The Distance Effect Annual Cycle in Earth's Climate

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This project aims to investigate the impact of two aspects of Earth’s orbital geometry on its climate. The Western Pacific Warm Pool of the tropical Pacific Ocean retains the largest and warmest sea surface water body on Earth while the eastern equatorial Pacific is characterized by strong upwelling of cold, nutrient-rich deep waters, termed the Pacific cold tongue. Understanding the evolution of the Pacific warm pool and cold tongue are important because they control the circum-Pacific climate and impact the globe via El Nino-Southern Oscillation (ENSO) teleconnections.Previous research indicates that the Pacific cold tongue has two annual cycles driven by distinct features of the Earth’s orbit. One of these cycles is driven by the seasonal migration of the InterTropical Convergence Zone (ITCZ) and is ultimately linked to the seasonal and latitudinal distribution of solar insolation due to the tilt of the Earth’s axis – the “tilt” effect. While this “tilt” effect annual cycle has been extensively studied, the other “distance” effect is less so. It is argued that the “distance” effect arises from seasonal variations in the strength of the Walker circulation and is forced by the annual evolution of the Earth-Sun distance due to the eccentricity of Earth’s orbit.This research project will investigate how the distance effect imprints its climate influence on Earth, specifically on the: 1) distance-effect seasonality of the atmospheric general circulation; 2) seasonality of regional climates, choosing regions where the distance effect has a disproportionately large impact relative to tilt, including the westerlies over the South Pacific; and 3) tropical Pacific mean state and El Nino-Southern Oscillation (ENSO).The potential Broader Impacts (B.I.) include support for graduate and undergraduate students, public outreach, and a more comprehensive understanding of climate with important societal impacts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.