New developments in Earth systems mass change studies with GRACE and GRACE Follow-On for monitoring of extreme events

The conventional data products from GRACE and GRACE Follow-On (GRACE-FO) are global snapshots of time-variable gravity or surface mass change, providing “average” fields of these quantities over a certain period like one month or 10 days. In this presentation, we propose an alternative approach based on along-orbit analysis of inter-satellite ranging residuals which represent “instantaneous” gravitational changes at satellite altitude due to mass changes happening beneath the satellites at the Earth surface. We first present the key improvement in distinguishing small-scale gravitational signals by GRACE-FO LRI (relative to KBR) associated with high-resolution (1) static gravity (global) and (2) time-variable gravity (mainly at polar regions). We then demonstrate that our approach opens new opportunities in Earth system mass change studies for monitoring of extreme, transient events. We do so by presenting multiple rapidly-changing geophysical applications: (1) GRACE KBR observations of large tsunamis with their unique characteristics in detecting the large-scale variability of tsunami wave field, (2) GRACE-FO LRI observations of the high-frequency gyre in the Argentine Basin and their validation with satellite altimetry, (3) GRACE-FO LRI observations of a rapid mass change in the Gulf of Carpentaria during a cyclone in 2019 and their application for validation of high-frequency ocean models (used for de-aliasing in satellite gravimetry), and (4) gravitational changes of Earth’s free oscillations excited by the 2004 Sumatra earthquake, their mapping into inter-satellite tracking explained by the Kaula theory and the potential detectability of gravitational oscillations related to Earth’s football mode by GRACE KBR data. The above transient mass changes cannot be adequately studied using the conventional data products of average snapshots (maps). Thus, the along-orbit analysis technique offers a unique opportunity to broaden the scope of geodetic and geophysical applications that can be addressed by GRACE and GRACE-FO satellites.