Publications by Fred Taylor

Mars Climate Sounder limb profile retrieval of atmospheric temperature, pressure, and dust and water ice opacity


A Kleinboehl, JT Schofield, DM Kass, WA Abdou, CR Backus, B Sen, JH Shirley, WG Lawson, MI Richardson, FW Taylor, NA Teanby, DJ McCleese

Spatial variability of carbon monoxide in venus' mesosphere from venus express/visible and infrared thermal imaging spectrometer measurements

Journal of Geophysical Research E: Planets 114 (2009)

PGJ Irwin, R De Kok, A Negrão, CCC Tsang, CF Wilson, P Drossart, G Piccioni, D Grassi, FW Taylor

[1] Observations of Venus' mesosphere by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS)-M instrument of Venus Express have been used to investigate the spatial distribution of CO above Venus' nightside cloud tops by fitting the CO absorption in the (1-0) CO band around 4.7 μm. We find little spatial variation in the abundance of CO at midlatitudes, with a retrieved abundance of approximately 40 ± 10 ppm just above the cloud tops between 65 and 70 km altitude. Unfortunately, we find it very difficult to constrain the abundance of CO in the cold polar collar, centered at about 70°S, as the retrieved temperature structure in the CO line-forming region masks the absorption lines. However, there is a possibility that CO increases toward the poles, as we detect a significant signature of high levels of CO over Venus' south polar dipole feature in all the observations analyzed so far. To constrain the abundance of CO more closely will require the analysis of higher-resolution VIRTIS-H observations. In addition, limb observations would greatly help to resolve any possible temperature/cloud ambiguities and allow us to assess vertical variations in the abundance of CO. Copyright 2008 by the American Geophysical Union.

Tropospheric carbon monoxide concentrations and variability on Venus from Venus Express/VIRTIS-M observations

Journal of Geophysical Research E: Planets 114 (2009)

CCC Tsang, PGJ Irwin, CF Wilson, FW Taylor, C Lee, R De Kok, P Drossart, G Piccioni, B Bezard, S Calcutt

[1] We present nightside observations of tropospheric carbon monoxide in the southern hemisphere near the 35 km height level, the first from Venus Express/Visible and Infrared Thermal Imaging Spectrometer (VIRTIS)-M-IR. VIRTIS-M data from 2.18 to 2.50 μm, with a spectral resolution of 10 nm, were used in the analysis. Spectra were binned, with widths ranging from 5 to 30 spatial pixels, to increase the signal-to-noise ratio, while at the same time reducing the total number of retrievals required for complete spatial coverage. We calculate the mean abundance for carbon monoxide at the equator to be 23 ± 2 ppm. The CO concentration increases toward the poles, peaking at a latitude of approximately 60°S, with a mean value of 32 ± 2 ppm. This 40% equator-to-pole increase is consistent with the values found by Collard et al. (1993) from Galileo/NIMS observations. Observations suggest an overturning in this CO gradient past 60°S, declining to abundances seen in the midlatitudes. Zonal variability in this peak value has also been measured, varying on the order of 10% (∼3 ppm) at different longitudes on a latitude circle. The zonal variability of the CO abundance has possible implications for the lifetime of CO and its dynamics in the troposphere. This work has definitively established a distribution of tropospheric CO, which is consistent with a Hadley cell circulation, and placed limits on the latitudinal extent of the cell. Copyright 2008 by the American Geophysical Union.

Thermal tides in the Martian middle atmosphere as seen by the Mars Climate Sounder


C Lee, WG Lawson, MI Richardson, NG Heavens, A Kleinboehl, D Banfield, DJ McCleese, R Zurek, D Kass, JT Schofield, CB Leovy, FW Taylor, AD Toigo

Infrared limb sounding of Titan with the Cassini Composite InfraRed Spectrometer: effects of the mid-IR detector spatial responses.

Appl Opt 48 (2009) 1912-1925

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

The composite infrared spectrometer (CIRS) instrument on board the Cassini Saturn orbiter employs two 1x10 HgCdTe detector arrays for mid-infrared remote sensing of Titan's and Saturn's atmospheres. In this paper we show that the real detector spatial response functions, as measured in ground testing before launch, differ significantly from idealized "boxcar" responses. We further show that neglecting this true spatial response function when modeling CIRS spectra can have a significant effect on interpretation of the data, especially in limb-sounding mode, which is frequently used for Titan science. This result has implications not just for CIRS data analysis but for other similar instrumental applications.

Venus express: Highlights of the nominal mission

Solar System Research 43 (2009) 185-209

DV Titov, H Svedhem, FW Taylor, S Barabash, JL Bertaux, P Drossart, V Formisano, B Häusler, O Korablev, WJ Markiewicz, D Nevejans, M Pätzold, G Piccioni, JA Sauvaud, TL Zhang, O Witasse, JC Gerard, A Fedorov, A Sanchez-Lavega, J Helbert, R Hoofs

Venus Express is the first European (ESA) mission to the planet Venus. Its main science goal is to carry out a global survey of the atmosphere, the plasma environment, and the surface of Venus from orbit. The payload consists of seven experiments. It includes a powerful suite of remote sensing imagers and spectrometers, instruments for in-situ investigation of the circumplanetary plasma and magnetic field, and a radio science experiment. The spacecraft, based on the Mars Express bus modified for the conditions at Venus, provides a versatile platform for nadir and limb observations as well as solar, stellar, and radio occultations. In April 2006 Venus Express was inserted in an elliptical polar orbit around Venus, with a pericentre height of km and apocentre distance of km and an orbital period of 24 hours. The nominal mission lasted from June 4, 2006 till October 2, 2007, which corresponds to about two Venus sidereal days. Here we present an overview of the main results of the nominal mission, based on a set of papers recently published in Nature, Icarus, Planetary and Space Science, and Geophysical Research Letters. © 2009 Pleiades Publishing, Ltd.

Introduction to the special section on Venus Express: Results of the Nominal Mission


DV Titov, FW Taylor, H Svedhem

Venus: our non-identical twin

PHYSICS WORLD 21 (2008) 31-34

F Taylor

Evidence for anomalous cloud particles at the poles of Venus


CF Wilson, S Guerlet, PGJ Irwin, CCC Tsang, FW Taylor, RW Carlson, P Drossart, G Piccioni

A correlated-k model of radiative transfer in the near-infrared windows of Venus


CCC Tsang, PGJ Irwin, FW Taylor, CF Wilson

Variable winds on Venus mapped in three dimensions

Geophysical Research Letters 35 (2008)

A Sánchez-Lavega, R Hueso, G Piccioni, P Drossart, J Peralta, S Pérez-Hoyos, CF Wilson, FW Taylor, KH Baines, D Luz, S Erard, S Lebonnois

We present zonal and meridional wind measurements at three altitude levels within the cloud layers of Venus from cloud tracking using images taken with the VIRTIS instrument on board Venus Express. At low latitudes, zonal winds in the Southern hemisphere are nearly constant with latitude with westward velocities of 105 ms - 1 at cloud-tops (altitude ∼ 66 km) and 60-70 ms - 1 at the cloud-base (altitude ∼ 47 km). At high latitudes, zonal wind speeds decrease linearly with latitude with no detectable vertical wind shear (values lower than 15 ms - 1), indicating the possibility of a vertically coherent vortex structure. Meridional winds at the cloud-tops are poleward with peak speed of 10 ms - 1 at 55° S but below the cloud tops and averaged over the South hemisphere are found to be smaller than 5 ms - 1. We also, report the detection at subpolar latitudes of wind variability due to the solar tide. Copyright 2008 by the American Geophysical Union.

Global and temporal variations in hydrocarbons and nitriles in Titan's stratosphere for northern winter observed by Cassini/CIRS

Icarus 193 (2008) 595-611

NA Teanby, PGJ Irwin, R de Kok, CA Nixon, A Coustenis, E Royer, SB Calcutt, NE Bowles, L Fletcher, C Howett, FW Taylor

Mid-infrared spectra measured by Cassini's Composite InfraRed Spectrometer (CIRS) between July 2004 and January 2007 (L s = 293 ° - 328 °) have been used to determine stratospheric temperature and abundances of C 2 H 2 , C 3 H 4 , C 4 H 2 , HCN, and HC 3 N. Over 65,000 nadir spectra with spectral resolutions of 0.5 and 2.5 cm -1 were used to probe spatial and temporal composition variations in Titan's stratosphere. Cassini's 180° orbital transfer in mid-2006 allowed low emission angle observations of the north polar region for the first time in the mission and allowed us to probe the full latitude range. We present the first measurements of composition variations within the polar vortex, which display increasing abundances right up to 90° N. The lack of a homogeneous abundance-latitude variation within the vortex indicates limited horizontal mixing and suggests that subsidence is greatest at the vortex core. Contrary to numerical model predictions and tropospheric cloud observations, we do not see any evidence for a secondary circulation cell near the south pole, which suggests a single Hadley-type circulation in the stratosphere at this epoch. This difference can be reconciled if the secondary cell is restricted to altitudes below 100 km, where there is no sensitivity in our data. Temporal variations in composition were observed in the south, with volatile species becoming less abundant as the season progressed. The observed variations are compared to numerical model predictions and observations from Voyager. © 2007 Elsevier Inc. All rights reserved.

First detection of hydroxyl in the atmosphere of Venus


G Piccioni, P Drossart, L Zasova, A Migliorini, J-C Gerard, FP Mills, A Shakun, AG Munoz, N Ignatiev, D Grassi, V Cottini, FW Taylor, S Erard, V-VET Team

Titan: Exploring an Earthlike World

World Scientific, 2008

A Coustenis, FW Taylor

Intense polar temperature inversion in the middle atmosphere on Mars

Nature Geoscience 1 (2008) 745-749

DJ McCleese, JT Schofield, FW Taylor, WA Abdou, O Aharonson, D Banfield, SB Calcutt, NG Heavens, PGJ Irwin, DM Kass, A Kleinböhl, WG Lawson, CB Leovy, SR Lewis, DA Paige, PL Read, MI Richardson, N Teanby, RW Zurek

Current understanding of weather, climate and global atmospheric circulation on Mars is incomplete, in particular at altitudes above about 30 km. General circulation models for Mars are similar to those developed for weather and climate forecasting on Earth and require more martian observations to allow testing and model improvements. However, the available measurements of martian atmospheric temperatures, winds, water vapour and airborne dust are generally restricted to the region close to the surface and lack the vertical resolution and global coverage that is necessary to shed light on the dynamics of Mars middle atmosphere at altitudes between 30 and 80 km (ref.7). Here we report high-resolution observations from the Mars Climate Sounder instrument on the Mars Reconnaissance Orbiter. These observations show an intense warming of the middle atmosphere over the south polar region in winter that is at least 10-20 K warmer than predicted by current model simulations. To explain this finding, we suggest that the atmospheric downwelling circulation over the pole, which is part of the equator-to-pole Hadley circulation, may be as much as 50 more vigorous than expected, with consequences for the cycles of water, dust and CO"2 that regulate the present-day climate on Mars. © 2008 Macmillan Publishers Limited.

Atmospheric structure and dynamics as the cause of ultraviolet markings in the clouds of Venus

NATURE 456 (2008) 620-623

DV Titov, FW Taylor, H Svedhem, NI Ignatiev, WJ Markiewicz, G Piccioni, P Drossart

Oxygen compounds in Titan's stratosphere as observed by Cassini CIRS

Icarus 186 (2007) 354-363

FW Taylor, de Kok R, Irwin PGJ, Teanby NA

South-polar features on Venus similar to those near the north pole

Nature 450 (2007) 637-640

G Piccioni, P Drossart, A Sanchez-Lavega, R Hueso, FW Taylor, CF Wilson, D Grassi, L Zasova, M Moriconi, A Adriani, S Lebonnois, A Coradini, B Bézard, F Angrilli, G Arnold, KH Baines, G Bellucci, J Benkhoff, JP Bibring, A Blanco, MI Blecka, RW Carlson, A Di Lellis, T Encrenaz, S Erard, S Fonti, V Formisano, T Fouchet, R Garcia, R Haus, J Helbert, NI Ignatiev, PGJ Irwin, Y Langevin, MA Lopez-Valverde, D Luz, L Marinangeli, V Orofino, AV Rodin, MC Roos-Serote, B Saggin, DM Stam, D Titov, G Visconti, M Zambelli, E Ammannito, A Barbis, R Berlin, C Bettanini, A Boccaccini, G Bonnello, M Bouye, F Capaccioni, A Cardesin Moinelo, F Carraro, G Cherubini, M Cosi, M Dami, M De Nino, D Del Vento, M Di Giampietro, A Donati, O Dupuis, S Espinasse, A Fabbri, A Fave, IF Veltroni, G Filacchione, K Garceran, Y Ghomchi, M Giustini, B Gondet, Y Hello, F Henry, S Hofer, G Huntzinger, J Kachlicki, R Knoll, K Driss, A Mazzoni, R Melchiorri, G Mondello, F Monti, C Neumann, F Nuccilli, J Parisot, C Pasqui, S Perferi, G Peter, A Piacentino, C Pompei, JM Reess, JP Rivet, A Romano, N Russ, M Santoni, A Scarpelli, A Semery, A Soufflot

Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition. ©2007 Nature Publishing Group.

Scientific goals for the observation of Venus by VIRTIS on ESA/Venus express mission

Planetary and Space Science 55 (2007) 1653-1672

P Drossart, G Piccioni, A Adriani, F Angrilli, G Arnold, KH Baines, G Bellucci, J Benkhoff, B Bézard, JP Bibring, A Blanco, MI Blecka, RW Carlson, A Coradini, A Di Lellis, T Encrenaz, S Erard, S Fonti, V Formisano, T Fouchet, R Garcia, R Haus, J Helbert, NI Ignatiev, PGJ Irwin, Y Langevin, S Lebonnois, MA Lopez-Valverde, D Luz, L Marinangeli, V Orofino, AV Rodin, MC Roos-Serote, B Saggin, A Sanchez-Lavega, DM Stam, FW Taylor, D Titov, G Visconti, M Zambelli, R Hueso, CCC Tsang, CF Wilson, TZ Afanasenko

The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA/Venus Express mission has technical specifications well suited for many science objectives of Venus exploration. VIRTIS will both comprehensively explore a plethora of atmospheric properties and processes and map optical properties of the surface through its three channels, VIRTIS-M-vis (imaging spectrometer in the 0.3-1 μm range), VIRTIS-M-IR (imaging spectrometer in the 1-5 μm range) and VIRTIS-H (aperture high-resolution spectrometer in the 2-5 μm range). The atmospheric composition below the clouds will be repeatedly measured in the night side infrared windows over a wide range of latitudes and longitudes, thereby providing information on Venus's chemical cycles. In particular, CO, H 2 O, OCS and SO 2 can be studied. The cloud structure will be repeatedly mapped from the brightness contrasts in the near-infrared night side windows, providing new insights into Venusian meteorology. The global circulation and local dynamics of Venus will be extensively studied from infrared and visible spectral images. The thermal structure above the clouds will be retrieved in the night side using the 4.3 μm fundamental band of CO 2 . The surface of Venus is detectable in the short-wave infrared windows on the night side at 1.01, 1.10 and 1.18 μm, providing constraints on surface properties and the extent of active volcanism. Many more tentative studies are also possible, such as lightning detection, the composition of volcanic emissions, and mesospheric wave propagation. © 2007 Elsevier Ltd. All rights reserved.

The 2003 November 14 occultation by Titan of TYC 1343-1865-1. II. Analysis of light curves

Icarus 192 (2007) 503-518

A Zalucha, A Fitzsimmons, JL Elliot, J Thomas-Osip, HB Hammel, VS Dhillon, TR Marsh, FW Taylor, PGJ Irwin

We observed a stellar occultation by Titan on 2003 November 14 from La Palma Observatory using ULTRACAM with three Sloan filters: u ′ , g ′ , and i ′ (358, 487, and 758 nm, respectively). The occultation probed latitudes 2° S and 1° N during immersion and emersion, respectively. A prominent central flash was present in only the i ′ filter, indicating wavelength-dependent atmospheric extinction. We inverted the light curves to obtain six lower-limit temperature profiles between 335 and 485 km (0.04 and 0.003 mb) altitude. The i ′ profiles agreed with the temperature measured by the Huygens Atmospheric Structure Instrument [Fulchignoni, M., and 43 colleagues, 2005. Nature 438, 785-791] above 415 km (0.01 mb). The profiles obtained from different wavelength filters systematically diverge as altitude decreases, which implies significant extinction in the light curves. Applying an extinction model [Elliot, J.L., Young, L.A., 1992. Astron. J. 103, 991-1015] gave the altitudes of line of sight optical depth equal to unity: 396 ± 7 and 401 ± 20  km (u ′ immersion and emersion); 354 ± 7 and 387 ± 7  km (g ′ immersion and emersion); and 336 ± 5 and 318 ± 4  km (i ′ immersion and emersion). Further analysis showed that the optical depth follows a power law in wavelength with index 1.3 ± 0.2. We present a new method for determining temperature from scintillation spikes in the occulting body's atmosphere. Temperatures derived with this method are equal to or warmer than those measured by the Huygens Atmospheric Structure Instrument. Using the highly structured, three-peaked central flash, we confirmed the shape of Titan's middle atmosphere using a model originally derived for a previous Titan occultation [Hubbard, W.B., and 45 colleagues, 1993. Astron. Astrophys. 269, 541-563]. © 2007 Elsevier Inc. All rights reserved.