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

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

Determining vertical cloud structure on Venus using near-infrared spectroscopy

European Planetary Science Congress 2009 (2009) 249-249

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

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.

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 b elow 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

The composition of Titan's stratosphere from Cassini/CIRS mid-infrared spectra

Icarus 189 (2007) 35-62

A Coustenis, RK Achterberg, BJ Conrath, DE Jennings, A Marten, D Gautier, CA Nixon, FM Flasar, NA Teanby, B Bézard, RE Samuelson, RC Carlson, E Lellouch, GL Bjoraker, PN Romani, FW Taylor, PGJ Irwin, T Fouchet, A Hubert, GS Orton, VG Kunde, S Vinatier, J Mondellini, MM Abbas, R Courtin

We have analyzed data recorded by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft during the Titan flybys T0-T10 (July 2004-January 2006). The spectra characterize various regions on Titan from 70° S to 70° N with a variety of emission angles. We study the molecular signatures observed in the mid-infrared CIRS detector arrays (FP3 and FP4, covering roughly the 600-1500 cm -1 spectral range with apodized resolutions of 2.54 or 0.53 cm -1 ). The composite spectrum shows several molecular signatures: hydrocarbons, nitriles and CO 2 . A firm detection of benzene (C 6 H 6 ) is provided by CIRS at levels of about 3.5 × 10 -9 around 70° N. We have used temperature profiles retrieved from the inversion of the emission observed in the methane ν 4 band at 1304 cm -1 and a line-by-line radiative transfer code to infer the abundances of the trace constituents and some of their isotopes in Titan's stratosphere. No longitudinal variations were found for these gases. Little or no change is observed generally in their abundances from the south to the equator. On the other hand, meridional variations retrieved for these trace constituents from the equator to the North ranged from almost zero (no or very little meridional variations) for C 2 H 2 , C 2 H 6 , C 3 H 8 , C 2 H 4 and CO 2 to a significant enhancement at high northern (early winter) latitudes for HCN, HC 3 N, C 4 H 2 , C 3 H 4 and C 6 H 6 . For the more important increases in the northern latitudes, the transition occurs roughly between 30 and 50 degrees north latitude, depending on the molecule. Note however that the very high-northern latitude results from tours TB-T10 bear large uncertainties due to few available data and problems with latitude smearing effects. The observed variations are consistent with some, but not all, of the predictions from dynamical-photochemical models. Constraints are set on the vertical distribution of C 2 H 2 , found to be compatible with 2-D equatorial predictions by global circulation models. The D/H ratio in the methane on Titan has been determined from the CH 3 D band at 1156 cm -1 and found to be 1.17 -0.28 +0.23 × 10 -4 . Implications of this deuterium enrichment, with respect to the protosolar abundance on the origin of Titan, are discussed. We compare our results with values retrieved by Voyager IRIS observations taken in 1980, as well as with more recent (1997) disk-averaged Infrared Space Observatory (ISO) results and with the latest Cassini-Huygens inferences from other instruments in an attempt to better comprehend the physical phenomena on Titan. © 2007 Elsevier Inc. All rights reserved.

Characterising Saturn's vertical temperature structure from Cassini/CIRS

Icarus 189 (2007) 457-478

LN Fletcher, PGJ Irwin, NA Teanby, GS Orton, PD Parrish, R de Kok, C Howett, SB Calcutt, N Bowles, FW Taylor

Thermal infrared spectra of Saturn from 10-1400 cm -1 at 15 cm -1 spectral resolution and a spatial resolution of 1°-2° latitude have been obtained by the Cassini Composite Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space Sci. Rev. 115, 169-297]. Many thousands of spectra, acquired over eighteen-months of observations, are analysed using an optimal estimation retrieval code [Irwin, P.G.J., Parrish, P., Fouchet, T., Calcutt, S.B., Taylor, F.W., Simon-Miller, A.A., Nixon, C.A., 2004. Icarus 172, 37-49] to retrieve the temperature structure and para-hydrogen distribution over Saturn's northern (winter) and southern (summer) hemispheres. The vertical temperature structure is analysed in detail to study seasonal asymmetries in the tropopause height (65-90 mbar), the location of the radiative-convective boundary (350-500 mbar), and the variation with latitude of a temperature knee (between 150 and 300 mbar) which was first observed in inversions of Voyager/IRIS spectra [Hanel, R., and 15 colleagues, 1981. Science 212, 192-200; Hanel, R., Conrath, B., Flasar, F.M., Kunde, V., Maguire, W., Pearl, J.C., Pirraglia, J., Samuelson, R., Cruikshank, D.P., Gautier, D., Gierasch, P.J., Horn, L., Ponnamperuma, C., 1982. Science 215, 544-548]. Uncertainties due to both the modelling of spectral absorptions (collision-induced absorption coefficients, tropospheric hazes, helium abundance) and the nature of our retrieval algorithm are quantified. Temperatures in the stratosphere near 1 mbar show a 25-30 K temperature difference between the north pole and south pole. This asymmetry becomes less pronounced with depth as the radiative time constant for the atmospheric response increases at deeper pressure levels. Hemispherically-symmetric small-scale temperature structures associated with zonal winds are superimposed onto the temperature asymmetry for pressures greater than 100 mbar. The para-hydrogen fraction in the 100-400 mbar range is greater than equilibrium predictions for the southern hemisphere and parts of the northern hemisphere, and less than equilibrium predictions polewards of 40° N. The temperature knee between 150-300 mbar is larger in the summer hemisphere than in the winter, smaller and higher at the equator, deeper and larger in the equatorial belts and small at the poles. Solar heating on tropospheric haze is proposed as a possible mechanism for this effect; the increased efficiency of ortho- to para-hydrogen conversion in the southern hemisphere is consistent with the presence of larger aerosols in the summer hemisphere, which we demonstrate to be qualitatively consistent with previous studies of Saturn's tropospheric aerosol distribution. © 2007 Elsevier Inc. All rights reserved.

The meridional phosphine distribution in Saturn's upper troposphere from Cassini/CIRS observations

Icarus 188 (2007) 72-88

LN Fletcher, PGJ Irwin, NA Teanby, GS Orton, PD Parrish, SB Calcutt, N Bowles, R de Kok, C Howett, FW Taylor

The Cassini Composite Infrared Spectrometer (CIRS) has been used to derive the vertical and meridional variation of temperature and phosphine (PH 3 ) abundance in Saturn's upper troposphere. PH 3 has a significant effect on the measured radiances in the thermal infrared and between May 2004 and September 2005 CIRS recorded thousands of spectra in both the far (10-600 cm -1 ) and mid (600-1400 cm -1 ) infrared, at a variety of latitudes covering the southern hemisphere. Low spectral resolution (15 cm -1 ) data has been used to constrain the temperature structure of the troposphere between 100 and 500 mbar. The vertical distributions of phosphine and ammonia were retrieved from far-infrared spectra at the highest spectral resolution (0.5 cm -1 ), and lower resolution (2.5 cm -1 ) mid-infrared data were used to map the meridional variation in the abundance of phosphine in the 250-500 mbar range. Temperature variations at the 250 mbar level are shown to occur on the same scale as the prograde and retrograde jets in Saturn's atmosphere [Porco, C.C., and 34 colleagues, 2005. Science 307, 1243-1247]. The PH 3 abundance at 250 mbar is found to be enhanced at the equator when compared with mid-latitudes. At mid latitudes we see anti-correlation between temperature and PH 3 abundance at 250 mbar, phosphine being enhanced at 45° S and depleted at 25 and 55° S. The vertical distribution is markedly different polewards of 60-65° S, with depleted PH 3 at 500 mbar but a slower decline in abundance with altitude when compared with the mid-latitudes. This variation is similar to the variations of cloud and aerosol parameters observed in the visible and near infrared, and may indicate the subsidence of tropospheric air at polar latitudes, coupled with a diminished sunlight penetration depth reducing the rate of PH 3 photolysis in the polar region. © 2006 Elsevier Inc. All rights reserved.

Planetary and, space science - Preface - Introduction to the Venus express special issue, vol. 2


FW Taylor