Can surface pressure be used to remove atmospheric contributions from GRACE data with sufficient accuracy to recover hydrological signals?

The Gravity Recovery and Climate Experiment (GRACE) satellite mission will resolve temporal variations in gravity orders of magnitude more accurately and with considerably higher resolution than any existing satellite. Effect s of atmospheric mass over land will be removed prior to estimating the gra vitational field, using surface pressure fields generated by global weather forecast centers. To recover the continental hydrological signal with ail accuracy of 1 cin of equivalent water thickness down to scales of a few hun dred kilometers, atmospheric pressure must be known to an accuracy of I mba r or better. We estimate errors in analyzed pressure fields and the impact of those errors on GRACE surface mass estimates by comparing analyzed field s with barometric surface pressure measurements in the United States and No rth Africa/Arabian peninsula. We consider (1) the error in 30-day averages of the pressure field, significant because the final GRACE product will ave rage measurements collected over 30-day intervals, and (2) the short-period error in the pressure fields which would be aliased by GRACE orbital passe s. Because the GRACE results will average surface mass over scales of sever al hundred kilometers, we assess the pressure field accuracy averaged over those same spatial scales. The atmospheric error over the 30-day averaging period, which will map directly into GRACE data, is generally <0.5 mbar. Co nsequently, analyzed pressure fields will be adequate to remove the atmosph eric contribution from GRACE hydrological estimates to subcentimeter levels . However, the short-period error in the pressure field, which would alias into GRACE data, could potentially contribute errors equivalent to 1 cm of water thickness. We also show that given sufficiently dense barometric cove rage, an adequate surface pressure field can be constructed from surface pr essure measurements alone.