Venus Clouds and Hazes
LW Esposito
10 July 2007
Venus cloud issues
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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
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
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)
Cloud Particles: Physical
Properties
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
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
[Imamura and Hashimoto, JAS, 2001]
Model Venus temperature profile
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…
Galileo NIMS
view of
mysterious
‘weather’ in the
deep atmosphere
of Venus
(Carlson et al.)
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?
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