Seasonality and Formation of Barrier Layers and Associated Temperature Inversions in the Eastern Tropical North Pacific
Shota Katsura, Janet Sprintall
Published in JOURNAL OF PHYSICAL OCEANOGRAPHY, MAR 2020
Seasonality and formation of barrier layers (BLs) and associated temperature inversions (TIs) in the eastern tropical North Pacific Ocean were investigated using raw and gridded Argo profiling float data, satellite data, and various sea surface flux data. BLs were observed frequently in boreal summer and autumn along the sea surface salinity (SSS) front south of the eastern Pacific fresh pool. TIs were found within the gap between the western and eastern Pacific warm pools in autumn when BLs were thickest. A mixed layer salinity budget was constructed to determine the formation mechanism responsible for BLs with TIs. This budget revealed that Ekman advection works to both freshen and cool the eastern tropical North Pacific in autumn and contributes to the formation of the thickest BLs with the warmest TIs through the tilting of the SSS front. Precipitation is a secondary contributor to BL formation in autumn. The BLs are also prevalent during summer but are thinner, are without associated TIs, and are primarily formed through precipitation. The largest rainfall associated with the intertropical convergence zone mostly occurred north of the band of thickest BLs in both summer and autumn. The geostrophic advection of salinity did not coherently contribute to the formation of BLs or TIs. The idea that Ekman advection contributes most to the formation of the thickest BLs with warm TIs was further corroborated because the horizontal salinity gradient was the dominant contributor to the density gradient and so is favorable for BL and TI formation.
Fig. 5. Distribution of BLT (colored dots) from Argo profiles in 2003–18 and −PSm/hm (contours; month−1) in (a) January, (b) April, (c) July, and (d) October. Gray shading indicates freshening where values are lower than −0.4 month−1.
Katsura, S. and J. Sprintall, 2020: Seasonality and Formation of Barrier Layers and Associated Temperature Inversions in the Eastern Tropical North Pacific. J. Phys. Oceanogr., 50, 791–808, https://doi.org/10.1175/JPO-D-19-0194.1