Abstract

By using gridded Argo data from 2004 to 2017, a systematic comparison study is conducted on the evolution features of the tropical Pacific Barrier Layer (BL) between El Niño and La Niña (ENSO) period. As of climatology, the BL in the tropical Pacific Ocean presents three distinctive zonal bands at about 12° N, 5° N, 10° S, separately, extending from the western Pacific warm pool eastwards to the eastern Pacific Ocean. Among them, the BL (>20m) in the warm pool occurs throughout the whole calendar year, whilst the BL at both 12° N and 10° S bands exist mostly often in Winter and Summer periods Composite analysis reveals that the ENSO-relevant BL variations are largely confined within the equatorial Pacific west of 160° W. Specifically, overwhelming thick (thin) BL occurs east of 160° E during El Niño (La Niña) year, respectively. It is deduced that the heavy rainfall, horizontal transport of low saline water and downwelling Kelvin waves are three main contributors for the unusual thick BL occurrence east of 160° E during the El Niño period. Correlation diagnosis verifies that the interannual BL changes lags the Nino 3.4 index by one month. Conversely, the BL variability leads the Nino 3.4 index by one month for the La Niña event and anomalous thickening of the Isothermal Layer (IL) triggered by water convergence and subduction is believed to be the main cause for the abnormally thick BL emergence west of 160° E.

Keywords: Barrier layer; El Niño-southern oscillation; Rainfall; Ocean advection; Kelvin wave

Abbreviations: IL: Isothermal Layer; ENSO: El Niño-Southern Oscillation; BL: Barrier Layer; NCEP: National Environmental Prediction Center; NCAR: National Atmospheric Environment Center; CPC: Climate Prediction Center; OLR: Outgoing Longwave Radiation; MLD: Mixed Layer; BLT: Barrier Layer Thickness; SPCZ: South Pacific Convergence Zone; ITCZ: Intertropical Convergence Zone