What is Applied Physics? What do its students do? And how is it different than the Physics department? Who better to help answer these questions than current AP students! Below are some short articles written by AP students about other AP students’ research interests, so that you can learn more about the wide variety of research going on here in UM’s Applied Physics program.
If you’re a current AP student and would like to be interviewed about your research so that it may be featured on here, or if you’re interested in interviewing and writing an article, please email APSC.firstname.lastname@example.org and let us know!
Written by Thomas Shaw
Morgan Whitcomb is a fourth year Ph.D. student in the University of Michigan’s Applied Physics program. They have been researching the dynamics of Antarctic ice, with their advisor Jeremy Bassis, a professor in the Climate and Space Sciences and Engineering department. The Bassis lab studies various problems in glaciology, such as the ice loss caused by climate change. Morgan is particularly involved in studying how climate change is affecting Antarctic ice. As the ice flows to the ocean, cracks, and melts, global sea levels rise. Understanding the extent and rate of this sea level rise is an important part of planning for the consequences of climate change. The peculiarities of the Antarctic ice sheet pose particular physical and modeling challenges, making it one of the largest unknowns in predictions of the impacts of climate change.
There are two types of melting ice that glaciologists have to worry about: sea ice and grounded ice. Grounded ice is supported by land, and when it melts the total sea level rise is well understood: every kilogram of grounded ice that melts adds one kilogram of water (which amounts to about one liter) to the oceans. Much of the ice of Greenland is of this type. On the other hand, sea ice and icebergs are entirely free-floating in the oceans. The contribution of sea ice melting is also well understood. This is Archimedes’ Principle: an object floating in water displaces a mass of water equal to the mass of the object. Thus, the volume of new ocean water is almost exactly equal to the volume already displaced by the iceberg .
But knowing how much water is added to the ocean is the easy part. Understanding how soon and how fast ice actually melts is more difficult. For example: as glaciers melt, cracks form that can cause large pieces of ice to break off and fall into the ocean. This process is called iceberg calving and helps determine how fast the water of a glacier moves into the sea. Concerted research efforts in this area have made progress in describing iceberg calving in Greenland. However, it turns out that results from Greenland don’t translate into understanding Antarctic ice.
Antarctica is unique because although it has a huge volume of grounded ice , it is also surrounded by huge floating ice shelves that support this grounded ice. These ice shelves, like glaciers, are prone to iceberg calving, but the physics of the process is different and has resisted prediction by the methods developed for the Greenland ice sheet. Furthermore, these processes have significant impacts on the rate of sea level rise. Morgan and Bassis have therefore prioritized this research as an important way of increasing the accuracy of projections of the effects of climate change on human timescales.
To make better projections, Morgan has been incorporating a recently developed physical model of calving into an existing computer model of ice dynamics. The added physics concerns how cracks in ice sheets grow. The growth depends on the spreading rate of the ice shelf, its rate of melting, and the stresses that are being applied to the ice sheet. Calving occurs when the height of the crack grows as large as the thickness of the ice shelf. To ensure the correctness of the implementation, Morgan has subjected the new code to extensive numerical checks. They are now working on verifying that the model reproduces the physics of the real world, using existing data from ice systems where the model applies.
Morgan has always felt strongly about sustainability, the environment, and climate change. Starting when they were a double major in Chemistry and Physics at the University of Colorado, Morgan began working on several very different research projects that fit their passion in this area. But each project had shortcomings. One project had interesting physics but not enough mathematical rigor to satisfy Morgan. Another had the opposite combination. When they got to U of M and heard a talk by Bassis on his work, Morgan was fascinated, even though they had no background in glaciology. The combination of application, mathematical and computational methods, and physical foundation suited Morgan’s passions, skills and curiosity.
 There’s a miniscule correction to account for dilution. As freshwater is added to the oceans, they get less salty, which in turn makes them less dense.
 If it all melted, it would produce 70 m of sea level rise, which would flood much of the East coast of the US, including Washington, D.C. and all of Florida. You can check out different sea level rise scenarios at http://www.floodmap.net/.