ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Proposal for an ISSI project Understanding the atmosphere of Venus

Scientific background

Lennart Bengtssonwith Roger Bonnet and André Balogh

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Scientific rationale• We need to better understand the atmosphere of Venus to

demonstrate the generalities of models of planetary atmospheres presently mainly tested for the Earth. New observations from ESA Venus Express and soon from the Planet-C by Japan is setting a suitable time schedule.

• Venus is here a primary candidate as there are both similarities and considerable differences to the Earth

• We may be able to obtain further insight in the evolution of the Venus atmosphere. Has there been a greenhouse run-away effect on Venus?

• We may obtain further insight into the long-term future of the Earth if being exposed to massive greenhouse gases in the future.

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

What do the dynamical regimes of Venus and Earth have in common?What do the dynamical regimes of Venus and Earth have in common?What accounts for the differences in the atmospheric dynamics ofWhat accounts for the differences in the atmospheric dynamics ofthese planets?these planets?Why study Venus’ atmospheric dynamics to understand the dynamicsWhy study Venus’ atmospheric dynamics to understand the dynamicsof Earth’s atmosphere?of Earth’s atmosphere?

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Major Dynamical Features of Earth’s AtmosphereMajor Dynamical Features of Earth’s AtmosphereTropical Hadley cell confined to equatorial latitudes (30).

QBOFerrel cells and polar cells.

Subtropical jet stream.Large-scale baroclinic eddies in mid-latitudes.

Thermal tides.Planetary waves.

Mesopause over the equator is colder than over the winter pole.Seasonal variations.

Major Dynamical Features of Venus’ AtmosphereMajor Dynamical Features of Venus’ Atmosphere

Superrotation.Polar vortex.

High latitude cloud level jet stream.Cloud level Hadley cell extending to polar latitudes?

Thermal tides?Planetary waves.

Mesospheric (70-100 km) temperature increase from equator to the pole.Seasonal variations?

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Earth and VenusEarth and Venus

There may be more similarity between Earth and Venus thanhitherto appreciated.

Earth’s circulation is driven from below by solar heating variations.On Venus, solar heating is focused at cloud heights where T, p

conditions are earthlike. The cloud level circulation on Venus mighthave some similar characteristics as circulation on Earth. RecentVenus GCM calculations by Sebastien Lebonnois suggest that

atmospheric circulation is driven largely from above, at cloud levels,where solar heating is concentrated, with the lower massive

atmosphere playing a more passive role. Earthlike features include acloud level Hadley cell and high latitude jets.

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Lebonnois (2007)

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Earth and Venus

The polar vortex on Venus may have some dynamical similaritiesto Earth’s hurricanes and stratospheric polar vortex.

Pioneer Venus OIR image (1980) superimposed on Mariner 10 UV images (1974)Figure courtesy of Sanjay Limaye

Venus Express VIRTIS UV and NIR images (2006)

Downloaded from VEXP Web site

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Relevance for the Earth‘s climatein the longer perspective

• Is it a risk that there will be a run-away climate on the Earth?

• Probably not, as there are counteracting processes in the Earth’s atmosphere, such as clouds acting as a sort of thermostat and that heat is transported to higher latitudes where cooling is more efficient.

• But, we can not be sure as cloud distribution may change due to atmospheric circulation changes

• It can not be excluded that Venus has undergone a climate run away.

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Project OutlineThree stage proposal

• Stage 1

• Invite an expert group on the atmospheres of Venus and Earth to a meeting in ISSI with the purpose of defining/refining the scientific objectives of the elements of the project and to make concrete proposals for its scope and implementation. (First quarter 2008)

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Project OutlineThree stage proposal

• Stage 2

• Set up an ISSI Working Group on the scientific and technical aspects of modelling the atmospheres of Venus and Earth. This WG would review the status of Venus atmospheric models and the applicability of terrestrial models to Venus. It would also review the research currently carried out into modelling the Venus atmosphere and define/propose new methodologies. The output of the WG would be (a) a book in the ISSI Scientific Report Series and (b) technical and methodological input to the preparation of the Workshop outlined below. (The WG, of about 10 or so members, with ad hoc experts as appropriate would start their work in the first half of 2008, with a target duration of 1 year.)

ISSI Proposal:The Atmosphere onVenus

8-9 Nov. 2007

Project OutlineThree stage proposal

• Stage 3

• Initiate an ISSI Workshop on the atmosphere of Venus, to be held in 2009. The main objective of such a workshop should be to summarize the knowledge situation and to explore how modelling and observational data could be suitably integrated. The expert group would advise on the detailed scope and contents of the Workshop and recommend a group of about five scientists to act as Convenors for the Workshop. It is proposed that the first meeting of the Convenors would take place in the 3rd quarter of 2008.