The ability of regional air quality models to skilfully represent pollutant
distributions throughout the atmospheric column is important to enabling
their skilful prediction at the surface. This ...provides a requirement for
model evaluation at elevated altitudes, though observation datasets
available for this purpose are limited. This is particularly true of those
offering sampling over extended time periods. To address this requirement
and support evaluation of regional air quality models such as the UK Met
Offices Air Quality in the Unified Model (AQUM), a long-term, quality-assured dataset of the three-dimensional distribution of key pollutants was collected over the southern United Kingdom from July 2019 to April
2022. Measurements were collected using the Met Office Atmospheric Survey
Aircraft (MOASA), a Cessna 421 instrumented for this project to measure
gaseous nitrogen dioxide, ozone, sulfur dioxide and fine-mode (PM2.5)
aerosol. This paper introduces the MOASA measurement platform, flight
strategies and instrumentation and is not intended to be an in-depth
diagnostic analysis but rather a comprehensive technical reference for
future users of these data. The MOASA air quality dataset includes 63 flight sorties (totalling over 150 h of sampling), the data from which are
openly available for use. To illustrate potential uses of these upper-air
observations for regional-scale model evaluation, example case studies are
presented, which include analyses of the spatial scales of measured
pollutant variability, a comparison of airborne to ground-based observations over Greater London and initial work to evaluate performance of the AQUM regional air quality model. These case studies show that, for observations of
relative humidity, nitrogen dioxide and particle counts, natural pollutant
variability is well observed by the aircraft, whereas SO2 variability
is limited by instrument precision. Good agreement is seen between
observations aloft and those on the ground, particularly for PM2.5.
Analysis of odd oxygen suggests titration of ozone is a dominant chemical
process throughout the column for the data analysed, although a slight
enhancement of ozone aloft is seen. Finally, a preliminary evaluation of
AQUM performance for two case studies suggests a large positive model bias
for ozone aloft, coincident with a negative model bias for NO2 aloft.
In one case, there is evidence that an underprediction in the modelled
boundary layer height contributes to the observed biases at elevated
altitudes.
The focus of this work is the development and improvement of chemistry schemes in both 1D and 3D atmosphere models, applied to exoplanets. With an ever increasing number of known exoplanets, planets ...orbiting stars other than the Sun, the diversity in the physical and chemical nature of planets and their atmospheres is becoming more apparent. One of the prime targets, and the focus of many observational and theoretical studies, are the subclass of exoplanets termed hot Jupiters, Jovian sized planets on very short period orbits around their host star.Due to their close orbit, with orbital periods of just a few days, the atmospheres of such planets are heated to very high temperatures (∼ 1000−2000 K) by the intense irradiation from the star. In addition, it is expected that these planets should have synchronised their rotation with their orbital period, a phenomenon called tidallocking, that leads to a permanently illuminated dayside and a perpetually dark nightside. This combination of intense heating and tidal-locking leads to an exotic type of atmosphere that is without analogue in our own Solar system.Observational constraints suggest that some of these atmospheres may be clear whilst others may be cloudy or contain haze. Some hot Jupiters appear to be inflated with radii larger than is expected for their mass. For the warmest hot Jupiters optical absorbing species TiO and VO are expected to be present, due to the thermodynamical conditions, where they can strongly influence the thermal structure of the atmosphere, yet so far these species have remained elusive in observations. Theoretical simulations of these planets appear to provide poor matches to the observed emission flux from the nightside of the planet whilst providing a much better agreement with the observed dayside flux.These outstanding questions can be tackled in two complimentary ways. Firstly, the number of exoplanets subject to intense observational scrutiny must be increased to improve the statistical significance of observed trends. Secondly, and in tandem, the suite of available theoretical models applied to such atmospheres must be improved to allow for a more comprehensive understanding of the potential physical and chemical processes that occur in these atmospheres, as well as for better comparison of model predictions with observations.In this thesis we present the development and application of one-dimensional (1D) and three-dimensional (3D) models to the atmospheres of hot exoplanets, with a focus on improving the representation of chemistry. One of the concerns of this work is to couple the radiative transfer and chemistry calculations in a onedimensional model to allow for a self-consistent model that includes feedback between the chemical composition and the thermal structure. We apply this model to the atmospheres of two typical hot Jupiters to quantify this effect. Implications for previous models that do not include this consistency are discussed.Another major focus is to improve the representation of chemistry in the Met Office Unified Model (UM) for exoplanet applications, a three-dimensional model with its heritage in modelling the Earth atmosphere that has recently been applied to exoplanets. We discuss the coupling of two new chemistry schemes that improve both the flexibility and capabilities of the UM applied to exoplanets. Ultimately these developments will allow for a consistent approach to calculate the 3D chemical composition of the atmosphere taking into account the effect of large scale advection, one of the processes currently hypothesised to cause the discrepancy between model predictions and observations of the nightside emission flux of many hot Jupiters.
To study the complexity of hot Jupiter atmospheres revealed by observations of increasing quality, we have adapted the UK Met Office Global Circulation Model (GCM), the Unified Model (UM), to these ...exoplanets. The UM solves the full 3D Navier-Stokes equations with a height-varying gravity, avoiding the simplifications used in most GCMs currently applied to exoplanets. In this work we present the coupling of the UM dynamical core to an accurate radiation scheme based on the two-stream approximation and correlated-k method with state-of-the-art opacities from ExoMol. Our first application of this model is devoted to the extensively studied hot Jupiter HD 209458b. We derive synthetic emission spectra and phase curves, and compare them to both previous models also based on state-of-the-art radiative transfer, and to observations. We find a reasonable a agreement between observations and both our days side emission and hot spot offset, however, our night side emissions is too large. Overall our results are qualitatively similar to those found by Showman et al. (2009) with the SPARCMIT gcm, however, we note several quantitative differences: Our simulations show significant variation in the position of the hottest part of the atmosphere with pressure, as expected from simple timescale arguments, and in contrast to the vertical coherency found by Showman et al. (2009). We also see significant quantitative differences in calculated synthetic observations. Our comparisons strengthen the need for detailed intercomparisons of dynamical cores, radiation schemes and post-processing tools to understand these differences. This effort is necessary in order to make robust conclusions about these atmospheres based on GCM results.
We present a grid of forward model transmission spectra, adopting an isothermal temperature-pressure profile, alongside corresponding equilibrium chemical abundances for 117 observationally ...significant hot exoplanets (equilibrium temperatures of 547-2710 K). This model grid has been developed using a 1D radiative-convective-chemical equilibrium model termed ATMO, with up-to-date high-temperature opacities. We present an interpretation of observations of 10 exoplanets, including best-fitting parameters and X(exp 2) maps. In agreement with previous works, we find a continuum from clear to hazy/cloudy atmospheres for this sample of hot Jupiters. The data for all the 10 planets are consistent with subsolar to solar C/O ratio, 0.005 to 10 times solar metallicity and water rather than methane-dominated infrared spectra. We then explore the range of simulated atmospheric spectra for different exoplanets, based on characteristics such as temperature, metallicity, C/O ratio, haziness and cloudiness. We find a transition value for the metallicity between 10 and 50 times solar, which leads to substantial changes in the transmission spectra. We also find a transition value of C/O ratio, from water to carbon species dominated infrared spectra, as found by previous works, revealing a temperature dependence of this transition point ranging from approximately 0.56 to approximately 1-1.3 for equilibrium temperatures from approximately 900 to approximately 2600 K. We highlight the potential of the spectral features of HCN and C2H2 to constrain the metallicities and C/O ratios of planets, using James Webb Space Telescope (JWST) observations. Finally, our entire grid (approximately 460 000 simulations) is publicly available and can be used directly with the JWST simulator PandExo for planning observations.
We present a primary transit observation for the ultra-hot ( T {sub eq} ∼ 2400 K) gas giant expolanet WASP-121b, made using the Hubble Space Telescope Wide Field Camera 3 in spectroscopic mode across ...the 1.12–1.64 μ m wavelength range. The 1.4 μ m water absorption band is detected at high confidence (5.4 σ ) in the planetary atmosphere. We also reanalyze ground-based photometric light curves taken in the B , r ′, and z ′ filters. Significantly deeper transits are measured in these optical bandpasses relative to the near-infrared wavelengths. We conclude that scattering by high-altitude haze alone is unlikely to account for this difference and instead interpret it as evidence for titanium oxide and vanadium oxide absorption. Enhanced opacity is also inferred across the 1.12–1.3 μ m wavelength range, possibly due to iron hydride absorption. If confirmed, WASP-121b will be the first exoplanet with titanium oxide, vanadium oxide, and iron hydride detected in transmission. The latter are important species in M/L dwarfs and their presence is likely to have a significant effect on the overall physics and chemistry of the atmosphere, including the production of a strong thermal inversion.
We present a primary transit observation for the ultra-hot (T sub(eq)~ 2400 K) gas giant expolanet WASP-121b, made using the Hubble Space Telescope Wide Field Camera 3 in spectroscopic mode across ...the 1.12-1.64 mu m wavelength range. The 1.4 mu m water absorption band is detected at high confidence (5.4sigma) in the planetary atmosphere. We also reanalyze ground-based photometric light curves taken in the B, r', and z' filters. Significantly deeper transits are measured in these optical bandpasses relative to the near-infrared wavelengths. We conclude that scattering by high-altitude haze alone is unlikely to account for this difference and instead interpret it as evidence for titanium oxide and vanadium oxide absorption. Enhanced opacity is also inferred across the 1.12-1.3 mu m wavelength range, possibly due to iron hydride absorption. If confirmed, WASP-121b will be the first exoplanet with titanium oxide, vanadium oxide, and iron hydride detected in transmission. The latter are important species in M/L dwarfs and their presence is likely to have a significant effect on the overall physics and chemistry of the atmosphere, including the production of a strong thermal inversion.
The effect of enhanced UV irradiation associated with stellar flares on the atmospheric composition and temperature of gas giant exoplanets was investigated. This was done using a 1D ...radiative-convective-chemical model with self-consistent feedback between the temperature and the non-equilibrium chemistry. It was found that flare-driven changes to chemical composition and temperature give rise to prolonged trends in evolution across a broad range of pressure levels and species. Allowing feedback between chemistry and temperature plays an important role in establishing the quiescent structure of these atmospheres, and determines their evolution due to flares. It was found that cooler planets are more susceptible to flares than warmer ones, seeing larger changes in composition and temperature, and that temperature-chemistry feedback modifies their evolution. Long-term exposure to flares changes the transmission spectra of gas giant atmospheres; these changes differed when the temperature structure was allowed to evolve self-consistently with the chemistry. Changes in spectral features due to the effects of flares on these atmospheres can be associated with changes in composition. The effects of flares on the atmospheres of sufficiently cool planets will impact observations made with JWST. It is necessary to use self-consistent models of temperature and chemistry in order to accurately capture the effects of flares on features in the transmission spectra of cooler gas giants, but this depends heavily on the radiation environment of the planet.
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