arXiv subjects

Daniel E. Horton

Publications and source records attributed to Daniel E. Horton.

4 recordsLinked to original sources

arXiv2026

Identifying heat-related diagnoses in emergency department visits among adults in Chicago: a heat-wide association study

Extreme heat is an escalating public health concern. Although prior studies have examined heat-health associations, their reliance on restricted diagnoses and diagnostic categories misses or misclassifies heat-related illness. We conducted a heat-wide association study to identify acute-care diagnoses associated with extreme heat in Chicago, Illinois. Using 916,904 acute-care visits -- including emergency department and urgent care encounters -- among 372,140 adults across five healthcare systems from 2011-2023, we applied a two-stage analytic approach: quasi-Poisson regression to screen 1,803 diagnosis codes for heat-related risks, followed by distributed lag non-linear models in a time-stratified case-crossover design to refine the list of heat-related diagnoses and estimate same-day and short-term cumulative odds ratios of acute-care visits during extreme heat versus reference temperature. We observed same-day increases in visits for heat illness, volume depletion, hypotension, edema, acute kidney failure, and multiple injuries. By analyzing the full diagnostic spectrum of acute-care services, this study comprehensively characterizes heat-associated morbidity, reinforcing and advancing existing literature.

stat.AP↗

arXiv2021

Persistence of Flare-Driven Atmospheric Chemistry on Rocky Habitable Zone Worlds

Low-mass stars show evidence of vigorous magnetic activity in the form of large flares and coronal mass ejections. Such space weather events may have important ramifications for the habitability and observational fingerprints of exoplanetary atmospheres. Here, using a suite of three-dimensional coupled chemistry-climate model (CCM) simulations, we explore effects of time-dependent stellar activity on rocky planet atmospheres orbiting G-, K-, and M-dwarf stars. We employ observed data from the MUSCLES campaign and Transiting Exoplanet Satellite Survey and test a range of rotation period, magnetic field strength, and flare frequency assumptions. We find that recurring flares drive K- and M-dwarf planet atmospheres into chemical equilibria that substantially deviate from their pre-flare regimes, whereas G-dwarf planet atmospheres quickly return to their baseline states. Interestingly, simulated O$_2$-poor and O$_2$-rich atmospheres experiencing flares produce similar mesospheric nitric oxide abundances, suggesting that stellar flares can highlight otherwise undetectable chemical species. Applying a radiative transfer model to our CCM results, we find that flare-driven transmission features of bio-indicating species, such as nitrogen dioxide, nitrous oxide, and nitric acid, show particular promise for detection by future instruments.

astro-ph.EP↗

arXiv2019

Habitability and Spectroscopic Observability of Warm M-dwarf Exoplanets Evaluated with a 3D Chemistry-Climate Model

Planets residing in circumstellar habitable zones (CHZs) offer our best opportunities to test hypotheses of life's potential pervasiveness and complexity. Constraining the precise boundaries of habitability and its observational discriminants is critical to maximizing our chances at remote life detection with future instruments. Conventionally, calculations of the inner edge of the habitable zone (IHZ) have been performed using both 1D radiative-convective and 3D general circulation models. However, these models lack interactive three-dimensional chemistry and do not resolve the mesosphere and lower thermosphere (MLT) region of the upper atmosphere. Here we employ a 3D high-top chemistry-climate model (CCM) to simulate the atmospheres of synchronously-rotating planets orbiting at the inner edge of habitable zones of K- and M-dwarf stars (between $T_{\rm eff} =$ 2600 K and 4000 K). While our IHZ climate predictions are in good agreement with GCM studies, we find noteworthy departures in simulated ozone and HO$_{\rm x}$ photochemistry. For instance, climates around inactive stars do not typically enter the classical moist greenhouse regime even with high ($< 10^{-3}$ mol mol$^{-1}$) stratospheric water vapor mixing ratios, which suggests that planets around inactive M-stars may only experience minor water-loss over geologically significant timescales. In addition, we find much thinner ozone layers on potentially habitable moist greenhouse atmospheres, as ozone experiences rapid destruction via reaction with hydrogen oxide radicals. Using our CCM results as inputs, our simulated transmission spectra show that both water vapor and ozone features on moist greenhouse atmospheres could be detectable by instruments NIRSpec and MIRI LRS onboard the James Webb Space Telescope.

astro-ph.EP↗

arXiv2018

Biosignature Anisotropy Modeled on Temperate Tidally Locked M-dwarf Planets

A planet's atmospheric constituents (e.g., O$_2$, O$_3$, H$_2$O$_v$, CO$_2$, CH$_4$, N$_2$O) can provide clues to its surface habitability, and may offer biosignature targets for remote life detection efforts. The plethora of rocky exoplanets found by recent transit surveys (e.g., the Kepler mission) indicates that potentially habitable systems orbiting K- and M-dwarf stars may have very different orbital and atmospheric characteristics than Earth. To assess the physical distribution and observational prospects of various biosignatures and habitability indicators, it is important to understand how they may change under different astrophysical and geophysical configurations, and to simulate these changes with models that include feedbacks between different subsystems of a planet's climate. Here we use a three-dimensional (3D) Chemistry-Climate model (CCM) to study the effects of changes in stellar spectral energy distribution (SED), stellar activity, and planetary rotation on Earth-analogs and tidally-locked planets. Our simulations show that, apart from shifts in stellar SEDs and UV radiation, changes in illumination geometry and rotation-induced circulation can influence the global distribution of atmospheric biosignatures. We find that the stratospheric day-to-night side mixing ratio differences on tidally-locked planets remain low ($<20\%$) across the majority of the canonical biosignatures. Interestingly however, secondary photosynthetic biosignatures (e.g., C$_2$H$_6$S) show much greater (${\sim}67\%$) day-to-night side differences, and point to regimes in which tidal-locking could have observationally distinguishable effects on phase curve, transit, and secondary eclipse measurements. Overall, this work highlights the potential and promise for 3D CCMs to study the atmospheric properties and habitability of terrestrial worlds.

astro-ph.EP↗