Publications by Patrick Irwin


Neptune’s HCl upper limit from Herschel/HIFI

Icarus (0)

N Teanby, B Gould, P Irwin


Uranus in Northern Midspring: Persistent Atmospheric Temperatures and Circulations Inferred from Thermal Imaging

The Astronomical Journal American Astronomical Society 159 (0) 45-45

MT Roman, LN Fletcher, GS Orton, N Rowe-Gurney, PGJ Irwin


2.5-D retrieval of atmospheric properties from exoplanet phase curves: Application to WASP-43b observations

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (0)

PGJ Irwin, V Parmentier, J Taylor, J Barstow, S Aigrain, GKH Lee, R Garland

We present a novel retrieval technique that attempts to model phase curve observations of exoplanets more realistically and reliably, which we call the 2.5-dimension (2.5-D) approach. In our 2.5-D approach we retrieve the vertical temperature profile and mean gaseous abundance of a planet at all longitudes and latitudes \textbf{simultaneously}, assuming that the temperature or composition, $x$, at a particular longitude and latitude $(\Lambda,\Phi)$ is given by $x(\Lambda,\Phi) = \bar{x} + (x(\Lambda,0) - \bar{x})\cos^n\Phi$, where $\bar{x}$ is the mean of the morning and evening terminator values of $x(\Lambda,0)$, and $n$ is an assumed coefficient. We compare our new 2.5-D scheme with the more traditional 1-D approach, which assumes the same temperature profile and gaseous abundances at all points on the visible disc of a planet for each individual phase observation, using a set of synthetic phase curves generated from a GCM-based simulation. We find that our 2.5-D model fits these data more realistically than the 1-D approach, confining the hotter regions of the planet more closely to the dayside. We then apply both models to WASP-43b phase curve observations of HST/WFC3 and Spitzer/IRAC. We find that the dayside of WASP-43b is apparently much hotter than the nightside and show that this could be explained by the presence of a thick cloud on the nightside with a cloud top at pressure $< 0.2$ bar. We further show that while the mole fraction of water vapour is reasonably well constrained to $(1-10)\times10^{-4}$, the abundance of CO is very difficult to constrain with these data since it is degenerate with temperature and prone to possible systematic radiometric differences between the HST/WFC3 and Spitzer/IRAC observations. Hence, it is difficult to reliably constrain C/O.


The solar reflected component in Jupiter's 5-μm spectra from NIMS/Galileo observations

Journal of Geophysical Research E: Planets 103 (1998) 23043-23049

P Drossart, M Roos-Serote, T Encrenaz, E Lellouch, KH Baines, RW Carlson, LW Kamp, GS Orton, S Calcutt, P Irwin, FW Taylor, A Weir

A comparison between low-flux dayside and nightside spectra of Jupiter recorded by the Galileo near-infrared mapping spectrometer (NIMS) experiment gives the first accurate estimate of the solar reflected component at 5 μm, in the equatorial zone of Jupiter. A minimum flux level of about 0.6 μW cm-2 sr-1V/μm is found on the dayside, compared with 0.1 /μW cm-2 sr-1/μm on the nightside. These fluxes are 100-800 times lower respectively than the bright 5-μm thermal emission in the north equatorial belt (NEB) hot spots. The day/night difference can be interpreted as a solar reflected component from a cloud, presumably the ammonia cloud, with an albedo of the order of 15%, located at a pressure level of 0.79 bar or at higher altitudes (corresponding to cloud temperature of 160 K or lower). Compared to the measurements in hot spots made at other wavelengths from ground-based observations and from NIMS real time spectra, they imply a high cloud opacity in cold regions at atmospheric levels where the cloud optical depth in the hot spots is very low. The residual flux on the nightside arises from (1) a very small cloud transparency giving some access to deeper thermal emission or (2) as high-resolution solid-state imaging (SSI) images of Galileo suggest, to cloud inhomogeneities, with clearer regions of medium brightness temperatures, mixed with dark regions of much lower thermal emission. If the former have the same brightness as a typical hot spot, a filling factor of a few percent is sufficient to explain the observed flux level on the nightside cold regions. Copyright 1998 by the American Geophysical Union.


Cloud structure and atmospheric composition of Jupiter retrieved from Galileo near-infrared mapping spectrometer real-time spectra

Journal of Geophysical Research E: Planets 103 (1998) 23001-23021

PGJ Irwin, AL Weir, SE Smith, FW Taylor, AL Lambert, SB Calcutt, PJ Cameron-Smith, RW Carlson, K Baines, GS Orton, P Drossart, T Encrenaz, M Roos-Serote

The first four complete spectra recorded by the near infrared mapping spectrometer (NIMS) instrument on the Galileo spacecraft in 1996 have been analyzed. These spectra remain the only ones which have been obtained at maximum resolution over the entire NIMS wavelength range of 0.7 - 5.2 μm. The spectra cover the edge of a "warm" spot at location 5°N, 85°W. We have analyzed the spectra first with reflecting layer models and then with full multiple scattering models using the method of correlated-k. We find that there is strong evidence for three different cloud layers composed of a haze consistent with 0.5-μm radius tholins at 0.2 bar, a cloud of 0.75-lim NH3 particles at about 0.7 bar, and a two-component NH4SH cloud at about 1.4 bars with both 50.0- and 0.45-μm particles, the former being responsible for the main 5-μm cloud opacity. The NH3 relative humidity above the cloud tops is found to decrease slightly as the 5-μm brightness increases, with a mean value of approximately 14%. We also find that the mean volume mixing ratio of ammonia above the middle (NtL4SH) cloud deck is (1.7± 0.1) × 10-4 and shows a similar, though less discernible decrease with increasing 5-μm brightness. The deep volume mixing ratios of deuterated methane and phosphine are found to be constant and we estimate their mean values to be (4.9± 0.2) × 10-7 and (7.7 ± 0.2) × 10-7, respectively. The fractional scale height of phosphine above the 1 bar level is found to be 27.1± 1.4% and shows a slight decrease with increasing 5-μm brightness. The relative humidity of water vapor is found to be approximately 7%, but while this and all the previous observations are consistent with the assumption that "hot spots" are regions of downwelling, desiccated air, we find that the water vapor relative humidity increases as the 5-μm brightness increases. Copyright 1998 by the American Geophysical Union.


Radiative transfer models for Galileo NIMS studies of the atmosphere of Jupiter

ADV SPACE RES 19 (1997) 1149-1158

PGJ Irwin, SB Calcutt, FW Taylor

Scientific results from NIMS observations of Venus have been extensively reported in the literature, while those of Jupiter have, at the time of writing, just barely commenced. The planning and interpretation of studies of these planets, with their massive atmospheres and exotic compositions (by terrestrial standards), requires a comprehensive treatment of radiative transfer in both. This paper describes work done at Oxford to develop the underlying theory and practical radiative transfer schemes, with particular reference to the NIMS wavelength range, spectral resolution, and scientific objectives for Jupiter. Equivalent work for Venus has already been reported in the literature (e.g. Kamp and Taylor, 1990) and will not be covered in detail here. (C) 1997 COSPAR. Published by Elsevier Science Ltd.


Temporal and spatial variations in the Venus mesosphere retrieved from Pioneer Venus OIR

Advances in Space Research 19 (1997) 1169-1179

PGJ Irwin

Measurements of the Venus mesosphere made in 1978/79 by the Pioneer Venus Orbiter Infrared Radiometer (OIR) have been reanalysed. An optimal estimation retrieval technique has been applied to data from individual orbits. These retrievals reveal the structure of transient features such as the polar dipole and polar collar and short term variations in water vapour abundance and cloud top height. High abundances of water vapour are observed at equatorial latitudes in the early afternoon with a spatial structure which appears consistent with the ultraviolet 'Y' shaped structure. Additionally a two to four day period is observed in both water vapour abundance and cloud top height which is the characteristic period of this ultraviolet feature. © 1997 COSPAR. Published by Elsevier Science Ltd.


ISO LWS far-infrared observations of jupiter and saturn

European Space Agency, (Special Publication) ESA SP (1997) 325-328

PG Oldham, MJ Griffin, GR Davis, T Encrenaz, T De Graauw, PJ Irwin, BM Swinyard, DA Naylor, M Burgdorf

Portions of the far-infrared spectra of Jupiter and Saturn measured in grating mode with the ISO Long Wavelength Spectrometer (LWS) are presented. The observed Jovian spectrum between 55 and 90 μm is compared to an atmospheric radiative transfer model using expected values for the constituent vertical concentration profiles. Rotational transitions of ammonia are responsible for the absorption features observed against the hydrogen continuum emission. There is good agreement between the model and data for an ammonia mole fraction of 2×10-4 constrained by saturation up to a 75 mbar cut-off, above which it is assumed all the ammonia is destroyed by ultraviolet radiation. Three sections of the saturnian spectrum are compared to synthetic spectra and absorption features due to methane are identified. The mole fraction of methane is constrained between 0.7-1.5 10-3.


Remote sounding of the Martian atmosphere in the context of the InterMarsNet mission: General circulation and meteorology

PLANET SPACE SCI 44 (1996) 1347-1360

FW Taylor, SB Calcutt, PGJ Irwin, DJ McCleese, JT Schofield, DO Muhleman, RT Clancy, CB Leovy

A concept has been developed for a remote sensing experiment to investigate the physics of the Martian atmosphere from a spin-stabilized orbiter, like that planned for the InterMarsNet mission. Using coincident infrared and microwave channels and limb-to-limb scanning, it can map the planet much more extensively than previously in temperature atmospheric dust loading, and humidity. When combined with one or more surface stations measuring the same variables, the sounder experiment can contribute to major progress in understanding the general circulation and dust and water cycles of the atmosphere of Mars, and the characterization of medium-scale meteorological systems. Copyright (C) 1996 Elsevier Science Ltd


ISO LWS measurement of the far-infrared spectrum of Saturn

Astronomy and Astrophysics 315 (1996)

GR Davis, MJ Griffin, DA Naylor, RG Oldham, BM Swinyard, PAR Ade, SB Calcutt, T Encrenaz, T De Graauw, D Gautier, PGJ Irwin, E Lellouch, GS Orton, C Armand, M Burgdorf, A Di Giorgio, D Ewart, C Gry, KJ King, T Lim, S Molinari, M Price, S Sidher, A Smith, D Texier, N Trams, SJ Unger

The spectrum of Saturn from 43 to 197 μm was measured with the ISO Long Wavelength Spectrometer (LWS) during the performance verification phase of the mission. The measurements were made using the LWS in grating mode, with spectral resolutions of 0.29 μm from 43 to 90 μm and 0.6 μm from 90 to 197 μm. The spectrum was compared with an atmospheric radiative-transfer model and four results were obtained: first, the slope of the measured continuum within each detector passband is in good agreement with the model; second, absorption features due to ammonia and phosphine were unambiguously detected, and all detected features were attributed to these two molecules; third, the ammonia absorption features agree reasonably well with the nominal model (based on Voyager IRIS measurements); and fourth, the phosphine absorption features disagree with the nominal model. Superior agreement with the measured spectrum was obtained with a modified PH3 profile in which the tropospheric mixing ratio was increased to 7 × 10-6 and the cutoff due to photodissociation was lowered to 300 mbar. These results are based on trial observations during performance verification of the LWS, and provide an indication of the results we expect to obtain when the spectrum of Saturn is measured comprehensively later in the mission.


Near-infrared spectroscopy and spectral mapping of Jupiter and the Galilean satellites: results from Galileo's initial orbit.

Science (New York, N.Y.) 274 (1996) 385-388

R Carlson, W Smythe, K Baines, E Barbinis, K Becker, R Burns, S Calcutt, W Calvin, R Clark, G Danielson, A Davies, P Drossart, T Encrenaz, F Fanale, J Granahan, G Hansen, P Herrera, C Hibbitts, J Hui, P Irwin, T Johnson, L Kamp, H Kieffer, F Leader, P Weissman

The Near Infrared Mapping Spectrometer performed spectral studies of Jupiter and the Galilean satellites during the June 1996 perijove pass of the Galileo spacecraft. Spectra for a 5-micrometer hot spot on Jupiter are consistent with the absence of a significant water cloud above 8 bars and with a depletion of water compared to that predicted for solar composition, corroborating results from the Galileo probe. Great Red Spot (GRS) spectral images show that parts of this feature extend upward to 240 millibars, although considerable altitude-dependent structure is found within it. A ring of dense clouds surrounds the GRS and is lower than it by 3 to 7 kilometers. Spectra of Callisto and Ganymede reveal a feature at 4. 25 micrometers, attributed to the presence of hydrated minerals or possibly carbon dioxide on their surfaces. Spectra of Europa's high latitudes imply that fine-grained water frost overlies larger grains. Several active volcanic regions were found on Io, with temperatures of 420 to 620 kelvin and projected areas of 5 to 70 square kilometers.


Remote sounding of the Martian atmosphere in the context of the InterMarsNet mission: General circulation and meteorology

Planetary and Space Science 44 (1996) 1347-1360

FW Taylor, SB Calcutt, PGJ Irwin, DJ McCleese, JT Schofield, DO Muhleman, RT Clancy, CB Leovy

A concept has been developed for a remote sensing experiment to investigate the physics of the Martian atmosphere from a spin-stabilized orbiter, like that planned for the InterMarsNet mission. Using coincident infrared and microwave channels and limb-to-limb scanning, it can map the planet much more extensively than previously in temperature, atmospheric dust loading, and humidity. When combined with one or more surface stations measuring the same variables, the sounder experiment can contribute to major progress in understanding the general circulation and dust and water cycles of the atmosphere of Mars, and the characterization of medium-scale meteorological systems. Copyright © 1996 Elsevier Science Ltd.


Calculated k distribution coefficients for hydrogen- And self-broadened methane in the range 2000-9500 cm<sup>-1</sup> from exponential sum fitting to band-modelled spectra

Journal of Geophysical Research E: Planets 101 (1996) 26137-26154

PGJ Irwin, SB Calcutt, FW Taylor, AL Weir

The spectral band data derived by Strong et al. [1993] for laboratory-measured transmission spectra of hydrogen-broadened methane at 10 cm-1 resolution have been fitted with k coefficients over a wide range of pressures and temperatures representing those likely to be encountered in the atmosphere of Jupiter. The mean fitting error is found to be only 2.0×10-3 in transmission. These data are essential for the scattering calculations likely to be necessary for analysis of the data from the Near Infrared Mapping Spectrometer aboard the NASA Galileo spacecraft. The new data have significant advantages over those previously derived by Baines et al. [1993] in that they cover a wider spectral range, are applicable to longer paths, and also apply to the hydrogen-broadened case, which is the dominant broadening mechanism in this atmosphere. A similar table has also been calculated for the self-broadening case for comparison. Copyright 1996 by the American Geophysical Union.


Characterization of the thermodynamic behaviour of pressure modulated cells for remote sensing of the atmosphere of Mars

Journal of Quantitative Spectroscopy and Radiative Transfer 52 (1994) 1-20

PGJ Irwin, SB Calcutt, FW Taylor

A radiometric experiment was conducted to investigate the thermodynamic behaviour of the H2O and CO2 pressure modulated cells of the Pressure Modulator Infrared Radiometer (PMIRR) which flew on "Mars Observer" in 1992. The wave forms and phases of the transmission, emission, pressure and piston position cycles, together with the mean absorption were, for the first time, all measured during the same experiment. The measured transmission and emission cycles were used to calculate the phase and amplitude of the temperature cycles and were found to be super-adiabatic for both cells, in reasonable agreement with a thermal diffusion model. Anomalies were seen in the H2O modulator driving frequency, as has been observed by other authors, but none were evident in the measured cell wave forms suggesting that the water vapour behaves as an ideal gas in the cell. © 1994.


Investigation of dielectric spaced resonant mesh filter designs for PMIRR

Infrared Physics 34 (1993) 549-563

PGJ Irwin, PAR Ade, SB Calcutt, FW Taylor, JS Seeley, R Hunneman, L Walton

The fabrication of the filters for the two longest wave channels of the Pressure Modulator Infra-red Radiometer (PMIRR), launched in September 1992 on Mars Observer, was not possible using conventional multilayer dielectric techniques. Thus the extension of far-infrared/microwave mesh filter designs was investigated using a new dielectric spacing material. Test filters were designed and fabricated and, using their measured transmission spectra, a new model of the behaviour of resonant meshes in both air and dielectrics was developed. The low transmission of these filters in the end made them unsuitable for PMIRR but the model provides a useful design tool for future dielectric spaced filters providing a new, less absorbing dielectric can be found. © 1993.


Neptune and Uranus: ice or rock giants?

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences Royal Society, The (0)

N Teanby, P Irwin, J Moses, R Hellad


ORTIS Design and development report

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PG Irwin, B Ellison, S Calcutt


Preliminary report on sub-millimetre spectra of Jupiter and Saturn.

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PG Irwin


Second report on sub-millimetre spectra of Jupiter, Saturn and Titan.

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PG Irwin


C2N2 vertical profile in Titan’s stratosphere

The Astronomical Journal American Astronomical Society (0)

M Sylvestre, N Teanby, M Dobrijevic, J Sharkey, P Irwin

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