HR: 1340h
AN: H23D-1155    [Abstracts]
TI: Global Cryospheric Impact on Satellite Gravity Measurements: 1980-2003
AU: * Ivins, E R
EM: eri@fryxell.jpl.nasa.gov
AF: Jet Propulsion Lab., Caltech, MS 300-233, 4800 Oak Grove Dr., Pasadena, CA 91109-8099 United States
AU: Dyurgerov, M
EM: dyurg@tintin.colorado.edu
AF: INSTAAR, University of Colorado at Boulder, Campus Box 450, Boulder, CO 80309-0450 United States
AB: It is widely appreciated that cryospheric mass exchange with the ocean is an important component of the low order gravity field changes. Traditionally, attention has been focused on the secular trend in the non-tidal gravity variability. Glacioisostatic adjustment (GIA) causes an ongoing oblateness decrease; $\dot{J}^{GIA}_2 \, \simeq \, -2 \, \mathrm{to} \, -9 \, \times \, 10^{-11} \mathrm{yr}^{-1}$, and a pear-shape change; $\dot{J}^{GIA}_3 \, \simeq \, 0 \, \mathrm{to} \, 3 \, \times \, 10^{-11} \mathrm{yr}^{-1}$, with an $n \, = \, 4$ and $5$ zonal rates at; $\dot{J}^{GIA}_4 \, \simeq \, -1 \, \mathrm{to} \, -6 \, \times \, 10^{-11} \mathrm{yr}^{-1}$ and $\dot{J}^{GIA}_5 \, \simeq \, 1 \, \mathrm{to} \, 4 \, \times \, 10^{-11} \mathrm{yr}^{-1}$. The GIA field changes generally deviate from the satellite laser ranging (SLR) observations, $\dot{J}^{Obs}_2 \, \simeq \, -2.9 \pm 0.3 \, \times \, 10^{-11} \mathrm{yr}^{-1}$, $\dot{J}^{Obs}_3 \, \simeq \, -0.9 \pm 0.4 \, \times \, 10^{-11} \mathrm{yr}^{-1}$, $\dot{J}^{Obs}_4 \, \simeq \, 1.2 \pm 0.9 \, \times \, 10^{-11} \mathrm{yr}^{-1}$ and $\dot{J}^{Obs}_5 \, \simeq \, 1.3 \pm 0.4 \, \times \, 10^{-11} \mathrm{yr}^{-1}$, with the notable exception of the oblateness rate. Secular changes in the cryosophere, and, possibly, the global oceans, are thought to provide the geophyiscal source for the residual differences, $\dot{J}^{Obs}_n \, - \, \dot{J}^{GIA}_n$. Here we compute the interdecadal and interannual cryospheric mass change contributions to global gravity fields with Stokes coefficients $n \, \leq \, 256$ from known constraints, and from estimates based upon quantitative climatological and glaciological extrapolation. We examine pre- and post-Mt. Pinatubo climate epochs, and the era after the mid-1990's, when well-documented accelerations of subpolar glacial mass loss are underway in Alaska and Patagonia. Northern hemispheric retreat, including that of Greenland (\textit{Rignot and Thomas}, 2002), may drive $\dot{J}^{Cryo.}_n$ trends during the last 9 years at rates of $1.7, 0.5$ and $1.1 \, \times \, 10^{-11} \mathrm{yr}^{-1}$ for zonals $n = 2,3$ and $4$, respectively. The southern hemisphere contribution is roughly $1.2, -1.0, 0.8$ and $-0.5 \, \times \, 10^{-11} \mathrm{yr}^{-1}$ for $n = 2,3,4$ and $5$, respectively. The two hemispheres contribute to eustatic sealevel rise at the rates $\dot{\xi}_{\mathrm{N}} \, \simeq \, 0.63$ and $\dot{\xi}_{\mathrm{S}} \, \simeq \, 0.42$ mm/yr (N = north, S = south). Hemispheric cancellation of $\dot{J}^{Cryo.}_3$, and the absence of a northern $\dot{J}^{Cryo.}_5$, might provide control on scenarios that hypothesize larger, but unconstrained, mass transfer from continents to oceans. Year-to-year measurements taken by the GRACE satellite should detect Alaskan glacier change, as well as change in areas of Greenland that are known to be thinning at rates of 0.25 m/yr, or more. We show that the sustained changes in geoid height, $\aleph$, are roughly $\dot{\aleph} \, \simeq \, -1.2$ to $-1.75$ mm/yr over wavelengths of 600 to 1200 km, and, as such, are feasible for detection by GRACE (\textit{Wahr et al.}, 2004) in Greenland, Alaska and Antarctica.
DE: 3010 Gravity
DE: 1827 Glaciology (1863)
DE: 1241 Satellite orbits
DE: 1655 Water cycles (1836)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting