Publications by Fred Taylor

Analysis of thermal emission from the nightside of Venus at 1.51 and 1.55 μm

Icarus 201 (2009) 814-817

CF Wilson, CCC Tsang, PGJ Irwin, FW Taylor, B Bézard, S Erard, RW Carlson, P Drossart, G Piccioni, RC Holmes

We present radiative transfer modelling of thermal emission from the nightside of Venus in two 'spectral window' regions at 1.51 and 1.55 μm. The first discovery of these windows, reported by Erard et al. [Erard, S., Drossart, P., Piccioni, G., 2009. J. Geophys. Res. Planets 114, doi:10.1029/2008JE003116. E00B27], was achieved using a principal component analysis of data from the VIRTIS instrument on Venus Express. These windows are spectrally narrow, with a full-width at half-maximum of ∼20 nm, and less bright than the well-known 1.7 and 2.3 μm spectral windows by two orders of magnitude. In this note we present the first radiative transfer analysis of these windows. We conclude that the radiation in these windows originates at an altitude of 20-35 km. As is the case for the other infrared window regions, the brightness of the windows is affected primarily by the optical depth of the overlying clouds; in addition, the 1.51 μm radiance shows a very weak sensitivity to water vapour abundance. © 2009 Elsevier Inc.

Variability of CO concentrations in the Venus troposphere from Venus Express/VIRTIS using a Band Ratio Technique

Icarus 201 (2009) 432-443

CCC Tsang, FW Taylor, CF Wilson, SJ Liddell, PGJ Irwin, G Piccioni, P Drossart, SB Calcutt

A fast method is presented for deriving the tropospheric CO concentrations in the Venus atmosphere from near-infrared spectra using the night side 2.3 μm window. This is validated using the spectral fitting techniques of Tsang et al. [Tsang, C.C.C., Irwin, P.G.J., Taylor, F.W., Wilson, C.F., Drossart, P., Piccioni, G., de Kok, R., Lee, C., Calcutt, S.B., and the Venus Express/VIRTIS Team, 2008a. Tropospheric carbon monoxide concentrations and variability on Venus with Venus Express/VIRTIS-M observations. J. Geophys. Res. 113, doi: 10.1029/2008JE003089. E00B08] to show that monitoring CO in the deep atmosphere can be done quickly using large numbers of observations, with minimal effect from cloud and temperature variations. The new method is applied to produce some 1450 zonal mean CO profiles using data from the first eighteen months of operation from the Visible and Infrared Thermal Imaging Spectrometer infrared mapping subsystem (VIRTIS-M-IR) on Venus Express. These results show many significant long- and short-term variations from the mean equator-to-pole increasing trend previously found from earlier Earth- and space-based observations, including a possible North-South dichotomy, with interesting implications for the dynamics and chemistry of the lower atmosphere of Venus. © 2009 Elsevier Inc. All rights reserved.

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.

Minor Species in the Deep Atmosphere of Venus: Dynamical Tracers seen by Venus Express

AAS/Division for Planetary Sciences Meeting Abstracts #41 41 (2009) #60.07-#60.07

C Tsang, CF Wilson, JK Barstow, B Bezard, PGJ Irwin, FW Taylor, G Piccioni, P Drossart, K McGouldrick, SB Calcutt

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.

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 (Ls= 293 ° - 328 °) have been used to determine stratospheric temperature and abundances of C2H2, C3H4, C4H2, HCN, and HC3N. Over 65,000 nadir spectra with spectral resolutions of 0.5 and 2.5 cm-1were 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

Mars Climate Sounder: An investigation of thermal and water vapor structure, dust and condensate distributions in the atmosphere, and energy balance of the polar regions


DJ McCleese, JT Schofield, FW Taylor, SB Calcutt, MC Foote, DM Kass, CB Leovy, DA Paige, PL Read, RW Zurek

Venus as a more Earth-like planet

NATURE 450 (2007) 629-632

H Svedhem, DV Titov, FW Taylor, O Witasse

A dynamic upper atmosphere of Venus as revealed by VIRTIS on Venus Express

NATURE 450 (2007) 641-645

P Drossart, G Piccioni, JC Gerard, MA Lopez-Valverde, A Sanchez-Lavega, L Zasova, R Hueso, FW Taylor, B Bezard, A Adriani, F Angrilli, G Arnold, KH Baines, G Bellucci, J Benkhoff, 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, P Irwin, Y Langevin, S Lebonnois, D Luz, L Marinangeli, V Orofino, AV Rodin, MC Roos-Serote, B Saggin, DM Stam, D Titov, G Visconti, M Zambelli, C Tsang, V-VET Te

Characteristics of Titan's stratospheric aerosols and condensate clouds from Cassini CIRS far-infrared spectra

Icarus 191 (2007) 223-235

NE Bowles, N A Teanby, P G J Irwin, R de Kok