Can AKIN

In this paper, we investigated a theoretically proposed and widely observed "flow regime transition" as we simulated a curated sample of 8 planets ranging from hot Jupiters to the regime of ultra-hot Jupiters $\left( 1100~\mathrm{K}\leq T_{\mathrm{eq}} \leq 2400~\mathrm{K}\right)$. The aforementioned flow transition is from a regime dominated by zonal jets, which is a common feature observed hot Jupiters, into a regime where the flow is dominated by day-to-night winds for the hotter planets. In order to facilitate this analysis, we developed a novel wavelet-based method and applied it to our sample of planets and dissected the simulated wind fields into time-dependent power spectra. This way we were able connect the flow transition to the disruption of the coupling between planetary-scale wave modes and smaller-scale eddy modes, a result of increasing stellar irradiation as we increase in equilibrium temperature.

This is the first paper published as a part of my PhD studies and highlights my main areas of expertise: Working with general circulation models (GCMs) applied to gas giant atmospheres and developing analysis techniques to infer useful physics from simulations.

Published Paper (A&A, 2025) Code

In this paper, we focused on the coolest class of brown dwarfs, called Y dwarfs. While recent years have seen a surge of observations and modelling efforts focused on these objects, 3D circulation models of Y dwarfs are a largerly unexplored area of research. For this purpose we curated a sample of models spanning the parameter space of temperature ranges $400~\mathrm{K} \leq T_{\mathrm{eff}} \leq 600~\mathrm{K}$ and rotation rates $P_{\mathrm{rot}} = 2.5 ~\text{-} 20\, \mathrm{h}$, effectively covering possible Y dwarf configurations. Additionally, we included multiple salt ($\mathrm{KCl},\,\mathrm{Na_{2}S}$) and sulfide ($\mathrm{MnS}$) species in our simulations to probe the interplay of rotation, convection and cloud thermal feedback effects. The resulting Y dwarf atmospheres are weakly dynamic and less variable than observations, resulting in our conclusion that the physical mechanisms behind their observed variability remains unknown.

This paper is my second first-author paper and also the final paper of my PhD. A result of my growing interest into performing 3D simulations brown dwarf atmospheres, it resulted in the development of many new physics modules for our in-house GCM THOR. The modifications can be found on my private GitHub repository linked below.

Published Paper (A&A, 2026) Code

In this paper, we report the detection of sodium and refractory metals in an evoporating tail of the ultra-hot Jupiter Kelt-9b. Combining four different datasets of optical transit observations and performing a cross-correlation analysis of our datasets reveals a distinct and robust absorption signal clearly separated from the planetary signal, which we interpret as consistent with an evaporative tail. We go through the different components in the measured signals, discuss possible alternative explanations and develop a simplified model to retrieve the physical properties of the tail. The result is, to our knowledge the first detection of an evaporating tail in the optical wavelength regime and the retrieved physical parameters are consistent with literature values.

I am a shared (between Nicholas Borsato, Leonardos Gkouvelis and myself) first-author on this paper. The mathematical formulation of the toy model along with the physics behind it and the code to simulate the system were developed through discussions between Leo and I, whereas the analysis of the data and the retrievals were performed by Nic Borsato.

In peer review Updated: 16 September 2025