Research
My research focuses on how waves and flows transport energy and information through the Sun, from the near-surface layers to the deep interior. By combining high-resolution observations with helioseismic analysis, I use waves as diagnostics of plasma conditions, magnetic structure, and large-scale dynamics that are otherwise difficult to measure directly.
Broadly, my work falls into three interconnected areas:
- Atmospheric gravity waves in the lower solar atmosphere
- Small-scale vortex dynamics and chromospheric swirls
- Global inertial modes, including equatorial Rossby waves
Across these projects, I aim to understand why the observed dynamics matter physically, how they can be measured reliably, and what they reveal about energy and momentum transport in a magnetized, stratified plasma.
Atmospheric gravity waves
Motivation
Atmospheric gravity waves are buoyancy-driven oscillations with typical frequencies of about 1–4 mHz. They are excited by turbulent convection and propagate obliquely through the photosphere and chromosphere. These waves are a plausible contributor to atmospheric dynamics and energy transport, but their behavior is strongly influenced by radiative damping and magnetic fields. As a result of their low temporal frequencies, short vertical wavelengths, and oblique propagation, observations have historically been limited on these waves.
Because of this sensitivity, gravity waves provide a powerful diagnostic of the upper photospheric magnetic field, a regime otherwise difficult to measure.
Observations and methods
I study atmospheric gravity waves using high-resolution, multi-height spectroscopy from the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope, combined with contextual data from the Solar Dynamics Observatory, especially HMI vector magnetograms.
My analysis includes Fourier spectral techniques applied to Doppler velocity and intensity fluctuations to compute phase differences and magnitude-squared coherence in horizontal wavenumber–frequency space. I also use time–distance and cross-correlation methods to measure horizontal propagation properties and compare them with simplified forward models. In magnetic regions, I apply coherence-weighted phase-difference mapping and analyze trends as functions of magnetic field strength and inclination.
Key results
In a multi-height disk-center study, I identified clear signatures of upward-propagating atmospheric gravity waves across several spectral diagnostics, with the expected negative phase differences persisting to chromospheric heights. Time–distance analysis yielded an average horizontal group speed of about 4.5 km s⁻¹. Comparisons with numerical models showed that radiative damping, with a characteristic timescale of roughly 60 seconds, cannot reproduce the observed phase behavior.
In a follow-up study focused on magnetic effects, I found that gravity wave propagation is strongly modulated by magnetic geometry. Waves are efficiently suppressed or reflected in intermediate to strong, predominantly vertical fields in the upper photosphere, while they propagate more freely in quiet-Sun and transverse field configurations. These results are consistent with forward modeling and support the use of gravity waves as magnetoseismology diagnostics of average magnetic properties in the lower solar atmosphere.
Chromospheric swirls
Motivation
Chromospheric swirls are small-scale vortex flows observed in the quiet-Sun chromosphere. They represent a mechanism by which photospheric convection and magnetic footpoint motions can couple to higher atmospheric layers. Such vortex dynamics are also linked to wave generation, including torsional Alfvénic perturbations, and therefore to energy and momentum transport.
Observations and methods
I analyze high-cadence, multi-height imaging data from the Dunn Solar Telescope using HARDcam narrowband Hα observations and simultaneous ROSA broadband channels, including G-band and Ca II K. These data provide co-temporal and co-spatial coverage from the low photosphere to the mid chromosphere.
Swirls are identified and tracked using image segmentation techniques. Their evolution is quantified through local correlation tracking and spectral analysis. Rotational and radial motions are extracted using polar coordinate time–angle and radius–time maps, with automated fitting methods to measure characteristic speeds and periods.
Key results
Using these data, I carried out the first systematic detection of chromospheric swirls in these observations, identifying a sample of 34 swirls with multi-height coverage. Typical lifetimes are about 8 minutes, with mean diameters of roughly 3.6 Mm and angular speeds near 0.04 rad s⁻¹. Median radial expansion speeds are approximately 18 km s⁻¹, with characteristic periods around 180 seconds.
Most swirls, about 76 percent, are associated with compact magnetic bright points that appear shortly after swirl formation. The close correspondence between swirl evolution and bright-point motion supports a magnetic footpoint origin. A detailed case study shows evidence consistent with an upward-propagating torsional Alfvénic perturbation contributing to swirl development. I do not find clear signatures of kink or sausage modes in these data, suggesting that such modes are absent or below the detection threshold for the available diagnostics.
Inertial modes and equatorial Rossby waves
Motivation
Equatorial Rossby waves are global-scale inertial modes that propagate retrograde relative to solar rotation. They have emerged as valuable probes of solar interior dynamics and solar-cycle variability, but their depth dependence and subsurface structure remain uncertain. Different helioseismic techniques have produced differing results, making observational constraints on their vertical structure particularly important.
Understanding these modes informs how angular momentum and energy are redistributed in rotating, stratified interiors and how large-scale flows interact with magnetic fields.
Observations and methods
I study Rossby waves using HMI/SDO helioseismic flow maps from two independent pipelines: ring-diagram horizontal flows at multiple near-surface depths and time–distance flows extending deeper into the interior.
Horizontal flows are converted to radial vorticity and decomposed into spherical harmonics. In the frequency domain, I isolate the Rossby wave ridge and compute normalized phase differences and cross power between depths relative to a near-surface reference layer.
Key results
I find a robust depth dependence in the Rossby wave phase structure. Deeper layers systematically lead in phase relative to shallower layers, with the magnitude of the phase shift increasing with depth. This behavior is consistent with a retrograde tilt of the Rossby wave structure relative to solar rotation.
The inferred tilt shows no clear solar-cycle dependence, suggesting a stable inclined structure over the time interval analyzed. In contrast, the depth-dependent cross power correlates positively with the solar cycle in both ring-diagram and time–distance data. Cross power decreases with depth down to about 9 Mm, with reductions of roughly 6–12 percent depending on the dataset. These results provide new observational constraints on near-surface Rossby wave structure and reinforce their diagnostic value for interior dynamics and angular momentum transport.
Publications highlighted here
- Vesa, Jackiewicz, and Reardon, 2023, The Astrophysical Journal: Multiheight Observations of Atmospheric Gravity Waves at Solar Disk Center
- Vesa et al., 2025, The Astrophysical Journal: Atmospheric Gravity Waves Modulated by the Magnetic Field Configuration
- Vesa, Shetye, and Verwichte, 2025, Monthly Notices of the Royal Astronomical Society: First High-Resolution Observations of Chromospheric Swirls with the Dunn Solar Telescope
- Vesa, Zhao, and Chen, 2026 (in press at The Astrophysical Journal): Structural Tilting and Depth-Dependent Behavior of Equatorial Rossby Waves