Antarctic circumpolar current from satellite gravimetric models ITG-GRACE2010, GOCE-TIM3 and satellite altimetry

Abstract

The Antarctic circumpolar current (ACC) is a clockwise ocean flow from west to east around Antarctica, connecting the Pacific, Indian and Atlantic oceans, and plays a key role in the heat transport and climate change. The geostrophic surface currents can be derived from the ocean dynamic height as the deviation of the actual sea level from satellite altimetry and the Earth's geoid. Although the gravity recovery and climate experiment (GRACE) and gravity field and steady-state ocean circulation explorer (GOCE) mission provided an initial estimate of global geostrophic currents, a more detailed Antarctic circumpolar current is still not well estimated. In this paper, the detailed ACC is estimated from the newest ITG-Grace2010 gravity model based on 7-years of GRACE data, and GO_CONS_GCF_2_TIM_R3 gravity model (hereafter referred to GOCE-TIM3) based on 12 months of GOCE data, with the mean sea surface height model MSS_CNES_CLS_11 from satellite altimetry, respectively. The evaluation and comparisons are performed with oceanographic models, the GOCO03S gravity model as well as in situ drifter's measurements. Results show that the Antarctic circumpolar current based on GOCE gravity field model depicts more details and transport characteristics with high accuracy and spatial resolution, e.g., Agulhas currents and Brazil-Malvinas Confluence regions, which are more consistent with the in situ drifter's results. The ACC based on ITG-Grace2010 model is similar with the result of the GOCE-TIM3 model with RMS of 8.39cm/s and 7.85cm/s, respectively, while the accuracy of GOCE-TIM3 is still higher. The correlation coefficients of the estimated velocities, compared to drifter results, are 0.70 and 0.76 for ITG-Grace2010 and GOCE-TIM3. ITG-Grace2010 model has more noise in the higher spherical harmonic coefficients and some better performances in the geostrophic currents are able to be obtained if the degrees are truncated to 160 for ITG-Grace2010, while the GOCE-TIM3 and GOCO03S model do not have this phenomenon. The gravity model GOCO03S with combined CHAMP, GRACE and GOCE observations almost have no improvement in ACC estimate when compared with GOCE-TIM3 results, while the RMS of GOCO03S is a little larger than the GOCE-TIM3 results.