Comments on “Interdecadal Change of the South China Sea Summer Monsoon Onset”

Abstract

Abstract In a recent paper, Kajikawa and Wang detected the interdecadal shift of the South China Sea summer monsoon (SCSSM) onset with a late SCSSM onset in an earlier epoch (1979–93) and an early SCSSM onset in a later epoch (1994–2008) and attributed this change to enhanced tropical cyclone (TC) activity and intraseasonal variability (ISV) related to 30–80-day and 10–25-day anomalies in the second epoch. This comment assesses the individual impact of TCs and ISV on the interdecadal change of the SCSSM onset by means of the removal of anomalies associated with TCs and ISV. Results herein show that TCs have no significant impact on the SCSSM onset in all years, except 2006 in which a strong and long-lived TC occurred over the South China Sea. After removing the 30–80-day anomaly, the difference in the mean SCSSM onset date in the two epochs decreases to some extent, implying that the 30–80-day anomaly can, in part, play a role in the interdecadal shift of the SCSSM onset. In contrast, the 10–25-day anomaly has an insignificant contribution to the interdecadal shift of the SCSSM onset. The discrepancy of ISV contribution results from the SCSSM background state, the magnitude and spatiotemporal scale of ISV, and the phase relationship between ISV and SCSSM transition from easterly to westerly.