and charging process are stronger, which lead to stronger warming sea surface temperature (SST) appear in tropical Indian Ocean and Maritime Continent extending to northwestern Pacific, resulting in larger SAH variations via warming tropospheric temperature. However, for El Niño with a high solar cycle (EL & HS) or La Niña with a high solar cycle (LA & HS), the variations in the SAH and the composite difference of the SAH between El Niño and La Niña events are quite weak in the high solar cycle phase. The charging process over tropical Indian Ocean induced by El Niño is weaker in the high solar cycle phase, which leads to weaker warming SST appear over tropical Indian Ocean, resulting in smaller SAH variations.Further investigation based on longer historic data also ensures that the 11-year solar cycle modulates the ENSO-SAH connection, with a more robust connection in the low solar cycle phase. The 11-year solar cycle should be considered when investigating the connection between the preceding winter ENSO and following summer SAH variations.