1. A better GRACE solution for improving the regional Greenland mass balance Z Xu 1, E.J.O Schrama 1, W. van der. Wal 1 1 Department of Astrodynamics and Space Missions, Faculty of Aerospace Engineering, Delft University of Technology, The Netherlands E-mail: Z.Xu-1@tudelft.nl INTRODUCTION The Greenland mass loss recently has drawn a lot of attention, and in GRACE data the shrinking Greenland Ice Sheet (GrIS) has been discovered. As the initial step in investigating the details of GrIS loss, this study also analyze GRACE solutions to estimate the mass balance in Greenland and make comparisons with published results. METHODOLOGY GRACE model: Data source: UT-CSR RL04 GRACE level 2 product Data type: Fully normalized spherical harmonic coefficients up to degree 60 Time interval: Jan 2003 – Sep 2011 C 20 : Replaced by external SLR model by Cheng & Ries (2004) Destriping: Noise removal: EOF was used to reduce the noise in the time series of each coefficient. The best 10 modes are selected to reconstruct the coefficient domain. Smoothing: Gaussian filter with a half width of 300km GIA Addition GIA model: Paulson and Zhong (2007) Figure 1: Map of Equivalent Water Height (EWH) made for the period from Feb 2003 to Sep 2011. EOF and 300km Gaussian filter were employed. Figure 2: Map of EWH map variation rate over last ten years. GIA was used to correct the data Greenland model: Figure 3: EWH rate of change over Greenland area between Feb 2003 and Sep 2011 as observed by GRACE. A maximum negative signal of 14.41 cm/year is found at 44 o W, 68 o N. The Gaussian smoothing radius is 300km. Figure 4: Solution 1 that the entire Greenland is one mascon, and outside is 0 everywhere. Figure 5: Solution 2 that each pixel in Greenland (from Figure 3) conducts an independent EHW, and combining them gives this map. Greenland mascon solutions: The mass distribution functions were retrieved from Figure 3 The new coefficients up to degree 60 were created based on the mass distribution functions. (analysis test) The EWH maps re-evaluated the Greenland mass balance. Mass balance analysis: Figure 6: Time series of ice mass changes for the GIS estimated from GRACE monthly mass solutions for the period from Feb 2003 to Sep 2011. Period This study Luthcke et al (2010) Wouters et al. (2008) Schrama and Wouters (2011) Velicogna (2009) 2003- 2007 -177±36-179±25 2003- 2009 -194±33 -177 ± 6 -201±19-230±33 2003- 2011 -226±33 Table 1: Greenland mass balance estimation from published studies (Schrama et al, 2011) and also the estimation for different period from this study. The errors in this study are from GRACE model, GIA model and Mass balance model. CONCLUSION From both figure and table, it can be noticed that the melting speed of GrIS has been increasing in latest 3 years Our mass change rates are comparable to other studies. REFERENCES Paulson A, Zhong S, Wahr J (2007) Inference of mantle viscosity from GRACE and relative sea level data. Geophys J Int 171:497-508. Cheng M, Tapley B.D ( 2004) Variations in the Earth's oblateness during the past 28 years, Jour Geophys Res v109, B9. Schrama E, Wouters B, Vermeersen B (2011) Present Day Regional Mass Loss of Greenland Observed with Satellite Gravimetry. Surv Geophys 32:337-385 ACKNOWLEDGEMENT The Netherlands Organisation for Scientific Research (NWO) is acknowledged for giving the financial support. Project nr. ALW-GO-AO/10-18