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.
In-person seminars are at 3:00 pm in INSCC room 110. To attend regular Wednesday seminars via Zoom, register here.
Monday, December 6
Between 1960-2000 wildfires burned approximately 1.5 million hectare per year. But since then, the annual area burned has more than doubled, with most of this increase accounted for by large mega fires in the Western U.S. The resulting emissions have exposed millions of people in the U.S. to very poor air quality for extended periods of times. In this analysis, we examine how fires have impacted the policy relevant air quality metrics for both PM2.5 and O3 (annual 98th percentile for PM2.5 and 4th highest daily 8-hour average for O3). Our analysis shows that for many cities in the western U.S., the increase in fires has offset the reduction in emissions from anthropogenic/industrial sources.
Because wildfires are now one of the largest sources of pollution in the U.S. it is important to understand the emissions and chemical processing. Fires can emit a wide range in pollutants depending on the vegetation type and combustion conditions. Once released, the aerosols will undergo chemical processing that will increase the O/C ratio and also increase the toxicity of the aerosols. For O3, a secondary pollutant, the story is more complicated. While fire emissions generate O3 precursors, there is a large degree of variability that is not well understood. We apply several tools to understand O3 production in wildfire smoke including photochemical models and statistical/machine learning methods.
While most of the impact has been in the western U.S., in 2023, we see that smoke from Canadian fires has strongly impacted air quality in the eastern U.S. with some of the highest O3 concentrations in eastern and midwestern cities for the last decade. In this presentation, we will provide an overview of our findings, with an emphasis on how both PM2.5 and O3 concentrations have been influenced by the dramatic increase in fires in the recent decade.
Special Seminar Tuesday, August 29
Speaker: Jeff Anderson, National Center for Atmospheric Research, Data Assimilation
Title: Removing the Kalman from the Ensemble Kalman Filter: Powerful New Data Assimilation Methods for Atmospheric Analyses and Forecasts
It is now a quarter of a century since the first application of an ensemble Kalman filter for atmospheric prediction. Since that time, many extensions to the ensemble Kalman filter have been proposed and algorithm variants that are fast and scalable have been developed. However, most extensions retain the underlying assumptions of the original Kalman filter: errors have a Gaussian distribution and there is a (noisy) linear relation between observations and forecast model state variables.
Ensemble (Kalman) filter assimilation algorithms can be described as two steps. Step 1 is computing ensemble increments for an observed variable given an observation and a description of its error. An efficient algorithm that allows the use of arbitrary distributions (not just Gaussians) for this step is described. Step 2 is computing increments for a model variable given the ensemble of observation increments. In ensemble Kalman filters, this is just a simple linear regression. However, doing the regression in a transformed space can remove this linearity constraint. Transforming with a probability integral transform followed by a probit transform (these technical terms correspond to very basic statistics), guarantees that the posterior ensembles for state variables share the advantages gained by the improved step 1. For example, if a state variable is bounded (like specific humidity or ozone concentration) then posterior ensembles will be bounded.
These new ensemble filter algorithms can lead to major improvements in analyses and forecasts, especially for bounded quantities and for remote sensing observations that have complex relations to model variables. Examples for tracer concentration and source estimation are presented.
Wednesday, August 30
Speaker: Alex Turner, Assistant Professor, Atmospheric Sciences, University of Washington
Title: Atmospheric methane: where did you come from, where did you go?
Methane is a key component of the global carbon cycle and the second most important anthropogenic greenhouse gas after CO2. Atmospheric concentrations have exhibited large variations over glacial cycles as well as enigmatic trends in the present. The variations, which remain scientifically elusive, are driven by the relative balance between the sources and sinks. Major sources of methane include: wetlands, fossil sources, and res. Oxidation by the hydroxyl radical (OH) is both the main sink for methane and the primary atmospheric oxidant. Here I will discuss our recent and ongoing work to characterize the processes driving variations in both past and modern atmospheres.
Wednesday, September 6
Speaker: John Peters, Penn State University
Title: Thunderstorms realize less of their CAPE in a warmer climate
ABSTRACT: Prior studies showing that convective available potential energy (CAPE) in the midlatitudes will likely increase as a response to global warming typically neglect entrainment in their calculations. As a step toward understanding how entrainment effects may respond to warming, a parcel model framework is constructed that allows for independent variations in the environmental temperature T, fractional entrainment rate, and free tropospheric relative humidity RH, while the CAPE is held constant. The buoyancy of entraining air parcels is evaluated within parameter space with a range of environmental surface T spanning from 285 K to 315 K, and a range of free-tropospheric RH spanning from 0 to 100. Buoyancy displays a negative relationship with T, with parcels in warmer environments realizing substantially smaller fractions of their CAPE because of the nonlinear dependency of the saturation specific humidity of air on temperature. This reduction in buoyancy at warmer temperatures is most pronounced for narrower updrafts with large fractional entrainment amid a dry free troposphere, and when the undiluted buoyancy profile is top-heavy. An analysis of large eddy simulations corroborate the parcel model results, showing reduced buoyancy and vertical velocities in clouds simulated in warmer environments relative to their counterparts in cooler environments. These results emphasize the need for the consideration of the effects of entrainment in studies of global warming influences on future midlatitude thunderstorm behavior, as this effect may partially counteract the influence of increases in CAPE on updraft intensity.
Wednesday, September 13
Speaker: Will Porter, Assistant Professor, Environmental Sciences, University of California- Riverside
Title: Dust, Algae, and Asthma: The Case of California's Evaporating Salton Sea
ABSTRACT: Windblown dust has long been an air quality and public health concern among residents living around California’s Salton Sea, a region characterized by serious socioeconomic and health outcome disparities. Dropping water levels and unique biogeochemistry within the Salton Sea water itself have raised concerns regarding the human health impacts of drying sediments exposed on shrinking shorelines, as well as potential lake spray emissions from the water surface. As particles emitted from different surface types can differ greatly in terms of composition, size distribution, and other properties, variability in the resulting health impacts of windblown dust reaching communities in the region may likewise be source dependent. Here I will share work being done in my group to analyze surface-specific health outcomes associated with windblown coarse PM around the region, as well as attempts to better understand and mitigate the unique issues linked to these emissions across the basin. I will further explore similarities and differences connecting evaporating inland lakes and seas worldwide, as well as some of the opportunities for sharing knowledge and tools to address the increasingly dry, dusty future facing many of these analogous areas.
Wednesday, September 20
Speaker: Michael Diamond, Assistant Professor, Meteorology and Environmental Science, Florida State University
Title: Detection of large-scale cloud microphysical changes within a major shipping corridor after implementation of the International Maritime Organization 2020 fuel sulfur regulations
ABSTRACT: New regulations from the International Maritime Organization (IMO) limiting sulfur emissions from the shipping industry are expected to have large benefits in terms of public health but may come with an undesired side effect: acceleration of global warming as the climate-cooling effects of ship pollution on marine clouds are diminished. Previous work has found a substantial decrease in the detection of ship tracks in clouds after the IMO 2020 regulations went into effect, but changes in large-scale cloud properties have been more equivocal. Using a statistical technique that estimates counterfactual fields of what large-scale cloud and radiative properties within an isolated shipping corridor in the southeastern Atlantic would have been in the absence of shipping, we confidently detect a reduction in the magnitude of cloud droplet effective radius decreases within the shipping corridor and find evidence for a reduction in the magnitude of cloud brightening as well. The instantaneous radiative forcing due to aerosol–cloud interactions from the IMO 2020 regulations is estimated to be of order 1 W m−2 within the shipping corridor, lending credence to global estimates of order 0.1 W m−2 from climate models. Although the contribution to warming since 2020 is expected to be small globally, the effects may be much larger regionally in the north Atlantic and Pacific. In addition to their geophysical significance, our results also provide independent evidence for general compliance with the IMO 2020 regulations.
Wednesday, September 27
Speaker: Ben Santer, Fowler Distinguished Scholar in Residence at Woods Hole Oceanographic Institution; Visiting Researcher at UCLA's Joint Institute for Regional Earth System Science & Engineering
Title: Exceptional Stratospheric Contribution to Human Fingerprints on Atmospheric Temperature
ABSTRACT: In 1967, scientists used a simple climate model to predict that human-causedincreases in atmospheric CO2 should warm Earth’s troposphere and cool thestratosphere. This important signature of anthropogenic climate change has beendocumented in weather balloon and satellite temperature measurements extendingfrom near-surface to the lower stratosphere. Stratospheric cooling has also beenconfirmed in the mid- to upper stratosphere, a layer extending from roughly 25 to 50km above Earth’s surface (S25-50). Until recently, however, S25-50 temperatureshad not been used in pattern-based attribution studies of anthropogenic climatechange. My talk will discuss the first such “fingerprint” study with satellite-derivedpatterns of temperature change that extend from the lower troposphere to the upperstratosphere. Including S25-50 information in the fingerprint increases signal-to-noise ratios by a factor of five, markedly enhancing fingerprint detectability. Keyfeatures of this global-scale human fingerprint include stratospheric cooling andtropospheric warming at all latitudes, with stratospheric cooling amplifying withheight. In contrast, the dominant modes of internal variability in S25-50 havesmaller-scale temperature changes and lack uniform sign. These pronounced spatialdifferences between S25-50 signal and noise patterns are accompanied by a largesignal in S25-50 (cooling of 1-2°C over 1986 to 2022) and S25-50 noise levels thatare over an order of magnitude smaller than the signal. This explains why extending“vertical fingerprinting” to the mid- to upper stratosphere yields incontrovertible evidence of human effects on the thermal structure of Earth’s atmosphere.
Wednesday, October 4 online seminar
Speaker: Xiaodong Chen, PNNL
Title: Understanding the western U.S. hydroclimate with regional climate modeling and machine learning
ABSTRACT: The western U.S. hydroclimate features significant footprints of both large-scale circulation patterns (atmospheric rivers) and local processes (precipitation and snowpack). Orographic precipitation and mountainous snowpack in the climate simulation require accurate topography and land heterogeneity information. Therefore, high-resolution regional climate modeling, or emerging “convection-permitting” modeling (CPM), is a good fit for this region. Meanwhile, machine learning has been recently proven as a powerful tool to explore and predict non-linear hydroclimatic processes. However, the potential of combining these two tools has not been well explored yet.
In this talk, I will go over a few studies based on a validated CPM simulation of the western U.S. and various machine learning techniques. They demonstrate the unique advantages of these tools: 1) CPM provides accurate physical descriptions of hydroclimatic processes (e.g., storms, snowmelt) in regions with complex terrain. It enables new insights into the regional hydrologic cycle and produces robust conclusions at climatic scales; 2) machine learning (e.g., deep learning, computer vision) can describe non-linear hydroclimatic processes at various spatial-temporal scales with computational efficiency. I will also discuss how they can benefit the development/evaluation of each other, and how their synergy can elucidate new insights into the hydroclimate system at regional to global scales.
Wednesday, October 18
Speaker: Adriana Raudzens Bailey, Dept. of Climate and Space Sciences and Engineering, University of Michigan; Investigator for NCAR Cold Air Outbreak Experiment in the Sub-Arctic Region
Title: Wintertime Mixed-Phase Clouds: What isotopes tell us about moisture sources and ice particle growth
ABSTRACT: Ice particle growth influences key characteristics, such as the lifetime, of mixed-phase clouds but remains difficult to study observationally and thus represent accurately in numerical simulations. Here I present a possible new approach to address this challenge based on the theoretical assumption that riming and vapor deposition will impart distinct signatures on the hydrogen and oxygen isotope ratios of ice. During winter ’22, three water vapor isotopic analyzers were deployed at the Storm Peak Laboratory (SPL) in Colorado. Using Purdue University’s prototype 3-phase separating inlet SPIDER, we measured simultaneously, for the first time, the isotopic composition of water in vapor, supercooled liquid, and ice within orographic clouds. Here, I compare our observations of the condensed phases to isotopic predictions based on the vapor measurements. The initial results suggest a strong correlation in ice isotope ratios with the supersaturation of the environment but little variation in ice deuterium excess, suggesting a limited role for vapor deposition in growing the particles. I also discuss the sensitivity of the measurements to the relative humidity within the SPIDER inlet and place the results within the broader context of the large-scale environment. Based on these findings, I discuss opportunities for refining real-time water isotopic measurements in mixed-phase clouds and for extending this observational approach to future missions, including CAESAR, which will fly through mixed-phase clouds in the Arctic this winter.
Wednesday, October 25
Speaker: Zhaoxia Pu, Professor, Department of Atmospheric Sciences, University of Utah
Title: Overview of a Report on Priorities for U.S. Weather Research
In December 2020, Congress charged the National Oceanic and Atmospheric Administration (NOAA) Science Advisory Board (SAB) to publish a report that provides the information (including benefits) necessary to prioritize federal investments in Weather research and forecasting over the next decade. In response, the NOAA SAB launched the Priorities for Weather Research (PWR) study, which, through a broad consultative process, engaged over 150 subject matter experts from across the Weather Enterprise to develop a report released in December 2021. This report has recently been cited in nearly all federal opportunities related to weather and climate research. It has also ignited continuous discussions within the community and in related areas.
As a NOAA Science Advisory Board member, Atmospheric Science Professor Zhaoxia Pu was part of the executive study team that led the PWR study and produced the report. In this seminar, she will offer an overview of the PWR report and share relevant stories. The primary focus will be on introducing and interpreting the priorities in weather research addressed in the report.
Wednesday, November 1
Speaker: Carrie Womack, Cooperative Institute for Research in Environmental Sciences, and NOAA Chemical
Title: Industrial halogen emissions and their effect on wintertime air quality in Salt Lake City, Utah
ABSTRACT: Salt Lake City has poor air quality in the winter during persistent cold
air pools, when emissions are trapped near the surface and react for many days to
form particulate matter (PM2.5). The majority of PM2.5 during these events is ammonium
nitrate aerosol, formed from the reactions of nitric acid and ammonia. In 2017, the
Utah Winter Fine Particulates Study measured the air quality in northern Utah for
4 weeks from the NOAA Twin Otter aircraft. During downwind transects of the US Magnesium
plant, large quantities of the halogen species Cl2, Br2, BrCl and HCl were observed
concurrently with complete titration of O3, indicating photochemical ozone destruction
by halogen radicals. We used the zero-dimensional box model F0AM to demonstrate how
halogens deplete ozone near the facility, but amplify the formation of nitric acid,
and therefore PM2.5, further downwind. Finally, we used a chemical transport model
to estimate the effect of these emission on air quality in Salt Lake City, and found
them to be potentially significant.
In this seminar, I will talk about this recent paper and the subsequent legislation in the Utah State Legislature to develop a statewide bromine inventory.
Wednesday, November 8
Speaker: Seth Lyman, Utah State University
Title: Mercury in the Atmosphere
ABSTRACT: Mercury, a toxic heavy metal, is ubiquitous in the environment. It is in every breath of air you have ever taken, every bit of food you have ever eaten, and every cell in your body. Its concentration in our environment and our bodies is typically below the threshold of harm, but humans can be exposed to toxic amounts of mercury by consuming contaminated fish (many Utah waterways have consumption advisories for fish because of mercury). Accumulation to toxic levels occurs in aquatic environments, but almost all global mercury pollution is emitted to the atmosphere, not waterways. Once emitted into the air, mercury can travel around the globe before undergoing oxidation/reduction reactions that determine where and when it is finally introduced to aquatic systems. These reactions are critically important for predicting when and where mercury will impact the environment, but knowledge about them is limited because it is difficult to measure oxidized mercury compounds (they exist in the low parts-per-quadrillion range). This seminar will explore the mercury biogeochemical cycle and dive into work scientists at USU are doing to develop better measurement instrumentation for atmospheric oxidized mercury.
Wednesday, November 29
Speaker: Havala Pye, Research Scientist U.S. Department of Environmental Protection
Agency Office of Research and Development Center for Environmental Measurement and
Title: Linking gas, particulate, and toxic endpoints to air emissions in the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM)
ABSTRACT: Chemical mechanisms are at the core of chemical transport models used to understand drivers of air quality and predict concentrations of pollutants in present day and future conditions. Mechanisms are traditionally focused on prediction of the criteria pollutant, ozone, and mass is often duplicated for purposes of predicting other endpoints such as the secondary organic aerosol (SOA) component of fine particle mass. In this work, Dr. Pye will present the recently developed Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) to show that coupling gas-phase radical chemistry and SOA formation can have benefits for representing the full range of atmospheric reactive organic carbon (ROC). These benefits include expanded coverage of ROC emissions, improved conservation of mass, and new SOA precursors not included in earlier generation mechanisms. This talk will also highlight recent applications of CRACMM in the Community Multiscale Air Quality (CMAQ) modeling system to understand ambient conditions such as those during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign.
Seminars from earlier semesters are listed here.