Obliquity-driven changes in East Asian seasonality

Abstract

Abstract Obliquity, as a factor controlling seasonality, has been considered a modulator of paleomonsoon evolution. However, in contrast to the clearly identified contribution of precession, East Asian proxy records rarely provide a robust signal of obliquity. By investigating climate simulations with extremely low versus high obliquity, this study examined the seasonal contribution of obliquity, finding that obliquity has substantial effects on the diversity of precipitation stages over East Asia–Western North Pacific (WNP). The sensitivity of greenhouse gases (GHG) to the effects of obliquity also suggests that the contribution of obliquity could depend on GHG concentrations. When GHG forcing is weak, summer precipitation migrates following the obliquity-driven meridional insolation changes over Africa, South Asia, and East Asia. In contrast to a condition of high obliquity with a continental origin of the monsoon, summer monsoon precipitation is confined to the subtropical area including the existence of the WNP monsoon trough in low obliquity. The intrinsic dynamic mode over East Asia–WNP, characterized by a meridional dipole pattern in circulation and precipitation, disappears when obliquity is extremely high. In winter, the strength of synoptic scale (the midlevel trough, Siberian high, and Aleutian low over and around East Asia) and larger scale (midlatitude westerly jet stream and Hadley circulation) circulation is coincidently weaker when compared with that in high obliquity. Obliquity-driven changes over East Asia–WNP are also partly sensitive to GHG concentrations. Furthermore, some major obliquity-driven changes weaken and even disappear when GHG concentrations increase.