Multidecadal Modulations of Tropical Atlantic impact on ENSO

<p><span>Observational studies have reported that tropical Atlanti</span><span>c interannual variability impacts</span><br><span>on ENSO in di</span><span>ff</span><span>erent seasons and periods: Atlantic Ni &#771;</span><span>nos (AN</span><span>) in boreal summer during</span><br><span>negative phases of the Atlantic Multidecadal Variability (</span><span>AMV); and tropical north Atlantic</span><br><span>(TNA) in boreal spring during positive AMV. Nevertheless, t</span><span>his relation is not clear for the</span><br><span>whole observational record. This paper is an step forward to</span><span>wards understanding of tropical</span><br><span>Atlantic impacts on ENSO: how and when do they occur? Using ob</span><span>servations and a pool of</span><br><span>preindustrial control simulations from the CMIP5 initiati</span><span>ve we investigate the background</span><br><span>ocean and atmospheric conditions promoting these tropical</span> <span>interbasin connections.Periods</span><br><span>with a negative AN-ENSO connection appear characterized by</span> <span>a shallower thermocline</span><br><span>over the western Pacific and deeper in the east, together with</span> <span>an increase in interannual</span><br><span>SST variability over the tropics.</span> <span>Periods with a negative TN</span><span>A-ENSO connection appear</span><br><span>characterized by a steeper thermocline in the Pacific and pos</span><span>itive interhemispheric SST</span><br><span>gradient in the the Atlantic. A decrease in tropical Pacific a</span><span>tmospheric and ocean variability</span><br><span>characterizes these periods.</span></p>