Terrestrial water storage variations and their effect on polar motion

Justyna Śliwińska,Małgorzata Wińska,Jolanta Nastula

doi:10.1007/s11600-018-0227-x

Abstract

The role of continental water in polar motion excitation can be illustrated by determining Hydrological Angular Momentum calculated from terrestrial water storage (TWS). In this paper we compare global and regional changes in TWS computed using Coupled Model Intercomparison Project Phase 5 climate models, Global Land Data Assimilation System (GLDAS) land hydrology models and observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. We also compare hydrological excitation functions derived from models with those obtained from the GRACE mission and the hydrological signal in observed polar motion excitation (the so-called geodetic residuals). The results confirm that GLDAS models of seasonal and non-seasonal TWS change are more consistent with GRACE data than climate models; on the other hand, none of the considered models are fully consistent with GRACE data or geodetic residuals. In turn, GRACE observations are most consistent with the non-seasonal hydrological signal in observed excitation. A detailed study of the contribution of different TWS components to the hydrological excitation function shows that soil moisture dominates.

Highlights

Earth’s rotation parameters, including polar motion and length of day variation, have been investigated for several decades (Munk and MacDonald 1960)
The influence of the land hydrosphere on polar motion excitation has been repeatedly investigated, most studies have focused on Hydrological Angular Momentum (HAM) functions derived from Gravity Recovery and Climate Experiment (GRACE) observations (Meyrath and van Dam 2016; Seoane et al 2011). This paper addresses this gap; the hydrological contribution to polar motion excitation is computed from data from multiple sources: climate (CMIP5) and hydrological (GLDAS) models, and GRACE observations
It is necessary to select carefully climate models. We addressed this problem by determining correlation coefficients and explained variance for terrestrial water storage (TWS) series computed from CMIP and those based on GRACE observations (Table 2)

Summary

Introduction

Earth’s rotation parameters, including polar motion and length of day variation, have been investigated for several decades (Munk and MacDonald 1960). HAM estimates have been based on observations of the time-varying gravity field provided by the GRACE (Gravity Recovery and Climate Experiment) mission (Brzeziński et al 2009; Chen and Wilson 2005), while other studies have used different land hydrosphere models (Jin et al 2012). They have been developed for different purposes and specific regions This comparison of TWS and HAM estimations attempts to answer the following questions: (i) Which GLDAS and CMIP5 models correlate best with GRACE data, both in terms of TWS and polar motion excitation; (ii) which model correlates best with observed polar motion; and (iii) which TWS components contribute the most to hydrological excitation functions. A summary and some conclusions are given in “Conclusions” section

Methodology

Findings

Conclusions