| Summary: | The near-polar CHAMP and GRACE satellites are now acquiring vitally important new information on the geoid and gravity field of the polar regions. This investigation demonstrates that CHAMP and GRACE data are dramatically reducing the large gaps in our knowledge of the Arctic region, constraining the long wavelength geopotential (>300 km) and beginning to yield the high accuracy marine geoid which is needed for Arctic oceanographic and sea ice studies. Using a detailed Arctic surface gravity field and an independent altimetric gravity field as benchmarks we have evaluated the immediate-to-long wavelength (> 300km) component of seven CHAMP and two GRACE satellite-only gravity models such as the GFZ EIGEN, the NASA PGS and UT/CSR. We evaluate, spectrally, the errors in - and differences between - these satellite-only models in the Arctic at wavelengths from 300 to 2500 km. The GRACE models accurately resolve Arctic gravity to full wavelengths as short as 500 kin while the CHAMP models do so to full wavelengths as short as 1000 km. However the CHAMP models continue to show improved resolution as more and better (e.g. lower elevation) data are incorporated. The best CHAMP models agree well with the detailed Arctic ARC-GP model to an rms (error of commission) of better than 2.06 mGal (gravity)and 31 cm (geoid) for all wavelengths (full) longer than 1100 km. GRACE-only geoids are precise to 40 cm or better (all wavelengths) over large areas of the Arctic. CHAMP and GRACE-based geoids could have the accuracy required to detect (together with altmetry) the poorly known dynamic topography of the Arctic Ocean. As an example. a GRACE/detailed-gravity hybrid geoid is presented.
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