Assessing the long-term variability of acetylene and ethane in the stratosphere of Jupiter

ICARUS 305 (2018) 301-313

H Melin, LN Fletcher, PT Donnelly, TK Greathouse, JH Lacy, GS Orton, RS Giles, JA Sinclair, PGJ Irwin

Haze and cloud structure of Saturn's North Pole and Hexagon Wave from Cassini/ISS imaging

Icarus (2018)

JF Sanz-Requena, S Pérez-Hoyos, A Sánchez-Lavega, A Antuñano, PGJ Irwin

© 2017 Elsevier Inc. In this paper we present a study of the vertical haze and cloud structure in the upper two bars of Saturn's Northern Polar atmosphere using the Imaging Science Subsystem (ISS) instrument onboard the Cassini spacecraft. We focus on the characterization of latitudes from 53° to 90° N. The observations were taken during June 2013 with five different filters (VIO, BL1, MT2, CB2 and MT3) covering spectral range from the 420 nm to 890 nm (in a deep methane absorption band). Absolute reflectivity measurements of seven selected regions at all wavelengths and several illumination and observation geometries are compared with the values produced by a radiative transfer model. The changes in reflectivity at these latitudes are mostly attributed to changes in the tropospheric haze. This includes the haze base height (from 600 ± 200 mbar at the lowest latitudes to 1000 ± 300 mbar in the pole), its particle number density (from 20 ± 2 particles/cm 3 to 2 ± 0.5 particles/cm 3 at the haze base) and its scale height (from 18 ± 0.1 km to 50 ± 0.1 km). We also report variability in the retrieved particle size distribution and refractive indices. We find that the Hexagonal Wave dichotomizes the studied stratospheric and tropospheric hazes between the outer, equatorward regions and the inner, Polar Regions. This suggests that the wave or the jet isolates the particle distribution at least at tropospheric levels.

LRG-BEASTS III: ground-based transmission spectrum of the gas giant orbiting the cool dwarf WASP-80


J Kirk, PJ Wheatley, T Louden, I Skillen, GW King, J McCormac, PGJ Irwin

Spatial variations in Titan's atmospheric temperature: ALMA and Cassini comparisons from 2012 to 2015

Icarus (2018)

AE Thelen, CA Nixon, NJ Chanover, EM Molter, MA Cordiner, RK Achterberg, J Serigano, PGJ Irwin, N Teanby, SB Charnley

© 2017 Elsevier Inc. Submillimeter emission lines of carbon monoxide (CO) in Titan's atmosphere provide excellent probes of atmospheric temperature due to the molecule's long chemical lifetime and stable, well constrained volume mixing ratio. Here we present the analysis of 4 datasets obtained with the Atacama Large Millimeter/Submillimeter Array (ALMA) in 2012, 2013, 2014, and 2015 that contain strong CO rotational transitions. Utilizing ALMA's high spatial resolution in the 2012, 2014, and 2015 observations, we extract spectra from 3 separate regions on Titan's disk using datasets with beam sizes ranging from 0.35 × 0.28'' to 0.39 × 0.34''. Temperature profiles retrieved by the NEMESIS radiative transfer code are compared to Cassini Composite Infrared Spectrometer (CIRS) and radio occultation science results from similar latitude regions. Disk-averaged temperature profiles stay relatively constant from year to year, while small seasonal variations in atmospheric temperature are present from 2012 to 2015 in the stratosphere and mesosphere (~100-500 km) of spatially resolved regions. We measure the stratopause (320 km) to increase in temperature by 5 K in northern latitudes from 2012 to 2015, while temperatures rise throughout the stratosphere at lower latitudes. We observe generally cooler temperatures in the lower stratosphere (~100 km) than those obtained through Cassini radio occultation measurements, with the notable exception of warming in the northern latitudes and the absence of previous instabilities; both of these results are indicators that Titan's lower atmosphere responds to seasonal effects, particularly at higher latitudes. While retrieved temperature profiles cover a range of latitudes in these observations, deviations from CIRS nadir maps and radio occultation measurements convolved with the ALMA beam-footprint are not found to be statistically significant, and discrepancies are often found to be less than 5 K throughout the atmosphere. ALMA's excellent sensitivity in the lower stratosphere (60-300 km) provides a highly complementary dataset to contemporary CIRS and radio science observations, including altitude regions where both of those measurement sets contain large uncertainties. The demonstrated utility of CO emission lines in the submillimeter as a tracer of Titan's atmospheric temperature lays the groundwork for future studies of other molecular species - particularly those that exhibit strong polar abundance enhancements or are pressure-broadened in the lower atmosphere, as temperature profiles are found to consistently vary with latitude in all three years by up to 15 K.

Venus Upper Clouds and the UV Absorber From MESSENGER/MASCS Observations


S Perez-Hoyos, A Sanchez-Lavega, A Garcia-Munoz, PGJ Irwin, J Peralta, G Holsclaw, WM McClintock, JF Sanz-Requena

The GTC exoplanet transit spectroscopy survey VIII. Flat transmission spectrum for the warm gas giant WASP-80b


H Parviainen, E Palle, G Chen, L Nortmann, F Murgas, G Nowak, S Aigrain, A Booth, M Abazorius, N Iro

The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter

Space Science Reviews 214 (2018)

O Korablev, F Montmessin, A Trokhimovskiy, AA Fedorova, AV Shakun, AV Grigoriev, BE Moshkin, NI Ignatiev, F Forget, F Lefèvre, K Anufreychik, I Dzuban, YS Ivanov, YK Kalinnikov, TO Kozlova, A Kungurov, V Makarov, F Martynovich, I Maslov, D Merzlyakov, PP Moiseev, Y Nikolskiy, A Patrakeev, D Patsaev, A Santos-Skripko, O Sazonov, N Semena, A Semenov, V Shashkin, A Sidorov, AV Stepanov, I Stupin, D Timonin, AY Titov, A Viktorov, A Zharkov, F Altieri, G Arnold, DA Belyaev, JL Bertaux, DS Betsis, N Duxbury, T Encrenaz, T Fouchet, JC Gérard, D Grassi, S Guerlet, P Hartogh, Y Kasaba, I Khatuntsev, VA Krasnopolsky, RO Kuzmin, E Lellouch, MA Lopez-Valverde, M Luginin, A Määttänen, E Marcq, J Martin Torres, AS Medvedev, E Millour, KS Olsen, MR Patel, C Quantin-Nataf, AV Rodin, VI Shematovich, I Thomas, N Thomas, L Vazquez, M Vincendon, V Wilquet, CF Wilson, LV Zasova, LM Zelenyi, MP Zorzano

© 2017, The Author(s). The Atmospheric Chemistry Suite (ACS) package is an element of the Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. This ensemble of spectrometers has been designed and developed in response to the Trace Gas Orbiter mission objectives that specifically address the requirement of high sensitivity instruments to enable the unambiguous detection of trace gases of potential geophysical or biological interest. For this reason, ACS embarks a set of instruments achieving simultaneously very high accuracy (ppt level), very high resolving power ( > 10,000) and large spectral coverage (0.7 to 17 μm—the visible to thermal infrared range). The near-infrared (NIR) channel is a versatile spectrometer covering the 0.7–1.6 μm spectral range with a resolving power of ∼20,000. NIR employs the combination of an echelle grating with an AOTF (Acousto-Optical Tunable Filter) as diffraction order selector. This channel will be mainly operated in solar occultation and nadir, and can also perform limb observations. The scientific goals of NIR are the measurements of water vapor, aerosols, and dayside or night side airglows. The mid-infrared (MIR) channel is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the 2.2–4.4 μm range. MIR achieves a resolving power of > 50,000. It has been designed to accomplish the most sensitive measurements ever of the trace gases present in the Martian atmosphere. The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum Fourier-transform spectrometer encompassing the spectral range of 1.7–17 μm with apodized resolution varying from 0.2 to 1.3 cm −1 . TIRVIM is primarily dedicated to profiling temperature from the surface up to ∼60 km and to monitor aerosol abundance in nadir. TIRVIM also has a limb and solar occultation capability. The technical concept of the instrument, its accommodation on the spacecraft, the optical designs as well as some of the calibrations, and the expected performances for its three channels are described.

Jupiter's auroral-related stratospheric heating and chemistry II: Analysis of IRTF-TEXES spectra measured in December 2014

ICARUS 300 (2018) 305-326

JA Sinclair, GS Orton, TK Greathouse, LN Fletcher, JI Moses, V Hue, PGJ Irwin

Analysis of gaseous ammonia (NH3) absorption in the visible spectrum of Jupiter

ICARUS 302 (2018) 426-436

PGJ Irwin, N Bowles, AS Braude, R Garland, S Calcutt

Investigations of the Mars Upper Atmosphere with ExoMars Trace Gas Orbiter

Space Science Reviews 214 (2018)

MA López-Valverde, JC Gerard, F González-Galindo, AC Vandaele, I Thomas, O Korablev, N Ignatiev, A Fedorova, F Montmessin, A Määttänen, S Guilbon, F Lefevre, MR Patel, S Jiménez-Monferrer, M García-Comas, A Cardesin, CF Wilson, RT Clancy, A Kleinböhl, DJ McCleese, DM Kass, NM Schneider, MS Chaffin, JJ López-Moreno, J Rodríguez

© 2018, Springer Science+Business Media B.V., part of Springer Nature. The Martian mesosphere and thermosphere, the region above about 60 km, is not the primary target of the ExoMars 2016 mission but its Trace Gas Orbiter (TGO) can explore it and address many interesting issues, either in-situ during the aerobraking period or remotely during the regular mission. In the aerobraking phase TGO peeks into thermospheric densities and temperatures, in a broad range of latitudes and during a long continuous period. TGO carries two instruments designed for the detection of trace species, NOMAD and ACS, which will use the solar occultation technique. Their regular sounding at the terminator up to very high altitudes in many different molecular bands will represent the first time that an extensive and precise dataset of densities and hopefully temperatures are obtained at those altitudes and local times on Mars. But there are additional capabilities in TGO for studying the upper atmosphere of Mars, and we review them briefly. Our simulations suggest that airglow emissions from the UV to the IR might be observed outside the terminator. If eventually confirmed from orbit, they would supply new information about atmospheric dynamics and variability. However, their optimal exploitation requires a special spacecraft pointing, currently not considered in the regular operations but feasible in our opinion. We discuss the synergy between the TGO instruments, specially the wide spectral range achieved by combining them. We also encourage coordinated operations with other Mars-observing missions capable of supplying simultaneous measurements of its upper atmosphere.

Seasonal evolution of C2N2, C3H4, and C4H2 abundances in Titan's lower stratosphere


M Sylvestre, NA Teanby, S Vinatier, S Lebonnois, PGJ Irwin

The formation and evolution of Titan's winter polar vortex.

Nature communications 8 (2017) 1586-1586

NA Teanby, B Bézard, S Vinatier, M Sylvestre, CA Nixon, PGJ Irwin, RJ de Kok, SB Calcutt, FM Flasar

Saturn's largest moon Titan has a substantial nitrogen-methane atmosphere, with strong seasonal effects, including formation of winter polar vortices. Following Titan's 2009 northern spring equinox, peak solar heating moved to the northern hemisphere, initiating south-polar subsidence and winter polar vortex formation. Throughout 2010-2011, strengthening subsidence produced a mesospheric hot-spot and caused extreme enrichment of photochemically produced trace gases. However, in 2012 unexpected and rapid mesospheric cooling was observed. Here we show extreme trace gas enrichment within the polar vortex dramatically increases mesospheric long-wave radiative cooling efficiency, causing unusually cold temperatures 2-6 years post-equinox. The long time-frame to reach a stable vortex configuration results from the high infrared opacity of Titan's trace gases and the relatively long atmospheric radiative time constant. Winter polar hot-spots have been observed on other planets, but detection of post-equinox cooling is so far unique to Titan.

CASTAway: An asteroid main belt tour and survey

Advances in Space Research (2017)

NE Bowles, C Snodgrass, A Gibbings, JP Sanchez, JA Arnold, P Eccleston, T Andert, A Probst, G Naletto, AC Vandaele, J de Leon, A Nathues, IR Thomas, N Thomas, L Jorda, V Da Deppo, H Haack, SF Green, B Carry, KL Donaldson Hanna, J Leif Jorgensen, A Kereszturi, FE DeMeo, MR Patel, JK Davies, F Clarke, K Kinch, A Guilbert-Lepoutre, J Agarwal, AS Rivkin, P Pravec, S Fornasier, M Granvik, RH Jones, N Murdoch, KH Joy, E Pascale, M Tecza, JM Barnes, J Licandro, BT Greenhagen, SB Calcutt, CM Marriner, T Warren, I Tosh

© 2017 COSPAR. CASTAway is a mission concept to explore our Solar System's main asteroid belt. Asteroids and comets provide a window into the formation and evolution of our Solar System and the composition of these objects can be inferred from space-based remote sensing using spectroscopic techniques. Variations in composition across the asteroid populations provide a tracer for the dynamical evolution of the Solar System. The mission combines a long-range (point source) telescopic survey of over 10,000 objects, targeted close encounters with 10-20 asteroids and serendipitous searches to constrain the distribution of smaller (e.g. 10 m) size objects into a single concept. With a carefully targeted trajectory that loops through the asteroid belt, CASTAway would provide a comprehensive survey of the main belt at multiple scales. The scientific payload comprises a 50 cm diameter telescope that includes an integrated low-resolution (R = 30-100) spectrometer and visible context imager, a thermal (e.g. 6-16 μm) imager for use during the flybys, and modified star tracker cameras to detect small ( 10 m) asteroids. The CASTAway spacecraft and payload have high levels of technology readiness and are designed to fit within the programmatic and cost caps for a European Space Agency medium class mission, while delivering a significant increase in knowledge of our Solar System.

HST/WFC3 observations of Uranus' 2014 storm clouds and comparison with VLT/SINFONI and IRTF/Spex observations

ICARUS 288 (2017) 99-119

PGJ Irwin, MH Wong, AA Simon, GS Orton, D Toledo

Jupiter's para-H-2 distribution from SOFIA/FORCAST and Voyager/IRIS 17-37 mu m spectroscopy

ICARUS 286 (2017) 223-240

LN Fletcher, I de Pater, WT Reach, M Wong, GS Orton, PGJ Irwin, RD Gehrz

The Martian Planetary Boundary Layer

in The Atmosphere and Climate of Mars, Cambridge University Press (2017) 7

PL Read, B Galperin, SE Larsen, SR Lewis, A Maatanen, A Petrosyan, N Renno, H Savijarvi, T Siili, A Spiga, A Toigo, L Vazquez

7.1 INTRODUCTION The Martian planetary boundary layer (PBL) consists of the layers of the atmosphere closest to the surface, within which interactions between the atmosphere and the surface itself are dominant. In general, this represents the lowest 1–10 km of the atmosphere, within which surface-driven intense convection may take place, with convective plumes and vortices rising to heights in excess of 5–10 km during the day (Thomas and Gierasch, 1985; Haberle et al., 1993b; ...

The Global Circulation

in The Atmosphere and Climate of Mars, Cambridge University Press (2017) 9

JR Barnes, RM Haberle, RJ Wilson, SR Lewis, JR Murphy, PL Read

This volume reviews all aspects of Mars atmospheric science from the surface to space, and from now and into the past.

Disruption of Saturn's quasi-periodic equatorial oscillation by the great northern storm

NATURE ASTRONOMY 1 (2017) 765-770

LN Fletcher, S Guerlet, GS Orton, RG Cosentino, T Fouchet, PGJ Irwin, L Li, FM Flasar, N Gorius, R Morales-Juberias

Jupiter's auroral-related stratospheric heating and chemistry I: Analysis of Voyager-IRIS and Cassini-CIRS spectra

ICARUS 292 (2017) 182-207

JA Sinclair, GS Orton, TK Greathouse, LN Fletcher, JI Moses, V Hue, PGJ Irwin

An experimental investigation of blocking by partial barriers in a rotating baroclinic annulus

Geophysical and Astrophysical Fluid Dynamics (2017) 1-33

SD Marshall, PL Read

© 2017 Informa UK Limited, trading as Taylor & Francis Group We present a series of experimental investigations in which a differentially-heated annulus was used to investigate the effects of topography on rotating, stratified flows with similarities to the Earth’s atmospheric or oceanic circulation. In particular, we compare and investigate blocking effects via partial mechanical barriers to previous experiments by the authors utilising azimuthally-periodic topography. The mechanical obstacle used was an isolated ridge, forming a partial barrier, employed to study the difference between partially blocked and fully unblocked flow. The topography was found to lead to the formation of bottom-trapped waves, as well as impacting the circulation at a level much higher than the top of the ridge. This produced a unique flow structure when the drifting flow and the topography interacted in the form of an “interference” regime at low Taylor number, but forming an erratic “irregular” regime at higher Taylor number. The results also showed evidence of resonant wave-triads, similar to those noted with periodic wavenumber-3 topography by Marshall and Read (Geophys. Astrophys. Fluid Dyn., 2015, 109), though the component wavenumbers of the wave-triads and their impact on the flow were found to depend on the topography in question. With periodic topography, wave-triads were found to occur between both the baroclinic and barotropic components of the zonal wavenumber-3 mode and the wavenumber-6 baroclinic component, whereas with the partial barrier two nonlinear resonant wave-triads were noted, each sharing a common wavenumber-1 mode.