1. Venus Clouds and Hazes
LW Esposito
10 July 2007

3. Venus cloud issues Vertical structure
Physical properties of cloud particles
Composition
Relationships to chemistry, dynamics, radiation, greenhouse, climate
Temporal variations and UV and NIR features
Hazes above and below main cloud

4. Cloud vertical structure
Upper, middle and lower clouds
Detached hazes seen above and below main cloud deck
NIR images show variation in middle cloud opacity

7. Cloud size distribution
Trimodal (?): modes 1,2,3 (smallest to largest). Is mode 3 non-spherical?
Mass is dominated by mode 3, but some doubt its existence!
Mode 1 composition and source unknown
Mode 2 consistent with Earth polarimetry and Venera 15 specroscopy as 1 micron spheres (likely H2SO4 droplets)

8. Cloud Particles: Physical Properties

9. Composition
Upper cloud mode 2 is likely 1micron sulfuric acid droplets
VEGA measures 1-10 mg/m3 H2SO4
Chemical models can produce cloud droplets from photolysis (at the top) and condensation (at the bottom)
Aerosol analysis shows sulfur, chlorine and phosphorous

10. Relationships to chemistry, dynamics, radiation, climate
Chemistry that makes clouds also recycles CO2 and creates reactants with surface and upper atmosphere
Clouds show the winds and also drive stability by absorbing incoming and outgoing radiation: this determines greenhouse effect and dynamic forcing
Cloud feedbacks to climate stability

13. [Imamura and Hashimoto, JAS, 2001]

15. Model Venus temperature profile

17. Unidentified UV and blue absorption
Positively identified SO2 and SO do not absorb beyond 320nm: they cannot explain Venus’ yellow color
The unknown absorber is correlated with SO2 and has a similar lifetime, it absorbs mainly between 58-62km
Possible candidates: S3, S4, S8, Cl2, FeCl3, SCl2, S2O, croconic acid, ammonium pyrosulfate, nitrosulfuric acid…

19. Galileo NIMS view of mysterious ‘weather’ in the deep atmosphere of Venus (Carlson et al.)

20. Open questions
Determine size distribution, its variability and confirm existence of large, non-spherical particles
Cloud particle composition(except for
mode 2 = H2SO4)
Identify unknown blue absorber(s)
What physical processes create the UV markings and the NIR holes in middle cloud?

21. Venus Express contributions
Measure cloud phenomena remotely: heights, winds, markings, outgoing radiation
Measure profiles and variability of condensable and source gases: H2SO4, SO2, SO, SO3, OCS, Sn, H3PO4, Cl2
Develop global picture
Connect markings to dynamics and composition