[A-CG30] Multi-scale ocean-atmosphere interaction in the tropics

[ACG30-04] Formation of Barrier Layers and Temperature Inversions in the Eastern Tropical Pacific Detected by Mooring Observation

*Shota Katsura¹, Janet Sprintall¹, Thomas Farrar², Dongxiao Zhang^3,4, Meghan Cronin³ (1.Scripps Institution of Oceanography, University of California, San Diego, 2.Department of Physical Oceanography, Woods Hole Oceanographic Institution, 3.NOAA Pacific Marine Environmental Laboratory, 4.Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington)

Keywords:Barrier Layer, Temperature Inversion, Eastern Tropical Pacific

It is known that salinity plays a dominant role in determining the stratification of the upper ocean, especially where barrier layers (BLs) form between the bases of the mixed layer and the isothermal layer in some regions. The BL interferes with heat and momentum exchange between surface and subsurface layers and can affect sea surface temperature and air-sea interactions. In the eastern tropical Pacific, BLs are distributed along the SSS front south of the eastern Pacific fresh pool in boreal summer and autumn and tend to be associated with temperature inversions (TIs) in boreal autumn. A mixed layer salinity and temperature budget was constructed based on time-series from three mooring observations to investigate the formation of BLs and TIs in the eastern tropical Pacific. BLs and TIs observed at the moorings showed a clear seasonality in their formation and amplitude, which is consistent with the previous climatological studies. However, in contrast to previous studies in the region, the mixed layer salinity budget indicates that precipitation was dominant for the surface freshening in boreal summer and autumn and contributed to the BL formation. The mixed layer temperature budget found that the penetration of shortwave radiation through the mixed layer base had a dominant contribution to the surface cooling and hence the TI formation during the boreal summer and autumn. Geostrophic and Ekman advection also occasionally contributed to the BL and TI formation. The existence of BLs significantly reduced the entrainment cooling and detrainment warming. In addition, the entrainment warmed the mixed layer when BLs with TIs existed. The shallower mixed layers associated with BLs were more sensitive to surface heat and freshwater flux than when BLs were not observed in the water column.