Wave number selection in the presence of noise: Experimental results

Chaos American Institute of Physics (2018)

D Zhilenko, O Krivonosova, M Gritsevich, PL Read

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

Retrieval of H<inf>2</inf>O abundance in Titan's stratosphere: A (re)analysis of CIRS/Cassini and PACS/Herschel observations

Icarus 311 (2018) 288-305

S Bauduin, PGJ Irwin, E Lellouch, V Cottini, R Moreno, CA Nixon, NA Teanby, T Ansty, FM Flasar

© 2018 Elsevier Inc. Since its first measurement 20 years ago by the Infrared Space Observatory (ISO), the water (H 2 O) mole fraction in Titan's stratosphere remains uncertain due to large differences between the determinations from available measurements. More particularly, the recent measurements made from the Herschel observatory (PACS and HIFI) estimated the H 2 O mole fraction to be 0.023 ppb at 12.1 mbar. A mixing ratio of 0.14 ppb at 10.7 mbar was, however, retrieved from nadir spatially-resolved observations of Cassini/CIRS. At the same pressure level (10.7 mbar), this makes a difference of a factor of 5.5 between PACS and CIRS measurements, and this has notably prevented current models from fully constraining the oxygen flux flowing into Titan's atmosphere. In this work, we try to understand the differences between the H 2 O mole fractions estimated from Herschel/PACS and Cassini/CIRS observations. The strategy for this is to 1) analyse recent disc-averaged observations of CIRS to investigate if the observation geometry could explain the previous observed differences, and 2) (re)analyse the three types of observation with the same retrieval scheme to assess if previous differences in retrieval codes/methodology could be responsible for the previous discrepancies. With this analysis, we show that using the same retrieval method better reconcile the previous measurements of these instruments. However, the addition of the disc-averaged CIRS observations, instead of confirming the consistency between the different datasets, reveals discrepancies between one of the CIRS disc-averaged set of observations and PACS measurements. This raises new questions regarding the possibility of latitudinal variations of H 2 O, which could be triggered by seasonal changes of the meridional circulation. As it has already been shown for nitriles and hydrocarbons, this circulation could potentially impact the latitudinal distribution of H 2 O through the subsidence or upwelling of air rich in H 2 O. The possible influence of spatial/time variations of the OH/H 2 O input flux in Titan's atmosphere is also discussed. The analysis of more observations will be needed in future work to address the questions arising from this work and to improve the understanding of the sources of H 2 O in Titan's atmosphere.

Descent rate models of the synchronization of the Quasi-Biennial Oscillation by the annual cycle in tropical upwelling

Journal of the Atmospheric Sciences American Meteorological Society (2018)

K Rajendran, I Moroz, SM Osprey, P Read

The response of the Quasi-Biennial Oscillation (QBO) to an imposed mean upwelling with a periodic modulation is studied, by modelling the dynamics of the zero wind line at the equator using a class of equations known as ‘descent rate’ models. These are simple mathematical models that capture the essence of QBO synchronization by focusing on the dynamics of the height of the zero wind line. A heuristic descent rate model for the zero wind line is described, and is shown to capture many of the synchronization features seen in previous studies of the QBO. Using a simple transformation, it is then demonstrated that the standard Holton-Lindzen model of the QBO can itself be put into the form of a descent rate model if a quadratic velocity profile is assumed below the zero wind line. The resulting non-autonomous ordinary differential equation captures much of the synchronization behaviour observed in the full Holton-Lindzen partial differential equation. The new class of models provides a novel framework within which to understand synchronization of the QBO, and we demonstrate a close relationship between these models and the circle map well-known in the mathematics literature. Finally, we analyse reanalysis datasets to validate some of the predictions of our descent rate models, and find statistically significant evidence for synchronization of the QBO that is consistent with model behaviour.

Dynamical models to explain observations with SPHERE in planetary systems with double debris belts


C Lazzoni, S Desidera, F Marzari, A Boccaletti, M Langlois, D Mesa, R Gratton, Q Kral, N Pawellek, J Olofsson, M Bonnefoy, G Chauvin, AM Lagrange, A Vigan, E Sissa, J Antichi, H Avenhaus, A Baruffolo, JL Baudino, A Bazzon, JL Beuzit, B Biller, M Bonavita, W Brandner, P Bruno, E Buenzli, F Cantalloube, E Cascone, A Cheetham, RU Claudi, M Cudel, S Daemgen, V De Caprio, P Delorme, D Fantinel, G Farisato, M Feldt, R Galicher, C Ginski, J Girard, E Giro, M Janson, J Hagelberg, T Henning, S Incorvaia, M Kasper, T Kopytova, J Lannier, H LeCoroller, L Lessio, R Ligi, AL Maire, F Menard, M Meyer, J Milli, D Mouillet, S Peretti, C Perrot, D Rouan, M Samland, B Salasnich, G Salter, T Schmidt, S Scuderi, E Sezestre, M Turatto, S Udry, F Wildi, A Zurlo

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


O Korablev, F Montmessin, A Trokhimovskiy, AA Fedorova, AV Shakun, AV Grigoriev, BE Moshkin, NI Ignatiev, F Forget, F Lefevre, 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, J-C Gerard, D Grass, S Guerlet, P Hartogh, Y Kasaba, I Khatuntsev, VA Krasnopolsky, RO Kuzmin, E Lellouch, MA Lopez-Valverde, M Luginin, A Maattanen, 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

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

Detection of hydrogen sulfide above the clouds in Uranus's atmosphere

Nature Astronomy 2 (2018) 420-427

PGJ Irwin, D Toledo, R Garland, NA Teanby, LN Fletcher, GA Orton, B Bézard

© 2018 The Author(s). Visible-to-near-infrared observations indicate that the cloud top of the main cloud deck on Uranus lies at a pressure level of between 1.2 bar and 3 bar. However , its composition has never been unambiguously identified, although it is widely assumed to be composed primarily of either ammonia or hydrogen sulfide (H 2 S) ice. Here, we present evidence of a clear detection of gaseous H 2 S above this cloud deck in the wavelength region 1.57-1.59 μm with a mole fraction of 0.4-0.8 ppm at the cloud top. Its detection constrains the deep bulk sulfur/nitrogen abundance to exceed unity ( > 4.4-5.0 times the solar value) in Uranus's bulk atmosphere, and places a lower limit on the mole fraction of H 2 S below the observed cloud of (1.0-2.5) × 10 -5 . The detection of gaseous H 2 S at these pressure levels adds to the weight of evidence that the principal constituent of 1.2-3-bar cloud is likely to be H 2 S ice.

New spectro-photometric characterization of the substellar object HR2562B using SPHERE


D Mesa, J-L Baudino, B Charnay, V D'Orazi, S Desidera, A Boccaletti, R Gratton, M Bonnefoy, P Delorme, M Langlois, A Vigan, A Zurlo, A-L Maire, M Janson, J Antichi, A Baruffolo, P Bruno, E Cascone, G Chauvin, RU Claudi, V De Caprio, D Fantinel, G Farisato, M Feldt, E Giro, J Hagelberg, S Incorvaia, E Lagadec, A-M Lagrange, C Lazzoni, L Lessio, B Salasnich, S Scuderi, E Sissa, M Turatto

Investigations of the Mars Upper Atmosphere with ExoMars Trace Gas Orbiter


MA Lopez-Valverde, J-C Gerard, F Gonzalez-Galindo, A-C Vandaele, I Thomas, O Korablev, N Ignatiev, A Fedorova, F Montmessin, A Maattanen, S Guilbon, F Lefevre, MR Patel, S Jimenez-Monferrer, M Garcia-Comas, A Cardesin, CF Wilson, RT Clancy, A Kleinboehl, DJ McCleese, DM Kass, NM Schneider, MS Chaffin, JJ Lopez-Moreno, J Rodriguez

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


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

D/H Ratios on Saturn and Jupiter from Cassini CIRS


JDR Pierel, CA Nixon, E Lellouch, LN Fletcher, GL Bjoraker, RK Achterberg, B Bezard, BE Hesman, PGJ Irwin, FM Flasar

Climatological variations in Titan's atmospheric chemistry mapped using ALMA


M Cordiner, C Nixon, S Charnley, N Teanby, Z Kisiel, P Irwin, M Palmer, J Lai, X Thelen, V Vuitton

Sulfur dioxide in the Venus Atmosphere: II. Spatial and temporal variability

ICARUS 295 (2017) 1-15

AC Vandaele, O Korablev, D Belyaev, S Chamberlain, D Evdokimova, T Encrenaz, L Esposito, KL Jessup, F Lefevre, S Limaye, A Mahieux, E Marcq, FP Mills, F Montmessin, CD Parkinson, S Robert, T Roman, B Sandor, A Stolzenbach, C Wilson, V Wilquet

Ertel potential vorticity versus Bernoulli streamfunction on Mars


TE Dowling, ME Bradley, J Du, SR Lewis, PL Read