Research Interests

Our lab studies changes in the modern climate on the surface of the Earth and their interaction with the solid Earth below. Recently we have focused on the several topics below, but we continually seek to understand what is the next most important research problem. In all areas, we integrate a variety of data and methods to gain a more complete understanding of the changing Earth.

Geographic pattern of the cumulative mass change over Antarctica for the period between 1/2003 and 6/2014.

Ice sheet and glacier mass balance

Since 2002, the GRACE satellites have been measuring Earth's gravitational field.
By examining monthly snapshots of the geopotential field we measure changes in the ice mass
of the world's ice sheets and mountain glaciers.
We use spherical Slepian functions to regionally localize the GRACE potential fields. With this technique we make better use of the available data and learn more information about where mass change is occurring in Greenland and Antarctica. Our work is able to resolve ice mass flux in unprecedented geographical and temporal detail. We are interested in the total amount of ice mass change over time, and how the map pattern of this mass flux changes year-to-year.

Relevant Publications:

- Harig & Simons, Geophys. Res. Lett., 2016
- Harig & Simons, Earth Planet. Sci. Lett., 2015
- Harig & Simons, Proc. Natl. Acad. Sci., 2012

Example dynamic topography output generated from imposing velocity at the surface of the continental keel under Australia.

Mechanical properties and dynamics of the lithosphere and mantle

Our understanding of Earth's deformation and dynamics fundamentally depends on the mechanical
properties of the mantle and lithosphere. By using three-dimensional finite-element, parallel-computing geodynamic
codes we can develop and run numerical experiments to investigate the influence of these properties
on deformation.
In our past work we have looked at how the shallow lithosphere can deform due to annual changes in the ice sheet above, how large continental keel regions move throughout the upper mantle, and how density instabilities in the mantle lithosphere causing sinking regions to downwell into the mantle. Although they tell us about vastly different time scales, each experiment gives us insight into the evolution of the solid Earth.

Relevant Publications:

- Mordret, Mikesell, Harig, Lipovsky, & Prieto, Sci. Adv., 2016
- Harig, Zhong, & Simons, Geochem., Geophys., Geosys., 2010
- Harig, Molnar, & Houseman, J. Geoph. Res., 2010
- Harig, Molnar, & Houseman, Tectonics, 2008

Slepian basis functions for Greenland.

Signal and spectral analysis on the sphere

As geoscientists we often deal with data distributed over the sphere, and we wish to consider a
specific local area of interest. How can we best represent the data in this local region? Estimating
the local signal and performing spectral analysis on the partial sphere is not a straightforward
problem.To address this, we have developed SLEPIAN, a software suite with a multitude of numerical and computational tools to accomplish spherical data analysis in the geosciences and beyond. At its core are routines that construct scalar spherical Slepian functions on arbitrarily shaped domains. A second group solves the linear inversion problem of extracting a signal from partially and noisily observed data on the surface of a sphere. A third group of algorithms performs quadratic estimation of the power spectral density to estimate from the data the amount of energy per area that the signal has as a function of spatial frequency. The fourth group is specifically for the analysis of time-variable gravitational potential data products from the GRACE mission.

As our work expands so will our software offerings, as we consider them an integral part of our research results, and necessary for reproducible research.

Relevant Publications: Relevant Software: