Stanford Earth Undergraduate Research Symposium
Friday, October 22, 2021
Hartley Conference Center and Patio, Mitchell Earth Sciences Building
- 2:30-3:30 pm - Select oral presentations in Hartley Conference Center
- 3:30-5:15 pm - Poster presentations on the Patio
- 2:30 pm - Acacia Lynch - Radiometric Calibration of Archival Radar Sounding Data
- 2:45 pm - Claire Morton- Soil Micronutrients and Human Health: Evidence from India
- 3:00 pm - Iris Xia- Using Radar Sounding and Topographic Imager Data to Measure Europa’s Tides
- 3:15 pm - Dakota Riemersma - Measuring Coral and Reef Change in the Chagos Archipelago from Structure from Motion Photogrammetry
Abstracts for Posters
Improving Catalysts for eNG Synthesis by Creating Structures Ideal for Cycling
The carbon neutral methanation of atmospheric carbon dioxide presents a novel energy storage pathway that allows for excess electricity produced to be stored as natural gas and then burned back for later use. Within this reaction, a nickel catalyst is used, where it can be supported on various other metals. One method to create these supports is through 3D printing, which presents a challenge when working with a support metal like copper, which has a melting point of over 1000 degrees Celsius, as we cannot extrude it via traditional 3D printing routes. Basing our methods off of information from Danaci et al, we have created multiple copper pastes, using hydroxypropyl cellulose as a binder and water as a solvent. The viscosity of the mixtures have been tested in order to try and optimize printing as well as minimize volume loss when the water evaporates away. Work to print structures is still ongoing. While doing this, we also are cycling Riogen 1% Ni on Al2O3 catalysts at around 400 psi in reaction conditions (without hydrogen), and we plan to analyze the catalysts both before and after this heat treatment in order to see the effects of such conditions. We also plan to do the same with the structures that we print and compare with the Riogen catalysts.
Collapsed Buried Lakes in Northwestern Greenland
Surface runoff is currently the dominant form of mass loss from the Greenland ice sheet. In order to understand its effect on global sea level rise, both in terms of magnitude and timing, we must account for the possibility that meltwater can be stored in the near-surface. Research conducted in Northwest Greenland has revealed a combination of ice slabs, buried lakes, and aquifers in the deep percolation and wet snow zones. Ice penetrating radar data also shows evidence of meltwater infiltration into firm space below the ice slabs, where liquid water is stored and then partially to fully refreezes into buried ice blobs. In order to understand how much and how often surface meltwater runs off to lower elevations or drains to the bed, we need a better understanding of how these subsurface features form, how long they persist, their interactions with one another, and how they may interact with the supraglacial and subglacial systems.
This research specifically focuses on three buried supraglacial lakes in Northwestern Greenland. These lakes are of particular interest because they show an occurrence of a cascading collapse, meaning they drained together in a short time period. The discovery of this drainage event has implications concerning the nature of the englacial drainage system, ice velocity, and ice dynamics in the region of the drainage. More research should be done to investigate the effects of the sudden drainage from these buried lakes, and to investigate if this is a common occurrence in the region.
Physiological Differences Between the Paleozoic and Modern Faunas: A Possible Explanation For Historical Extinction Selectivity Trends
The Earth has experienced several major extinction events in its history with differential selectivity between clades, yet the mechanisms that drive this selection are unresolved. Extinction intensity itself also has decreased over the Phanerozoic Era (the last 540 million years). Recently, Payne et al., 2020 suggested that physiological changes in organisms through time is one possibility that could explain these trends in extinction. To test this hypothesis, this project explores if physiological traits related to temperature-dependent hypoxia tolerance vary by higher taxa or by evolutionary ‘Faunas.’ To do this, we first obtained geo-referenced occurrence points for extant invertebrate species by digitizing their distribution maps in the Beneath Pacific Tides: Subtidal Invertebrates of the West Coast field guide and matched these occurrences to temperature and oxygen values at the ocean floor obtained from the World Ocean Atlas database. From these data, we used the lowest levels of oxygen occupied by a species as an indicator of its hypoxia tolerance and used the slope of a quantile regression at the 5th percentile of inhabited oxygen values across temperatures to quantify the temperature sensitivity of this hypoxia tolerance (E0). After grouping these species-level traits as extant representatives of the Paleozoic or Modern Faunas, we find significant differences in both hypoxia tolerance and its temperature sensitivity. Specifically, extant representatives of the Paleozoic Fauna are more hypoxia tolerant but also more temperature sensitive. These results support the notion that physiology may shape extinction patterns across geological time. Since a biota composed of members that are more temperature sensitive are expected to be less robust to a given temperature insult, the Paleozoic Fauna’s high temperature sensitivity compared to that of the Modern Fauna provides a possible explanation for the observed decrease in extinction intensity over the Phanerozoic.
Radiometric Calibration of Archival Radar Sounding Data
Since the 1960s, radar sounding has been a leading method of characterizing the englacial properties and thickness of ice sheets, with multi-year data sets giving insight into past and future changes to the ice sheets. However, since data collected prior to the 1990s was gathered and stored on analog (optical) film, it has been largely underutilized for modern glaciological studies and in large-scale comparisons with modern radar sounding data—meaning 20 years of data has not been investigated using modern radiometric analysis techniques. Recent efforts at Stanford University to scan and calibrate archival film data—specifically, data from the 1970s expeditions of the Scott Polar Research Institute, Cambridge (SPRI) and Technical University of Denmark (TUD)—will enable valuable multi-decadal comparisons and reanalysis of archival data with modern methods and techniques. Here, we expand upon the process of calibrating the fast-time A-Scope power traces with the along-track Z-Scope logarithmic power traces using a deterministic circuit model, a process made difficult by the sparse A-Scope sampling and poorly characterized Z-scope compression scheme. This research lays a foundation for further work archiving analog data and making it compatible with digital measurements, eventually enabling the full use of the multi-decadal ice sheet data with far-reaching implications for climate modelling and our understanding of sea level rise.
Fast And Furious — Natural Equilibriums In Laissez-Faire Traffic Simulations
Fumes filling the air, car horns blaring wildly, and cars anxiously darting in and out. Such are the scenes of traffic today—polluting, noisy, and frustrating. Recognizing this source of environmental strain and annoyance, policymakers have consulted legacy traffic models to inform consequential legislative efforts. Many legacy traffic models omit critical factors regarding driver behavior and roadways—lane changing, acceleration dynamics, and types of lanes—which have inhibited progress for efficacious transportation policy. As such, we developed a Laissez-Faire traffic simulation that takes into account realistic lane changing, acceleration dynamics, and different types of lanes to gauge how modern-day traffic compares to optimal Laissez-Faire equilibriums. Our results suggest that for most common roadways with standard infrastructure occupied by light-duty passenger vehicles, modern-day traffic is already very close to the optimal Laissez-Faire equilibrium. As such, efforts to reduce congestion and emissions are better met through other means like decommissioning vehicles with internal combustion engines, improving driving efficiency, and promoting communal transportation.
Soil Micronutrients and Human Health: Evidence from India
Soil micronutrients are a critical determinant of crop productivity and potentially affect micronutrient uptake and the health of human populations. In this study, we examine the link between soil micronutrient properties and health outcomes among children and adult populations in India, a region that suffers from particularly high levels of child malnutrition and micronutrient deficiency. We link health data from nearly 0.3 million children and a million adult women across India with detailed soil quality information drawn from a nationwide soil health testing program. We rely on the plausibly exogenous variation in soil properties to identify the causal effect of micronutrient content on health outcomes. Our results suggest that soils deficient in key micronutrients such as zinc and iron are associated with higher levels of stunting, wasting, and underweight among children. We also find that soil micronutrient deficiency is associated with lower heights among adult women, suggesting that the detrimental effects of poor soils can persist into adulthood. These estimates remain consistent across a variety of specifications. Our results imply that targeted interventions to enhance soil quality are a potential solution for improving health outcomes in developing countries.
Using Radar Sounding and Topographic Imager Data to Measure Europa’s Tides
We investigate the use of radar sounding data in combination with stereographic camera derived digital terrain models (DTMs) to perform altimetric measurements on planetary bodies, with a focus on quantifying tidal dissipation. Specifically, we use data from the Shallow Radar (SHARAD) instrument onboard the Mars Reconnaissance Orbiter and compare inferred altimetry measurements at crossover points, i.e., points where the spacecraft ground tracks intersect. Unlike classical altimetry which is aimed to retrieve the topography itself, this method is intended to provide a geodetic reference which can be used to determine differences in elevation due to tides. We chose the USGS MC-11 region as our study area, given its extensive coverage by the High Resolution Stereo Camera (HRSC) orbiting Mars. Using a DTM of the area, we simulate surface “cluttergrams” using an incoherent clutter simulator and match them with the pulse compressed and ionosphere-corrected SHARAD radargrams to obtain differential altimetry measurements to the crossover plane. In comparison to an approach without a priori information of the topography, our method allows us to not only mitigate the ambiguity of surface returns but also use individual off-nadir reflectors as statistically independent range measurements. Our sample consists of 939 ground tracks and 5150 crossover points, with a differential measurement taken for each crossover point. Our results contribute to the usage of radar sounders as altimeters for geodetic purposes and will help inform the science goals of the upcoming NASA Europa Clipper Mission, for which quantifying radial tidal deformations is an important objective. With the same methodology, the REASON radar instrument onboard the Clipper can be used analogously to better understand tides on Europa.
Automated Identification of Ice Sheet Surface and Bed from Archival Radar Film Data
Mass loss from ice sheets is a key causal factor of sea level rise yet has a tremendous amount of uncertainty associated with it. A major reason for this uncertainty is the spatial and temporal sparsity of subsurface data available. Ice-penetrating radar data recorded on optical film in the 1970’s has been recently digitized and expands the temporal span by multiple decades in some regions of the Antarctic Ice Sheet.
In order for the data to be used in ice sheet models, the thickness of the ice must be extracted from the film images. To do this, a supervised machine learning algorithm is used to label the surface and bed of the ice sheet. The training data for this algorithm was created using a combination of previously labelled archival data from Greenland and Antarctica and a human-supervised line-detection algorithm.
Our findings will be made available to the public to help advance our understanding of ice mass loss in Antarctica and the associated broader implications for global sea level rise.
Measuring Collective Environmental Literacy in Local Communities
The scale and complexity of socio-environmental issues like climate change necessitate moving beyond a focus on individuals. No matter how well-read, dedicated, or networked, an individual’s impact is limited when dealing with issues that feature a large spatial and temporal scale. Therefore, confronting the complexity and scale of such issues necessitates a transition to collective action at the community level. In order to facilitate collective action, we must first measure it and better understand the supporting factors. This research pilot tests semi-structured individual interviews as a potential method to measure a community’s Collective Environmental Literacy (CEL). The lab partnered with over a dozen environmentally connected Palo Alto community members to conduct interviews which were then coded in NVIVO. Preliminary findings identified a list of CEL ingredients and suggested that differences in prioritization of these ingredients lead to differences in the individual’s perception of their communities’ CEL. In the future, the efficacy of individual interviews as a CEL collection method should be utilized in addition to others with the intent to improve the quality and applicability of the measurement.
Modeling Seismic Waves From Volcanoes
Magma fluid dynamics is a field of knowledge in which the scope can be vastly widened. In order to do so, however, we must improve the methods of measuring magma. Indirect measurement of magma currently consists of recording seismic waves from volcanoes and simulating them with known accompanying sources, and then performing a waveform inversion. This project helps provide a methodology to show that the process for this source simulation and waveform inversion can be improved. The current processes use a homogeneous half-space as the model for the earth that the seismic waves are traveling through. In the real world, however, the seismic waves move through heterogeneous media. By working on creating and modeling the seismic waves caused by a simulated source through a modeled heterogeneous medium, we can more precisely combine our source-reading pairs and more accurately perform a waveform inversion. The code that this project culminated in will help this process, as it provides a framework for precisely this process of heightening the accuracy of recognizing the source forces that cause seismic waves.
Anoxic Microsites and Agricultural Soil Carbon Protection: Methanogen Variation across Soil Factors
Gabriella Barratt Heitmann
Anoxic microsites may serve an important role in climate regulation and the carbon cycle, particularly in mitigating carbon dioxide emissions from soil, but their existence is currently poorly understood. To better understand their presence in upland soils, samples were collected from long-term agricultural experiments across the US Midwest with varying tillage types, fertilizer amendments, and landscape positions. The soils were analyzed using digital droplet PCR (ddPCR) to search for the presence of methanogenic DNA (the mcrA gene), which serves as a proxy for the existence of anoxic microsites. Regarding tillage, in two sites, more mcrA was amplified in undisturbed (UN) soils than in the no-till (NT) and conventional till (CT) treatment groups; another site had more mcrA amplicons in both the UN and NT treatments than the CT. Regarding fertilizer, there were more mcrA amplicons in the amended treatment of one site. For landscape position, more mcrA was amplified in soils from the footslope position than in the channel or shoulder. These results imply there is a negative relationship between increasing degree of tillage and methanogen presence and a positive relationship between manure amendments and methanogen presence. There does not appear to be a clear gradient between landscape position and methanogen presence. While more analysis is needed, the presence of the mcrA gene indicates there are anoxic microsites in upland soils, which should be considered in future studies about soil carbon and land management practices
Relationships Between Anoxic Microsites, Carbon, and Field Management in Agricultural Soils
As the largest dynamic reserve of carbon, soils are crucial to our ability to understand carbon cycle dynamics and the potential for climate change mitigation. One aspect of soils and their relationship with carbon that remains understudied is anoxic microsites, which are portions of otherwise oxic soils that lack oxygen. These microsites may have important effects on the tendency of soils to either sequester or release carbon, as anaerobic respiration is slower than aerobic. In this study, we sought to understand the relationship between anoxia, management (e.g., tillage and carbon additions), and carbon release in agricultural soils.
Using soil samples from three different locations, we evaluated whether anoxia was present by measuring the ratio of Fe 2+ to total Fe, which increases with anoxia. We also measured total carbon in the soils and water extractable carbon (a proxy for biologically available carbon).
We found no clear trends between Fe 2+ and total carbon in soils. Variations between sites nullified any trends that might have otherwise existed. However, water extractable organic carbon, a proxy for biologically available carbon, increases with anoxia to a significance of p >.05.
Our results confirm that anaerobic respiration is happening to at least some extent in all soils sampled. However, the experiments we ran were mostly inconclusive with regards to the relationships with anoxia. For example, whether conventional tillage or no tillage soils had more anoxia varied from site to site. More research is therefore needed to measure the relationship between anoxia and other relevant indicators of carbon flux, in addition to gathering more data on the variables we measured.
Deciphering Signals of Early Mountain Building in the Patagonian Andes: Geochemistry of the Cretaceous Zapata Formation, Southern Chile
An extensional phase during the breakup of Gondwana in the Middle to Late Jurassic initiated the process of mountain building in the Patagonian Andes. The extension culminated in the development of an extensional backarc basin, the Rocas Verdes basin, which transitioned to the contractile Magallanes retroarc foreland basin, in which the Zapata and Punta Barrosa Formations were deposited during the Early Cretaceous. The transition of the basin from extensional backarc to contractional foreland was the result of crustal shortening and the development of the Andean fold-thrust belt, which is the initiation of the Patagonian Andes orogenic cycle. The basin inversion transition and fold-thrust belt development is recorded as the deposition of turbidites in the Punta Barrosa Formation and the onset of coarse grained sedimentation on top of the the shales of the Upper Zapata Formation. While the deposition of the Punta Barrosa sandstone formation has previously been used to mark the initiation of mountain building in the Patagonian Andes, the initiation of mountain building may be recorded earlier than previously thought, in the Upper Zapata Formation. This project shows that there are geochemical signals present in the Upper Zapata that indicate the initiation of mountain building occurred approximately 99 million years ago. In the Upper Zapata, a section of samples display a large decrease in Rare Earth Element (REE) fractionation, aligning with our hypothesis. The decrease in REE fractionation in these samples brought it to values similar to that of the Sarmiento Ophiolite which is the predicted change in source material after the fold thrust belt likely exposed the Sarmiento Ophiolite. This result reveals that the initiation of mountain building in the southern Patagonian Andes is recorded in the Upper Zapata Formation, and occurred around 7 million years earlier than the previously used marker.
Evaluating Basaltic Basins In The Northwestern United States As A Means For Large Scale CO2 Disposal
As anthropogenic CO2 emissions continue to increase, developing methods for globally available, high volume, and non-volatile CO2 storage becomes increasingly important. The injection of supercritical CO2 into basaltic basins at suitable depths requires fewer physical trapping mechanisms than the current dominant methods for CO2 storage and provides massive storage potential. In this study, 288 basins in the northwestern United States, areas defined by 4th level Hydrologic Unit Code (HUC), were evaluated using a geographic information system (GIS) in terms of their potential storage volume, their basalt content, their proximity to anthropogenic CO2 sources, and the feasibility of injection. For the last category, the density of transmission lines, major roads, protected lands, natural gas pipelines, and groundwater wells was included. An index incorporates these attributes into a single score using an iterative approach that projects the overall suitability of CO2 storage in any of the 288 basins studied. This approach could be feasibly expanded to other regions in the United States or elsewhere, assuming the presence of sufficient data relevant to geology and infrastructure.
Reduced Tillage Increases Yield in Semi-Arid Maize Fields
Conservation tillage has many benefits including reduced erosion, increased soil health, and decreased labor and fuel input costs. Despite these benefits, yield impacts remain an important adoption factor for many farmers. Previous research suggests that conservation tillage is likely to have the largest yield benefits in arid conditions, but a lack of field-level analyses across climatic, management and soil conditions limits our understanding. Satellite imagery provides the opportunity to monitor agricultural lands at sub-field resolution across large spatial scales and wide environmental gradients.
In this study, we investigate the yield impacts of conservation tillage in the semi-arid western US Cornbelt. We use sub-field resolution datasets on tillage practices and crop yields derived from satellite data spanning four states (Nebraska, Kansas, South Dakota, and North Dakota) between 2008 and 2020. We use a causal forests analysis, an adaptation of the random forests machine- learning algorithm for causal inference on observational data, to estimate heterogenous yield outcomes for several thousand maize and soybean fields across gradients in climate, soil quality and irrigation status. We find that reduced tillage leads to higher maize yields, especially in rainfed fields. Our results strengthen understanding of the impact of conservation agriculture practices on crop yields and help define environments most likely to benefit from conservation tillage.
Measuring Coral and Reef Change in the Chagos Archipelago from Structure from Motion Photogrammetry
The world’s coral reefs face numerous threats through ocean acidification, rising temperatures, storms, and mass bleaching events. In turn, studying and understanding coral reefs is increasingly important. While research conducted on reefs is traditionally done in-situ on the colony scale, this project was able to digitally model and analyze coral at a larger “reef” scale. Over two sampling years, (2019 and 2021) thousands of underwater photos were captured at 3 unique sampling sites. Through Structure-from-Motion (SfM) photogrammetry (using the software tool Agisoft Metashape Pro), 6 high quality digital models of the 3 sites were created and analyzed. Models were aligned with their respective site pairs in another tool “CloudCompare” so that computational differencing could be performed. Linear extensional growth of individual tabular Acropora coral colonies were measured, then compiled to calculate an average growth rate for each site. Growth rates were found to be ~115 mm/yr, which is consistent with rates derived from other studies, both in Chagos (Lange and Perry 2020) and in other reef systems (Anderson et. al 2017). Volumetric differencing was also performed on the models to estimate the net gain/loss of coral on the reef. Using this volume and estimates of coral density and pore space, calcification was quantified in terms of mass of CO2 released. The models created through this project can be further analyzed to obtain additional physical reef metrics such as curvature, rugosity, and fractal dimensionality.
Fe-bearing colloids in anoxic sediments: How do they form? Are they stable?
Fe-bearing colloids have demonstrated the potential to act as carriers for contaminants in subsurface environments and floodplain soils, playing a role in the pollution of groundwaters. Further evidence supports the idea that iron sulfide (FeS) colloids can impact the mobility of metal contaminants and nutrients in sediments that interact with groundwater. As a result, in environments with complex soil conditions, including those with a considerable stock of organic matter, it is important to model the transport of FeS and/or organic colloids. In order to investigate the formation and longevity of iron sulfide (FeS) colloids we conducted sulfidation experiments of ferrihydrite. We monitored FeS colloid stability over time and measured how an organic matter coating of the ferrihydrite would influence colloid behavior. By quantifying levels of Fe(II) using inductively coupled plasma optical emission spectroscopy (ICP-OES) together with colorimetric analyses of Fe(II) and Fe(III) with the ferrozine assay, we compared the levels and rate of colloid formation between pristine ferrihydrite and the organic-ferrihydrite assemblages at 6-h, 1-day, 3-day, and 8-days following sulfidation. The results generated indicate that the organic-matter coating of the ferrihydrite promoted the creation of nanoscale FeS colloids upon sulfidation of ferrihydrite. The organic matter also showed signs of preventing the aggregation of the FeS colloids, with functional groups that likely contribute to their enhanced stability. This investigation focused on FeS colloids in anoxic conditions, however hydrologic events have the potential to introduce oxygen that influences the colloids. Therefore, we suggest that future research should explore the impact of oxygen intrusion on the FeS colloids.
Exploring Collective Environmental Literacy And Community Resilience In Watsonville, CA
As environmental and sustainability issues such as climate change continue to manifest in myriad ways, communities across the world must take collective action to mitigate or adapt to them. The dynamic process by which a community comes together to address environmental or sustainability issues is called collective environmental literacy (CEL). This project aims to create and pilot instruments for measuring CEL in a community and better understand the community-scale variables that foster or hinder CEL and collective action. The project also begins to explore the relationship between CEL and community resilience. An interview protocol was developed as an instrument to explore how a community learns and communicates about environmental issues, takes action against such issues, and perceives CEL and resilience within their community. In August 2021, six interviews were conducted with Regeneración, a nonprofit climate justice organization in Watsonville, CA. Through qualitative coding and preliminary analysis of the interview transcripts, some key themes were identified. Community members of Watsonville learn about environmental issues through a variety of ways, but informal communication and personal experience seem to be major forms. Various examples of individual and collective action in Watsonville were identified, with organizations like Regeneración and city staff facilitating many examples. Although there was no general consensus on the level of CEL in Watsonville, interviewees identified a lack of time and money as barriers to CEL. The interviews did not show any major themes for the relationship between CEL and community resilience, which indicates more research should be done on this topic. While these initial interviews provided a glimpse at CEL in Watsonville, the protocol should be revised and further expanded to other communities.
A Case Study Of The Outflow Interactions Between Tropical Cyclones
Previous studies of the interactions between spatially proximate, or binary, tropical cyclones (TCs) have focused on the interactions between their vortices rather than the interactions between their outflows. Vortex interactions are important in that they can influence TC track and intensity; the Fujiwhara effect is a well-studied phenomenon in which sufficiently close and intense tropical cyclones exhibit cyclonic rotation about a centroid between their respective centers. However, outflow interactions are also impactful and are relevant to more sets of binary TCs, because the outflows of TCs that are too far apart to exhibit the Fujiwhara effect can still interact. Additionally, the outflow layer has been less studied until recent times, due to insufficient upper-level observations.
Hurricanes Marco and Laura were two tropical cyclones active in the Atlantic during late August in 2020. Before Hurricane Marco degenerated on August 25, the two storms were within a close distance in the Atlantic basin. Besides their proximity, hurricanes Marco and Laura are interesting to study because of the rarity of binary TCs in this region. We analyzed potential interactions between these hurricanes to gain a better understanding of how the outflows between TCs can interact. We found their centers via a pre-established method based on geopotential height, analyzed whether centroid-relative motion (the Fujiwhara effect) occurred, determined the location of the outflow layers based on area-weighted divergence, and performed other analyses. We also created a new, more complex algorithm to determine the location of the principal outflow jet (an area of intense, focused outflow, which represents a dominant aspect of the outflow) and model the three-dimensional structure of the jet, unlike previous algorithms which give two-dimensional representations. Using this algorithm, we intend to analyze the outflows further, since pre-existing methods were not intended for binary TCs.
Integrated Kinetic Energy of a Mature Tropical Cyclone in a Variety of Sea Surface Temperatures
Severe tropical cyclone disasters occur more frequently in recent years, causing significant impacts on the life and property of human beings. This brings the need to understand how increasing sea surface temperature (SST) changes the energy and development of tropical cyclones. This study analyzes simulated tropical cyclones produced by the Cloud Model 1 (CM1) program under increasing SSTs from 297.5 K to 310 K with 1.5 K increments. At each SST, a simulated cyclone is produced with 1,200 snapshots, each 2 hours apart, creating a 100-day time series. A high-resolution period of each cyclone is produced with 192 snapshots, each 15 minutes apart, creating a 2-day time series.
We aim to quantify how the integrated kinetic energy (IKE) of simulated, idealized tropical cyclones is affected by changes in SST, compare IKE with the maximum surface wind speed by superimposing their time-series graphs, and observe the changes in IKE and surface wind distribution during an eyewall replacement cycle on Hovmoller diagrams. The reason to use IKE is that IKE is a more comprehensive indication of the intensity of a tropical cyclone compared to the more commonly used maximum surface wind speed.
Preliminary findings are that the IKE of a tropical cyclone and the SST have a positive linear relationship; the maximum surface wind speed always peaks before IKE does, and the two quantities do not always move in the same direction; and during an eyewall replacement cycle, while the maximum surface wind speed decreases, the IKE sustains—due to conservation of angular momentum—until the new eyewall is established.