1. Don Chambers Center for Space Research, The University of Texas at Austin Josh Willis Jet Propulsion Laboratory, California Institute of Technology R. Steven Nerem Colorado Center for Astrodynamics Research, University of Colorado at Boulder GRACE Science Team Meeting Potsdam, Germany 15 October 2007 Closing the Globally Averaged Sea Level Budget on Seasonal to Interannual Time Scales

2. Near global measurements of total mean sea level (MSL) since 1993 Steric (thermal expansion) component from sparse in situ temperature profilers before 2003 »Temporal/spatial density is now good between ± 65° and after July 2003 with Argo profilers GRACE measures monthly mass component of MSL since August 2002 How well do the components (steric, mass) agree with the total? 2

3. Jason-1 »GDR-B data; monthly averages; IB applied Argo »Removed instruments with bad pressure sensors »Monthly steric height from temperature/salinity relative to 900m GRACE »CSR_RL04, replacing C20 with SLR time-series and using new geocenter time-series [Swenson et al., 2007; see poster] »Corrected for GIA using model of Paulson et al. [2007] Argo density limits time-span from July 2003 on Jason-1 coverage limits area to ± 65° 3

4. GIA in GRACE Observation GIA is a large correction in ocean mass from GRACE »Order of 1 to 2 mm/year Models are still in a state of flux, but with GRACE observations the estimated rates are decreasing and uncertainty improving »Paulson et al. [2007] ocean GIA signal = -0.9 ± 0.2 mm/year Upper mantle viscosity (Pa s) Lower mantle viscosity (Pa s) X Milne et al., 2001 GPS rates in Fennescandia (rate used by Lombard et al., 2007) 4 X Paulson et al., 2007 GRACE and sea level data

5. 5

6. 6 With 3-month smoothing

7. Why the Trend Difference? Some evidence of a small drift in Jason-1 from comparison with tide gauges, but not large enough to explain difference From G. Mitchum

8. Amplitude of 3.8-year sinusoid estimated along with trend and seasonal sinusoids from 02/2003 to 01/2007 in cm of water Smoothed with 750 km Gaussian CSR_RL04 GFZ_RL04 Standard deviation of K 2 tide differences (FES2004-FES2002) for Jan 2005 in mm of geoid K 2 “error” map K 2 Tide Alias Estimating 3.8-year sinusoid along with trend changes CSR ocean mass trends by < 0.2 mm/year, but GFZ trends by ~ 0.6 mm/year

9. Trend Maps 9 Jason-1 Argo

10. Ocean Bottom Pressure Trends 10 GRACE ECCO

11. 11 Removing trend only

12. 12 Removing trend and seasonal periods 3-month smoothing Most of the interannual variations in MSL are related to ocean mass variation and not steric changes

13. Conclusions Observations of sea level budget is balance for periods of a few months to ~ 4 years »Mass variation is larger than steric for both seasonal and interannual periods 4-year trends do not agree within uncertainty Appears to be either a problem in Jason-1 or Argo south of 30°S »No tide gauges in area check Jason-1 »Another problem with Argo profilers? »Warming below 900 m? 13

14. Extras

15. 3-Year Trends 15 Jason - GRACE Argo