USTC 2024 Outstanding Graduation Thesis Award
Published:
USTC awarded my undergraduate thesis a 2024 Outstanding Graduation Thesis Award. The thesis studied the 2022 Tonga volcanic eruption’s disturbance of the mesosphere and lower thermosphere using WACCM-X simulations and observations.
Author: Koutian Wu; GitHub: ktwu01
The award list, issued by the USTC Office of Teaching Affairs in June 2024, names 87 graduating students. My thesis was one of them.
The question
On January 15, 2022, the Hunga Tonga–Hunga Haʻapai volcano in the South Pacific erupted with a force rarely seen in the instrument era. The blast sent a pressure pulse around the planet several times. Barometers on every continent recorded it. The question my thesis asked was what that pulse did far above the weather, in the mesosphere and lower thermosphere, the layer between roughly 70 and 110 kilometers where meteors burn up and the atmosphere starts to thin into space.
That layer is hard to observe. It is too high for weather balloons and too low for most satellites to sample directly. Two tools reach it well: meteor radars, which measure winds from the drift of meteor trails, and whole-atmosphere models such as WACCM-X, which simulate the atmosphere from the ground up to about 500 kilometers.
What I did
I worked with the WACCM-X simulation and observations from four meteor radar stations.
- Point every station at the volcano. A wave spreading out from a point source travels along great circles. I projected each station’s measured winds onto the great-circle direction from the eruption, so that every station looked at the same component of the disturbance.
- Compare model and observation directly. I put WACCM-X output next to the radar data in three ways: vertical profiles, perturbation amplitudes, and wavelet spectra that show how the wave’s period changes over time.
The model and the radars agreed that the eruption’s waves reached the upper atmosphere at stations far from Tonga, confirming in both simulation and observation that a single volcano can send disturbances around the whole Earth and up to the edge of space.
I presented an early version as a poster at the AGU Fall Meeting 2023 in San Francisco, with H.-L. Liu, Wen Yi, and Xianghui Xue as coauthors.
Why it was worth a thesis
Natural experiments this clean are rare in atmospheric science. Most waves in the upper atmosphere come from many overlapping sources: storms, mountains, jet streams. The Tonga eruption was a single, sudden, well-located source, and everything that followed had a known start time and place. That makes it a test case for the models. If WACCM-X can reproduce the arrival, amplitude, and period of a wave whose source we know exactly, we can trust it more on the waves whose sources we cannot see.
One eruption gave the upper atmosphere a clean signal, and the job was to read it carefully.
See the official award list.
