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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 2024

In-person seminars are at 3:00 pm in INSCC room 110.

Past Seminars

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
 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 
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:  

  1. 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). 
  2. 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) 
  3. 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
  The "Pattern Effect": How sea surface temperature patterns modulate radiative feedbacks and climate sensitivity
  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
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
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.

Last Updated: 4/18/24