Climate Impacts Of ENSO Diversity On Double ITCZs Over The Eastern Pacific Ocean During Spring

During the boreal spring(March-April),a unique double intertropical convergence zone(ITCZ)pattern emerges over the eastern tropical Pacific Ocean.Different types of ENSO events have different climatic impacts on such double ITCZs.Based on reanalysis data during 1979-2018,this study examines the regulation of mixed El Ni(?)o events on the double ITCZs over the eastern Pacific Ocean.This study also contrasts how the three strongest eastern Pacific type(EP-type)El Ni(?)os modulate double ITCZs.In addition,we investigated the changes in the impacts of La Ni(?)a events on double ITCZs before and after 2000.Our results indicate that: 1.The mixed El Ni(?)o event in 2009/10 has the characteristics of both eastern Pacific-type(EP-type)and central Pacific-type(CP-type)El Ni(?)os.The regulation of the 2009/10 event on double ITCZs during the boreal spring of 2010 not only reflects the modulation process of EP-type El Ni(?)o,i.e.,an increase of equatorial precipitation;but also the regulation characteristics of CP-type El Ni(?)o events on double ITCZs,i.e,the enhanced northern ITCZ and weakened southern ITCZ.In March-April of 2010,influenced by a meridionally SST warming with a maximum at the equator,the northern and southern ITCZs moved equatorward,which led to an enhancement of equatorial precipitation.At the same time,a north-warm and south-cool contrast of SST anomalies caused a strengthened northern ITCZ and a weakened southern ITCZ.2.In recent four decades,there were three record-breaking El Ni(?)o events: 1982/83,1997/98,and 2015/16 events.We compare the modulation processes of three extreme EP-type El Ni(?)o events on double ITCZs,highlighting the internal diversity within EP-type El Ni(?)o events.Our results show that the impact of 2015/16 El Ni(?)o on the location and intensity of double ITCZs is completely different from that of 1982/83 and1997/98 El Ni(?)os.In March-April of 1983 and 1998,a meridionally symmetric structure of SST warming with a maximum at the equator drived both northern and southern ITCZs move equatorward,which increased the equatorial precipitation.The SST anomalies during March-April of 2016 exhibited a meridionally symmetric structure with a minimum at the equator,which were linked to the enhanced precipitation in southern and northern ITCZs and weakened precipitation at the equator.3.Besides the modulation of El Ni(?)o events,we analyzed the changes in the modulation of La Ni(?)a events before and after 2000 on the double ITCZs.In March-April of the La Ni(?)a decaying year,there was a meridionally "south-cold,north-colder and equator-coldest" SSTA pattern over the eastern Pacific Ocean before2000.The SST north of the equator decreased more than that south of the equator,resulting in an weakened northern ITCZ and an strengthened southern ITCZ.At the same time,the reduction of SST at the equator was more significant than that off the equator,which increased the distance between the northern and southern ITCZs,reducing the equatorial precipitation.In March-April of the La Ni(?)a decaying year,a meridionally "equator-cold,north-colder,south-coldest" SSTA pattern occurred over the eastern Pacific Ocean after 2000.The SST at the equator was relatively higher,which moved both southern and northern ITCZs equatorward.At the same time,the SST south of the equator was relatively lower than that north of the equator,which led to a weaker southern ITCZ.