An epoch-dependent change in driver of heat storage rate variability during recent decades in the upper wester North Pacific

Abstract

The upper 400 m heat budget obtained from a high-resolution ocean general circulation model for recent decades suggests that winter heat storage rate (HSR) on interannual to decadal time scales is mainly determined by oceanic heat advection rather than by net air-sea heat flux (HF) in the western North Pacific region. The role of heat advection in driving the HSR variability becomes particularly prominent after 1990. Similar observation that there is a significant epoch-dependent change in the relative contribution of surface HF and ocean heat advection to winter HSR is also found by analyzing NCEP heat flux and HadISST datasets. The net HF acts to dampen temperature anomalies caused by the ocean dynamics while the HF could play an important role before 1990 due to its stronger variability caused by △T (air-sea temperature difference) variability. On the other hand, the variability of ocean heat advection, which represents ocean dynamics, is not very sensitive to the selection of periods. The ocean dynamics causing the upper-ocean heat storage rate is principally associated with the meridional shift of the Oyashio Extension front, which is significantly correlated with both the West Pacific and Pacific-North America teleconnection patterns. rather than by net air-sea heat flux (HF) in the western North Pacific region. The role of heat advection in driving the HSR variability becomes particularly prominent after 1990. Similar observation that there is a significant epoch-dependent change in the relative contribution of surface HF and ocean heat advection to winter HSR is also found by analyzing NCEP heat flux and HadISST datasets. The net HF acts to dampen temperature anomalies caused by the ocean dynamics while the HF could play an important role before 1990 due to its stronger variability caused by △T (air-sea temperature difference) variability. On the other hand, the variability of ocean heat advection, which represents ocean dynamics, is not very sensitive to the selection of periods. The ocean dynamics causing the upper-ocean heat storage rate is principally associated with the meridional shift of the Oyashio Extension front, which is significantly correlated with both the West Pacific and Pacific-North America teleconnection patterns.