Equatorial Pacific Thermostad response to El Niño. Issue 11 (30th November 2016)

• Record Type: Journal Article
• Authors: Johnson, Gregory C.; Birnbaum, Abigail N.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 11(2016:Nov.)
• Page Start: 8368
• Page End: 8378
• Publication Date: 2016-11-30
• Subjects: Pacific Equatorial Themostad -- El Niño; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2016JC012304
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: El Niños are characterized by a shift of warm surface water from the western to eastern equatorial Pacific due to weakening of easterly trade winds. This shift is associated with the pycnocline (or thermocline), the large vertical density gradient beneath the surface mixed layer, shoaling in the west and deepening in the east, inducing a redistribution of ocean heat with global impacts. Here the response of the Equatorial Pacific Thermostad, a layer of low vertical stratification below the pycnocline to, El Niño is investigated using a monthly Argo float climatology and Argo float deep velocity data. A mean, seasonal cycle, trend, and time‐lagged linear response to the Niño3.4 index are fit by least squares to temperature and salinity at each grid point as well as to deep float velocities (omitting the trend). The results of these fits are used to characterize the response of physical properties in the Thermostad, including layer thickness and velocity, to El Niño by comparing the mean properties following neutral conditions (Niño3.4 = 0°C) versus those following a moderate El Niño (Niño3.4 = 1°C). Following an El Niño, a strengthening of the westward‐flowing Equatorial Intermediate Current of about 2.7 × 10 6 m 3 s −1 shifts about 97 × 10 12 m 3 of Thermostad water from the east to the west, allowing conservation of volume within the Thermostad as the pycnocline above deepens in the east and shoals in the west. This transport and volume change imply a 14 month time scale, consistent with El Niño. Key Points: Argo temperature‐salinity profile and deep velocity data are used to investigate the subsurface response of the equatorial Pacific to ENSO Following a moderate El Niño westward flow in the depth range of the Equatorial Intermediate Current strengthens by about 2.7 Mm 3 /s This anomalous westward flow effects a shift of about 97 Tm 3 of Equatorial Pacific Thermostad water from the eastern to western Pacific