Lulu Jia

Load Love numbers and Green's functions for elastic Earth models PREM, iasp91, ak135, and modified models with refined crustal structure from Crust 2.0

Load Love numbers and Greens functions are computed for elastic Earth models PREM, iasp91 and ak135, and their modified models with refined crustal structure from Crust 2.0. It is found that the differences of results between iasp91 or ak135 and PREM, and the effects of refinement of crustal structure are significant for the Love numbers of degrees from around 200 to very high numbers, and for the Greens functions in the near-field. The results of the models given in this paper are applicable to the studies related to loading processes (present surface mass transport as measured by GRACE and GPS, ocean tide loading, etc.), making it possible to use different models or assess the uncertainties of solutions of the loading problems under investigation. In order to ensure the stability of the solutions for degrees larger than 360 (or when the resolution is less than 55km), a variable transformation on the solution vector is used in this paper and proved to work effectively.

Increased water storage in North America and Scandinavia from GRACE gravity data

Changes in continental water storage have been difficult to constrain from space-borne gravity data in regions experiencing both ice melting and glacial isostatic adjustment. Separation of the hydrologic and isostatic signals reveals increases in water storage in both North America and Scandinavia over the past decade. Space-borne gravity data from the Gravity Recovery and Climate Experiment (GRACE) have revealed trends in present-day continental water storage in many parts of the world. In North America and northern Europe, it has been difficult to provide reliable estimates because of the strong background signals of glacial isostatic adjustment1. Attempts to separate the hydrologic signal from the background with numerical models2 are affected by uncertainties in our understanding of the precise glacial history and mantle viscosity3,4. Here we use a combination of GRACE data and measurements from the global positioning system to separate the hydrological signals without any model assumptions. According to our estimates, water storage in central North America increased by 43.0±5.0 Gt yr−1 over the past decade. We attribute this increase to a recovery in terrestrial water storage after the extreme Canadian Prairies drought between 1999 and 2005. We find a smaller rise in water storage in southern Scandinavia, by 2.3±0.8 Gt yr−1. In both North America and Scandinavia, our computed increases in water storage are consistent with long-term observations of terrestrial water level. We suggest that the detected mass gains in terrestrial water storage need to be taken into account in studies on global sea-level rise.