| Date | Time | Seminar TItle | Presenter(s) | Affiliation(s) | Location |
|---|---|---|---|---|---|
| Jun 17, 2021 (Thu) | 3:30pm | TBD (*MMM Distinguished Lecturer) | *Dr. David Henderson | James Cook University, Australia | FL2-1022 Large Auditorium |
Title: Current Advances in Urban Hydrometeorological Research at the University of Georgia
Speaker: Dr. Marshall Shepherd, University of Georgia
Date: Thursday, 16 July 2020
Time: 3:30pm - 4:30pm MST
If you would like to join us by Zoom, please contact Nancy Sue Kerner for access, nskerner@ucar.edu.
Abstract:
Dr. Shepherd is a leading scholar studying aspects of hydrometeorological extremes, urban climate, and societal implications. Dr. Shepherd has advanced understanding of how urbanization, precipitation and convection are related. For this work, he has received the 2004 Presidential Early Career Award for Scientists and Engineers (PECASE) and the 2018 Helmut Landsberg Award. In this lecture, Dr. Shepherd will layout what we know about urban effects on precipitation and convective processes and where the research is headed in the future. He'll draw on past literature, research, and ongoing projects. Where relevant, Dr. Shepherd will also tie the basic research together with opportunities for applications and assessment of societal risk.
For more information contact Nancy Sue Kerner, nskerner@ucar.edu.
MMM Seminar - Thursday, April 23, 2020 - 3:30pm
Speaker: Gary Lackmann
Affiliation: North Carolina State University
Extratropical persistent flow anomalies (PAs), a subset of which are known as “blocking” events, are often associated with high-impact weather. Flooding, wildfires, heat waves, droughts, and cold-air outbreaks can be associated with PAs. These events can take place throughout the annual cycle, therefore, methods for their objective identification must be effective in all seasons. Despite their importance to society, the question of how the frequency, intensity, and duration of PAs will respond to climate change remains an open question. This is due in part to the complexity of this multifaceted phenomenon. Previous work has proposed increases in blocking and PA activity due to Arctic amplification. We can also hypothesize that the subset of blocking events resulting from latent heat release would to increase in frequency and intensity with warming owing to larger vapor content. Other GCM-based studies have found decreases in the frequency of blocking in warmer climates, while several studies have identified serious deficiencies in GCM representation of blocking. How will PAs change in a warmer climate?
Here, we present a new PA index, extending the method of Dole and Gordon (1983) to increase versatility. We apply this index to a reanalysis dataset, seeking trends in PA activity. We next examine changes in PA characteristics between the present climate and projected end-of-century conditions using high-resolution time-slice simulations from the Model for Prediction Across Scales (MPAS). In the future MPAS simulations, the Arctic Ocean is nearly devoid of autumn sea ice, making these runs ideal for studying the influence of Arctic amplification on midlatitude PA activity. Finally, we use an idealized oceanic channel model to study bivariate sensitivity of PAs to domain-average temperature and to baroclinicity (jet strength).
Using the ERA Interim reanalysis, we identify only weak trends in both positive and negative PA activity, including both annual and seasonal values. Results from the MPAS and channel model experiments will be shared at the seminar, because we would not want the abstract to give away all of the punchlines!
virtual seminar https://www.ucar.edu/live?room=fl21022
Viewers may submit their questions throughout the presentation to: Judith Berner; berner@ucar.edu
MMM Seminar - Thursday, March 12, 2020 - 3:30pm
Speaker: Janice Coen
Affiliation: NCAR/MMM
Large, destructive wildfires have become prevalent across the western U.S. and other fire-prone areas yet the mechanisms through which a specific fire became large and what environmental factors were important, particularly in light of varying climate, are frequently not understood. The most extreme events frequently lie at an end of a spectrum. At one end, fire growth is driven by strong ambient winds and is characterized by practitioners as a "wind-driven" event. At the other end of the spectrum, fire growth amplifies due to an internal feedback loop in which winds are generated by heat released by the fire itself ("plume-driven" events). The limitations of current generation operational fire models in simulating extreme fires in particular has enhanced perceptions that fire behavior has become more unpredictable.
Progress has been made in understanding and predicting fire behavior by recognizing wildland fires and the atmosphere in which they occur as a fluid dynamical system. We draw from convective-scale (hundreds of meters horizontal grid spacing) simulations of the weather leading up to and fire growth during exceptional wildfire events exemplifying each type with the CAWFE? coupled weather-wildland fire modeling system using satellite active fire detection data and airborne fire mapping to initialize and evaluate event simulations. Results show that even extreme fire behavior may be modeled, provided that fine-scale circulations are well represented and fire feedbacks upon circulations are included. Large, destructive wildfires may be driven by internal feedbacks or small-scale circulations thus may surprise due to the lack of apparent ambient triggers or exceptional conditions. In fires occurring during California wind events, while mesoscale weather forecasts capture broad spatial patterns of accelerated winds, CAWFE simulations that refine to convective scales show common factors such as a shallow river of fast-moving stable air but several different types of dynamic microscale flow regimes, where ignitions and rapid early fire growth appear linked to microscale phenomena and wind extrema coincident with ignitions attributed to electrical system anomalies. We examine our collective ability to reproduce extreme events and the challenges and limitations in our remote sensing systems, fire prediction tools, and meteorological models that add to events' mystery and apparent unpredictability.
Refreshments: 3:15 PM
MMM Seminar - Thursday, March 5, 2020 - 3:30pm
Speaker: Andrew C. Winters
Affiliation: University of Colorado
The atmosphere often exhibits a three-step pole-to-equator tropopause structure, with each break in the tropopause associated with a jet stream. The polar jet stream (PJ) typically resides in the break between the polar and subtropical tropopause and is positioned atop the strongly baroclinic, tropospheric-deep polar front at ~50°N. The subtropical jet stream (SJ) resides in the break between the subtropical and the tropical tropopause and is situated on the poleward edge of the Hadley cell at ~30°N. On occasion, the latitudinal separation between the PJ and the SJ vanishes, resulting in a vertical jet superposition. Prior case study work indicates that jet superpositions are often attended by a dynamical and thermodynamic environment that is particularly favorable for the development of high-impact weather. Furthermore, this prior work suggests that there is considerable variability among antecedent environments conducive to jet superpositions. These considerations motivate a comprehensive examination of the relative importance of dynamical processes that operate within the double-jet environment to produce jet superpositions.
This study focuses on the identification of North American jet superposition events in the Climate Forecast System Reanalysis dataset during November–March 1979–2010. Jet superposition events are classified into three characteristic types: “Polar Dominant” events consist of events during which only the PJ is characterized by a substantial excursion from its climatological latitude band; “Subtropical Dominant” events consist of events during which only the SJ is characterized by a substantial excursion from its climatological latitude band; and “Hybrid” events consist of events characterized by an excursion of both the PJ and SJ from their climatological latitude bands. Following their classification, frequency distributions are constructed to highlight the geographical locations most often associated with jet superpositions within each event type. Composite analyses are also constructed in an effort to illuminate the dominant dynamical processes that support the production of jet superpositions for each event type. Predicated on the results from the preceding analyses, the relevance of jet superpositions to the development of high-impact weather within a changing climate is discussed.
Refreshments: 3:15 PM
MMM Seminar - Thursday, February 27, 2020 - 3:30pm
Speaker: Zeljka Fuchs-Stone
Affiliation: Director, Climate and Water Consortium, New Mexico Tech
The OTREC (Organization of Tropical East Pacific Convection) field project took place from August 5 to October 3, 2019. The operational center was in Liberia, Costa Rica. During OTREC, we performed 127 research flight hours in the area of the Eastern Pacific and Southwest Caribbean. We deployed 665 dropsondes in a grid to evaluate mesoscale thermodynamic and vorticity budges. We also used the Hiaper Cloud Radar to determine the characteristics of cloud populations. Both of these tools were deployed from the NSF/NCAR Gulfstream V aircraft.
The Eastern Pacific has a strong meridional gradient in sea surface temperature. The southwest Caribbean exhibits uniform ocean temperatures. The two regions together provide a broad range of atmospheric conditions and a great deal of diversity in convective behavior.
The main goal of the project was to study deep convection in diverse environments to improve global weather and climate models. In this talk I will present an overview of OTREC, the highlights of the field project and the preliminary results that include the thermodynamics of the environment and the vertical mass flux profiles.
*MMM Seminar - Thursday, February 20, 2020 - 3:30pm
*Please note special location - FL2-1001/Small Auditorium
Speaker: Samuel Childs
Affiliation: Colorado State University
Eastern Colorado is one of the most active hail regions in the U.S., and recent damaging events have affirmed the need for improved prediction of hailstorm characteristics and effective warning communication. This work offers a multidisciplinary synthesis of eastern Colorado (37-41°N, 102-105.3°W) hailstorms. Climatologically, severe (1.0 in+) hail reports and days are increasing across the domain since 1997, although hail is preferentially reported where people live or drive. Still, the upward trend in hail days is not seen in the national record. To estimate how the frequency and spatial distribution of hailstorms across eastern Colorado may change by the end of the 21st century, threshold exceedances of convective proxies for severe hail reports are compared between control and future high-resolution dynamically-downscaled WRF simulations. An increase of up to 3 severe hail days per year is projected by the period 2071-2100, with the highest increase across the north-central eastern Plains. These projections, paired with high-resolution population projections taken from the Shared Socioeconomic Pathways, are input into a Hail Monte Carlo model, which predicts an increase in human exposure up to 178% by 2100. Results are sensitive to the overlap between future population and meteorological projections, however, and simulations that predict decreasing human exposure have a corresponding increase in agricultural exposure due to hailstorm frequency increasing most in places where population is not expected to grow. An interview study conducted in Summer 2019 with eastern Colorado agriculturalists revealed feelings of anxiety and dejection from hailstorms due to the financial losses incurred. Farmers also highlighted that small hail, either in large volume or driven by a strong wind, is most damaging to crops, which is contrast to the 1.0 in severe threshold used by the NWS. Results from this work are bringing awareness of the vulnerabilities faced by the agricultural sector and inspiring continued research into hail prediction.
Refreshments: 3:15 PM
MMM Seminar - Thursday, February 13, 2020 - 3:30pm
Speaker: Chris Riedel
Affiliation: University of Oklahoma
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 are features that 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 high forecast uncertainties associated with them. 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 are used in order to evaluate the impact of this identified systematic bias and help elucidate TPV forecast sensitivity to initial states.
Refreshments: 3:15 PM
MMM Seminar - Thursday, February 6, 2020 - 3:30pm
Speaker: Ian Bolliger
Affiliation: UC Berkeley
Hurricanes are one of the costliest natural disasters, imparting over $50 billion in losses per year in the U.S. alone. Because each event can cause significant immediate damage, as well as long-lasting negative impact, the resilience of coastal regions depends crucially on quantifying the present and future risk of hurricane-driven economic losses. In this study, we construct and apply an open-source, physical-econometric catastrophe model that directly simulates high-resolution storm surge and wind from >100,000 real and synthetic storm events, accounting for probabilistic local sea level rise. We merge this hazard model with a property sale price dataset for all U.S. properties and insurance claims data from historical storms to empirically derive a damage function for both of these hazards. We then project damages from 1980-2100 using seven climate models, two emissions scenarios, and 100 stochastic realizations of each hurricane season. We use the distribution of realized losses to quantify how hurricane risk has changed across the Atlantic and Gulf coastlines over the past 35 years and how it may change over the next century. Preliminary results suggest that the U.S. economic risk from hurricanes may have grown by as much as 100% relative to a 1980s baseline and may further grow another 300% by the end of the century, under RCP 8.5. These results have informed reports and regulation from Blackrock Investment Institute, the First Street Foundation, the American Flood Coalition, and the Bank of England, each of which seek to better account for changing hurricane patterns in assessing risk to their assets and/or population.
Refreshments: 3:15 PM
*MMM Seminar - Thursday, January 30, 2020 - 3:30pm
*Please note special location - FL2-1001/Small Auditorium
Speaker: Xiaoxu Tian
Affiliation: University of Maryland
A four-dimensional variational (4D-Var) vortex initialization (VI) system is developed for a nonhydrostatic axisymmetric numerical model with convection accounted for (the RE87 model). Derivations of the tangent linear and adjoint models of the RE87 model and the correctness checks are presented. As an initial evaluation of the 4D-Var VI system, a cost function that measures the model fit to satellite microwave retrievals of tropical cyclone (TC) warm-core temperatures and total precipitable water (TPW) from the following four polar-orbiting satellites within a slightly longer than 1-h assimilation window is minimized using the limited-memory quasi-Newton minimization algorithm: the Suomi National Polar-orbiting Partnership, NOAA-20, Fengyun-3D, and Global Change Observation Mission – Water Satellite 1. An azimuthal spectral analysis in cylindrical coordinates centered on the TC centers shows that the warm core and TPW fields within TCs are dominated by the axisymmetric component. The 4D-Var VI results assimilating the axisymmetric component of the above satellite retrievals produced a significant reduction in the cost function and the norm of the gradient as the minimization process is completed. The gradient of the cost function is accurately computed by a single integration of the RE87 adjoint model. In the cases of Hurricane Florence and Typhoon Mangkhut, improved forecast of intensifications and more realistic vertical structures of all model state variables (e.g., temperature, water vapor mixing ratio, liquid water content mixing ratio, tangential and radial wind components, and vertical velocity) are obtained when compared with a parallel run initialized simply by the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis.
Refreshments: 3:15 PM
MMM Seminar - Thursday, January 23, 2020 - 3:30pm
Speaker: Forrest J. Masters
Affiliation: University of Florida
The presentation will offer a forward-looking perspective that the civil (wind) engineering and atmospheric science fields are poised to reverse this trend by leveraging recent advancements in automation, data fusion and machine learning, heterogenous computing, multi-modal sensing, and other technologies reinventing modalities for scientific research and technology transfer. To build that case, we will begin by exploring the evolution of field reconnaissance efforts in landfalling Atlantic tropical cyclones to characterize the intensity and structure of damaging winds and how it is has influenced complementary research in atmospheric boundary layer wind tunnels (BLWTs). Key highlights will include activities and findings originating from the Florida Coastal Monitoring Program (which has led field experiments in 34 storms, including Harvey, Michael, and Dorian) and the Digital Hurricane Consortium, which represents the broader community of landfall experimentalists that deploy anemometry, mobile doppler radars, and storm surge/wave sensors.
The presentation will then explore cyber physical wind engineering experiments conducted in the NSF Natural Hazards Engineering Research Infrastructure (NHERI) BLWT using its computer-controlled terrain generator (the “Terraformer”) and other exciting new technologies that are reinventing the conventional design-build-test paradigm. Examples will include mechatronic building modeling to optimize the design of wind sensitive structures and the development of a new 300+ fan system to simulate non-stationary and non-neutral flows for the study of bluff-body aerodynamics in unsteady winds, flows over geomorphically complex terrain, and internal boundary layer formations. All systems are available for use by NCAR. Information will be given about how to access these resources as well as the lab/field data.
The presentation will conclude with remarks about how these research activities interrelate with the rapid transformation now taking place at engineering campuses worldwide, which is being driven by the so-called 4th Industrial Revolution (i.e., the integration of artificial intelligence, robotics, and the internet of things into industry and mainstream life), reduced barriers to adopt technology, and the emergence of student bodies that are increasingly more prepared for living and working in a “digital” world than previous generations. The perceived ripple effect on atmospheric science will then be discussed from an engineering perspective, with the goal of identifying opportunities in a future where data streams are sufficiently rich and forecasting tools are sufficiently skilled that the role of the “human in the loop” is far diminished by today’s standards.
Refreshments: 3:15 PM
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