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The cloudy veil of Venus - ESA

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The cloudy veil of VenusColin WilsonESAC Seminar, 12 April 2012OXFORD


ESAC Seminar, 12 April 2012OXFORD


True-colour image of Venus(Mariner 10, 1974)ESAC Seminar, 12 April 2012OXFORD


UV image of Venus(Pioneer Venus, 1979)ESAC Seminar, 12 April 2012OXFORD


Summary• Introduction – past missions & Venus Express• Radiative Balance &Vertical Structure• Lower Clouds• Chemistry &Upper Clouds• Winds & polar vortex• Hunting for active volcanoesESAC Seminar, 12 April 2012OXFORD


Why Venus?• Venus is our nearest neighbour.• Venus should be the most Earthlike planet we know.– Created at roughly the same time (4.4 billion years ago)– Apparently similar bulk composition– Roughly the same size & density• Early Venus was probably much like early Earth– Hot dense atmosphere rich in CO 2 and water– On Earth, CO 2 was sequestered in carbonate rocks– On Venus, CO 2 is all still in atmosphere – 92 bar surface pressure– If Earth’s carbonates were evaporated, Earth’s atmosphere wouldhave similar atmospheric CO 2 and N 2 abundances as Venus.• Venus also illustrates the probable fate of the Earth.– In ~ 1 billion years, with a brighter sun, sunlight level at Earth maybe similar to that at Venus today.– Will we be able to avoid the runaway greenhouse warming that isfound at Venus?ESAC Seminar, 12 April 2012OXFORD


Why Venus (II)?• Venus is the same size as Earth, but rotates more slowly.– Planet rotates once every 243 Earth days– One Venus year = 223 Earth days– However, atmosphere at cloud-tops rotates once every 5 days,• 50x faster than solid planet– How does atmospheric circulation on slowly-rotating planets work?• Relevance to Titan & exoplanets• Venus today has a climate very different from the Earth– 92 bar CO 2 leads to intense greenhouse warming– Surface temperatures exceed 450 °C– Main cloud-forming volatile is sulphuric acid, rather than water• Venus atmosphere is optically thick– Thick cloud layer covers whole planet– 95% of sunlight absorbed at cloud deck, not at/near surface as on EarthESAC Seminar, 12 April 2012OXFORD


Venus missions 1961 - 1972ESAC Seminar, 12 April 2012†F = flyby, O = Orbiter, L = lander, B = balloonOXFORD


Venus missions 1961 - 1972ESAC Seminar, 12 April 2012Mariner 2 (NASA):First successfulplanetary flyby, 1962†F = flyby, O = Orbiter, L = lander, B = balloonOXFORD


Venus missions 1961 - 1972First in situanalysis ofanother planet’satmosphere, 1967ESAC Seminar, 12 April 2012†F = flyby, O = Orbiter, L = lander, B = balloonOXFORD


Venus missions 1961 - 1972ESAC Seminar, 12 April 2012†F = flyby, O = Orbiter, L = lander, B = balloonOXFORD


Venus missions 1972 - presentESAC Seminar, 12 April 2012OXFORD


Venus missions 1972 - presentVenera probes: color imagesof surface (1978 – 1985)ESAC Seminar, 12 April 2012OXFORD


Venus missions 1972 - presentVega Balloons deployedon Venus (1985)ESAC Seminar, 12 April 2012OXFORD


Venus missions 1972 - presentESAC Seminar, 12 April 2012American Pioneer Venus orbiter & probes (1978 - )OXFORD


Venus missions 1972 - presentMagellan radar mapper (1989 - 1994)ESAC Seminar, 12 April 2012OXFORD


Venus missions 1972 - presentESAC Seminar, 12 April 2012Galileo flyby 1990: first view of lowerclouds using near-IR spectral windowsOXFORD


Venus ExpressPFS – spectrometer, 2 – 25 μmVIRTIS – imaging spectrometer, 0.25 –5 μmSPICAV – UV / nIR spectrometer,primarily for solar / stellar occultationVMC – wide-angle camera with 4spectral channelsVeRa – radio occultation & bistaticradarMAG – magnetometerAspera – in situ ion & neutral species• Launched Nov 2005• In Venus orbit since 11 April 2006– Orbit is polar, apocentre above S pole• Mission extended until end 2014• Fuel runs out in 2015 ?ESAC Seminar, 12 April 2012OXFORD


Venus ExpressPFS – spectrometer, 2 – 25 μmVIRTIS – imaging spectrometer, 0.25 –5 μm 1 μmSPICAV – UV / nIR spectrometer,primarily for solar / stellar occultationVMC – wide-angle camera with 4spectral channelsVeRa – radio occultation & bistaticradarMAG – magnetometerAspera – in situ ion & neutral species• Launched Nov 2005• In Venus orbit since 11 April 2006– Orbit is polar, apocentre above S pole• Mission extended until end 2014• Fuel runs out in 2015 ?ESAC Seminar, 12 April 2012OXFORD


Summary• Introduction – past missions & Venus Express• Radiative Balance &Vertical Structure• Lower Clouds• Chemistry &Upper Clouds• Winds & polar vortex• Hunting for active volcanoesESAC Seminar, 12 April 2012OXFORD


Radiation budget on EarthESAC Seminar, 12 April 2012NASA/LARCOXFORD


Radiation budget on Venus475 W/m 2625 W/m 2150 W/m 2100ESAC Seminar, 12 April 201220 W/m 2 absorbed at surfaceTitov et al., 2007OXFORD


pressure (bar)Temperature structure (Earth)0.0130 km0.11200 250 300Temperature (K)20 km10 km0 kmStratosphereStableTroposphereConvectiveESAC Seminar, 12 April 2012OXFORD


Temperature structure (Earth)What drives cloud-level convection?20 kmSolarheating ofground /lower atm.StratosphereStableTroposphereConvectiveLW Cooling tospace10 km0 kmESAC Seminar, 12 April 2012OXFORD


Tropospheric convective cumulus cloud (Earth)pdrafts bring moist,arm air to coldergions where waterpour condenses.HICKER CLOUDUPDRAFTSESAC Seminar, 12 April 2012OXFORDNOAA


Convective clouds on Venus?ESAC Seminar, 12 April 2012OXFORD


Vega balloon vertical velocities at 55 km altitudeLinkin et al 1986ESAC Seminar, 12 April 2012OXFORD


ESAC Seminar, 12 April 2012Galileo Venus flyby image 1990 – nightside near-IR emissionOXFORD


pressure (bar)Temperature structure (Venus)0.01Earth0.1VenusUpper cloud60 km110Lower/middlecloud layerToo hot forH 2 SO 4 clouds!50 km100200 300 400 500 600 700 800Temperature (K)0 kmESAC Seminar, 12 April 2012OXFORD


Temperature structure (Venus)What drives cloud-level convection?Solarheating ofground /lower atm.Upper cloudLower/middlecloud layer60 km50 km30 km0 kmESAC Seminar, 12 April 2012OXFORD


Temperature structure (Venus)What drives cloud-level convection?Solarheating ofground /lower atm.Upper cloudLower/middlecloud layerLower convectivelayer60 km50 km30 km0 kmESAC Seminar, 12 April 2012OXFORD


Temperature structure (Venus)What drives cloud-level convection?Upper cloud60 kmLower/middlecloud layer50 kmSolarheating ofground /lower atm.Lower convectivelayerIR heating ofcloudbase30 km0 kmESAC Seminar, 12 April 2012OXFORD


Temperature structure (Venus)What drives cloud-level convection?Upper cloudLW Cooling tospace60 kmLower/middlecloud layer50 kmSolarheating ofground /lower atm.Lower convectivelayerIR heating ofcloudbase30 km0 kmESAC Seminar, 12 April 2012OXFORD


Temperature structure from descent probesStatic stability measures deviation of measured dT/dz from adiabatic lapse rateStatic stability near 0 indicates convection.Main Convective layer is at ~ 50 – 60 km altitudeUpper cloud (60 – 70 km altitude) is very stableESAC Seminar, 12 April 2012OXFORD


Temperature structure - VEx radio occultation• As VEx sets behind Venus, radio signal is bent by atmosphere of Venus.• Examining Doppler shift of signal yields• profile of refractive index gradients• density, pressure and temperature profiles 40 – 90 km• Examining absolute magnitude of signal reveals losses, due to• beam spreading• absorption in atmosphere - assumed to be H 2 SO 4• any other loss processesESAC Seminar, 12 April 2012OXFORD


Temperature structure - VEx radio occultationVEx radio occultations have been returning data showinglatitude and local time dependence of stability profilesTellmann et al., JGR 2009ESAC Seminar, 12 April 2012OXFORD


Temperature structure - VEx radio occultationVenus Express measures temperature profiles from 40 – 90 km using radiooccultation (>300 profiles to date)Tellmann et al., JGR 2009VEx radio occultations appear to show that polar regions may have fardeeper convection than previously thought.ESAC Seminar, 12 April 2012OXFORD


Venus clouds – Sulphur cycle60 - 75 kmStratosphereNet H 2 SO 4 source (photochemical)Net transports:H 2 SO 4 :H 2 O cloudsSO 2H 2 OOCSH 2 SO 4S xCO~40 kmNet H 2 SO 4 sink (thermal decomposition)• SO 2 & H 2 O : volcanic source?• H 2 SO 4 & S x : cloud-forming agentsESAC Seminar, 12 April 2012OXFORD


Venus clouds – Sulphur cycle60 - 75 kmStratosphereNet H 2 SO 4 source (photochemical)60 kmNet transports:50 – 60 km50 kmSO 2H 2 OOCSH 2 SO 4S xCO~40 kmNet H 2 SO 4 sink (thermal decomposition)• SO 2 & H 2 O : volcanic source?• H 2 SO 4 & S x : cloud-forming agentsESAC Seminar, 12 April 2012OXFORD


Lower clouds –constraints on cloud base altitude• Regions of thicker cloud have a slightly lower cloudbase altitude, and higheracid concentration, than regions of thin cloud. (Barstow et al., 2012).ESAC Seminar, 12 April 2012OXFORD


• Wavelength dependence of scattering depends on particle size,so wavelength ratios give rough indication of particle size• No consistent correlation of particle size with cloud thickness!• (unlike Earth thunder clouds)Lower clouds –particle size• However, large particles found towards polar vortexIncreasingparticle sizeIncreasingcloudinessESAC Seminar, 12 April 2012Increasingparticle sizeImage: Sandrine GuerletOXFORD


Lower clouds –temporal evolution• Individual cloud features can be tracked in image sequences fromVenus Express / VIRTIS imagery• Features evolve with a time constant of approximately 1 Earthday.• Features at lower latitudes evolve more quickly.ESAC Seminar, 12 April 2012OXFORD


Lower clouds –temporal evolution of lower cloudsESAC Seminar, 12 April 20121.74 µm VEx/VIRTIS imagesTypical feature lifetime OXFORD ~ 1 Earth dayMcGouldrick et al, 2012


Sulfuric acid profiles - VEx radio occultationAnalysis of VEx profiles is in progress!Kolodner & Steffes, 1998using Magellan dataESAC Seminar, 12 April 2012OXFORD


UV image of Venus(Pioneer Venus, 1979)Upper clouds –sounding from orbitESAC Seminar, 12 April 2012OXFORD


VEx/VMC images of upper cloudsESAC Seminar, 12 April 2012VEx/VMCOXFORD


ESAC Seminar, 12 April 2012OXFORDVEx/VMC


Upper clouds - morphology> 60º polar collar & vortex30-60º ‘streaky’ cloud features< 30º ‘blotchy’ cloud featuresESAC Seminar, 12 April 2012OXFORD


But what causes UV contrast?Suggestions include:• Formaldehyde CH2O• Carbon suboxide C3O2• Nitrosylsulfuric acid NOHSO4• Nitrogen dioxide NO2 and nitrogen tetroxide N2O4• Ammonium nitrite NH3NO2• Ammonium pyrosulfate (NH4)S2O5• Amides• Chlorine Cl2• Sulfur dichloride, SCl2• Iron chloride FeCl3• Perchloric acid HClO4• Disulfur monoxide S2O• AND• Elemental sulfur allotropes (S 3 , S 4 , S 8 , ... )Can VEx resolve this dilemna?ESAC Seminar, 12 April 2012OXFORD


How do UV features arise?60 -70 km : atmosphere has highconvective stability – not consistentwith convective cells!60 km50 - 60 km : convective regionfrom VeRa observations50 kmESAC Seminar, 12 April 2012OXFORD


How do UV features arise?UV dark60 -70 km : atmosphere has highconvective stability – not consistentwith convective cells!60 km50 - 60 km : convective regionfrom VeRa observations50 kmESAC Seminar, 12 April 2012OXFORD


How do UV features arise?60 -70 km : atmosphere has highconvective stability – not consistentwith convective cells!60 kmUV dark?High hazesUV-bright50 - 60 km : convective regionfrom VeRa observations50 kmESAC Seminar, 12 April 2012OXFORD


How do UV features arise?60 -70 km : atmosphere has highconvective stability – not consistentwith convective cells!Stratospheric cloud layer decoupled from lower/middle cloud?‣ Almost half of solar energy input isabsorbed by the UV absorber(Crisp, Icarus, 1986). This is ~ 400 Wm -2 at sub-solar point.60 km50 kmH 2 Oenrichment?ESAC Seminar, 12 April 2012OXFORD


UV contrast & cloud-top height (VEx/VIRTIS)• Cloud-top height measured on the dayside by measuring depth of CO 2 absorption linein reflected sunlight (Ignatiev et al., 2007)• No variation at low latitudes; decrease of ~7 km toward polesESAC Seminar, 12 April 2012Ignatievet al.,2009OXFORD


Sanchez-Lavega et al., 20083-D Wind fields reveal strong vertical shearUsing multiple wavelengths including near-IR channels, VExmeasures the drift speed of clouds.UUV dark60 kmUU50 kmE-W wind speed at 70 km, 60 km, 50 km altitude(Sanchez-Lavega et al. 2008)• Very strong vertical wind shear at 60-70 km!• Casues turbulent mixing despite stratification.ESAC Seminar, 12 April 2012OXFORD


Polar VortexESAC Seminar, 12 April 2012[Suomi and Limaye, 1978-S.hemisph., Mariner 10]OXFORD


Venus – VEx / VMCESAC Seminar, 12 April 2012Limaye et al., 2009OXFORDEarth - hurricane Frances


Upper cloud – thermal IR imagery• Polar view of N pole of Venus at 15 µm wavelength, Pioneer Venus(Taylor et al.1979)• Little variation at low latitudes but curious ‘double vortex’ at poleESAC Seminar, 12 April 2012OXFORD


Upper cloud – thermal IR imagery• Polar view of S pole of Venus, with sun to the top• Thermal infrared image at 3.7 µm (VIRTIS/VEx, from orbit 28)VEX/VIRTISESAC Seminar, 12 April 2012OXFORD


Upper cloud – thermal IR imageryVEx/VIRTISESAC Seminar, 12 April 2012OXFORD


Upper cloud – thermal IR imageryVEx/VIRTISESAC Seminar, 12 April 2012OXFORD


Upper cloud – thermal IR imagery“High”temperatureregion is withinthe vortex“Low”temperatureregion is justoutside,sorrounding thevortexESAC Seminar, 12 April 2012G. Piccioni et al., Nature 29 November 2007OXFORD


The many many faces of the vortexESAC Seminar, 12 April 2012Inverted thermal images from VEx/VIRTIS:Darker means deeper and higher temperatureOXFORD


The many many faces of the vortexESAC Seminar, 12 April 2012Inverted thermal images from VEx/VIRTIS:Darker means deeper and higher temperatureOXFORD


Luz et al., 2011ESAC Seminar, 12 April 2012OXFORD


Clouds top radiation (65 km)Deep atmosphere (50 km)On average, the vortex is insolid-body rotation...ESAC Seminar, 12 April 2012OXFORD


... But viewed in detail, theflow is extremely complex.ESAC Seminar, 12 April 2012OXFORD


Hunting active volcanoesSmrekar et al.ESAC Seminar, 12 April 2012OXFORD


Venus clouds – volcanic source?• Lower clouds: No correlation of clouds or SO 2 / H 2 O /CO with topographic features has (yet) been found.ESAC Seminar, 12 April 2012OXFORD


Upper clouds – did we see a volcanic eruption?ESAC Seminar, 12 April 2012Limaye et al.,EGU 2010OXFORD


Long-term variability of SO 2 and haze particlesEsposito, Adv. Spa. Res., 1985• Episodic vulcanism?ESAC Seminar, 12 April 2012OXFORD


Evolution SO 2 mixing ratio above Venus’ clouds(From Denis Belyaev et al., SPICAV/SOIR teams)ESAC Seminar, 12 April 2012OXFORD


Evolution SO 2 mixing ratio above Venus’ clouds(From Denis Belyaev et al., SPICAV/SOIR teams)ESAC Seminar, 12 April 2012OXFORD


Hunting vulcanogenic cloudsThe search continues...Smrekar et al.ESAC Seminar, 12 April 2012OXFORD


The endESAC Seminar, 12 April 2012Thanks for your attentionEVE / BalintOXFORD


Future missionsVenus Express is making the clouds of Venus ever more familiar...ESAC Seminar, 12 April 2012OXFORD


Akatsuki (aka Venus Climate Orbiter)• Launched May 2010• Failed VOI December 2010• To attempt VOI 2015/2016using AOCS thrusters• Payload:6 cameras – UV, vis, near IR,lightning50 kHz imaging at 777 nmoxygen line• Equatorial orbit to follow cloudfeaturesThis mission has a strong focus on dynamicsLack of spectrometers means little newconstraints on composition.ESAC Seminar, 12 April 2012OXFORD


Cloud-level balloon missionCompatible with ESA M-class mission opportunity• At 55 km, T=20°C, p=0.5 bar• Explore heart of convectivecloud layer• Full circumnavigation ofplanet in cluesto early evolution of planetESAC Seminar, 12 April 2012OXFORD


Balloon-deployed microprobes- With ESA and UK funding, we have undertaken a pair of studies into balloon deployed probesweighting from 100 – 2000 g.- Probes, deployed from balloon at ~60 km altitude, would provide access to surface and lowatmosphere- Balloon is carried around the planet in ~4-5 days, allowing good spatial coverage- Microprobes weigh 100 g, 46 mm x 110 mm L-Wind profiles derived from tracking microprobes(from balloon)- Microprobes measure pressure, temperature,upwards & downwards light flux using 10 gscience payload.- Design is technologically conservative, feasibleusing today’s technology-Slightly larger (200 g) microprobes would allowchemistry payload- Even larger (1-2 kg) probes would allow surfaceimagingCould be provided as a UK-provided, high visibility, UKSpace - branded subsystemESAC Seminar, 12 April 2012Image credit: Oxford Univ. / Qinetiq / ESAOXFORD


Fixed-wing aircraft to study upper cloud?GAP project, ScrippsESAC Seminar, 12 April 2012OXFORD


Transit of VenusTransit of Venus : 6 June 2012 at 00:04Information day at ESAC : 9 May 2012 at 14:00M. FrassatiESAC Seminar, 12 April 2012OXFORD

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