Regional and Seasonal Responses of Tropical Precipitation to Past Climate Changes

The Intertropical Convergence Zone (ITCZ) is a perennial rain belt located near the equator. Previous modeling results have shown that the annual, global average position of the ITCZ has remained stable over the past 20,000 years. However, paleoclimate proxy data indicates a wider latitude of migration in response to glaciation and orbital forcings than is predicted in models. Satellite observation data shows that the location of the ITCZ can vary widely between regions and over the course of the year. We analyzed model results from the Geophysical Fluid Dynamics Lab (GFDL) Coupled Model version 2 (CM2) under two precession paradigms, a June perihelion case (~11,000 years ago) and a December perihelion case (~present day), to understand the regional and seasonal responses of tropical precipitation to these orbital forcings. Our results demonstrate large variability in the regional and seasonal location of the ITCZ in the June perihelion and December perihelion cases. Not only did the position of the ITCZ vary, the rainfall intensity differed substantively across regions and seasons. Our results also illustrate that the global linear relationship between precipitation centroid and sea surface temperature extends to the Indian, Pacific, and Atlantic oceans for both the June perihelion and December perihelion cases. Because sea surface temperature proxies are well-established, this linear trend can be used to approximate the local position of the ITCZ in past climates. Mechanisms of energy transport between the Northern and Southern hemispheres determine the position of the ITCZ; further analysis of cross-equatorial energy transport could provide insight into the regional and seasonal variability described in this research.