Coherent evidence from Aquarius and Argo for the existence of a shallow low-salinity convergence zone beneath the Pacific ITCZ
KeywordAquarius/SAC-D mission; Sea surface salinity front; Surface freshwater flux; Ekman dynamics; Tropical low-salinity waters
Aquarius observations feature a prominent zonal sea-surface salinity (SSS) front that extends across the tropical Pacific between 2–10°N. By linking to Argo subsurface salinity observations and satellite-derived surface forcing datasets, the study discovered that the SSS front is not a stand-alone feature; it is in fact the surface manifestation of a low-salinity convergence zone (LSCZ) located within 100 m of the upper ocean. The near-surface salinity budget analysis suggested that, although the LSCZ is sourced from the rainfall in the Inter-tropical convergence zone (ITCZ), its generation and maintenance are governed by the wind-driven Ekman dynamics, not the surface evaporation-minus-precipitation flux. Three distinct features highlight the relationship between the oceanic LSCZ and the atmospheric ITCZ. First, the seasonal movement of the LSCZ is characterized by a monotonic northward displacement starting from the near-equatorial latitudes in boreal spring, unlike the ITCZ that is known for its seasonal north-south displacement. Second, the lowest SSS waters in the LSCZ are locked to the northern edge of the Ekman salt convergence throughout the year, but have no fixed relationship with the ITCZ rain band. Collocation between the LSCZ and ITCZ occurs only during August-October, the time that the ITCZ rain band coincides with the Ekman convergence zone. Lastly, the SSS front couples with the Ekman convergence zone but not the ITCZ. The evidence reinforces the findings of the study that the Ekman processes are the leading mechanism of the oceanic LSCZ and the SSS front is the surface manifestation of the LSCZ.
Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 7625–7644, doi:10.1002/2014JC010030.
Showing items related by title, author, creator and subject.
Yu, Lisan (John Wiley & Sons, 2015-06-08)The Intertropical Convergence Zone (ITCZ) is a major source of the surface freshwater input to the tropical open ocean. Under the ITCZ, sea-surface salinity (SSS) fronts that extend zonally across the basins are observed ...
On sea surface salinity skin effect iInduced by evaporation and implications for remote sensing of ocean salinity Yu, Lisan (American Meteorological Society, 2010-01)The existence of a cool and salty sea surface skin under evaporation was first proposed by Saunders in 1967, but few efforts have since been made to perceive the salt component of the skin layer. With two salinity missions ...
Variability of near-surface circulation and sea surface salinity observed from Lagrangian drifters in the northern Bay of Bengal during the Waning 2015 Southwest Monsoon Hormann, Verena; centurioni, luca; Mahadevan, Amala; Essink, Sebastian; D'Asaro, Eric A.; Kumar, B. Praveen (The Oceanography Society, 2016-06)A dedicated drifter experiment was conducted in the northern Bay of Bengal during the 2015 waning southwest monsoon. To sample a variety of spatiotemporal scales, a total of 36 salinity drifters and 10 standard drifters ...