Estimating seasonal and interannual variability in ice mass loss using a stochastic filter and decade-long GRACE time series
Abstract
Monthly gravity estimates produced by the Gravity Recovery and Climate Experiment (GRACE) satellite mission have been used to investigate the mass loss of glaciers and ice sheets. The mass loss signals have significant temporal (seasonal and interannual) as well as spatial variability. To obtain accurate estimates of present-day melting from decade-long GRACE measurements, a model that allows for variabilities in both mass loss rates and seasonal signals would seem appropriate. A stochastic filter approach enables us to estimate variable melting rates and seasonal amplitudes. However, it requires the statistical information on various signals and errors in the monthly GRACE estimates. Unfortunately, monthly GRACE gravity fields are contaminated by order-dependent correlated errors in the short-wavelength components, manifesting themselves as north-south elongated linear stripes in the map of surface mass changes. The widely used 'ad-hoc' destriping method is not able to preserve statistical information, and is thus inappropriate for the stochastic filter approach. In this study, we present decade-long mass variations estimated using a Kalman filter approach, which is designed to separate geophysical signals and correlated 'stripe' contamination in a series of GRACE monthly spherical-harmonic coefficient (SHC) estimates. This technique preserves statistical information, and thus enables us to estimate the impact on the SHC uncertainties associated with the destriping. The calculations are statistically rigorous and enable estimation of space-dependent robust uncertainties for ice melting rates. The Kalman-filter approach also provides smooth estimates of the gravity field that are devoid of stripes and that do not require smoothing. We use the newly produced gravity fields to revisit mass loss signals in the cryosphere, with an emphasis on investigating seasonal and interannual variabilities.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.G32A..08W
- Keywords:
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- 1200 GEODESY AND GRAVITY;
- 0762 CRYOSPHERE Mass balance 0764 Energy balance