[A-CG34] Climate Variability and Predictability on Subseasonal to Multidecadal Timescales

[ACG34-06] Role of oceanic processes in the formation mechanism of warm SST anomalies in 2010s around Hawaii

★Invited Papers

*Naoya Takahashi¹, Kelvin J. Richards¹, Niklas Schneider¹, Hariharasubramanian Annamalai¹, Wei-Ching Hsu², Masami Nonaka³ (1.International Pacific Research Center, University of Hawai‘i at Manoa, 2.University of Georgia, 3.Application Laboratory, Japan Agency for Marine-Earth Science and Technology)

Keywords:Subtropical air-sea interaction, Sea surface temperature, Inter-annual variation, Ekman transport

Warm sea surface temperature (SST) anomalies have been observed in the subtropical North Pacific around Hawaii in the recent decade, appearing from 2013. We examined the formation mechanisms of the warm SST anomalies in terms of relative contribution of atmospheric surface forcing and oceanic dynamics, using the latest ECMWF reanalysis products (ERA5 for atmosphere and ORAS5 for ocean) from January 1979 to December 2018. Results of the mixed layer temperature budget diagnosis in the target domain (10-20 N and 180-160 W) indicates that contributions from anomalous latent heat fluxes to the recent subtropical SST anomalies are dominant. However, oceanic advective contributions also significantly dampen the SST anomalies and are negatively correlated (r = -0.38) with the latent heat fluxes. For example, the +1.0K SST increased from 2011 to 2015 results from +1.5K contributions from sum of surface heat flux and -0.5K from meridional oceanic advection. The anti-correlation between atmospheric forcing and oceanic meridional advection reflects co-variations of wind-driven latent heat flux and meridional Ekman advection due to the weakening of the trade wind. Our results are consistent with “opposing flux hypothesis (Larson et al. 2018)” in the trade wind regime, providing its observational evidence. Role of mixed layer depth anomalies to the recent SST anomalies will also be discussed.