Effect of high-frequency wind on intraseasonal SST variabilities over the mid-latitude North Pacific region during boreal summer

Abstract

The effect of high-frequency (period <20 days) wind on the intraseasonal (period 20–100 days) sea surface temperature (SST) anomalies over the mid-latitude North Pacific region (35°–45°N, 160°E–170°W) during boreal summer was examined through the diagnosis of reanalysis data and numerical experiments. The reanalysis data diagnosis shows that the near-surface high-frequency (HF) wind is weaker (stronger) during the intraseasonal SST warming (cooling) phase. The phase-dependent amplitude of HF wind is controled by the strength change of the upper-tropospheric westerly jet stream. Because the magnitude of the HF wind over the target region shows significantly positive correlation with the total wind speed, a weaker (higher) HF wind in the SST warming (cooling) phase tends to decrease (increase) total wind speed, which can further suppress (enhance) upward surface latent heat and sensible heat fluxes and strengthen the intraseasonal SST variability. The numerical experiments with an oceanic general circulation model demonstrate that the HF wind can amplify the intraseasonal SST variability over the target region mainly through nonlinearly rectifying intraseasonal surface latent and sensible heat fluxes. The HF wind can explain about 20 % of the intraseasonal SST variability in the target region.