Precession of the Earth's rotation axis drives naturally asynchronous precipitation variation at low-latitudes

Many proxies reveal that the low-latitude precipitation varies at a periodic of ∼23 ka, which is governed by precessional forcing. Classical theory proposed that precession-induced increased summer insolation in the Northern Hemisphere (perihelion) corresponds to decreased summer insolation in the Southern Hemisphere (aphelion), hence, controlling the inter-hemisphere temperature contrast and driving the meridional shift of the ITCZ. Accordingly, the low-latitude precipitations are expected to be in-phase (for the Northern Hemisphere) or anti-phase (for the Southern Hemisphere) with the Northern Hemisphere summer insolation. However, in the past two decades, collective proxies showed that the low-latitude precipitation follows very different rhythms, very often out-of-phase with hemispheric summer insolation. For example, the Eastern Asian precipitation evolutes resembling the Northern Hemisphere summer insolation, whereas the Malaysian precipitation correlates the variations in October insolation. The mechanism driving this phenomenon has puzzled the paleoclimate community for more than two decades, however, remains elusive. In this study, by combining theoretical analysis, numerical simulations, and geological records, we proposed a new hypothesis, suggesting that the precession regulates the low-latitude precipitation by altering the latitude of perihelion. The “latitude of perihelion” is defined as the latitude of overhead Sun at the time of perihelion. We demonstrated that wherever (the latitude) and whenever (the season) perihelion occurs, the incoming solar radiation at the corresponding latitude reaches its maximum, driving the strongest land-sea temperature contrast and regional precipitation over land in the corresponding season. The perihelion occurs towards different latitudes and in different seasons depending on the precessional phase. Therefore, the precipitation at different latitudes naturally follow different rhythms.