PAOC Spotlights

Senior Theses - 2011

Fri May 13th, 2011

Friday, May 13th, was the EAPS annual senior thesis presentation day. Of the eight Course 12 seniors participating, three, Anastasia Maheras, John (Vince) Agard and Todd Mooring, were advised by PAOC faculty.

John (Vince) Agard presents his senior thesis work to EAPS students, staff and faculty - image: PAOC













Anastasia Maheras (Environmental Science) has been working with Prof. Noelle Eckley Selin comparing atmospheric mercury observations with results from a chemistry transport model used to inform policy development and regulation.

John (Vince) Agard (Atmospheres, Oceans & Climate) has been working with Prof. Kerry Emanuel looking at a quasi-decadal signal observed in the lower stratosphere seeking possible connections to known oscillatory phenomena such as ENSO.

Todd Mooring (Atmospheres, Oceans & Climate) has been working with Prof. Paul O'Gorman looking at how the length of atmospheric eddies increases in simulations of future global warming.

Read on to savour a taste of each of their projects:


Elemental and Reactive Gaseous Mercury Deposition and Diurnal Cycles over Terrestrial Environments

Anastasia Maheras (advisor Prof. Noelle Eckley Selin)

Originally from Columbus, Ohio, Anastasia has been majoring in EAPS specializing in Environmental Science. She returns to PAOC this Fall to study for a Masters degree, advised by Kerry Emanuel.

Anastasia has been studying the atmospheric component of the global biogeochemical mercury cycle to determine the mechanisms behind diurnal trends and amplitudes in elemental and reactive gaseous mercury concentrations over terrestrial environments. Using the 3D chemical transport model GEOS-Chem to compare with results from a one box model of her own devising, Anastasia was able to investigate how well GEOS-Chem was able to repoduce detailed local behaviors.

Mercury is a significant neurotoxin for humans and other species that is being addressed in the policy realm on both national and international levels. Being able to model atmospheric mercury processes correctly is an important part of regulation and policy drafting.

Commenting on Anastasia's project, Prof. Selin said: "Anastasia has come up with some very interesting results in her thesis looking at the fate of reactive gaseous mercury over the western U.S. In addition, the box model she's developed to look at the influence of different processes affecting mercury in the atmosphere will be a useful tool for future investigations of mercury atmospheric chemistry".

Comparing GEOS-Chem model results with measurements for three sites in Nevada (Weiss-Penzias et al. (2009)) Anastasia attributed the significant differences in elemental mercury concentrations she found to an under-representation of mercury emissions at naturally enriched sites and reactive gaseous mercury diurnal variations that differed by a factor of 3-4, with GEOS-Chem underestimating the diurnal trend.

Based on the diurnal nature of this error, Anastasia was able to conclude that for her test site, GEOS-Chem under represents the magnitude of elemental mercury emissions, the amount of oxidation occurring in the atmosphere, and the scale of entrainment from the free troposphere.


A Global and Tropical Quasi-Decadal Oscillation of the Atmosphere and Ocean

John Vincent Agard (advisor Prof. Kerry Emanuel)

Originally from Gaithersburg, MD, Vince's project evolved from a UROP he bagan last summer. Vince has been majoring in EAPS (with a focus on Atmospheres, Oceans and Climate), and this year  added a second major in Physics. He returns to PAOC next year as a doctoral student. His advisor will be Kerry  Emanuel .Vince's project was to investigate the nature of a mysterious quasi-decadal signal that is apparent in Atlantic tropical sea surface temperature and lower stratosphere temperature.

Using power spectrum analysis and Fourier decomposition Vince showed how he had been able to characterize the temporal and vertical manifestations of the signal and use EOF analysis  to analyze its spatial characteristics.

Finding that the signal in the SST data displayed significant coherence with similar oscillatory signals in ENSO (the El Nino Southern Oscillation), PDO (Pacific Decadal Oscillation) and AMO (Atlantic Multidecadal Oscillation) indices, Vince concluded that the observed oscillation was more likely to be related to them than the (~11 year) solar activity cycle - an alternative suggested candidate.

Prof. Emanuel commented of Vince's work: "We began with the hypothesis that the signal was related to the 11-year solar cycle, but Vince was able to show that it is not coherent with the solar cycle. He was able to cast some light on the physical nature of the phenomenon by associating its spatial and temporal variability with that of the Pacific Decadal Oscillation".

Finally, Vince demonstrated how the lower stratospheric temperature signal provided a small but measurable contribution to the signal of tropical cyclone potential intensity in the Atlantic MDR (Main Development Region).

Vince looks forward to further exploring the causal origins of this phenomenon as he returns to work with Kerry Emanuel as a graduate student this fall.


Changes in Atmospheric Eddy Length with the Seasonal Cycle and Global Warming

Todd A. Mooring (advisor Prof. Paul A. O'Gorman)

Originally from Lincoln, Nebraska, Todd is a double major in EAPS and Physics. He begins graduate studies at Princeton this fall. His advisor was Prof. Paul O'Gorman. Asked about his experience, Todd relates, "Prof. O'Gorman has been great to work with.  He is nearly always available to answer questions, explain things, or discuss where to take the project next.  I look forward to working with him to get the thesis rewritten for submission to a journal." Todd's project expanded on recent work by Kidston et al. (2010) demonstrating that the length of atmospheric eddies increases in simulations of future global warming. Studying eddy length in the NCEP2 reanalysis (a model-data synthesis that reconstructs past atmospheric circulation) and general circulation models (GCMs) from the Coupled Model Intercomparison Project phase 3 (part of the IPCC process) Mooring compared eddy lengths to hypothesized controlling scales such as the Rossby and Rhines scales and found that the GCMs did indeed reproduce the seasonal variation in the eddy lengths seen in the reanalysis.

Todd demonstrated that an effective Rossby radius that takes into account the effects of water vapor on the dynamics of the atmosphere was better than the traditional dry Rossby radius in explaining the seasonal cycle of eddy length in the northern hemisphere.  This improvement was found to be contingent upon the choice of the free troposphere depth as the height scale in the Rossby radius calculation (no improvement was seen if the scale height was chosen instead).

Prof. O'Gorman summed up Todd's project: "Todd has been working to understand how water vapor affects the size of atmospheric eddies - the familiar low and high pressure systems in the midlatitudes - in different seasons and in a warmer atmosphere. His results help us to understand and evaluate the projected increase in the size of the eddies found in simulations of 21st-century climate change".









PAOC congratulates all three seniors for their hard work and looks forward to following their graduate careers with interest.