Multi-Temporal Scale Global Gravity Field Determination From GRACE Follow-On: Pentad Polar Regions and Monthly Low-to-Mid Latitudes

Abstract

The Gravity Recovery and Climate Experiment and GRACE Follow-On (GRACE-FO) missions have successfully detected Earth's mass redistributions on a monthly basis. Recently, various groups have developed daily and 5-day interval “regularized” mass concentration (mascon) solutions. These solutions support mass variations at gridded areas focusing primarily on improved detection of land mass change signal. Instead of deriving regularized mascon solution, we present the derivation of multi-temporal scale but Level2-like global gravity solution using line-of-sight gravity difference and the Slepian function by exploiting increased satellite sampling at high latitude regions. Our spherical harmonics solution features time-varying gravity over the polar regions every 5-day while the low-to-mid latitude regions every 30-day. This allows avoiding the under-sampling problem without incorporating regularization, while also reducing the aliasing problem in the polar region. Our new solution strategy is tested with synthetic experiment with the Earth System Model. The synthetic test shows that 5-day solutions exhibit comparable error level to the 30-day solution in the polar region after the suppression of the correlation error. Our multi-temporal scale global gravity solutions successfully identify intra-month surface mass change signals not previously identified by usual monthly-mean gravity field solutions. They are associated with residual ocean tidal mass change, rapid snowfall accumulation in an Antarctic basin, and high-frequency ocean mass changes in the Arctic ocean. Our approach demonstrates the feasibility of generating shorter interval global gravity solutions without any regularization or loss of accuracy and opens opportunities to fully utilize GRACE-FO measurements with various spatial coverages.