Precession driven low-latitude hydrological cycle paced by shifting perihelion

Abstract. Paleoclimate proxies reveal a significant precessional impact on the low-latitude hydrological cycle. Classical theory suggests that precession modulates the inter-hemisphere summer insolation difference, and hence controls the meridional displacement of the Inter-Tropical Convergence Zone. Accordingly, low-latitude precipitation variations are expected to be in-phase (for the Northern Hemisphere) or anti-phase (for the Southern Hemisphere) with the Northern Hemisphere summer insolation. However, increasing number of proxies, particularly those absolutely dated ones, reveal that variations in terrestrial precipitation at different low-latitudes follow distinct precession rhythms that are very often out-of-phase with hemispheric summer insolation. The mechanism underlying such spatial complexity remains elusive. In this study, we argued that the precession driven low-latitude hydrological cycle is paced by shifting perihelion, rather than the hemispheric summer insolation. More specifically, precession of the Earth’s rotation axis alters the occurrence season and latitude of perihelion. When perihelion occurs, increasing insolation raises the moist static energy over land faster than over ocean due to differing thermal inertia. This thermodynamically moves the tropical convergence precipitation from the ocean to the land, contributing to enhancing the terrestrial precipitation over the latitudinal rain belt. As perihelion shifts towards different latitudes and seasons at different precessional phases, this leads asynchronous terrestrial precipitation maxima at different latitudes. Our hypothesis, supported by both model simulations and geologic records, suggests that the insolation in individual seasons is equally important in shaping the orbital scale climate changes at low-latitude. This offers an alternative dynamical interpretation for the complex evolution of low-latitude hydrological cycle under precessional forcing.