Modulation of observed sea surface temperature variation by the quasi-biweekly oscillation in the tropical western Pacific during boreal summer

Using 17-year in situ buoy observations, this study investigates how sea surface temperature (SST) over the tropical western Pacific Ocean is modulated by the quasi-biweekly oscillation (QBWO) during boreal summer. The 10-buoy mean phase-by-phase composites of SST indicate that SST evolution lags behind the convection cycle by approximately one quarter, with the maximum SST occurring in Phase -90 degrees (29.68 degrees C) and the minimum SST occurring in Phase 90 degrees (29.37 degrees C). The diurnal cycle of SST (dSST) is in phase with the convection cycle, with the minimum dSST occurring during the convectively active phase (0.34 degrees C) and the maximum dSST occurring during the convectively suppressed phase (0.61 degrees C). The fluctuation in the dSST reaches 0.27 degrees C, which is similar to that in the SST (0.31 degrees C). This kind of oscillation can be well explained by the evolution of the sea surface forcing parameters, especially the shortwave radiation and wind speeds, observed from the buoys. In addition, the composite range of the dSST suggests an interesting asymmetry between Phase -90 degrees and 90 degrees. The interaction of the background summer mean state and the 10-30-day intraseasonal anomalies causes the asymmetry in wind speed between Phase -90 degrees and 90 degrees, which in turn results in the asymmetry in the dSST between these two phases. Since QBWOs are more likely to occur during El Nino developing summers than during El Nino decaying summers, the 10-30-day intraseasonal SST and dSST variances during El Nino developing summers are stronger than those during El Nino decaying summers.

Automated summary

Using 17 years of in situ buoy observations, this study investigates how sea surface temperature (SST) over the tropical western Pacific Ocean is modulated by the quasi-biweekly oscillation (QBWO) during boreal summer. The findings show that SST evolution lags behind the convection cycle, with the minimum and maximum SST occurring at different phases. Additionally, the study highlights the asymmetry in wind speed and SST between different phases, which is influenced by the background summer state and intraseasonal anomalies associated with El Nino events.