Using GRACE Data to Estimate Climate Change Impacts on the Earth’s Moment of Inertia

Diandong Ren,Aixue Hu

doi:10.3389/feart.2021.640304

Abstract

The widely used 15-year Gravity Recovery and Climate Experiment (GRACE) measured mass redistribution shows an increasing trend in the nontidal Earth’s moment of inertia (MOI). Various contributing components are independently evaluated using five high-quality atmospheric reanalysis datasets and a novelty numerical modeling system. We found a steady, statistically robust (passed a two-tailed t-test atp= 0.04 for dof = 15) rate of MOI increase reaching ∼11.0 × 1027kg m2/yr, equivalent to a 11.45 sμ/yr increase in the length of day, during 2002–2017. Further analysis suggests that the Antarctic ice sheet contributes the most, followed by the Greenland ice sheet, the precipitation-driven land hydrological cycle, mountain glaciers, and the fluctuation of atmosphere, in this order. Short-term MOI spikes from the GRACE measurements are mostly associated with major low/mid-latitude earthquakes, fitting closely with the MOI variations from the hydrological cycle. Atmospheric fluctuation contributes the least but has a steady trend of 0.5 sμ/yr, with horizontal mass distribution contributing twice as much as the vertical expansion and associated lift of the atmosphere’s center of mass. The latter is a previously overlooked term affecting MOI fluctuation. The contribution to the observed MOI trend from a warming climate likely will persist in the future, largely due to the continuous mass loss from the Earth’s ice sheets.

Highlights

In recent decades, the net top-of-atmosphere energy imbalance reached 1 W m−2 (Trenberth and Fasullo 2013; Hu and Bates 2018)
Despite its design lifetime of less than a decade, the Gravity Recovery and Climate Experiment (GRACE) mission provided about 15 years of quality data
We found that the mass shed from the polar ice sheets, mountain glacier retreats, and the atmospheric fluctuations all contribute to an increased moment of inertia (MOI) and the slowing down of the rotation of the earth

Summary

Introduction

The net top-of-atmosphere energy imbalance reached 1 W m−2 (Trenberth and Fasullo 2013; Hu and Bates 2018). The polar ice sheets respond to this climate change by increasing creeping and other related total mass shedding mechanisms (Ren and Leslie, 2011). The kinetic energy of winds is very unevenly distributed spatially and is concentrated in polar and subtropical jet streams. Subtropical jet stream changes have an important influence on the angular momentum of the earth system (Lee et al, 2019). What makes the situation compelling is that the mid-latitude meridional temperature gradients are being modified by anthropogenic climate change (Ren 2010; Vallis et al, 2015) and the jet streams are expected to further adjust in response to these changes (Francis and Vavrus, 2012; Haarsma et al, 2013; Francis and Vavrus, 2015)

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