Fall 2015

Tuesday Afternoons at 4:00 PM

Natural Science Annex 101

September 29, 2015

Speaker: Bruce Buffett, UC Berkeley

Title: Geomagnetic reversals and excursions: Insights into the origins of Earth's magnetic field

Abstract: Palaeomagnetic observations offer important insights into the origin of Earth's magnetic field, but a detailed reconstruction of the underlying dynamics is not feasible. A practical alternative is to construct a stochastic model for the time evolution of the dipole field. Slow changes in the field are described by a deterministic (drift) term, whereas short-time fluctuations are represented by a random (noise) term. Estimates for the drift and noise terms can be recovered from a time series of variations in the axial dipole moment over the past 2 million years. The results are used to predict a number of statistical properties of the palaeomagnetic field, including the average rates of magnetic reversals and excursions. A physical interpretation of the stochastic model suggests that reversals and excursions are part of a continuum of time variations in Earth's magnetic field, arising from convective fluctuations in the core. Relatively modest changes the amplitude of convective fluctuations can produce large changes in reversal rates, including the well-known occurrence of superchrons lasting longer than 10 million years.

Hosts: Earl O'Bannon

October 6, 2015

Speaker: IRES Students, UCSC

Title: Summer Research Project in Israel

Hosts: Delphine Defforey

October 13, 2014

Speaker: Shalev Siman Tov, UCSC

Title: The nature of carbonate fault mirrors

Hosts: Stephanie Taylor

October 20, 2015

Speaker: Brad Lipovsky, Stanford

Title: Stick-slip motion in the West Antarctic Ice Sheet

Hosts: Grace Barcheck

October 27, 2015

Speaker: Adrian Borsa, Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, UC San Diego

Title: When the Rains Fail, the Mountains Rise: what GPS can tell us about the hydrological cycle in the western USA and beyond

Hosts: Sarah Beganskas

November 3, 2015

Speaker: Jenny Suckale, Stanford

Title: The thermomechanics of shear margins

Hosts: Grace Barcheck

November 10, 2015

Speaker: Rob Dunbar, Stanford

Title: Modern and Holocene Climate Change in the Southern Ocean and South Pacific: Evidence from New Archives and Tracers

Hosts: Vicky Yuan

November 17, 2015

Speaker: Curt Storlazzi, USGS

Title: Corals, climate change, and atoll sustainability: Will Micronesians be the US's first climate change refugees?

Hosts: James Shope

November 24, 2015

Speaker: Andrew Barbour, USGS

Title: How plate boundary faults in California affect the relationship between pore pressure and dynamic strain

Hosts: Zak Kornberg

December 1, 2015

Speaker: Andrew Roberts, Naval Postgraduate School

Title: Modeling Arctic sea ice loss in next generation fully coupled Earth System Models

Abstract: Arctic sea ice is undergoing a climatic decline more rapid than at any time since the 14th and probably even the 6th century. Earth System Models are our primary tool to understand these changes in the context of global climate, yet their sea ice components collectively offer a surprisingly large spread in the timing of total loss of summer Arctic sea ice within the next century. Estimates range from within the next two decades, to after 2100. Part of the reason for this stems from limitations in the physics represented within sea ice models. While the sophistication of sea ice models has steadily grown since their inception in the late 1960s and 1970s, the resolution of coupled sea ice models has lagged other improvements and processes represented within them, and this necessarily precludes resolving important physics of the Arctic. A core reason for the resolution lag is that there still remains fundamental physics to be settled of how sea ice deforms, and without this advance, it is difficult for models to transcend the so-called multi-floe scale of between 2 and 10 km. Sea ice floes are individual slabs of frozen seawater, often carrying freeboard snow, and they give polar seas their characteristic fractured egg-shell appearance. Modeling sea ice at the multi-floe scale means we can no longer treat it as a continuum without special considerations, and that is where existing models break down. The way forward partly lies in the fractal geometry of floes, which is reflected in the multi-fractal deformation properties of sea ice, and partly in new approaches available for modeling dissipative systems. In this presentation, I detail recent advances made to model sea ice at the multi-floe scale in a new fully coupled Arctic System Model, which is a collaborative effort among seven institutions in the U.S., with the support of the National Science Foundation, the Department of Energy the Office of Naval Research, and the High Performance Computing Modernization Program in the Department of Defense.

Hosts: Saffia Hossainzadeh