We use the Köppen-Geiger climate classification and MODIS MCD12Q1 Land Cover Type 1 (IGBP) to inform daily estimates of VPD on a 1 km by 1 km grid for all of the Continental United States, parts of Northern Mexico and Southern Canada (CONUS+). The CONUS+ dataset runs from 2001-2023. Yearly data is available in NetCDF file format on Hydroshare. The published Scientific Data paper is available here: https://doi.org/10.1038/s41597-025-04544-5
In collaboration with partners at the North Carolina Forest Service, North Carolina Wildlife Commission, The Nature Conservancy, and private land owners, we investigate vegetation regrowth dynamics after prescribed fire. We compare in situ measurements of LAI using a LiCor 2200C Plant Canopy Analyzer with remostely sensed LAI from Moderate Resolution Imaging Spectroradiometer (MODIS). We currently look for patterns in the seasonal variation of LAI after prescribed fire and when there is no fire. We are also interested in understory regrowth dynamics which might provide insights into the benefits of prescribed fire.
IN THE NEWS (see below)
Flash droughts are extreme events marked by the rapid dry down of soils due to lack of precipitation, high temperatures, and dry air. Phenologic state, or growth stage, is an important metric for modeling how vegetation modulates land–atmosphere interactions. Reduced stomatal conductance during drought leads to cascading effects on carbon and water fluxes. We investigate how uncertainty in vegetation phenology and stomatal regulation propagates through vegetation responses during drought and non-drought periods by coupling a land surface hydrology model to a predictive phenology model. We assess the role of vegetation in the partitioning of carbon, water, and energy fluxes during flash drought and carry out a comparison against drought and non-drought periods. Results show that the compounding effects of reduced precipitation and high vapor pressure deficit (VPD) on vegetation distinguish flash drought from other drought and non-drought periods.
Coupling Noise- and Rate-Induced Tipping in a Simple Model of Tropical Cyclone Formation
This work expands on the my master's thesis on noised-induced tipping in a 2-D model of cyclogenesis. Previously, under the noisy regime, we held constant the bifurcation parameters, which represented wind shear and thermodynamics. Here, we allow one of the parameters to vary in time and explore tipping from a non-cyclone regime into a cyclone regime, and the tipping time to the cyclone state.
Collaborators: John Gemmer (WFU), Katie Slyman & Chris Jones (UNC-CH).
In the summer of 2019, I attended a summer school and began a year long academic engagement program as part of the Mathematics and Climate Research Network (MCRN). The group of 15 students and 6 faculty mentors broke into 3 teams to focus on one project (Polar Vortex, Data Assimilation, El Niño). I am part of the El Niño group.
Student Collaborators:
Kolja Kypke (Guelph)
Kath Landgren (Cornell)
Katherine Slyman (UNC-CH)
Wenzhong Wang (UNC-CH)
Advisors:
John Gemmer (WFU)
Mary Silber (Chicago)
Impact of Noise on a Dynamical Systems Model of El Niño
Abstract. The El Nino Southern Oscillation (ENSO) is a climatic phenomenon that fluctuates between El Nino, La Nina and neutral states. El Nino events, associated with higher sea surface temperatures in the Eastern Equatorial Pacific, are caused by atmospheric and oceanic interactions. While these events occur roughly every four years, larger and more intense El Nino events occur on decadal scales, and are associated with extreme weather worldwide. Forecasting an El Nino event in a previous spring would be desirable but it is challenging due to the lack of predictability. We consider this lack of predictability in the context of a noisy, low order ENSO model. This model takes the form of a three dimensional stochastic dynamical system with seasonal forcing. It is known that the deterministic skeleton in the autonomous setting has the structure of a fast slow system, which can exhibit mixed-mode oscillations. We exploit this understanding of the deterministic system to interpret the results of Monte Carlo simulations. In particular we focus on potential bottlenecks in phase space, through which both large and small El Nino events traverse, as a possible source of unpredictability. We are interested in how noisy trajectories emerge from these bottlenecks, and the timing of this exit in the presence of the seasonal periodic forcing.
I completed my master's thesis in mathematics at Wake Forest University under the direction of Dr. John Gemmer in May 2020.
Noise-induced Tipping in a Simple Model of Tropical Cyclone Formation
Abstract: A presumed impact of global climate change is the increase in frequency and intensity of tropical cyclones. Because of the destruction that can occur when tropical cyclones make landfall, understanding their formation should be of interest to governments, risk analysts, as well as climate scientists. As early as 1986, Kerry Emanuel posed that the dynamics of a tropical cyclone can be modeled as a Carnot engine that transfers thermal energy from the ocean into mechanical energy in the form of cyclonic winds. In 2017, Emanuel modeled tropical cyclone formation by developing a low-dimensional dynamical system which couples tangential wind speed of the eye wall with inner-core moisture. In this thesis we present the existence and stability of fixed points for this dynamical system, using a piecewise approximation to ocean feedback. The fixed points in this system correspond to the dissipation or presence of a cyclone. The model admits a saddle-node bifurcation dependent upon wind shear and thermodynamic parameters. By converting the model into a system of stochastic differential equations with additive Gaussian white noise to simulate small scale thermodynamic disturbances, we can explore the most probable path of transition from a non-cyclone state to a cyclone state. Understanding of the formation and stability might provide insight into the underlying mechanisms that govern the formation of cyclones.
As the capstone project for education masters degree, I completed an action research project in the framework of physics eduction.
Building a Sence of Community in a High School Physics Class
Abstract: It was the goal of this study to see if using praise and encouragement strengthened the sense of community in a physics classroom. In order to motivate students, it is critical that teachers establish a safe and respectful environment. In this study, I sought to discover the impacts of building a sense of community in the classroom. Strategies geared for establishing the sense of community in the classroom included establishing an environment of mutual respect, providing encouragement, and collaborative group work. Given the promising research on environments of care and respect leading to increased motivation to learn, in this study I explored instructional practices that build a sense of community and their subsequent impact on students’ motivation to learn physics. Right now, most emphasis is put on student engagement in an established classroom community. This study examined both the process and outcomes of building a classroom community. This study sought to show how praise and encouragement, through teamwork in small and large group settings, increased motivation in the physics classroom.
As an undergraduate at the University of North Caorlina Wilmington, I completed my honors thesis in physics education.
Designing a PER-based Introductory Physics Lab
Abstract: Physics Education Research (PER) faculty investigate how students develop their understanding of physics concepts and phenomena. They have found that students do not walk away from introductory physics courses with a coherent knowledge of physics principles even if they make a good grade in the course. When asked to explain their reasoning or describe their solution, students do not make correct conjectures about the physics. Through a modified laboratory exercise, designed from an analysis of research from introductory physics courses, we look for more effective ways to achieve student understanding. The exercises are designed to increase student involvement in class through hands-on activities with a focus on increasing students’ communication with the instructor, lab group, and the class.