Past Department Seminars

Fall 2023

Special Seminar Tuesday, August 29

Speaker: Jeff Anderson, National Center for Atmospheric Research, Data Assimilation Research Section
Title: Removing the Kalman from the Ensemble  Kalman Filter: Powerful New Data Assimilation  Methods for Atmospheric Analyses and Forecasts 
Abstract:
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?
Abstract:
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 Sciences Laboratory
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 Modeling 
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.

Wednesday, 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 PM_2.5 and O₃ (annual 98th percentile for PM_2.5 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 PM_2.5 and O₃ concentrations have been influenced by the dramatic increase in fires in the recent decade. 

Spring 2022

Wednesday, April  6

Speaker: Andrew Hoell

NOAA Physical Sciences Laboratory
Boulder, Colorado, USA

Title: Where Have All the Hydrological Droughts Gone in the Missouri River Basin?

Abstract:

Physical factors related to increases in annual runoff from the 20th to 21st centuries in the Missouri River Basin that led to fewer hydrological droughts amid climate change are diagnosed in observed analyses and four ensembles of fully coupled climate model simulations with prescribed time-varying greenhouse gasses and aerosols.

 

Wednesday, March 2

Speaker: Seth Arens

Research Integration Specialist, University of Colorado Boulder

Title: Developing applied and usable climate research through stakeholder engagement

Abstract:

Western Water Assessment (WWA) is a NOAA-funded applied research program, based of the University of Colorado, Utah and Wyoming, that works with stakeholders in the Intermountain West to develop applied and usable science to assist in building resilience to climate change. Beginning in October 2021, WWA officially partnered with the Universities of Utah and Wyoming in order to more effectively work in the Intermountain West region. In this seminar, Seth Arens, a University of Utah-based research scientist for WWA, will discuss the process of engaging with stakeholders to develop usable science and examples of projects in Utah and Colorado. Science needed to inform management of resources, community resilience and natural hazard preparedness in the face of climate change requires an interdisciplinary approach. WWA projects often draw on experience from a variety of disciplines, including atmospheric science, hydrology, ecology and social sciences.

Wednesday, February 9

Speaker: Dr. Ed Zipser 

Professor , Department of Atmospheric Sciences

Title: Extreme Convection vs. Extreme Rainfall: A Global View

Abstract:

Without doubt, there is more than one type of extreme weather event. Without doubt, some extremely intense convective storms also produce extreme rainfall rates. Also without doubt, some extreme rainfall rates come from storms without hail or without any symptoms of extreme convective intensity; some even without any lightning. There are examples of both types here in
the western U.S. This talk examines the population of the full spectrum of extreme events over land and ocean, from tropics to high latitudes, with the goal of clarifying the environmental conditions conducive to these widely different events.
One archetype is common in the Great Plains of the U.S. with excessive rainfall and intense convection. Another is more characteristic of global oceans and monsoonal regions, with extreme short-term rainfall rates from cloud systems without strong convection. We also distinguish between extreme short-term rainfall rates and hourly or even daily extreme rainfall rates that are more likely responsible for catastrophic floods; these come almost exclusively from mesoscale convective systems (MCSs), organized on scales up to hundreds of km with lifetimes of many hours or more, vs. single-cell convective storms. Not surprisingly, each type of extreme event tends to have a preferred diurnal and seasonal cycle, consistent with the different environments that favor each distinctive type. Last but not least, attempts to project how and where the frequency of these extreme events will change with
climate change will require examination of how their distinctive environments will change in different regions of the globe. (This is an important task that is well beyond the scope of this talk.) 

Wednesday, February 2

Speaker: Dr. Logan Mitchell 

Professor , Department of Atmospheric Sciences

Title: The (untold) History of Air Quality in Utah

Abstract:

Utah has a rich history related to air pollution, however it is not widely known or documented despite air quality being a top issue of public concern.  Episodic air pollution events in Utah are caused by anthropogenic emissions of air pollutants being trapped by a combination of meteorological and topographical factors and affected by atmospheric chemistry.  The air pollution composition has changed over time as fuel sources shifted from wood to coal to petroleum and natural gas.  Native Americans and early settlers first noted air pollution, but it rose in prominence as a public issue in the 1880’s as Utah’s urban areas grew.  Since then scientific advances have increased fundamental understanding, emission control technologies have advanced, groups of concerned citizens worked to raise public awareness, policymakers have enacted legislation to improve air quality, and courts have upheld rights to clean air. Utah’s air quality future holds challenges and opportunities. Population growth and the changing climate will exacerbate current air quality trends, however technologically and economically viable clean energy technologies could be deployed to reduce air pollution bringing substantial public health and economic benefits.

Wednesday, January 26

Speaker: Dr. Yoshi Chikamoto

Assistant Professor , Department of Earth System Modeling

Title: Multi-year predictability of Colorado River water supply driven my remote ocean impact

Abstract:

Skillful multi-year forecasts of the Colorado River water supply are crucial for water resource managers to mitigate severe drought damages in Intermountain West. Yet, such forecasts remain challenging due to unpredictable weather noise and the lack of dynamical model capability. In this talk, I want to share our recent research demonstrating that the annual water supply of the Colorado River is predictable up to several years in advance by utilizing ocean information and the global climate model. This research has been published in a new Nature's journal, Communications Earth & Environment. I will also discuss a possible mechanism based on a recent perspective of tropical inter-basin interactions.

Wednesday, January 19

Speaker: Dr. John Horel

Professor , Department of Atmospheric Sciences

Title: The Department of Atmospheric Sciences: Where are We Going? A Townhall on Future Direction

Abstract:

Even with COVID’s extensive impacts, the Department is doing well with Increased course enrollments, a record number of first-year graduate students, and successful grant funding from federal, state, and commercial sources. Changes are happening across campus and in the Department. President Taylor Randall is proposing initiatives to become a top public university with a college town feel. At the Department level, a search is underway for a new faculty member, Storm Peak Laboratory will become a Department facility, construction will begin later this year on a state-of-the-art building to be shared with Physics and Astronomy, and college-level reorganizations will lead to increased collaboration between Atmospheric Sciences, Biology and Geology & Geophysics.    

What does this mean for all of us? After an overview of what is happening, let’s chat using small groups online. How can we help each other deal with COVID fatigue and the present disconnect from one another? How can we design new and improve existing course offerings? How can we enhance the Utah Weather Center as the central hub for everyone coming to the new building?  

Wednesday, Dec 1

Speaker: Dr. Timothy Garrett

Professor , Department of Atmospheric Sciences

Title: Atmospheric Scientists should not play DICE: Misplaced trust in economists when making climate change forecasts

Abstract:

Winner of the 2018 economics Nobel, William Nordhaus, used a widely used model he created DICE to conclude that 6 degrees C global warming would diminish the world GDP by just 8.5 percent relative to an economy about 10 times higher than today’s. Meanwhile, those in the earth science community warn that even 2 degrees C warming poses possible existential risks to humanity as societal and climate tipping points are triggered. The gulf is tremendous. Yet models similar to DICE are widely used not only to guide climate policy but as a resource to atmospheric scientists for predicting where climate is headed in the coming century and beyond. In this talk I will discuss some of the underlying failings of economic modeling efforts that have led to a historic trivialization of “climate damages” by the climate economics community, and recommend remedies for representing interactions between the global economy and climate in a self-consistent physically-based manner

Wednesday, Nov 17

Speaker: Dr. Chris Riedel

NCAR Advanced Study Program (ASP) Postdoctoral Fellow

Title: Arctic Moisture Biases and Sensitivity in a Global High-Resolution Cycled Data Assimilation Modeling System

Abstract:

In recent decades, the duration of skillful forecasts in global models has steadily increased in the mid-latitudes. Much of this improvement can be attributed to the development of higher resolution models, advances in data assimilation techniques, and – perhaps more importantly – growing understanding of physical processes associated with various atmospheric phenomena. However, forecasts in polar regions are not experiencing an equivalent increase in skillful forecast duration even with these improvements. The poles pose a unique modeling challenge that may perhaps be due to a relative dearth in the coverage of conventional observations, which places more weight on satellite remote sensing observations with higher uncertainty for forecast analyses and scientific studies. Additionally, atmospheric features are inherently smaller in the polar regions due to the Earth’s rotation, implying that higher resolution, more computationally expensive NWP model grids are needed to resolve features of equal geographic size in the midlatitudes. Thus, understanding of key polar processes associated with polar weather features is only in its infancy and potentially not well-accounted for in current models. Recent studies highlight the influence polar regions can have on forecast skill in the mid-latitudes, which suggests improved understanding of key polar processes could help extend the current forecast barrier.

In this study, we focus on a predominantly Arctic feature called a tropopause polar vortex (TPV), which can persist for many days to months. The location of TPVs on the tropopause and the known impacts that water vapor has on their growth and evolution leads to poor observational sampling and associated high forecast uncertainties. An overview and evaluation of a new research tool called Model for Prediction Across Scales (MPAS) with ensemble Kalman Filter data assimilation from the Data Assimilation Research Testbed (DART), or MPAS-DART configured for Arctic studies will be discussed.

The ability of MPAS-DART to represent key characteristics of TPVs is investigated along with potential biases that might degrade TPVs in the cycling system. Using observations and analysis increments, initial evaluation of MPAS-DART suggests the existence of systematic model biases in the Arctic. We apply the mean initial tendency and analysis increment method to further quantify these systematic biases. This method provides a way to identify potential model errors associated with either model dynamics or physical parameterizations. A moisture bias is identified in the upper-troposphere lower-stratosphere region, which leads to increased cooling near the tropopause. Special dropsonde observations from the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) are used to evaluate the impact of this identified systematic bias and help elucidate TPV forecast sensitivity to initial states. Additional experiments help determine physical drivers of the moisture bias in the UTLS region.

Wednesday, Nov 10

Speaker: Dr. Rosimar Rios-Berrios

National Center for Atmospheric Research

Title: Multi-Scale Variability of Tropical Rainfall Systems in a Hierarchy of Aquaplanet Experiments

Abstract:

Tropical rainfall systems are important components of Earth’s climate system—from being key players in redistributing heat and moisture from the tropics to the high latitudes to manifesting into powerful high-impact phenomena (e.g., hurricanes) that can impact millions of lives around the world every year. Despite being so important, climate and weather prediction models struggle to accurately capture tropical weather systems and their multiscale variability. This is thought to be in part due to deficiencies in convection parameterizations or due to poor knowledge of how tropical systems of different scales interact with each other. This study tackles both issues by studying the multi-scale variability of tropical rainfall systems in a hierarchy of aquaplanet experiments with varying horizontal cell spacing—from 120 km to 3 km. In the first part of this talk, I will introduce the aquaplanet experiments and will demonstrate that storm-resolving resolution captures a broader range of tropical weather systems thanks in part to a better coupling between cold pools and rainfall. In the second part, I will present an example of multi-scale interactions between tropical weather systems through an analysis of equatorial Kelvin waves and their influence on tropical cyclogenesis frequency. I will conclude with a discussion of implications of this study to the future of climate and weather prediction of tropical rainfall.

Wednesday, Nov 3

Speaker: Dr. Daniel L. Mendoza

Research Assistant Professor, Department of Atmospheric Sciences

University of Utah

Title: Black Carbon and Rising Temperatures as Environmental Justice Markers

Abstract:

A changing climate has largely led to an increased number of extreme events including heat waves, wildfires, and dust storms. However, not all groups are affected equally by these events. Lower income and communities of color are generally the most affected by environmental hazards, both due to their proximity to these events, as well as a lower amount of resilient and safe structures or their ability to use them. The Summer of 2021 affected Utah's air quality at a nearly unprecedented level due to ongoing wildfires in the Western U.S. in addition to being one of the hottest summers on record. Further compounding this issue was the beginning of an economic inflationary period deeply affecting the most vulnerable members of society. I will present recent analyses of temperature differences across sociodemographic gradients in addition to black carbon measurements across communities compounded with land use differences. Implications for health and the broad economy will also be discussed as we look toward equitable urban planning and policy outcomes.

Wednesday, Oct 27

Speaker:

Dr. Eric Maloney

Professor, Department of Atmospheric Sciences

Colorado State University

Title: Using the Tropics to Predict the Midlatitudes at 2-4 Week Leads: Current and Future Climate

Abstract:

Tropical heating has been long-known to cause teleconnections to the extratropics. One phenomenon that contributes to such teleconnections is the Madden-Julian oscillation (MJO), which produces eastward-moving pulses of tropical convection across the Indian and west Pacific Oceans that repeats every 40-50 days. We will first show that certain phases of the MJO, when anomalous convection has a dipole-like structure, produce a particularly strong and consistent teleconnection to the north Pacific and Western U.S. These teleconnections modulate precipitation events such as atmospheric rivers that impinge upon the U.S. West Coast. We will then show that recent versions of the NOAA Unified Forecast System exhibit notable West Coast precipitation errors due to a poor MJO simulation, which can be addressed by nudging the tropics to correct the MJO. Finally, how subseasonal teleconnections may change in a future warmer climate will be discussed, including competing effects of MJO changes and midlatitude jet stream changes on teleconnection strength and location. Possible implications of warming-induced MJO changes for east Pacific and Atlantic hurricane prediction will also be mentioned.

Wednesday, Oct 20

Speaker: Dr. Ismail Gultepe, Ph.D

Eng. in Meteorology, Environment and Climate Change Canada Adjunct Professor

Ontario Tech University, Oshawa, Toronto, ONT, Canada

Title: Fog and visibilitly; observations and models

Abstract:

This talk will focus on fog and visibility issues related to marine, continental, and Arctic regions. During the talk, fog types and their microphysical characteristic related to environmental conditions will be summarized and observational techniques will be explained. Then, NWP methods will be discussed with respect to observations and parameterizations.

Wednesday, October 6, 2021

Title: Cold Fog Amongst Complex Terrain (CFACT)

Speaker: Dr. Zhaoxia Pu, Professor and Dr. Sebastian Hoch,  Research Associate Professor

Abstract: 

Cold Fog Amongst Complex Terrain (CFACT)  is a field campaign and science project sponsored by the National Science Foundation (NSF) that investigates cold fog formation and evolution in mountain valleys.  The overarching goals of the CFACT project are to 1) investigate cold fog development and environment conditions in complex terrain with the latest observation technology, 2) improve microphysical parameterizations and visibility algorithms used in numerical weather prediction (NWP) models, and 3) develop data assimilation and analysis methods for current and next-generation (e.g., sub-kilometer scale) numerical weather prediction models. 

The CFACT field campaign will be conducted in Heber Valley, Utah, during January and February 2022, with the support from the NSF Lower Atmospheric Observing Facilities (LAOF), managed by NCAR’s Earth Observing Laboratory. The deployment of a network of ground-based in-situ instruments and remote sensing platforms will help to obtain comprehensive measurements of thermodynamic profiling, cloud microphysics, physical and chemical properties of aerosols, and dynamics of the environment. Comprehensive data analysis, data assimilation, modeling, verification and validation, and predictability studies will be conducted following the field campaign. 

            The seminar will emphasize the science objectives, plans for the field campaign, and ongoing research efforts.

 

Wednesday, September 29, 2021

Title: How the near-ground wind profile influences supercell tornadogenesis

Speaker: Dr. Brice Coffer, Senior Research Scholar, North Carolina State University

Bio: Brice Coffer is a Senior Research Scholar in the Department of Marine, Earth, and
Atmospheric Sciences at North Carolina State University. He most often studies the dynamics of
nontornadic and tornadic supercells, including the impact of low-level winds upon
tornadogenesis (or the lack thereof) and improving forecasting techniques for these storms. He
obtained his BS in meteorology at University of Oklahoma in 2012 and did his post-graduate
studies at NCSU, where he finished his Masters in 2014 and PhD in 2017. Brice has also
worked for the National Severe Storms Laboratory and has participated in a variety of field
projects, including VORTEX2, DC3, IPHEx, PECAN, VORTEX-SE, and the upcoming PERiLS
project in 2022-23.

Abstract: 

What separates seemingly similar supercell thunderstorms which produce tornadoes with those that do not? What are the range of possible outcomes in similar storms in similar environments? Using what we learn from field projects, can we improve the commonly used tornado forecasting parameters? In this presentation, I will discuss observations from scientific storm chasing, high-resolution ensemble modeling of supercells, and recent collaborations with the Storm Prediction Center on operational improvements in supercell tornado forecasting.

Wednesday, September 22, 2021

Title: Quantifying the impact of wildfires on air quality in Western US urban centers: observational analyses and preliminary model results

Speaker: Taylor Wilmot (Ph.D)

Abstract: 

Wildfires are degrading air quality in the Western US during the months of August and September, as revealed by decadal scale trend analyses (2000-2019) of atmospheric composition, wildfire emissions, and fire area burned datasets. Overlap of increasing and statistically significant trends in upper quantile fine particulate matter, organic carbon, and absorption aerosol optical depth highlight the impact of wildfires on air quality in the Pacific Northwest during the month of August. September is characterized by emerging trends across the Pacific Northwest, western Montana, and Wyoming. Trend analyses of wildfire derived PM2.5/burned area are used to identify potential wildfire emission “hotspots” with relevance to human exposure to degraded air quality. The proximity of potential wildfire emission hotspots and extreme air quality trends, as well as their similar spatial shifts from August to September, further supports the hypothesis that wildfires are driving extreme air quality trends in Western US urban centers. Preliminary results from atmospheric transport modeling for a test site in Spokane, Washington support partial attribution of air quality trends at this site to wildfire sources, while also pointing to observationally determined wildfire emissions hotspots as being relevant PM2.5 sources on a regional scale. Initial results of wildfire plume rise modeling, related to developing work on a more sophisticated atmospheric modeling approach, suggest potential hotspots and mountainous ecoregions across the Western US are exhibiting trends toward enhanced plume top heights and PM2.5 injection aloft.

Wednesday, September 22, 2021

Title: Quantifying the impact of wildfires on air quality in Western US urban centers: observational analyses and preliminary model results

Speaker: Taylor Wilmot (Ph.D)

Abstract: 

Wildfires are degrading air quality in the Western US during the months of August and September, as revealed by decadal scale trend analyses (2000-2019) of atmospheric composition, wildfire emissions, and fire area burned datasets. Overlap of increasing and statistically significant trends in upper quantile fine particulate matter, organic carbon, and absorption aerosol optical depth highlight the impact of wildfires on air quality in the Pacific Northwest during the month of August. September is characterized by emerging trends across the Pacific Northwest, western Montana, and Wyoming. Trend analyses of wildfire derived PM2.5/burned area are used to identify potential wildfire emission “hotspots” with relevance to human exposure to degraded air quality. The proximity of potential wildfire emission hotspots and extreme air quality trends, as well as their similar spatial shifts from August to September, further supports the hypothesis that wildfires are driving extreme air quality trends in Western US urban centers. Preliminary results from atmospheric transport modeling for a test site in Spokane, Washington support partial attribution of air quality trends at this site to wildfire sources, while also pointing to observationally determined wildfire emissions hotspots as being relevant PM2.5 sources on a regional scale. Initial results of wildfire plume rise modeling, related to developing work on a more sophisticated atmospheric modeling approach, suggest potential hotspots and mountainous ecoregions across the Western US are exhibiting trends toward enhanced plume top heights and PM2.5 injection aloft.

Wednesday, September 19, 2021

Title: Peering at Hazy Worlds Near and Far Through Laboratory Experiments

Speaker: Sarah Moran (NASA/Ames)

Abstract: 

Photochemical hazes are found across the Solar System and in exoplanetary atmospheres, with important effects on atmospheric chemistry and subsequent possible impacts on observations. These affect current observatories like Hubble, future observatories like JWST, as well as potential upcoming planetary missions. I will present results of the composition of haze particles produced from exoplanet and Triton laboratory studies in the JHU PHAZER laboratory. With high resolution mass spectrometry, we detected many complex molecular species in the haze particles, including those with prebiotic applications. I will also discuss the implications of these chemical measurements as they compare to existing atmospheric models of exoplanets. Our experimental exoplanetary haze analogues exhibit diverse physical properties, which may help us understand their role as potential cloud condensation nuclei and their role in subsequent atmospheric evolution. Finally, I will discuss how we can apply what we’ve learned from the laboratory into atmospheric models for existing and future observations of sub-Neptune-sized exoplanets as well as Neptune's moon, Triton.

Wednesday, September 15, 2021

Title:  Enhancing prediction of landfalling hurricanes through advanced data assimilation and improved PBL parameterization

Speaker: Zhaoxia Pu

Abstract: 

Under global climate change, hurricanes are becoming more dangerous. Landfalling hurricanes especially have significant societal and economic impacts. However, accurate prediction of hurricane landfall time, location, inland precipitation, and wind gusts remain a challenge in operational forecasting. This seminar summarizes our recent studies in enhancing the prediction of landfalling hurricanes through advanced data assimilation and improved physical parameterization schemes in computer models. Our most recent efforts on research to operational (R2O) transition with NCEP regional Hurricane Weather Research and Forecasting system will be highlighted.

Wednesday, September 8, 2021

Title: An Evolving NWS and Student Internship Opportunities

Speaker: Jon Rutz

Abstract:

The National Weather Service (NWS) is undergoing a revolution as new scientific and technological advances lead us to modernize our forecast process and change our institutional culture. The importance of ensemble-based data sets and probabilistic thinking is increasing our ability to provide actionable decision support services to our partners and the public, but also presents a steep learning curve for new and current employees. While meteorology will always be the backbone of our organization, meteorological knowledge is no longer sufficient for beginning or maintaining a successful NWS career. Greater value is now placed on complementing the traditional meteorological skill set with additional skills in areas such as statistics, computer programming, communication, and others. This leads to considerations for which skills should be prioritized and deprioritized, for those who wish to pursue NWS employment.

The NWS Western Region Science and Technology Infusion division is an exciting workplace, with a chance to lead many of the changes described above. We periodically have openings for internship positions that offer non-competitive placement within the NWS upon completion and expect such an opening Jan-Apr 2022. We will highlight some past student projects and we especially encourage students to attend and ask questions about the program.

Wednesday, September 1, 2021

Speaker: Atmospheric Sciences Grad

 

Wednesday, August 25, 2021

Speaker: Atmospheric Sciences Faculty

Abstract: This seminar will be the Department Research Group Introductions. Learn more about the U's ATMOS resarch groups .

Spring 2021  
  

 Wednesday, January 27, 2021

Seminar begins at 3:00pm
Speaker: Dr. Michael Williams, University of Missouri, Department of Educational Leadership & Policy Analysis
Title: Mentoring Minoritized Students and How to Create a Supportive Mentoring Environment

Wednesday, January 20, 2021

Seminar begins at 3:00pm
Speaker: Dr. Akua Asa-Awuku, University of Maryland, Chemical and Biomolecular Engineering
Title:  Aerosols or Droplets? Fundamental Particles in our Evolving World

Wednesday, December 2, 2020

Seminar begins at 3:00pm
Speaker: Dr. Anna Gannet Hallar, University of Utah, Department of Atmospheric Sciences
Title: Storm Peak Laboratory: 40+ Year History of this Mountain-Top Research Facility

Abstract: Storm Peak Laboratory (SPL), located near Steamboat Springs, CO, is an internationally recognized high-elevation research station that has been used for 40 years. Most recently, SPL is in the process of transferring operations to the University of Utah from the Desert Research Institute. To date, research at SPL has produced over 140 peer-reviewed publications. Cloud and aerosol measurements began at the Steamboat Springs Ski Resort in northwestern Colorado in 1979. Today’s permanent mountaintop facility underwent an NSF-funded extensive remodel and expansion in 2012, making it easily accessible for researchers, teachers, and students of all abilities. SPL has a full kitchen and overnight living accommodations for 11 people. SPL operates under a special use permit from the U.S. Forest Service, and Gannet Hallar has served as the Director of SPL for 14 years.

Wednesday, November 18, 2020

Seminar begins at 3:00pm
Speaker: Dr. Peter Caldwell, LLNL
Title: Moving from Circulation-Resolving to Cloud-Resolving Scales in the E3SM Model

Abstract: The Energy Exascale Earth System Model (E3SM) was created in 2014 to address US Department of Energy’s climate-change questions. Its debut model release performed well in the CMIP6 intercomparison but suffered from biases typical of CMIP-class models. Increasing atmospheric resolution from 100 km to 25 km reduced some but not all of these biases. With upcoming GPU architectures, climate model resolution can now be further refined to 3 km. This move to even higher resolution has huge potential benefits because it allows deep convective motions and associated process interactions – long known to be a major source of model bias and climate change uncertainty in lower-resolution climate models – to be explicitly simulated. In this talk, I’ll describe the development of the E3SM model, its resolution sensitivity, and ongoing efforts to create a global model which explicitly simulates deep convection.

Seminar recording below:

Wednesday, November 11, 2020

Seminar begins at 3:00pm
Speaker: Dr. Annarelli Morales, NCAR ASP
Title: Exploring Environmental and Microphysical Controls on Orographic Precipitation

Abstract: Orographic precipitation provides a substantial source of freshwater to communities worldwide, while also posing hydrometeorological and socioeconomic risks. Understanding where, how much, and what type of precipitation will occur remains a forecasting challenge. The environmental conditions upstream of a topographical barrier can bring the ingredients necessary for precipitation, but once clouds form over mountain slopes, the details become more complex as hydrometeors form and interact with each other and their environment. To understand better the environmental and microphysical controls on orographic precipitation, novel sensitivity analysis (SA) methods are applied to idealized simulations of moist neutral flow over a bell-shaped mountain using a high-resolution cloud model (CM1) and testing various environmental conditions (e.g., horizontal wind speed) and microphysical parameters (e.g., snow fallspeed coefficient). These SA methods include 1) the Morris-one-at-a-time (MOAT) method exploring interactions between a large set of parameters through multivariate perturbations, providing a subset of the most important or sensitive parameters; and 2) a Markov chain Monte Carlo (MCMC) algorithm to explore a large parameter space efficiently, gaining insight into environmental and microphysical parameter interactions and relationships. This presentation will introduce these SA methods and their application to the study of orographic precipitation, present results and major conclusions from two recent studies, and discuss open questions that remain to be explored.

Wednesday, November 4, 2020

Seminar begins at 3:00pm
Speaker: Dr. Heather Holmes, University of Utah, Department of Chemical Engineering
Title: Modeling the Spatial Distribution of Air Pollution Concentrations in the Western U.S.

Abstract: Air pollution is the top environmental risk factor impacting human health globally. Cities in the western U.S. have the worst air quality in the country, especially for PM2.5 (particulate matter less than 2.5mm in diameter). Nearly 78 million people live in the western U.S. and growth continues as this region experiences rapid population increase. While the population density is low and correspondingly there should be fewer sources of anthropogenic air pollution, many areas in the western U.S. are currently violating the federal air pollution standard. This is exacerbated by unique air pollution sources (e.g., windblown dust and wildfire smoke) and the local meteorological and orographic effects in the Intermountain Region. The mountainous terrain and elevation changes create synoptic weather patterns that lead to complex winds and atmospheric mixing that impact air pollution transport, dispersion, and accumulation. This talk will discuss the limitations of satellite remote sensing, numerical weather prediction, and chemical transport modeling and focus on two key drivers impacting pollutant concentrations: wildfire smoke and temperature inversions. 

Seminar recording below:

Friday, October 30, 2020

Seminar begins at 3:00pm
Speaker: Dr. Marcus Hultmark, Associate Professor of Mechanical and Aerospace Engineering, Princeton University https://engineering.princeton.edu/faculty/marcus-hultmark 
Title:Laboratory Studies of Wind Turbines – High Reynolds Number Aerodynamics

Abstract:
Wind turbines and wind farms present unique challenges, fluid mechanically, as they combine extremely high Reynolds numbers with additional time scales imposed by the rotation, and three-dimensional effects. This implies that resolved numerical solutions are too computationally expensive and investigations in conventional wind tunnels are impossible due to the flow speeds and rotational rates needed in order to satisfy the dynamic similarity requirements. At Princeton, we achieve the conditions a large wind turbine experiences, experimentally, by compressing the air around a model-scale turbine up to 238 bar. This yields conditions similar to those experienced by a field-sized turbine using a model that is only 20cm in diameter. Using pressure enables tests at high Reynolds numbers but at low velocities, which implies that realistic non-dimensional frequencies can be tested even with such a small model. The power output and forces are investigated over an unprecedented range of Reynolds numbers, and it is shown that aerodynamic scale-effects persist at higher Reynolds numbers than previously believed, and that the boundary layer state is critical for turbine performance. We use nanoscale hot-wires to investigate the wake created by the wind turbine to investigate the flow structures and shear layers in the wake, as well as trends with Reynolds number.

Wednesday, October 21, 2020

Seminar begins at 3:00pm
Speaker: Dr. Rodman Linn, Los Alamos National Laboratory
Title: Process-Based Fire/Atmosphere Modeling to Advance Wildland Fire Science and Assist Decision Makers

Abstract: Advancements in computing and numerical modeling have generated new opportunities for the use of coupled fire/atmosphere models in wildfire research. Models such as FIRETEC attempt to represent the interaction between dominant processes that determine wildfire behavior, including: convective and radiative heat transfer, aerodynamic drag and buoyant response of the atmosphere to heat released by the fire.  Models such as FIRETEC are not practical for operational faster-than-real-time fire prediction due to their computational and data requirements.  However, their process-based model-development approach creates an opportunity to provide additional perspectives concerning aspects of fire behavior that have been observed in the field and in the laboratory; allow for sensitivity analysis that is impractical through observations and pose new hypothesis that can be tested experimentally.  Certainly, there needs to be continued efforts to validate the results from these numerical investigations, but, even so, they suggest relationships, interactions and phenomenology that should be considered in the context of the interpretation of observations, design of fire behavior experiments, development of new operational models and even risk management.  From what we have learned so far from models like FIRETEC and field experiments we have developed a fast-running coupled fire/atmosphere model QUIC-Fire, attempts to capture some of the most important impacts of the processes with a wildland fire.  Early results from QUIC-Fire provide and illustration of the potential gains for decision support tool from emphasizing the coupled fire/atmosphere interaction winds.

Seminar recording below:

Wednesday, October 14, 2020

Seminar begins at 3:00pm
Speaker: Dr. Xiyue (Sally) Zhang, NCAR ASP
Title: Seasonal Cycle of Polar Clouds and Their Response to Climate Change

Abstract: The uncertainty in polar cloud feedbacks calls for process understanding of cloud response to climate warming. As an initial step, we investigate the seasonal cycle of polar clouds by adopting a novel modeling framework using large eddy simulations (LES), which explicitly resolve cloud dynamics. Resolved horizontal and vertical advection of heat and moisture from an idealized GCM are prescribed as forcing in the LES. The LES are also forced with prescribed sea ice thickness, but surface temperature, atmospheric temperature, and moisture evolve freely without nudging. We show that the LES closely follow the GCM seasonal cycle in the current climate, and the seasonal cycle of low clouds in the LES resembles observations in the Arctic: maximum cloud liquid occurs in late summer and early autumn, and winter clouds are dominated by ice in the upper troposphere. Large-scale advection of moisture provides the main source of water vapor for the liquid clouds in summer, while a temperature advection peak in winter makes the atmosphere relatively dry and reduces cloud condensates. In a warmer climate, we found a significant decrease of the low-level clouds during summer and autumn, while liquid clouds increase at all levels in spring and winter. Offline radiative transfer calculations estimate a positive cloud feedback that is dominated by longwave radiative feedback. Furthermore, we explore the role large-scale circulation plays in governing polar cloud changes with warming in a comprehensive GCM (CESM1).

Seminar recording below:

Monday, October 12, 2020

Thesis defense begins at 3:00pm
Speaker: M.S. Candidate Brittany Welch
Title: Evaluating Image Derived Estimates of Visibility and Pavement Condition

Abstract: Winter weather leads to hazardous driving conditions nationwide that requires state transportation departments to spend millions of dollars for road maintenance. Those agencies maintain Road Weather Information Systems to transfer and process data from Environmental Sensor Stations (ESS) that monitor weather and pavement conditions continuously. However, the hundreds of ESS across Utah, Wyoming, and Colorado are insufficient by themselves to monitor completely the extensive road networks in those states.
State transportation agencies also invest heavily in video camera systems installed along roadways to monitor traffic flow and road state. Monitoring streaming video and still camera images from hundreds of cameras is a time-consuming task for agency staff during winter storms. Commercial products, such as the Helios® Real-time Ground Weather Intelligence System of the Harris Corporation, apply automated image processing techniques to transportation camera networks to help monitor adverse weather and pavement conditions.
The objective of this study is to help assess whether image-derived estimates of visibility and road state have sufficient accuracy to potentially reduce transportation agency staff workloads and help reduce winter road maintenance costs. Observations from ESS are compared to Helios® camera-based estimates of visibility and pavement conditions during the 2018-2019 and 2019-2020 winters in Utah, Wyoming, and Colorado. Aggregate statistics across each state revealed that while Helios has high accuracy during low impact, high traction road weather conditions, the product had lower accuracy for high impact, low traction situations. Case studies and cumulative statistics based on over 400,000 estimates of visibility and 150,000 estimates of road state helped identify common situations where Helios’ ability to estimate pavement state could be improved by, for example, reducing the number of Dry road reports when the prior image is missing, and improved treatment of rapid road state transitions, moving or zooming cameras, sun glare, or obscured camera images.

Defense recording below:

Wednesday, October 7, 2020

Seminar begins at 4:00pm
Speaker: Spencer Donovan and Dhiraj Singh - Department of Mechanical Engineering
Title: Turbulence and Snowflakes

Contact Holly Moreno (holly.moreno@utah.edu) to gain access to the seminar

Wednesday, September 30, 2020

Seminar begins at 3:00pm
Speaker: Dr. Bill Anderegg, University of Utah
Title:  Leveraging plant physiology to improve carbon cycle projections and land-atmosphere feedbacks

Abstract: Widespread forest mortality events of many tree species in the last two decades prompt concerns that drought, insects, and wildfire may devastate forests in the coming decades. We study how drought and climate change affect forest ecosystems, including tree physiology, species interactions, carbon cycling, and biosphere-atmosphere feedbacks. This research spans a broad array of spatial scales from xylem cells to ecosystems and seeks to gain a better mechanistic understanding of how climate change will affect forests around the world.

Seminar recording below: 

Wednesday, September 23, 2020
Seminar begins at 3:00pm
Speaker: Dr. Sisi Chen, National Center for Atmospheric Research (NCAR)
Title:  Formation of Clouds and Rain: Cloud-Aerosol-Turbulence Interactions in Natural and Seeded clouds

Abstract:Clouds are turbulent in nature, and aerosol particles are the major cloud condensation nuclei. Interactions between aerosols, cloud droplets and turbulence happen at a broad spectrum of spatial scales, which are unable to be fully-resolved in current weather and climate models. The microphysical processes at scales smaller than a grid-box of a large-eddy-simulation (LES)
are in fact key to the formation of clouds and rain. This talk looks at the microphysical processes using a high-resolution cloud model called direct numerical simulation (DNS). The DNS is capable of resolving the finest scales of turbulent flows and tracking the motion and growth of millions of aerosols and droplets. With its high accuracy, DNS provides a process-level understanding of the effect of aerosol and turbulence on the evolution of clouds, which can help improve microphysical parameterizations in models of larger scales. The model is also beneficial to field experiments such as cloud seeding as it provides detailed information which is challenging to be measured due to the limitation of current instruments.

Seminar recording below:

Wednesday, September 16, 2020
Seminar begins at 3:00pm
Speaker: Dr. John Lin, University of Utah
Title:  Adventures in Taiwan: How I spent my sabbatical in the midst of COVID-19

About the Speaker: Dr. John Lin is a Professor in the Department of Atmospehric Sciences at the University of Utah. His research focuses on the exchange of greenhouse gases and pollutants between the land surface and the atmosphere. He leads the "Land-Atmosphere Interactions Research" (LAIR) group, where they make use of computer models of the atmosphere to interpret observations. Professor Lin is also the founding member of the Utah-Atmospheric Trace gas & Air Quality lab ("U-ATAQ"), which carries out observations of greenhouse gases and air quality throughout Utah.

Seminar recording below:

Wednesday, September 2, 2020
Seminar begins at 3:00pm
Speaker: Dr. Ian Glenn, Post Doc, University of California Los Angeles  
Title: Not as bright as you might expect: An aerosol-cloud brightening investigation

Abstract: Clouds could be brightened by the addition of aerosol, if that aerosol acts as cloud condensation nuclei (CCN) and increases the total number of cloud drops, thus reflecting more sunlight (assuming the total amount of liquid remains constant). But aerosol interactions with clouds are realized in nature with considerable concurrent meteorological variability. Due to the implications for mitigation of climate warming, an important research challenge is to disentangle the radiative effects of aerosol and other meteorological drivers that can also change the total cloud amount and brightness at the same time. To this end, I performed large eddy simulations of non-precipitating shallow cumulus constrained by observations at a continental site in Oklahoma. These simulations include the variability of different meteorological states on days with different aerosol conditions. I used a statistical “mutual information” analysis which suggested that meteorological variability masks the strength of the relationship between aerosol-induced CCN variability and the total amount of sunlight reflected by the clouds. I will show that this is mostly due to variation in the horizontal heterogeneity of the simulated cloud fields. Put simply, a field of many slightly different clouds can never be brightened by aerosol variability as much as a cloud with a homogeneous distribution of thermodynamic properties. If one were to assume that a field of clouds behaved as if they had homogeneous properties when affected by aerosol, as in some recent work, this would lead to a consistently positive albedo bias. I have developed an analysis framework that allows the implementation of an albedo bias correction, and quantitatively isolates the radiative effect of aerosol-cloud-interactions from other meteorological effects in simulations of shallow cumulus. This work ultimately implies that artificially increasing aerosol concentrations to attempt to mitigate CO2 climate warming is just not that bright of an idea.

 Seminar recording below: