A Cloudy Day on Venus

Transcription

1 A Cloudy Day on Venus Hueso, et. al Compe,,on between lower atmospheric thermodynamic equilibrium chemistry and upper atmosphere photochemistry Fast atmospheric sulfur cycle Middle atmosphere Slow atmospheric sulfur cycle Branch between H 2 SO 4 and S x depends on availability of O 2 or the O 2 :CL 2 ratio Path to H 2 SO 4 preferred if [O 2 ] > k 10 /k 9 [OCS] Differences in upwelling and subsidence = patchiness and transience of UV markers in cloud tops 1

2 Clouds do more than make a day dreary Impact local and large- scale global dynamics Change atmospheric radia,ve balance Act a sites for complex chemistry 645 W/m W/m W/m 2 absorbed Impacts controlled by microphysical cloud characteris,cs Effec,ve radius Variance Refrac,ve index Cloud number density Match to total op,cal depth, polarimetric data, brightness, etc We can study clouds across the spectrum IR visible UV polarimetric data Probes al,tude, different types of absorbers, absorber microphysical proper,es (size, shape, refrac,ve index, composi,on), wind speeds 2

3 VIRTIS VMC 3

4 Variability in UV observations trace an unknown UV absorber at cloud top that acts as a trace gas for clouds and winds Dark equatorial regions = warm T, intense convection Bright mid-latitudes = cooler T, higher cloud tops Polar Vortex ESA/VIRTIS-VenusX/INAF-IASF/LESIA-Obs. de Paris (G. Picconi, INAF-IASF) Hueso, et. al Extremely variable on timescales < 24hr Center of rotation moves on 5-10 day timescale Indicates extreme weather with high latitudinal wind speed gradients May extend 50km and deeper, average 10-30K warmer, 2000km across Incident Light Non-polarized Partially Partially Non-polarized Light incident on a scattering particle will induce electron oscillation perpendicular to the direction of propagation. Depending on the viewing angle, emitted light will be polarized, partially polarized, or non-polarized. 4

5 Glories atmospheric phenomenon similar to rainbow visible to observers between sun and cloud require : 1) spherical droplets, 2) of similar size In polarimetric data, see glory as area with highly nega,ve % of linear polariza,on linear polarization degree (%) Dependence of model on: refractive index effective radius nr determines degree of polarization reff determines angular position of glory nr-=1.42 reff==1.3um nr-=1.41 nr-=1.43 effective variance linear polarization degree (%) reff==1.1um reff==1.2um wide distribution decreases strength of glory veff==0.05 haze optical depth submicron particles (haze) generate strong + polarization at high angle th==0.8 veff==0.07 th==0.2 veff==0.09 th==0.0 5

6 latitude (*N) latitude (*N) linear polarization degree (%) linear polarization degree (%) orbit at 1.101um, r eff =1.05um orbit at um, r eff =1.05um linear polarization degree (%) linear polarization degree (%) orbit at 1.101um, r eff =1.2um orbit at 1.274um, r eff =1.2um Near poles, degree of polariza,on can only be fit by increased haze op,cal depth Degree of linear polarization (%) glory t h= =0.0 increased polarization at high latitudes (red) independent of t h= =0.05 t h= =0.17 Latitude (*) Phase angle 3 cloud decks (lower, middle, upper) can be observed across EM spectrum controlled by balance of thermodynamic equilibrium and photolysis reac,ons and the amount of O 2 composed of spherical par,cles, 75% H 2 SO 4 solu,on with r eff ~1.1, n r 1.01um 6