Fig. 2: Seasonal evolutions of circulation and diagnosed results for N2L onset.

a–e Horizontal patterns of anomalous SST (shaded, units: °C), precipitation (crossed, units: \({mm}\) \({{day}}^{-1}\)) and wind fields at 850 hPa (vector, units: \(m\) \({s}^{-1}\)) from the preceding autumn to the developing autumn of N2L events. f Mixed-layer heat budget diagnosed results for N2L averaged over (5°S–5°N, 160°–110°W) during SO(−1) (units: °C mon⁻¹). The x-axis from left to right represents MLTA tendency (\(\frac{\partial {T}^{{\prime} }}{\partial t}\)), the sum of advection and heat flux, the sum of advection, the sum of heat flux, the individual advection and heat flux terms: \(-\bar{u}\frac{\partial {T}^{{\prime} }}{\partial x}\), \(-{u}^{{\prime} }\frac{\partial \bar{T}}{\partial x}\), \(-{u}^{{\prime} }\frac{\partial {T}^{{\prime} }}{\partial x}\), \(-\bar{v}\frac{\partial {T}^{{\prime} }}{\partial y}\), \(-{v}^{{\prime} }\frac{\partial \bar{T}}{\partial y}\), \(-{v}^{{\prime} }\frac{\partial {T}^{{\prime} }}{\partial y}\), \(-\bar{w}\frac{\partial {T}^{{\prime} }}{\partial z}\), \(-{w}^{{\prime} }\frac{\partial \bar{T}}{\partial z}\), \(-{w}^{{\prime} }\frac{\partial {T}^{{\prime} }}{\partial z}\), net longwave radiation (\({{lw}}^{{\prime} }\)), net solar radiation (\({{sw}}^{{\prime} }\)), surface latent heat flux (\({{lh}}^{{\prime} }\)) and surface sensible heat flux (\({{sh}}^{{\prime} }\)), respectively. The error bars represent one standard deviation. Orange solid (white hollow) dots denote statistically significant (insignificant) terms. g SSTA (shaded, units: °C), zonal wind anomaly at 850hPa (vector, units: \({{m\ s}}^{-1}\)), h zonal wind anomaly at 850hPa averaged over 160°–110°W (solid line, units: \({{m\ s}}^{-1}\)) and 150°E–100°W (dashed line, units: \({{m\ s}}^{-1}\)), i thermocline depth (shaded, units: \(m\)) and horizontal ocean currents (vector, units: \({{m\ s}}^{-1}\)), j zonal geostrophic current and Ekman current averaged over (2°S–2°N, 160°–110°W) (units: \({{m\ s}}^{-1}\)) during SO(−1) of N2L. The green (brown) crosses in a–e denote the regions of significant positive (negative) precipitation anomalies. Black dots a–e, g, i represent SSTA and thermocline depth that exceed the 95% confidence level, respectively. The blue arrow in (a) denotes the easterly anomaly along the equatorial Pacific.