2:20 PM - 2:35 PM
[ACG33-03] Mechanisms of Reemergence in the North Pacific revealed by Mixed Layer Heat Budget Analysis
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.
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.