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Posts
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portfolio
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publications
Time-dependent density-functional-theory investigation of the collisions of protons and α particles with uracil and adenine
Published in Physical Review A, 2017
Advanced simulation techniques in quantum mechanics have made it possible to understand the effects of high-energy radiation on the molecules that form the basis of key biological functions in great detail. This paper leverages these techniques to understand how high-energy protons and α particles, commonly used in modern radiation therapy, exchange energy and electrons with uracil and adenine, two of the four RNA base molecules.
Recommended citation: Covington, C., Hartig, K., Russakoff, A., Kulpins, R., & Varga, K. (2017). Time-dependent density-functional-theory investigation of the collisions of protons and α particles with uracil and adenine. Physical Review A, 95(5), 052701. https://doi.org/10.1103/PhysRevA.95.052701
3D-printed machines that manipulate microscopic objects using capillary forces
Published in Nature, 2022
Industrial techniques for braiding and weaving fibers struggle to handle micrometer-scale filaments without snapping them. We introduce a novel approach to manipulating filaments on this scale, using centimeter-scale 3D printed devices that take advantage of a repulsive capillary force to gently trap and steer floats and filaments to produce braids of varying complexity.
Recommended citation: Zeng, C., Faaborg, M. W., Sherif, A., Falk, M. J., Hajian, R., Xiao, M., Hartig, K., Bar-Sinai, Y., Brenner, M. P., & Manoharan, V. N. (2022). 3D-printed machines that manipulate microscopic objects using capillary forces. Nature, 611(7934), Article 7934. https://doi.org/10.1038/s41586-022-05234-7
Processes Contributing to North American Cold Air Outbreaks Based on Air Parcel Trajectory Analysis
Published in Journal of Climate, 2023
Despite the observed warming trend of about 1°C globally and 2-3°C in the wintertime Arctic, it is unclear whether wintertime cold air outbreaks over North America have warmed in line with this trend. In this paper, we use the CESM climate model to show that merely originating in the Arctic is not always enough to guarantee that an air mass develops into a cold air outbreak. Instead, Arctic air must receive additional cooling from the surface as it travels over the continent, which may be delaying the decline in cold air outbreaks until Arctic sea ice and North American snow cover retreat further.
Recommended citation: Hartig, K., Tziperman, E., & Loughner, C. P. (2023). Processes Contributing to North American Cold Air Outbreaks Based on Air Parcel Trajectory Analysis. Journal of Climate, 36(3), 931–943. https://doi.org/10.1175/JCLI-D-22-0204.1
Suppression of cold air outbreaks over the interior of North America in a warmer climate
In Revision, Journal of Climate 2023
In spite of the mean warming trend over the last few decades and its amplification in the Arctic, some studies have found no robust decline or even a slight increase in wintertime cold air outbreaks over North America. But fossil evidence from warmer paleoclimate periods indicates that the interior of North America never dropped below freezing even in the depths of winter, which implies that the maintenance of cold air outbreaks is unlikely to continue indefinitely with future warming. This study uses an air parcel trajectory analysis of cold air outbreaks in a pre-industrial vs a much warmer, Eocene-like climate to identify the mechanism of the suppression of cold extremes. We demonstrate a remarkable similarity in both the dynamics and diabatic effects acting on cold air masses in the two climate scenarios.
Understanding the physical processes in the evolution of a cold air outbreak over China in late November 2022 from a Lagrangian perspective
Published in Advances in Climate Change Research, 2023
A nationwide cold air outbreak hit China from 26 November to 1 December 2022. This study uses the evolution of dry static energy along air parcel trajectories to investigate the variation in cooling sources across the regions impacted by this cold air event. Longwave radiative cooling is the largest contributor to the temperature evolution in all regions, with latent heat processes as a secondary effect. Central Siberia and Lake Baikal are identified as key areas where particularly intense cooling of air parcels occurred.
Recommended citation: Che, J.-N., Liu, B., Li, S.-F., You, C., Hartig, K., & Chen, L. (2023). Understanding the physical processes in the evolution of a cold air outbreak over China in late November 2022 from a Lagrangian perspective. Advances in Climate Change Research. https://doi.org/10.1016/j.accre.2023.08.009
Evidence for upwards but not downwards influence between the troposphere and the wintertime stratosphere
Submitted, Journal of Climate 2024
A vortex forms in the wintertime polar stratosphere every year. While there have been many attempts over the years to identify the upward influence that surface weather has on this vortex and a possible downward influence of vortex disruptions on surface conditions, results very dramatically across studies. In this work, we attempt to pick out both the time scales and the patterns of both the upward and downward teleconnection between the troposphere and the wintertime stratosphere using time-lagged Maximum Covariance Analysis. While we find good evidence of two time scales for an upward influence that propagates from the surface to the 10 hPa level, we failed to detect evidence of a downward influence on surface temperature.
talks
Talk 1 on Relevant Topic in Your Field
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Conference Proceeding talk 3 on Relevant Topic in Your Field
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teaching
EPS 101: Global Warming Science
Undergraduate course, Harvard University, Dept. of Earth & Planetary Science, 2021
In the spring term of 2020 and 2021, I served as a teaching fellow for the undergraduate class EPS 101: Global Warming Science. Through a combination of lectures, python coding assignments, and policy memos, students were introduced to the scientific principles underpinning global warming as well as the changes predicted to occur over the next century. Each week, we covered a new topic, ranging from the greenhouse effect to sea level rise, drought, and hurricanes.