Chris Dr. Christopher Harig is an associate research scholar in the Department of Geosciences at Princeton University. His research covers areas of geodesy and geodynamics. His current work studies the melting of Earth's ice sheets due to climate change measured by satellite gravimetry. In previous work, Chris studied the dynamics of the lithosphere and upper mantle using geodynamic computer models, placing constraints on the rheology of these layers. Frederik
Dr. Frederik J. Simons is an Associate Professor of Geosciences at Princeton University. His research encompasses various aspects of solid-earth geophysics. More specifically, he studies the physical properties of the lithosphere, focusing on the elastic and thermomechanical properties of the continents, by seismic tomography and the spectral analysis of gravity and topography. With his colleagues, Frederik has developed mathematical methods for the analysis of processes on the sphere, for geodesy, geomagnetism, and cosmology, designed wavelet-based signal processing methods for seismology, and developed oceanic instrumentation to close the seismic coverage gap over the Earth's oceans.
EPSL Harig, Christopher and Frederik J. Simons. Accelerated West Antarctic ice mass loss continues to outpace East Antarctica gains. Earth Planet. Sci. Let., 415, 134-141, 2015. Link to reprint (pdf)

Abstract: While multiple data sources have confirmed that Antarctica is losing ice at an accelerating rate, different measurement techniques estimate the details of its geographically highly variable mass balance with different levels of accuracy, spatio-temporal resolution, and coverage. Some scope remains for methodological improvements using a single data type. In this study we report our progress in increasing the accuracy and spatial resolution of time-variable gravimetry. We determine the geographic pattern of ice mass change in Antarctica between January 2003 and June 2014, accounting for glacio-isostatic adjustment using the IJ05_R2 model. Expressing the unknown signal in a sparse Slepian basis constructed by optimization to prevent leakage out of the regions of interest, we use robust signal processing and statistical estimation methods. Applying those to the latest time series of data from the Gravity Recovery and Climate Experiment (GRACE) we map Antarctica's mass loss in space and time as well as can be recovered from satellite gravity alone. West Antarctica is losing ice mass at a rate of -121 +- 8 Gt/yr and has experienced large acceleration of ice mass losses along the Amundsen Sea coast of -18 +- 5 Gt/yr^2, doubling the mass loss in the past six years. The Antarctic Peninsula shows slightly accelerating ice mass loss, with larger accelerated losses in the southern half of the Peninsula. Ice mass gains due to snowfall in Dronning Maud Land have continued to add about half the amount of West Antarctica's loss back into the continent over the last decade. We estimate the overall mass losses from Antarctica since January 2003 at a rate of -92 +- 10 Gt/yr.

EOS Harig, Christopher, Kevin W. Lewis, Alain Plattner, and Frederik J. Simons. A suite of software analyzes data on the sphere. Eos, 96, 2015.

Description: The software improves data analysis over small portions of a spherical planetary surface. Among other applications, it has helped track Greenland's ice loss over time.

PNAS Harig, Christopher and Frederik J. Simons. Mapping Greeenland's mass loss in space and time. Proc. Natl. Acad. Sc., 109(49), 19934-19937. doi:10.1073/pnas.1206785109, 2012. Link to reprint (pdf) Link to Supporting Information (pdf)

Abstract: The melting of polar ice sheets is a major contributor to global sea-level rise. Early estimates of the mass lost from the Greenland ice cap, based on satellite gravity data collected by the Gravity Recovery And Climate Experiment (GRACE), have widely varied. While the continentally and decadally averaged estimated trends have now more or less converged, to this date there has been little clarity on the detailed spatial distribution of Greenland's mass loss, nor on how the geographical pattern has varied on relatively shorter time scales. Here we present a spatially and temporally resolved estimation of the ice mass change over Greenland between April 2002 and August 2011. While the total mass loss trend has remained linear, actively changing areas of mass loss were concentrated on the southeastern and northwestern coasts, with ice mass in the center of Greenland steadily increasing over the decade.

Other Relevant Publications:

Christopher Harig, Shijie Zhong & Frederik J. Simons Constraints on upper-mantle viscosity from the flow-induced pressure gradient across the Australian continental keel
Geochem., Geophys., Geosys., 2010, 11, Q06004 doi:10.1029/2010GC003038

Frederik J. Simons & F. A. Dahlen Spherical Slepian functions and the polar gap in geodesy Geoph. J. Int., 2006, 166 (3), 1039-1061 doi:10.1111/j.1365-246X.2006.03065.x