1. Ingo Sasgen 1, Henryk Dobslaw 1, Zdenek Martinec 2, and Maik Thomas 1 (1) GeoForschungsZentrum Potsdam, Department 1: Geodesy and Remote Sensing Section 1.3: Earth System Modelling, 14473 Potsdam, Germany. GRACE-based Antarctic snow accumulation related to ENSO (2) School of Theoretical Physics, Dublin Institute for Advanced Studies, Dublin, Ireland.

2. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Region of interest in Antarctica m/a surface-elevation change Satellite-laser altimetry (ICESat) Rate of surface-elevation change (2003 – 2007) [2] [1] Genthon & Cosme, 2003; [2] Pritchard et al. 2009 Mean annual accumulation Precipitation minus evaporation ECMWF ERA40 (1958 – 2001) [1]

3. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Antarctic Peninsula (198 × 10 3 km 2 ): warming faster than global average [1] ongoing ice shelf disintegration and glacier acceleration [2] Antarctic Peninsula and Amundsen Sea Sector [1] Vaughan et al. 2001; [2] Scambos et al., 2004; [3] Rignot et al., 2008 Amundsen Sea Sector ( 432 × 10 3 km 2 ): ice velocities and ice discharge extreme compared to the rest of the continent [3] Both regions receive about 20 % of Antarctic precipitation P-E > 400 mm/a defines study area (dark grey areas in left figure)

4. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Antarctic Peninsula and Amundsen Sea Sector P-E > 400 mm/a defines study area (dark grey areas in left figure) Can inter-annual mass anomalies from GRACE be explained with SMB estimates based on ECMWF data? Are inter-annual variations related to large-scale changes in the atmospheric circulation?

5. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO GRACE processing [1] Flechtner et al. 2007; [2] Sasgen et al. 2006 GRACE data: 80 monthly GRACE gravity fields (GFZ RL04, unconstrained) [1] Stokes potential coefficients up to degree and order 120 August 2002 to August 2009 Filtering: Wiener optimal filtering [2] Isotropic Adaptive to signal-to-noise ratio Resulting spatial resolution ~ 450 km Gravimetric inversion: Forward modelling approach Simulation of geoid-height anomaly and adjustment to GRACE data Robust w.r.t biases Potential disturbance  Mass change

6. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO ECMWF surface mass balance ECMWF operational data: Model resolution T799L91 (i.e., 25 km) 6 hourly forecasts (precipitation, evaporation) 6 hourly analyses (surface pressure, spec. humidity, wind) Surface mass balance: 0.5° regular grid, 6 hours Moisture transports: 1° at 25 pressure levels

7. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Seasonal variability and trends Offset, trends and annual harmonics are removed in the following. Area 198 x 10 3 km 2 Trend28.8 +/- 3.3 Gt / a Annual9.3 +/- 7.6 Gt Area 432 x 10 3 km 2 Trend81.4 +/- 5.8 Gt / a Annual24.1 +/- 7.8 Gt

8. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Antarctic Peninsula GRACE

9. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Antarctic Peninsula GRACE GRACE (11 months) temporal averaging required to remove high-frequency noise

10. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Antarctic Peninsula GRACE GRACE (11 months) ECMWF Correlation: 0.82 (filtered) 0.37 (unfiltered) Rms 16.4 Gt Rms 13.2 Gt

11. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Amundsen Sea Sector GRACE

12. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Amundsen Sea Sector GRACE GRACE (5 months)

13. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Amundsen Sea Sector GRACE GRACE (5 months) ECMWF Correlation: 0.70 (filtered) 0.67 (unfiltered) Rms 28.6 Gt Rms 20.2 Gt

14. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Anti-correlation between AP and AS Antarctic Peninsula Amundsen Sea Sector Correlation: GRACE -0.40 ECMWF -0.38

15. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO ENSO signals in Antarctic snow accumulation Amundsen Sea Low is strengthened under La Nina conditions, causing decreased Precipitation in the Amundsen Sea Sector and increased precipitation in the Antarctic Peninsula. Cullather et al. (1996), Bromwich et al. (1999) Amundsen Sea Low is strengthened under La Nina conditions, causing decreased Precipitation in the Amundsen Sea Sector and increased precipitation in the Antarctic Peninsula. Cullather et al. (1996), Bromwich et al. (1999) Can this be confirmed by GRACE? L La Nina

16. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO 2. ENSO signals in Antarctic snow accumulation Amundsen Sea Low is strengthened under La Nina conditions, causing decreased Precipitation in the Amundsen Sea Sector and increased precipitation in the Antarctic Peninsula. Cullather et al. (1996), Bromwich et al. (1999) Amundsen Sea Low is strengthened under La Nina conditions, causing decreased Precipitation in the Amundsen Sea Sector and increased precipitation in the Antarctic Peninsula. Cullather et al. (1996), Bromwich et al. (1999) Can this be confirmed by GRACE? L El Nino

17. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO 2. ENSO signals in Antarctic snow accumulation La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector (AS) La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector (AS) Amundsen Sea Low Pressure anomaly strong Direction of moist air towards Peninsula Dry wind from Antarctic interior in AS accumulated SOI (5 months)

18. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO 2. ENSO signals in Antarctic snow accumulation La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector (AS) La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector (AS) Amundsen Sea Low Pressure anomaly strong Direction of moist air towards Peninsula Dry wind from Antarctic interior in AS Averaged La Nina months from ECMWF operational data

19. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO 2. ENSO signals in Antarctic snow accumulation La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector Averaged El Nino months from ECMWF operational data Amundsen Sea Low Pressure anomaly weak Direction of moist air directly towards Amundsen Sea Sector

20. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO 2. ENSO signals in Antarctic snow accumulation Amundsen Sea Sector La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector Correlations -0.26 (unfiltered ) -0.33 (filtered)

21. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO 2. ENSO signals in Antarctic snow accumulation Antarctic Peninsula La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector La Nina = increased precipitation in the Antarctic Peninsula El Nino = increased precipitation in the Amundsen Sea Sector Correlations -0.30 (unfiltered ) -0.39 (filtered)

22. Sasgen, Dobslaw, Martinec, Thomas: Antarctic snow accumulation related to ENSO Conclusions Inter-annual variability from GRACE can be explained with SMB estimates based on ECMWF data Anti-correlation between Antarctic Peninsula and Amundsen Sea Sector is -0.38 (GRACE filtered) Correlation with accumulated SOI lagged by 10 months amounts to 0.39 (Antarctic Peninsula) and -0.33 (Amundsen Sea Sector) Sasgen, I., Dobslaw, H., Martinec, Z., Thomas, M. (2010), Satellite gravimetry observation of Antarctic snow accumulation related to ENSO, Earth Planet. Sci. Lett,, doi:10.1016/j.epsl.2010.09.015, in press.