Department Seminars
The Department of Atmospheric Sciences Seminar is designed to inform students through
the presentation of scholarly works of students, faculty, staff and external scientists.
Videos of past seminars can be viewed on our YouTube channel here.
Current Seminars
Spring 2025
In-person seminars are at 3:00 pm in INSCC room 110.
January 10, 2024 - Cassandra Gaston, Assistant Professor, Dept. of Atmospheric Sciences, Rosenstiel School of Marine
and Atmospheric Sciences University of Miami
Title: PlayaDustEffectsonAtmospheric Halogens and Air Quality
Abstract: Wintertime secondary pollutants, such as ground-level ozone and secondary particulate
matter, is a major problem in the western United States whose formation mechanisms
are poorly understood. A possible explanation for this phenomenon is the production
of chlorine radicals that are thought to originate from the photolysis of nitryl chloride
(ClNO2), formed when dinitrogen pentoxide (N2O5) reacts with chloride-containing aerosol. One aspect of this hypothesis that has
puzzled the atmospheric chemistry community is, where does the aerosol chloride come
from especially in regions far from the ocean? In this talk, I will provide evidence
that an underexplored, inland source of chlorine radicals is from saline playas (e.g.,
dried lakebeds), including the shrinking Great Salt Lake. Playas emit large quantities
of dust, and our laboratory studies, using playa material from different regions of
the south and southwestern United States, showed that playa dust can interact with
N2O5 and efficiently produce ClNO2. We attempted to predict our laboratory results using current parameterizations of
reactive chlorine chemistry that rely on bulk measurements of particulate chloride
and predictions of aerosol liquid content, but consistently overpredicted our results.
By performing detailed bulk and single-particle analysis on different playa dust samples,
we found that playa dust mineralogy, particularly at the particle surface, determines
the reactivity of these dusts with N2O5 rather than bulk aerosol chloride content. We have extended our exploratory results
to focus on regional emissions of dust from the Great Salt Lake and find that dust
emitted from the Northern and Southern arms of the basin have vastly different reactivities
and potentials to generate ClNO2, which also is likely due to differences in dust mineralogy. Because both climate
change and water use practices are predicted to increase the geographic extent of
playas worldwide, this work has implications for current and future air quality considerations.
January 17, 2024 - Kerri Pratt, Department of Earth & Environmental Science, University of Michigan
Title: Observations & Modeling of Wintertime Atmospheric Chlorine Chemistry: Connections
to Snow & Road Salt
Abstract: Recent laboratory and computational chemistry studies have shown that N2O5 reacts
at the atmospheric particle surface, with ClNO2 produced from chloride-containing
particles. However, multiphase reactions are typically simulated using mass-based
chemical composition, which assumes homogeneous distribution of chemical components
across all particles with complete surface availability for reaction. We developed
a new approach to parametrize N2O5 uptake and ClNO2 yield that considers the heterogeneity
of the aerosol population and applied this in three wintertime environments – Ann
Arbor, MI, Kalamazoo, MI, and East Boothbay, ME. Single-particle mass spectrometry
and electron microscopy with energy-dispersive X-ray spectroscopy measured single-particle
composition and showed that only a fraction of the particulate surface area in each
study contained chloride. We assigned N2O5 uptake and ClNO2 yield values to each particle
type, based on lab-based aerosol proxy data, and weighted these by particle surface
area. This new approach more accurately simulated ClNO2, compared to existing methods
that frequently overestimate ClNO2 production. In the inland, wintertime environment,
road salt aerosol was identified as a dominant chloride aerosol source, with uncertainties
remaining in the contribution from residential wood burning aerosols. This new single-particle-based
parameterization is expected to be applicable to other multiphase reactions that occur
at the particle surface. In addition, we showed through outdoor chamber studies and
gradient flux measurements that the saline snowpack is also an important source of
ClNO2 in the wintertime urban environment.
January 24, 2024 - Atmospheric Sciences graduate students
Meet grad students and learn about their research!
January 31, 2024 - Summer Rupper, Professor, Department of Geography, University of Utah
Title: Tapping into Spy Satellite Imagery to Measure Glacier Change and Sensitivity to Climate
in the Water Towers of Asia
Abstract: The high mountain regions of Asia are host to more snow and ice than anywhere outside
of the Polar Regions. Changes in snow and ice storage in these remote landscapes have
the potential to impact the nearly 1 billion people living downstream. While it is
clear that glaciers are generally retreating globally, there is a significant paucity
of data on glacier changes in high-mountain Asia. These glacial systems are extremely
remote, occur at very high altitudes, and are often located along disputed borders
in geopolitically unstable regions. This has hampered our understanding of these systems,
the mechanisms driving the changes, and the downstream impacts. Here we tap into historical
spy satellite imagery to measure the change in glacier volume across the Himalayan
range over the past ~50 years, filling in critical temporal and spatial gaps in glacier
observations and glacier response to climate. We then use these data to reevaluate
(1) glacier sensitivity to climate change and (2) the potential to use glacier observations
as a climate proxy over the modern era.
February 14, 2024 - No seminar - special seminar February 15, 11:00 am
February 21, 2024 - Daniel Baldassare Ph.D. Defense
Title: Improved Estimates of the Hadley Cell in the Past, Present, and Future
February 28, 2024 - Manvendra Dubey, Ph.D., Los Alamos National Laboratory
Title: Greenhouse Gases Observations 1957-2100: Past, Present & Future
Abstract: Dr. David Charles Keeling’s precise CO2 observations at the remote Mauna Loa site discerned its global rise that is attributed
to emissions from human activities. His Keeling curve built the observational framework to examine anthropogenic climate change that has
expanded to encompass other greenhouse gases (GHG) and monitoring modalities. The
accelerating GHG rise and the heat absorbed by them led to concerns about climate
change that continue to exacerbate with time.
My lecture will:
- Trace how multiple long-term atmospheric CO2 observations (in situ surface, and total column from ground and satellites) have helped quantify that vegetation and ocean soak up half of the human CO2 emissions and elucidate regional fluxes (national to Amazon).
- Describe international agreements that slowed the rise of halocarbons and strengthening policies to reduce CH4, CO2 and N2O emissions. Highlight how novel CH4 observations are helping constrain emissions (at Four Corners, dairies, cities, and oil and gas plays)
- Discuss the future trajectory of CO2 and monitor efficacy of decarbonizing efforts and carbon credits. Stress that positive carbon-climate feedback pose a risk, and their early detection will be key to accelerate decarbonization at scale.
March 13, 2024 - Rachel Edie
March 20, 2024 - Karlie Rees
March 27, 2024 - Cristian Proistosescu, Department of Atmospheric Sciences and Department of Geology, University of Illinois
Urbana-Champaign
Title: The "Pattern Effect": How sea surface temperature patterns modulate radiative feedbacks
and climate sensitivity
Abstract: I will highlight recent progress on understanding the impacts of sea surface temperature
patterns on atmospheric circulation, clouds, and radiation: the so-called “the pattern
effect”. The pattern effect has large implications for both attributing recent global warming
trends as well as projecting future ones. Specifically, I will show that the regional
pattern of temperature change over 1981 to 2014 has led to a temporary slowdown of
global-mean warming over this period – a slowdown that climate models fail to replicate
due to systematic biases in their simulations of regional temperature trends in the
Pacific.
In the last part of my talk, I will discuss a pressing question raised by the recent work on the pattern effect: what has caused the observed pattern of surface temperatures over the last four decades, and why do all climate models fail to simulate it?
March 29, 2024 special seminar, 11:00 am, INSCC 110. Stephen Arrowsmith, Professor in Earth Science at Southern
Methodist University
Title: Meteorological Acoustics: Studying Atmospheric Phenomena using Low-Frequency
Sound Waves
Abstract: What can sound tell us about atmospheric processes? The long-range propagation of
low-frequency sound is strongly affected by temperatures and winds above the ground.
This lecture reviews how sound played a key role in our early understanding of the
atmosphere, and highlights some recent studies using sound to explore processes in
the boundary layer, troposphere, and stratosphere.
Stephen Arrowsmith is a Professor in Earth Science at Southern Methodist University. He specializes in understanding how seismic and acoustic waves are excited, how they propagate, and how to unravel the information they contain. His group at SMU tackles both fundamental and societally-impactful problems using seismic and acoustic waves.
April 3, 2024 - William Ying-Hwa Kuo, Director of UCAR Community Programs, University Corporation for Atmospheric Research,
Boulder, Colorado
Title: Impact of Radio Occultation on the Prediction of Tropical Cyclogenesis
Abstract: Tropical cyclones are one of the most devastating severe weather systems responsible
for a huge loss of lives and properties every year. Accurate prediction of tropical
cyclogenesis by numerical models has been a significant challenge, largely because
of the need for more observations over the tropical oceans. The atmospheric limb sounding
technique, which uses radio signals transmitted by global navigation satellite systems
(GNSS), has evolved as a robust global observing system. This technique, known as
radio occultation (RO) can provide valuable water vapor and temperature observations
for the analysis and prediction of tropical cyclogenesis. Using the WRF modeling and
data assimilation system, we show that the assimilation of RO data from the COSMIC
mission can substantially improve the skills of the model in predicting the tropical
cyclogenesis for ten typhoon cases that took place over the Western Pacific from 2008
to 2010. To gain insight into the impact of GPS RO data assimilation, we perform a
detailed analysis of the formation process of Typhoon Nuri (2008) and examine how
the assimilation of the GPS RO data enables the model to capture cyclogenesis. The
joint Taiwan-U.S. COSMIC-II mission was launched in June 2019. It has been providing
more than 6,000 GPS RO data per day over the tropics since March 2020. The assimilation
of COSMIC-2 RO data has been shown to increase the probability of detection and reduce
the false alarm of tropical cyclogenesis prediction.
April 10, 2024 - Hannah Horowitz, Assistant Professor, Department of Civil and Environmental Engineering, University
of Illi-
nois at Urbana-Champaign, Urbana, IL
Title: Aerosol-atmospheric chemistry-cloud interactions in the Arctic and Southeast
Atlantic Ocean
Abstract: Marine aerosols like sea salt aerosols and sulfate derived from plankton emissions
of dimethyl sulfide (DMS) influence climate by directly scattering radiation and serving
as cloud condensation or ice nuclei. Here I will present recent work in our group
from two projects. First, we go to the Arctic, where on annual basis clouds have a
warming effect due to trapping of longwave radiation. Sources of sea salt aerosols
during the cold season when this effect is most pronounced remain uncertain. Here
we investigate the impact of cracks in sea ice, or leads, on Arctic sea salt aerosol
emissions and concentrations, and feedbacks on atmospheric chemistry. We implement
Arctic-wide emissions of sea salt aerosols from leads in the 3-D atmospheric chemical
transport model GEOS-Chem using satellite observations to quantify their impacts.
Next we move to the southeast Atlantic (SEA) ocean, which is marked by a persistent
deck of low-level stratocumulus clouds. This region has the largest uncertainty in
simulating aerosol-cloud interactions, and differences in model simulations of its
stratocumulus clouds is responsible for significant intermodel spread in predictions
of future global warming. Most previous research has centered on the impact of biomass
burning aerosols during its peak season (August – October). This region is also the
home of large DMS emissions due to the Benguela upwelling system, but their impact
on aerosols during the rest of the year remains underexplored. We apply the GEOS-Chem
3-D atmospheric chemical transport model at high resolution to investigate the potential
role of marine aerosols in aerosol-cloud interactions in this region across all seasons,
and how uncertainties in atmospheric chemistry and emissions affect our understanding.
We evaluate the model against observed aerosol optical depth from AERONET and aerosol
composition from aircraft campaigns in the region (ORACLES and CLARIFY).
April 17, 2024 - Ramón Barthelemy, Department of Physics, University of Utah
Title: Sex and Gender Based Harassment in Physics and Astronomy
Abstract: Sex and gender based harassment are prevalent across academia as a whole, but also
within the STEM fields. The field of physics has a well-documented history of discrimination
against women and other groups, with the term sexual harassment being coined when
describing the behavior of a Cornell physics faculty member in the 1970’s. This talk
will discuss the current data on sex and gender based harassment in STEM and a longitudinal
10-year study on the experiences of graduate women in physics who are now professionals
in the field. The talk will conclude with actions and steps everyone can take to make
STEM a better place.
Seminars from earlier semesters are listed here.