Interannual Variability of Regional Hadley Circulation and El Niño Interaction.

El Niño‐Southern Oscillation (ENSO) triggers variations of the global Hadley circulation (HC), while the latter may potentially feedback to ENSO events. Previous studies mainly investigated the interactions between ENSO and the global zonal‐mean HC. Here, we present a regional perspective of HC variability by introducing zonal variations. Results show that El Niño intensifies the regional HC over the central‐eastern Pacific, while weakening the regional HC over both the Indo‐Pacific warm pool and the tropical Atlantic. The background seasonal cycle modulates the equatorial‐asymmetric component of HC, with an anticlockwise (clockwise) asymmetric circulation over the central equatorial Pacific before (after) El Niño peaks. Remarkably, the asymmetric HC in boreal spring leads ENSO with a lead correlation of up to 0.68, mediated by the wind‐evaporation‐sea surface temperature (SST) feedback and other atmosphere‐ocean dynamics. The antecedent HC anomaly may contribute to ENSO predictability. Plain Language Summary: By decomposing the atmospheric circulation to its irrotational and nondivergent components, we integrated the three‐dimensional structure of the Hadley circulation (HC), and investigate its interactions with El Niño‐Southern Oscillation (ENSO). In particular, we focus on the zonal variation of the HC and its equatorial‐symmetric and asymmetric components associated with ENSO variability. We find that an El Niño event may intensify the HC over the central‐eastern Pacific, but weaken the circulation over the Indo‐Western Pacific and the tropical Atlantic. The intensity of the ENSO‐related asymmetric HC anomaly is as large as that of the symmetric HC. The asymmetric HC anomaly is characterized by a clear seasonal feature. In boreal spring (MAM) before an El Niño signal becomes clear, a strong anticlockwise (asymmetric) HC across the central equatorial Pacific usually lead the El Niño event, with an 8‐month lead correlation with the November‐December‐January (NDJ, the peak season) Niño‐3.4 index of up to 0.68, implying that the MAM asymmetric HC and its associated atmosphere‐ocean interactions may largely contribute to the development of ENSO events. Further analysis indicated that the wind‐evaporation‐sea surface temperature feedback and the Bjerknes feedback play important roles in the interactions between the ENSO events and HC. Key Points: The three‐dimensional structure of El Niño‐related Hadley circulation (HC) anomaly shows a strong zonal variationThe direction of the equatorial‐asymmetric HC associated with El Niño events shows a clear seasonal featureThe asymmetric HC over equatorial central Pacific in spring may contribute to the development of an El Niño event [ABSTRACT FROM AUTHOR]