Japan Geoscience Union Meeting 2019

Presentation information

[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-CG Complex & General

[A-CG33] Extratropical oceans and atmosphere

Mon. May 27, 2019 1:45 PM - 3:15 PM 104 (1F)

convener:Kazuaki Nishii(Graduate School of Bioresources, Mie University), Yoshi N Sasaki(Hokkaido University), Hatsumi Nishikawa(Institute of Low Temperature Science, Hokkaido University), Shun Ohishi(Division for Land-Ocean Ecosystem Research, Institute for Space-Earth Environmental Research, Nagoya University), Chairperson:Kazuaki Nishii(三重大学)

2:20 PM - 2:35 PM

[ACG33-03] Mechanisms of Reemergence in the North Pacific revealed by Mixed Layer Heat Budget Analysis

*Kazumichi Murata1, Shoichiro Kido1, Tomoki Tozuka1 (1.Department of Earth and Planetary Science, School of Science, The University of Tokyo)

Keywords:Reemergence, North Pacific, mixed layer heat budget analysis

Wintertime sea surface temperature (SST) anomalies that disappear in summer and

recur in the following winter is called “reemergence”. Previous studies suggested that

temperature anomalies that subduct into the subsurface during the shoaling phase of the

mixed layer are preserved under the mixed layer due to isolation from atmospheric

forcing and reentrained into the surface mixed layer. Since reemergence is considered to

play an important role in the Pacific Decadal Oscillation, it is important to understand its

mechanisms, but past studies are mostly based on statistical analyses. Therefore, in this

thesis, the mechanisms of reemergence in the North Pacific is clarified quantitatively by

an online mixed layer heat budget analysis with an ocean model simulation.

Following a method proposed by a previous study, areas with reemergence are

detected and the focus of this study is the Reemergence Area (RA, 35°-40°N, 155°-

145°W) in the central North Pacific. In the RA, the Reemergence Years (RYs) are

determined and the mixed layer heat budget analysis is conducted with the integration of

the Regional Ocean Model System (ROMS) covering the RA. In contrast to past studies

that suggested importance of anomalous entrainment term, it is shown that several

mechanisms are operating in reemergence. In particular, the anomalous Ekman

meridional advection of the mean meridional temperature gradient induced by zonal wind

stress anomalies plays an important role in many RYs. Also, coincidence in the sign of

SST anomalies in winter and surface heat flux anomalies in the following autumn leads

to recurrence of SST anomalies in some RYs. On the other hand, the conventional

mechanism related to the mean entrainment of anomalous temperature contributes to

reemergence in two RYs.