1. where P c (mm) is corrected precipitation, P g is gauge-measured precipitation, ΔP w and ΔP e are wetting loss and evaporation loss, respectively, ΔP t is trace precipitation; CR (%) is daily catch ratio, which is a function of the daily 6-hour mean wind speed W s (s m -1 ) at the gauge height for various precipitation types. Precipitation type was classified based on daily air temperature. The percent solid precipitation was estimated as follows (see Figure 3): where P PS is solid precipitation (%) and T is daily 6-hour mean temperature (˚C). ANNUAL ACCUMULATION FOR GREENLAND UPDATED USING ICE CORE DATA DEVELOPED DURING 2000-2006 AND ANALYSIS OF DAILY COASTAL DATA Dayong Shen a, Roger C. Bales a,b, Joseph R. McConnell c, John Burkhart a, Qinghua Guo a,b a School of Engineering, University of California, Merced; b Sierra Nevada Research Institute, University of California, Merced; c Desert Research Institute, Reno, NV C11A-0086 2. DATA (Figures 1-2) Figure 1. To develop an accumulation map of Greenland and a total accumulation map of Greenland, two data sets were used for kriging interpolation. Each data set involves 39 new ice core data developed during 2000-2006 by PARCA group, plus 250 ice core and snowpit data used by Bales et al. 4 and 26 coastal accumulation estimates (20 points reported by Danish Meteorological Institute (DMI) and 6 points used by Ohmura et al. 6 ). Figure 2. Distribution of record lengths for point accumulation estimates using ice cores and snowpits. In the current analysis none of the estimates based on a single year’s measurement, which as estimates of a long-term mean have large uncertainty, were used. Figure 3. Relationship between temperature and solid precipitation. The original curve was published by Ohmura et al. 6. In this study we digitalized the original curve and developed curve-fitting equations to help divide total precipitation into solid precipitation and liquid precipitation, as long as the mean air temperature is available for the corresponding period. Biases of wind-induced undercatch, wetting loss and trace amount of precipitation were corrected on a daily basis following Yang et al. 7 : 3. BIAS CORRECTION OF DAILY PRECIPITATION MEASUREMENTS (Figures 3-4 and Table 1), if T ≥ -11.6˚C and T≤7.4˚C, if T < -11.6˚C, if T > 7.4˚C Figure 4. Precipitation for 20 coastal stations before versus after bias correction. The bias correction for the 20 stations averaged 47.3%. This compares well with the results of Yang et al. 7, who reported corrections to the gauge-measured annual totals of 50-75% in the northern and 20- 40% in the southern part of Greenland. (1) Precipitation before bias correction g cm -2 yr -1. (2) Precipitation after bias correction g cm -2 yr -1. (3) Total accumulation g cm -2 yr -1 where E is evaporation estimates from ERA-40 from E. Hanna. (4) Accumulation g cm -2 yr -1. (5) SISIMIUT (average of 4230 and 4234). (6) Average of ILLOQQORTOORMIUT and UUNARTEQ. (7) Data for 1961,1962,1963,1965 and1977 are missing. (8) Average of NERIUNAQ, QORNOQ and KAPSIGDLIT. Table 1. Data for coastal stations in Greenland. Evaporation estimates were interpolated using Inverse Distance Weighting based on 5-km resolution ERA-40 values from 1958 to 2005. Figure 6. Accumulation prediction map based on kriging. Using only solid precipitation minus evaporation (P s - E) from coastal stations. Accumulation generally increases from northern Greenland to southern Greenland, and is higher in southern coastal areas. The average accumulation over Greenland is 29.0 g cm -2 yr -1 while the average accumulation over the ice sheet is 30.0 g cm -2 yr -1. Figure 5. For this map, we used total precipitation minus evaporation (P c - E) from coastal stations for the interpolation. Using this data set, the average total accumulation over Greenland is 36.5 g cm -2 yr -1 while the average total accumulation over the ice sheet is 34.6 g cm -2 yr -1. Figure 9. Accumulation prediction standard error map based on kriging. Also shown for reference are the points used to develop the kriged surface. Here the uncertainty involves data uncertainty and algorithm uncertainty. The range of the prediction standard error is 5.0-9.2 g cm -2 yr -1. Figure 8. Difference between accumulation prediction map in this research and that published by Bales et al. 4. Our new accumulation map indicates much lower accumulation in the southwest and much higher in the southeast, meaning that long term mass balance in both catchments is closer to steady state than previously estimated 8. Also shown are Greenland drainage basins. Average accumulation in each basin was calculated and listed in Table 2. 4. INTERPOLATION The interpolation was carried out using kriging. For accumulation interpolation, a third-order trend was removed from the data with trend analysis. Kriging was performed on the residuals and the trend added back to the kriged residuals to estimate the final accumulation. For total accumulation interpolation, a third-order trend was removed with trend analysis from the data after natural logarithmic transformation before kriging method was employed. 5. RESULTS (Figures 5-9 and Tables 2-3) 6. CONCLUSIONS Compared to the prediction map published by Bales et al. 4, in the inland areas the accumulation is almost the same as previously predicted. The changes in spatial patterns of accumulation from earlier accumulation maps suggest that the Greenland ice sheet is closer to balance than previously estimated. ACKNOWLEDGEMENTS We acknowledge NASA grant NNG04GB26G to University of California, Merced, NASA grants NAG5-12752 and NAG04GI66G, as well as NSF grant OPP-0221515 to the Desert Research Institute. Table 3. Comparison of the interpolation results from different data sources. Figure 7. Accumulation map published by Bales et al. 4. Table 2. Average accumulation by basin. * Bales et al. 4. REFERENCES 1. Arendt, A. A., K. A. Echelmeyer, W. D. Harrison, C. S. Lingle, V. B. Valentine, Science, 97, 382 (2002). 2. Zwally, H.J., W. Abdalati, T. Herring, K. Larson, J. Saba, and K. Steffen, Science, 297, 218-222 (2002). 3. Rignot, E., and S. Kanagaratnam, Science, 311, 986-990 (2006). 4. Bales, R. C., J. R. McConnell, E. Mosley-Thompson, and B. Csatho, J. Grophys. Res., 106(D24), 33813-33825 (2001). Cumulative percent of points Number of years in record Temperature, ºC Solid precipitation, % Uncorrected precipitation, g cm -2 yr -1 Bias corrected precipitation, g cm -2 yr -1 5. Ohmura A., and N. Reeh, J. Glaciol., 37(125), 140-148 (1991). 6. Ohmura, A., P. Calanca, M. Wild, and M. Anklin, Zeitschrift fur Gletscherkunde und Glazialgeologie, Universitatsverlag Wagner, Innsbruck, Band 35, Heft 1, 1-20 (1999). 7.Yang, D., S. Ishida, B.E. Goodison, T. Gunther, J. Geophys. Res., 105(D6), 6171-6182 (1999). 8.Thomas, R., B. Csatho, C. Davis, C. Kim, W. Krabill, S Manizade, J. McConnell, and J. Sonntag, J. Geophys. Res., 106(D24), 33707-33716 (2001). 1. INTRODUCTION Greenland is the second most intensely ice-covered landmass after Antarctica. The latest evidence suggests that Greenland's ice is moving towards the sea faster than previously believed 1,2,3. Understanding ice sheet mass balance is critically dependent on accurate spatial accumulation estimates across Greenland. Bales et al. 4 used kriging to interpolate point measurements and to generate an accumulation map of Greenland. The kriged result shows that lower uncertainty was achieved over much of the central and northern part of the ice sheet, with an accumulation pattern that retained features of the map published 10 years earlier by Ohmura and Reeh 5. But in the coastal areas, especially northwest, southeast and southern Greenland, the kriged result was based on few data points, stimulating additional field research to develop more accumulation records. In this research, we developed an accumulation map of Greenland using data set from Bales et al. 4 plus new ice cores, as well as a more detailed analysis of coastal weather station data. For reference, we also developed a total accumulation map of Greenland. Our main aim was to develop improved accumulation estimates, and assess uncertainty in accumulation.