Local phase relationship between sea surface temperature and net heat flux over weekly to annual periods in the extratropical North Pacific

The relationship between sea surface temperature (SST) and net heat flux (NHF) in the North Pacific over weekly to annual period bands was investigated using gridded datasets of SST obtained by the Advanced Microwave Scanning Radiometer for the Earth Observing System, and flux data produced by the Modern-era Retrospective-analysis for Research and Applications Reanalysis. This study focused on the phase difference between the SST and NHF, which can suggest the driving force between two co-varying parameters. The SST delay behind the NHF, with phase differences from π/4 to π/2, which suggests that the SST change would be controlled by the NHF, was commonly found over all periods. In the intra-annual (100- to 200-day periods) band, part of the coherent variations showed negative phase differences (around -π to -π/3), which were found in the western North Pacific and along ~30°N in the central North Pacific. The spatial scales of SST variability in the shorter band (weekly to intraseasonal: less than 100-day periods) are dominantly over 200 km. In contrast, the scales in the intra-annual band were in the range 50-150 km, where the negative phase differences were frequently found.