Publications by Patrick Irwin


Optimal estimation retrievals of the atmospheric structure and composition of HD189733b from secondary eclipse spectroscopy

Monthly Notices of the Royal Astronomical Society (2011)

J-M Lee, LN Fletcher, PGJ Irwin


Models of the global cloud structure on Venus derived from Venus Express observations

Icarus (2011)

JK Barstow, CCC Tsang, CF Wilson, PGJ Irwin, FW Taylor, K McGouldrick, P Drossart, G Piccioni, S Tellmann


Spatial and temporal variations in Titan's surface temperatures from Cassini CIRS observations

Planetary and Space Science (2011)

V Cottini, CA Nixon, DE Jennings, R de Kok, NA Teanby, PGJ Irwin, FM Flasar


Saturn's tropospheric composition and clouds from Cassini/VIMS 4.6-5.1 μm nightside spectroscopy

Icarus (2011)

LN Fletcher, KH Baines, TW Momary, AP Showman, PGJ Irwin, GS Orton, M Roos-Serote, C Merlet


Uranus' cloud structure and seasonal variability from Gemini-North and UKIRT observations

Icarus 212 (2011) 339-350

PGJ Irwin, NA Teanby, GR Davis, LN Fletcher, GS Orton, D Tice, A Kyffin

Observations of Uranus were made in September 2009 with the Gemini-North telescope in Hawaii, using both the NIFS and NIRI instruments. Observations were acquired in Adaptive Optics mode and have a spatial resolution of approximately 0.1″ NIRI images were recorded with three spectral filters to constrain the overall appearance of the planet: J, H-continuum and CH4(long), and long slit spectroscopy measurements were also made (1.49-1.79μm) with the entrance slit aligned on Uranus' central meridian. To acquire spectra from other points on the planet, the NIFS instrument was used and its 3″×3″ field of view stepped across Uranus' disc. These observations were combined to yield complete images of Uranus at 2040 wavelengths between 1.476 and 1.803μm. The observed spectra along Uranus central meridian were analysed with the NEMESIS retrieval tool and used to infer the vertical/latitudinal variation in cloud optical depth. We find that the 2009 Gemini data perfectly complement our observations/conclusions from UKIRT/UIST observations made in 2006-2008 and show that the north polar zone at 45°N has continued to steadily brighten while that at 45°S has continued to fade. The improved spatial resolution of the Gemini observations compared with the non-AO UKIRT/UIST data removes some of the earlier ambiguities with our previous analyses and shows that the opacity of clouds deeper than the 2-bar level does indeed diminish towards the poles and also reveals a darkening of the deeper cloud deck near the equator, perhaps coinciding with a region of subduction. We find that the clouds at 45°N,S lie at slightly lower pressures than the clouds at more equatorial latitudes, which suggests that they might possibly be composed of a different condensate, presumably CH4 ice, rather than H2S or NH3 ice, which is assumed for the deeper cloud. In addition, analysis of the centre-to-limb curves of both the Gemini/NIFS and earlier UKIRT/UIST IFU observations shows that the main cloud deck has a well-defined top, and also allows us to better constrain the particle scattering properties. Overall, Uranus appeared to be less convectively active in 2009 than in the previous 3years, which suggests that now the northern spring equinox (which occurred in 2007) is passed the atmosphere is settling back into the quiescent state seen by Voyager 2 in 1986. However, a number of discrete clouds were still observed, with one at 15°N found to lie near the 500 mb level, while another at 30°N, was seen to be much higher at near the 200 mb level. Such high clouds are assumed to be composed of CH4 ice. © 2011 Elsevier Inc.


Thermal Structure and Dynamics of Saturn's Northern Springtime Disturbance

Science (2011) 1-5

LN Fletcher, BE Hesman, PGJ Irwin, KH Baines, TW Momary, A Sanchez-Lavega, F Michael Flasar, PL Read, GS Orton, A Simon-Miller, R Hueso, GL Bjoraker, A Mamoutkine, T Del Rio-Gaztelurrutia, JM Gomez, B Buratti, RN Clark, PD Nicholson, C Sotin


The science of EChO

ASTROPHYSICS OF PLANETARY SYSTEMS: FORMATION, STRUCTURE, AND DYNAMICAL EVOLUTION (2011) 359-370

G Tinetti, JY-K Cho, CA Griffith, O Grasset, L Grenfell, T Guillot, TT Koskinen, JI Moses, D Pinfield, J Tennyson, M Tessenyi, R Wordsworth, A Aylward, R van Boekel, A Coradini, T Encrenaz, I Snellen, MR Zapatero-Osorio, J Bouwman, VC du Foresto, M Lopez-Morales, I Mueller-Wodarg, E Palle, F Selsis, A Sozzetti, J-P Beaulieu, T Henning, M Meyer, G Micela, I Ribas, D Stam, M Swain, O Krause, M Ollivier, E Pace, B Swinyard, PAR Ade, N Achilleos, A Adriani, CB Agnor, C Afonso, CA Prieto, G Bakos, RJ Barber, M Barlow, P Bernath, B Bezard, P Borde, LR Brown, A Cassan, C Cavarroc, A Ciaravella, C Cockell, A Coustenis, C Danielski, L Decin, R De Kok, O Demangeon, P Deroo, P Doel, P Drossart, LN Fletcher, M Focardi, F Forget, S Fossey, P Fouque, J Frith, M Galand, P Gaulme, JIG Hernandez, D Grassi, MJ Griffin, U Groezinger, M Guedel, P Guio, O Hainaut, R Hargreaves, PH Hauschildt, K Heng, D Heyrovsky, R Hueso, P Irwin, L Kaltenegger, P Kervella, D Kipping, G Kovacs, A La Barbera, H Lammar, E Lellouch, G Leto, ML Morales, MAL Valverde, M Lopez-Puertas, C Lovis, A Maggio, J-P Maillard, JM Prado, J-B Marquette, FJ Martin-Torres, P Maxted, S Miller, S Molinari, D Montes, A Moro-Martin, O Mousis, NN Tuong, R Nelson, GS Orton, E Pantin, E Pascale, S Pezzuto, E Poretti, R Prinja, L Prisinzano, J-M Reess, A Reiners, B Samuel, JS Forcada, D Sasselov, G Savini, B Sicardy, A Smith, L Stixrude, G Strazzulla, G Vasisht, S Vinatier, S Viti, I Waldmann, GJ White, T Widemann, R Yelle, Y Yung, S Yurchenko


Scattering particles in nightside limb observations of Venus' upper atmosphere by Venus Express VIRTIS

Icarus 211 (2011) 51-57

R de Kok, PGJ Irwin, CCC Tsang, G Piccioni, P Drossart

Nightside infrared limb spectra of the Venus upper atmosphere, obtained by Venus Express VIRTIS, show strong scattering of thermal radiation. This scattering of upward-going radiation into the line-of-sight is dominant below 82.5. km even at a wavelength of 5 μm, which is indicative of relatively large particles. We show that 1 μm-sized sulfuric acid particles (also known as mode 2 particles) provide a good fit to the VIRTIS limb data at high altitudes. We retrieve vertical profiles of the mode 2 number density between 75 and 90. km at two latitude ranges: 20-30°N and 47-50°N. Between 20 and 30°N, scattering by mode 2 particles is the main source of radiance for altitudes between 80 and 85. km. Above altitudes of 85. km smaller particles can also be used to fit the spectra. Between 47 and 50°N mode 2 number densities are generally lower than between 20 and 30°N and the profiles show more variability. This is consistent with the 47-50° latitude region being at the boundary between the low latitudes and high latitudes, with the latter showing lower cloud tops and higher ultraviolet brightness (Titov, D.V., Taylor, F.W., Svedhem, H., Ignatiev, N.I., Markiewicz, W.J., Piccioni, G., Drossart, P. [2008]. Nature 456, 620-623). © 2010 Elsevier Inc.


Structure and dynamics of the Martian lower and middle atmosphere as observed by the Mars Climate Sounder: Seasonal variations in zonal mean temperature, dust, and water ice aerosols

JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 115 (2010) ARTN E12016

DJ McCleese, NG Heavens, JT Schofield, WA Abdou, JL Bandfield, SB Calcutt, PGJ Irwin, DM Kass, A Kleinbohl, SR Lewis, DA Paige, PL Read, MI Richardson, JH Shirley, FW Taylor, N Teanby, RW Zurek


Upper limits for undetected trace species in the stratosphere of Titan

Faraday Discussions 147 (2010) 65-81

CA Nixon, RK Achterberg, NA Teanby, PGJ Irwin, JM Flaud, I Kleiner, A Dehayem-Kamadjeu, LR Brown, RL Sams, B Bézard, A Coustenis, TM Ansty, A Mamoutkine, S Vinatier, GL Bjoraker, DE Jennings, PN Romani, FM Flasar

In this paper we describe the first quantitative search for several molecules in Titan's stratosphere in Cassini CIRS infrared spectra. These are: ammonia (NH3), methanol (CH3OH), formaldehyde (H 2CO), and acetonitrile (CH3CN), all of which are predicted by photochemical models but only the last of which has been observed, and not in the infrared. We find non-detections in all cases, but derive upper limits on the abundances from low-noise observations at 25°S and 75°N. Comparing these constraints to model predictions, we conclude that CIRS is highly unlikely to see NH3 or CH3OH emissions. However, CH3CN and H2CO are closer to CIRS detectability, and we suggest ways in which the sensitivity threshold may be lowered towards this goal. © 2010 The Royal Society of Chemistry.


ORTIS - ORbiter terahertz infrared sounder

21st International Symposium on Space Terahertz Technology 2010, ISSTT 2010 (2010) 208-

BN Ellison, PGJ Irwin, SB Calcutt, S Rea, B Alderman, N Bowles, R Irshad, J Hurley

Accurate measurement of the temperature, composition and dynamics of Jupiter's atmosphere is one of the main scientific goals of ESA's and NASA's Outer Planet Mission proposals. Infrared remote sounding provides a powerful tool for achieving these objectives and was used by Voyager/IRIS and Cassini/CIRS, but is insensitive to some altitudes and gases. The sub-millimetre wavelength (terahertz) region of the electromagnetic spectrum, which has not been significantly exploited to date in the discipline of planetary science, provides unique spectral information over a range of atmospheric pressures and, when combined with infrared data, is a powerful in situ planetary atmospheric sounder. We will describe a novel low mass and low power consumption combined terahertz/IR instrument proposed for inclusion on the Jupiter Ganymede Orbiter that will greatly improve our understanding of the atmosphere of Jupiter. Through the combination of high spectral resolution 2.2THz spectroscopy (R=10<sup>6</sup>) and lowspectral resolution IR radiometry, the entire temperature profile of the Jovian atmosphere from 0.6 to 10<sup>-3</sup> bar can be evaluated (filling in the currently unmeasured levels between 0.1 and 0.01 bar). In addition, the tropospheric and stratospheric composition can be determined (especially water vapour) and observations of the Doppler shifting of sub-millimetre lines can also be used to measure horizontal wind speeds.


Structure and dynamics of the Martian lower and middle atmosphere as observed by the Mars Climate Sounder: Seasonal variations in zonal mean temperature, dust, and water ice aerosols

Journal of Geophysical Research E: Planets 115 (2010)

DJ McCleese, NG Heavens, JT Schofield, WA Abdou, JL Bandfield, SB Calcutt, PGJ Irwin, DM Kass, A Kleinböhl, SR Lewis, DA Paige, PL Read, MI Richardson, JH Shirley, FW Taylor, N Teanby, RW Zurek

The first Martian year and a half of observations by the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter has revealed new details of the thermal structure and distributions of dust and water ice in the atmosphere. The Martian atmosphere is shown in the observations by the Mars Climate Sounder to vary seasonally between two modes: a symmetrical equinoctial structure with middle atmosphere polar warming and a solstitial structure with an intense middle atmosphere polar warming overlying a deep winter polar vortex. The dust distribution, in particular, is more complex than appreciated before the advent of these high (∼5 km) vertical resolution observations, which extend from near the surface to above 80 km and yield 13 dayside and 13 nightside pole-to-pole cross sections each day. Among the new features noted is a persistent maximum in dust mass mixing ratio at 15-25 km above the surface (at least on the nightside) during northern spring and summer. The water ice distribution is very sensitive to the diurnal and seasonal variation of temperature and is a good tracer of the vertically propagating tide. Copyright 2010 by the American Geophysical Union.


SEASONAL CHANGES IN TITAN'S POLAR TRACE GAS ABUNDANCE OBSERVED BY CASSINI

ASTROPHYSICAL JOURNAL LETTERS 724 (2010) L84-L89

NA Teanby, PGJ Irwin, R de Kok, CA Nixon


Seasonal changes in Titan's polar trace gas abundance observed by cassini

Astrophysical Journal Letters 724 (2010)

NA Teanby, PGJ Irwin, R De Kok, CA Nixon

We use a six-year data set (2004-2010) of mid-infrared spectra measured by Cassini's Composite InfraRed Spectrometer to search for seasonal variations in Titan's atmospheric temperature and composition. During most of Cassini's mission Titan's northern hemisphere has been in winter, with an intense stratospheric polar vortex highly enriched in trace gases, and a single south-to-north circulation cell. Following northern spring equinox in mid-2009, dramatic changes in atmospheric temperature and composition were expected, but until now the temporal coverage of polar latitudes has been too sparse to discern trends. Here, we show that during equinox and post-equinox periods, abundances of trace gases at both poles have begun to increase.We propose that increases in north polar trace gases are due to a seasonal reduction in gas depletion by horizontal mixing across the vortex boundary. A simultaneous south polar abundance increase suggests that Titan is now entering, or is about to enter, a transitional circulation regime with two branches, rather than the single branch circulation pattern previously observed. © 2010. The American Astronomical Society. All rights reserved.


Saturn's emitted power

Journal of Geophysical Research E: Planets 115 (2010)

L Li, BJ Conrath, PJ Gierasch, RK Achterberg, CA Nixon, AA Simon-Miller, FM Flasar, D Banfield, KH Baines, RA West, AP Ingersoll, AR Vasavada, AD Del Genio, CC Porco, AA Mamoutkine, ME Segura, GL Bjoraker, GS Orton, LN Fletcher, PGJ Irwin, PL Read

Long-term (2004-2009) on-orbit observations by Cassini Composite Infrared Spectrometer are analyzed to precisely measure Saturn's emitted power and its meridional distribution. Our evaluations suggest that the average global emitted power is 4.952 ± 0.035 W m-2 during the period of 2004-2009. The corresponding effective temperature is 96.67 ± 0.17 K. The emitted power is 16.6% higher in the Southern Hemisphere than in the Northern Hemisphere. From 2005 to 2009, the global mean emitted power and effective temperature decreased by ∼2% and ∼0.5%, respectively. Our study further reveals the interannual variability of emitted power and effective temperature between the epoch of Voyager (∼1 Saturn year ago) and the current epoch of Cassini, suggesting changes in the cloud opacity from year to year on Saturn. The seasonal and interannual variability of emitted power implies that the energy balance and internal heat are also varying. Copyright © 2010 by the American Geophysical Union.


HARMONI: A single-field wide-band integral-field spectrograph for the European ELT

Proceedings of SPIE - The International Society for Optical Engineering 7735 (2010)

N Thatte, M Tecza, F Clarke, RL Davies, A Remillieux, R Bacon, D Lunney, S Arribas, E Mediavilla, F Gago, N Bezawada, P Ferruit, A Fragoso, D Freeman, J Fuentes, T Fusco, A Gallie, A Garcia, T Goodsall, F Gracia, A Jarno, J Kosmalski, J Lynn, S McLay, D Montgomery, A Pecontal, H Schnetler, H Smith, D Sosa, G Battaglia, N Bowles, L Colina, E Emsellem, A Garcia-Perez, S Gladysz, I Hook, P Irwin, M Jarvis, R Kennicutt, A Levan, A Longmore, J Magorrian, M McCaughrean, L Origlia, R Rebolo, D Rigopoulou, S Ryan, M Swinbank, N Tanvir, E Tolstoy, A Verma

We describe the results of a Phase A study for a single field, wide band, near-infrared integral field spectrograph for the European Extremely Large Telescope (E-ELT). HARMONI, the High Angular Resolution Monolithic Optical & Nearinfrared Integral field spectrograph, provides the E-ELT's core spectroscopic requirement. It is a work-horse instrument, with four different spatial scales, ranging from seeing to diffraction-limited, and spectral resolving powers of 4000, 10000 & 20000 covering the 0.47 to 2.45 μm wavelength range. It is optimally suited to carry out a wide range of observing programs, focusing on detailed, spatially resolved studies of extended objects to unravel their morphology, kinematics and chemical composition, whilst also enabling ultra-sensitive observations of point sources. We present a synopsis of the key science cases motivating the instrument, the top level specifications, a description of the opto-mechanical concept, operation and calibration plan, and image quality and throughput budgets. Issues of expected performance, complementarity and synergies, as well as simulated observations are presented elsewhere in these proceedings[1]. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Abundances of Jupiter's trace hydrocarbons from Voyager and Cassini

Planetary and Space Science 58 (2010) 1667-1680

CA Nixon, RK Achterberg, PN Romani, M Allen, X Zhang, NA Teanby, PGJ Irwin, FM Flasar

The flybys of Jupiter by the Voyager spacecraft in 1979, and over two decades later by Cassini in 2000, have provided us with unique datasets from two different epochs, allowing the investigation of seasonal change in the atmosphere. In this paper we model zonal averages of thermal infrared spectra from the two instruments, Voyager 1 IRIS and Cassini CIRS, to retrieve the vertical and meridional profiles of temperature, and the abundances of the two minor hydrocarbons, acetylene (C2H2) and ethane (C 2H6). The spatial variation of these gases is controlled by both chemistry and dynamics, and therefore their observed distribution gives us an insight into both processes. We find that the two gases paint quite different pictures of seasonal change. Whilst the 2-D cross-section of C 2H6 abundance is slightly increased and more symmetric in 2000 (northern summer solstice) compared to 1979 (northern fall equinox), the major trend of equator to pole increase remains. For C2H2 on the other hand, the Voyager epoch exhibits almost no latitudinal variation, whilst the Cassini era shows a marked decrease polewards in both hemispheres. At the present time, these experimental findings are in advance of interpretation, as there are no published models of 2-D Jovian seasonal chemical variation available for comparison. © 2010 Elsevier Ltd. All rights reserved.


Infrared limb sounding of Titan with the cassini composite infrared spectrometer: Effects of the mid-IR detector spatial responses: Errata

Applied Optics 49 (2010) 5575-5576

CA Nixon, NA Teanby, SB Calcutt, S Aslam, DE Jennings, VG Kunde, FM Flasar, PGJ Irwin, FW Taylor, DA Glenar, MD Smith

We provide a revised Table 5 for the paper by Nixon et al. [Appl. Opt. 48, 1912 (2009)], in which the abundances of 13CO2 and C 18O were incorrect . © 2010 Optical Society of America.


Venus Cloud Properties from Venus Express VIRTIS Observations

AAS/Division for Planetary Sciences Meeting Abstracts #42 42 (2010) 994-994
Part of a series from Bulletin of the American Astronomical Society

J Barstow, FW Taylor, CCC Tsang, CF Wilson, PGJ Irwin, P Drossart, G Piccioni


Far-infrared opacity sources in Titan's troposphere reconsidered

Icarus 209 (2010) 854-857

R de Kok, PGJ Irwin, NA Teanby

We use Cassini far-infrared limb and nadir spectra, together with recent Huygens results, to shed new light on the controversial far-infrared opacity sources in Titan's troposphere. Although a global cloud of large CH4 ice particles around an altitude of 30km, together with an increase in tropospheric haze opacity with respect to the stratosphere, can fit nadir and limb spectra well, this cloud does not seem consistent with shortwave measurements of Titan. Instead, the N2-CH4 collision-induced absorption coefficients are probably underestimated by at least 50% for low temperatures. © 2010 Elsevier Inc.

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