Use of DART Data in the Assessment of GRACE-FO Solutions

The Gravity Recovery and Climate Experiment (GRACE) satellite mission provided the first global observation of changes in ocean bottom pressure (OBP), and the time series of these observations will continue with the launch of GRACE Follow-On (GRACE-FO). The limited number of in situ OBP observations provide insight in to the quality and applicability of these GRACE-derived OBP estimates, as well as an assessment of ocean models used to help remove the effects of high-frequency OBP variations in the GRACE solutions (i.e. dealiasing). Typically, in situ observations are only available after recovery of the instrument. However, the real time availability of Deep-ocean Assessment and Reporting of Tsunamis (DART) data allows for their use in the evaluation of rapid availability GRACE-FO products, such as the quick-look products from CSR.

We collect DART data from the National Data Buoy Center (NDBC) website daily and process it (remove outliers, dedrift, remove semi-diurnal and diurnal tidal estimates) to create daily averages. As we are particularly interested in the monthly to seasonal information that the GRACE observations may add to the ocean model estimates of OBP, we use a method for removing the drift that helps prevent the removal of seasonal signals (Williams et al., Ocean Sci., 2014). Data from two regions present particularly good targets for comparisons of the data sets. The western North Pacific has large, coherent OBP changes, which are typically well modeled by the Release 6 AOD1B product (Dobslaw et al., GJI, 2017). The equatorial Pacific has smaller OBP changes that allow pressure changes due to the annual mass exchange between the continents and the ocean (not included in the ocean model and observed by GRACE-FO) to be more prominent. We present our processing of the DART data, and their comparison to OBP estimates from the ocean models used in dealiasing and the CSR quick-look products.