Venus Clouds and Hazes LW Esposito 10 July 2007

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

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