10-20-16 | Spatio-temporal surface mass redistribution in Amazon and Greenland recovered by GRACE


Dr. Jooyoung Eom
Korea Polar Research Institute

Time and Place

October 20, 2016 – Thursday – 3:00 PM
WPR Building, Conference Room 2.806
3925 W. Braker Lane, Suite 200, Austin, Texas 78759

Empirical Orthogonal Functions (EOF) method is examined to separate signals associated with surface mass variation from GRACE errors in Amazon Basin and Greenland Ice Sheet (GrIS). Because the two regions are different climatologically and geographically, spatio-temporal variability of signal and error in GRACE are distinct. Therefore, rotated EOF (REOF) and extended EOF (EEOF), which are modified version of conventional EOF, are used for different features of signal and error in the two regions. In Amazon Basin, the river discharge is estimated using water mass variation on the main stem. To achieve this, the terrestrial water storage (TWS) changes confined to the main stem have to be extracted not only from the GRACE error, but also from TWS variations adjacent to the main stem. In Greenland, detail month-to-month ice mass variations are estimated based on from separation between signal and aliasing error.

The REOF method over the Óbidos sub-basin successfully estimates river discharge in the basin. The resulting time series represents relative river discharge variations consistent to in-situ discharge estimate. However, the estimates are generally larger than in-situ data in high water seasons. The REOF method is extended to the entire Amazon Basin based on the results for Óbidos sub-basin.

The EEOF provides higher temporal and spatial ice mass variations in GrIS, and this method is superior to the spatial filtering conventionally used in this region. In particular, results of EEOF remarkably agree with surface mass balance (SMB) outputs of regional climate model during winter season when SMB is a major contributor to mass changes in GrIS. On the base of this consistency, GRACE observations and the regional climate model are used to retrieve ice discharge near the coastal region. The GRACE-based ice discharge remarkably agrees with results independently obtained from ice thickness and velocity survey in amplitude and spatial distribution.

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