Research interests of Prof. Neshyba
Clouds are recognized as one of the largest sources of uncertainty in climate feedbacks,
partly because of uncertainties how cloudiness will respond to greenhouse gas warming,
and partly because of uncertainties in how clouds interact with light. Chasing down some
of these uncertainties has led my students and me into investigations over a vast range of
scales, from the molecular scale, to the micrometer-level scale, to the scale of entire
cirrus clouds.
At the molecular level, we’d especially like to understand what governs the mobility of
molecules at the ice surface. That’s because because mobility plays a key role in how ice
crystals grow and disappear. It turns out that a technique called molecular dynamics
(MD) is useful to develop insight into this kind of behavior. Our MD work has shown, for
example, that water molecules at the ice surface are sometimes mobile in a lopsided way,
as indicated in the left-hand-side of the figure above; we’re still not completely sure why.
Much of this work has been carried out in collaboration with researchers at the Czech
Institute for Organic Chemistry and Biochemistry, who are experts in MD.
Other work in my lab has been directed at understanding the roughness of the surface of
the ice crystals. This roughness occurs on a vastly larger scale than the molecular-level
scale treated by MD, on the order of microns or tens of microns (called the mesoscopic
scale). We can get at this structure using variable pressure scanning electron microscopy,
as shown in the middle image in the figure above. These efforts have revealed that the
roughness of ice, previously thought to be random, is actually sensitive to the symmetry
of the underlying ice crystal: different facets develop roughness of characteristic
symmetry. That’s kind of exciting because it gives us a handle on the mechanism by
which mesoscopic roughening occurs, which in turn means we might be able to predict
the atmospheric conditions under which roughening is likely to occur.
Branching out to the largest scale are radiative transfer studies. We create models of
cirrus ice crystals on a computer, and use a technique called “ray tracing” to investigate
how the cirrus clouds scatter light from the sun. We’ve found that the symmetry of the
roughness matters in how ice crystals scatter light, in a way that should be detectible in
remote-sensing observations of the atmosphere. Recently, we have begun exploring how
3d printing of such crystals might be useful in such efforts.
It turns out that it would be very useful to be able to bridge some of these scales,
especially from the molecular to the mesoscopic. Bridging scales is very challenging
from a theoretical point of view, because it’s not possible, computationally, to simulate
all scales of the problem at the same time. So this effort includes both computer
programming and theoretical aspects.
References; student co-author names are given in bold face
“Radiative consequences of low-temperature infrared refractive indices for supercooled
water clouds”, P.M. Rowe, S.P. Neshyba, and Von P. Walden, Atmos. Chem. Phys., 13,
11925-­‐11933 (2013). (see http://www.atmos-chem-phys.net/13/11925/2013/acp-1311925-2013.html)
“Roughness metrics of prismatic facets of ice”, S.P. Neshyba, B. Lowen, M. Benning, A.
Lawson, and P.M. Rowe, J. Geophys. Res. – Atmospheres, 118, 3309-3318 (2013). (see
http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50357/abstract)
• Listed in the Special Research Spotlight of EoS, 94, 244 (2013); see
http://onlinelibrary.wiley.com/doi/10.1002/2013EO27/pdf.
• Marked for “Editor Highlight” on the JGR homepage; see
http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%2921698996/homepage/EditorsHighlights.html
• Listed in the Council of Undergraduate Research website on undergraduate
research highlights,
http://www.cur.org/highlights/highlight_category/?code=Geosciences#2251
“Arrhenius analysis of anisotropic surface diffusion on the prismatic facet of ice”, Ivan
Gladich, William Pfalzgraff, Ondrej Maršálek, Pavel Jungwirth, Martina Roeselová, and
Steven Neshyba, Physical Chemistry Chemical Physics, 13 (invited paper), 19960-9
(2011).
“Comparative molecular dynamics study of vapor-exposed basal, prismatic, and
pyramidal surfaces of ice”, William Pfalzgraff, Steven Neshyba, and Martina Roeselová,
J. Phys. Chem. A, Buch Memorial Issue (invited paper) DOI: 10.1021/jp111359a (2011).
“A responsivity-based criterion for accurate calibration of FTIR spectra: identification of
in-band low-responsivity wavenumbers”, Penny M. Rowe, Steven Neshyba, Christopher
Cox, and Von P. Walden, Optics Express, 19, 5930-5941 (2011). (see
www.opticsinfobase.org/abstract.cfm?uri=oe-19-7-5930.)
“A responsivity-based criterion for accurate calibration of FTIR spectra: theoretical
development and bandwidth estimation”, Penny M. Rowe, Steven Neshyba, and Von P.
Walden, Optics Express, 19, 5451-5463 (2011). (see
www.opticsinfobase.org/abstract.cfm?uri=oe-19-6-5451.)
“Scanning electron microscopy and molecular dynamics of surfaces of growing and
ablating hexagonal ice crystals”, William Pfalzgraff, Ryan Hulscher, and Steven
Neshyba, Atmos. Chem. Phys., 10, 2927-2935 (2010). (see www.atmos-chem-
phys.net/10/2927/2010/; www.atmos-chem-phys-discuss.net/9/20739/2009.html is the
discussion paper associated with this article)
“Molecular Dynamics study of ice-vapor interactions via the quasi-liquid layer”, Steven
Neshyba, Erin Nugent, Martina Roeselová, Pavel Jungwirth, J. Phys. Chem. C, 113,
4597-4604, doi: 10.1021/jp810589a (2009).