Current Visiting Fellows
The formation of surface lakes on Antarctic ice shelves and their impact on ice-shelf stability
Alison Banwell is a glaciologist collaborating with Waleed Abdalati at CIRES and Ted Scambos at NSIDC. Her project uses a combination of modeling, satellite remote sensing, and field-derived data analysis to investigate the formation of surface lakes on Antarctic ice shelves, and the effects of those lakes on ice-shelf stability. This is important because the most likely way for the Antarctic Ice Sheet to contribute to sea level rise over the coming centuries involves the breakup of its ice shelves, which buttress approximately 75% of the ice sheet’s edges and currently prevent the rapid discharge of inland ice into the ocean. A trigger of ice-shelf disintegration is thought to be surface-stress variations associated with surface meltwater ponding and draining, causing ice-shelf weakness, flexure, and potential fracture. For example, the widespread break-up of the Larsen B Ice Shelf in 2002 may have been partially triggered by the drainage of over 2500 surface lakes.
Identifying the Dynamics of Vulnerability in Community Water Usage along the Front Range
Jen Henderson will work with CIRES Fellow Lisa Dilling, Director of the Western Water Assessment, and Rebecca Morss and Olga Wilhemi, of NCAR, to understand the complex nature of water-related vulnerabilities that arise in communities preparing for climate change and climate variability. She will study these dynamics of vulnerability through a qualitative, empirical analysis of current and future water use and management practices for two mid-size cities in Colorado. Henderson hypothesizes that this work will reveal how adaptations made to water use strategies in one place within the system may have unintended, and perhaps unseen, consequences at another point in the system. Research questions at the heart of this project ask the following: What does vulnerability mean for different stakeholder and lay publics? How is the term vulnerability itself taken for granted in ways that exclude specific demographics or problems? How do these vulnerabilities shift and migrate, or spill over to different sectors, as communities adopt mitigation strategies and build adaptive capacities for climate variability? By looking at different stressors these communities experience, she hopes to make visible groups that have become more vulnerable to water issues and reveal common problems that transcend the situatedness of a particular issue and relevant dissimilarities that result in vulnerabilities of different types and scope. Henderson is looking forward to working with scholars in Boulder and communities across the Front Range to advance an understanding of local climate related impacts and offer decision makers a valuable analysis of emerging vulnerabilities.
Entrainment and Mixing in Shallow Convective Clouds
Fabian Hoffmann is working with Graham Feingold, and others at CIRES and NOAA, to broaden our understanding of clouds in the climate system. He focuses on the process of entrainment and mixing, i.e., the engulfment of cloud-free air into clouds. This processes affect the micro- and macrophysical properties of clouds by changing number and size of droplets, and hence a cloud’s ability to reflect sunlight as well as its probability to produce rain. For this purpose, Fabian is extending his Lagrangian cloud model, a novel method to represent cloud microphysics by individually simulated particles, by a detailed representation of entrainment and mixing. This approach not only fosters our process-level understanding of entrainment and mixing, e.g., on how and where mixing takes place inside a cloud, but also enables an assessment of the macrophysical properties of an entire cloud field, i.e., at a scale at which entrainment and mixing are usually crudely parameterized in other models.
How does the Atlantic Meridional Overturning Circulation influence the pace of anthropogenic surface warming?
Elizabeth Maroon will work with Jennifer Kay, Kristopher Karnauskas, and others at CIRES to study how the Atlantic Meridional Overturning Circulation (AMOC) interacts with the atmosphere to set the pace of global warming. Much of the excess heat trapped by greenhouse gases is absorbed by the ocean, which slows the rate of surface warming. As a result, the ocean plays an important role in setting how fast the surface warms. To improve our climate projections, we must have a full understanding of how the atmosphere and ocean interact to influence the rate of ocean heat uptake. The AMOC is a key component of the ocean circulation. While climate models show that the AMOC slows with greenhouse warming, how the AMOC influences ocean heat uptake is not well understood. Elizabeth will study how the AMOC’s strength, heat transport, and circulation vary in coupled ocean-atmosphere climate models. Because the AMOC can influence both tropical and extratropical climate through its heat transport, the interaction of regional atmospheric climate feedbacks with the AMOC will also be examined. Elizabeth completed her PhD at the University of Washington and is excited to join the research community at CIRES, especially because it was an undergraduate internship with CIRES scientists that started her career.
Aqueous-phase formation of secondary organic aerosol during wildfires: A modeling study
Renee McVay is collaborating with Joost de Gouw and members of the NOAA ESRL Chemical Sciences Division to model secondary organic aerosol (SOA) formation during wildfires with the regional model WRF-Chem. Biomass burning is the largest contributor to organic aerosol emissions globally, which have important climate and health consequences. Aerosols are either emitted directly (primary organic aerosols) or formed via gas-to-particle conversion during ageing of smoke plumes (SOA). The potential of wildfires to form SOA is still very uncertain. McVay will be working to update SOA formation in WRF-Chem by including non-traditional pathways to SOA, such as aqueous-phase reactions, that have heretofore been neglected but have the potential to form significant SOA. These updates will be constrained by environmental chamber experiments. Simulations using the updated WRF-Chem will be compared to field measurements of organic aerosols in wildfires as part of the Fire Influence on Regional and Global Environments Experiment (FIREX) campaign. This project will enhance understanding of SOA formation during wildfires and the dependence of this formation on chemical and meteorological conditions. This knowledge will enable better predictions of air quality, weather, and climate effects of wildfires. The updated WRF-Chem model will also be useful to fire managers and first responders for weather forecasting during wildfires.
Using atmosphere-biosphere data assimilation to improve terrestrial biosphere models and the North American carbon balance
Dr. Ivar van der Velde is a meteorologist with a keen interest in the land-atmosphere exchange processes of atmospheric trace gases. He is working together with Dr. John Miller and Dr. Stephen Montzka at NOAA Earth System Research Laboratory’s Global Monitoring Division to study the global terrestrial carbon dioxide sink with a focus on North America. This sink remains uncertain in a warming world where droughts may be more extreme and more frequent. The impact of droughts is likely to be net carbon release, potentially leading to more extreme drought conditions. These feedbacks between the terrestrial carbon cycle and climate are poorly understood and represent a first order uncertainty in climate prediction. It is therefore critical to improve the representation of the terrestrial biosphere in carbon-climate models. Ivar’s previous work at Wageningen University in the Netherlands indicated that the combined use of atmospheric CO2 and its isotopologue (δ13C) could potentially help to constrain the net carbon balance and underlaying exchange processes. In the current project he is focussing on the development of a data assimilation system that utilizes a novel combination of atmospheric CO2 and δ13C data to optimize well-known model parameters in terrestrial biosphere models. The main research goals are to improve our understanding of the large-scale moisture controls on carbon dioxide fluxes. This will be valuable for the plant-physiological research community and will help define where NOAA should measure CO2 and δ13C in the United States and around the globe in order to better understand the drivers of carbon exchange variability. In his spare time Ivar can be found exploring Colorado’s hiking trails and investigating the quality of Boulder’s brewery pubs.
Improving Biosand Water Filters using Insights from Microbial Ecology
Tara Webster is a microbial ecologist and environmental engineer. She is collaborating with Noah Fierer and Balaji Rajagopalan to improve our understanding of the microbial processes in biosand filters. Biosand filters hold great promise to provide clean drinking water in both developed and developing countries. Effective pathogen removal relies on the activity of a complex microbial community within the filter. However, little is known about the factors that shape microbial community structure and function in these systems. Currently, filter start-up and maintenance are based on empirical observations, leading to highly variable performance. To address this variability requires a better understanding of how filter design impacts microbial community development and pathogen removal. This research will determine how biotic and abiotic design decisions can shape microbial community structure to improve biosand filter performance. In partnership with a non-profit in Bangladesh these results will be translated to the field where community-scale filter design and operation can be improved.
Meltwater movement, ponding and refreezing on the Greenland Ice Sheet and Antarctic Ice Shelves
Ian Willis will work with Mike Willis to study water production, ponding, and refreezing in Greenland and Antarctic ice shelves, which have important implications for ice sheet/shelf mass balance, runoff, ice dynamics, and ultimately sea level change. The first aim of his proposal is to amass a large, remotely-sensed data set which will be used to quantify spatial and temporal patterns of surface and subsurface water extents across the firn zone of the GrIS (Greenland Ice Sheet) and across several AISs (Antarctic Ice Shelves). The recent advent of Google Earth Engine will help considerably with this task. The second aim of his proposal is to work towards incorporating the horizontal advection of water and its storage, refreezing, and draining in snow/firn aquifers, on both the GrIS and AISs, into a numerical modelling framework. Such a model will help to better make sense of recent observations made on the GrIS and AISs, increase understanding of important hydrological processes operating on those ice masses, and ultimately enhance the ability to predict their future behavior.
Reconstructing Pliocene precipitation: Constraining El Niño teleconnections in a warm world
Jody Wycech is working with Peter Molnar, Balaji Rajagopalan, and Kris Karnauskas to study the atmospheric teleconnections of El Niño during the Pliocene (5.3-2.6 Ma). The Pliocene is the most recent time interval in Earth history when global climate was warmer than the present, and as such is considered an analog to future climate conditions. Temperature reconstructions argue for a mean El Niño-like state during the Pliocene, but global precipitation anomalies produced by Pliocene El Niño are understudied. To this end, Wycech will reconstruct Pliocene rainfall in the southeastern United States and India, which respectively experience wetter conditions and a weaker summer monsoon during modern El Niño events. The Pliocene precipitation reconstruction will be completed using Ba/Ca ratios in the shells of marine protists (planktic foraminifera) recovered from sediments near river mouths to gauge freshwater runoff. These results will provide novel insights into El Niño conditions in our future warmer world.