Subsurface temperature anomalies in the North Pacific Ocean associated with the ENSO cycle

Multi-year Simple Ocean Data Assimilation (SODA) and National Centers for Environmental Prediction (NCEP) datasets were used to investigate the leading patterns of subsurface ocean temperature anomalies (SOTA) and the corresponding atmospheric circulation structure in the Pacific Ocean (20°S–60°N). In this paper, the evolution of North Pacific SOTA associated with El Niño-southern oscillation (ENSO), and their relationship with the overlying zonal/meridional atmospheric circulations were elucidated. The results indicate that: (1) there are two dominant modes for the interannual variability of the North Pacific SOTA. The primary mode is the dipole pattern of the central and western North Pacific SOTA associated with the leading mode of ENSO, and the second mode is the zonal pattern related to the second mode of ENSO. These two modes consist of the temporal-spatial variation of the SOTA in the North Pacific. (2) During the developing phase of the El Niño event, positive (negative) SOTA appears in the western (central) portion of the North Pacific Ocean. During the mature and decaying phase of the El Niño event, the western positive center and the central negative center continue to be maintained and enhanced. Meanwhile, the position of the western positive center slightly changes, and the central negative center moves eastward slowly. After the El Niño event vanishes, the positive SOTA disappears, and the central negative SOTA becomes weak and remains in the northeastern Pacific Ocean. The results for La Niña are generally the opposite. (3) During the El Niño/La Niña cycle, formation and evolution of the SOTA, with opposite signs in central and western North Pacific Ocean, resulted from vertical movement of the two northern branches of the Hadley Cell with opposite direction, as well as the positive feedback of the air-sea interaction induced by dynamic processes in the mid-latitudes. The former gives rise to the initial SOTA, and the latter intensifies SOTA. Under the forcing of these two processes, SOTA evolution is formed and sustained during the El Niño/La Niña events. Also discussed herein as background for the ENSO cycle are the possible connections among the West Pacific subtropical high, the strength of the Kuroshio near the East China Sea, the Kuroshio meanders south of Japan, the Aleutian Low, and cold advection in the central North Pacific Ocean.