Venus atmosphere is enigmatic with many unsolved questions. Two prominent puzzles are:

Transcription

1 Venus atmosphere is enigmatic with many unsolved questions. Two prominent puzzles are: How is it that Venus clouds rotate at a rate 50x that of the solid body and why has the atmospheric rotation rate not decayed How has Venus climate evolved with time and how will it evolve in the future what processes led to it being a hellacious, high pressure, acid rain bearing planet did its climatic history at any stage resemble that of Earth

2 Many of Venus unsolved atmosphere questions relate directly to UV studies. The energy that drives super-rotation is derived from energy absorbed at UV wavelengths by SO2, SO and unnamed absorber whose absorption extends from 300 to 600 nm, but absorbs most strongly between 300 and 400 nm A central component of Venus climate history is the cloud coverage and formation history which is controlled by the UV photolysis of SO 2 and SO gas.

3 Many of Venus unsolved atmosphere questions relate directly to UV studies. HST has the unique capability to observe both with spectra and imaging Venus cloud tops at the wavelengths diagnostic of the temporal and spatial variation of the UV Vis absorbers that influence Venus climate and supply energy for the cloud super-rotation

4 The rotation rate enigma Understanding the cloud rotation rate requires understanding how the energy that drives the wind rotation is distributed, what can influence the level of energy deposited and how is energy and angular momentum exchanged between the surface and the atmosphere. Imaging from the Akatsuki mission has revealed the existence of topographic wakes or gravity waves formed as the atmosphere flows around regions of high elevation These waves propagate from the surface to cloud tops growing in latitude extent as they propagate upward.

5 The rotation rate enigma Understanding the cloud rotation rate requires understanding how the energy that drives the wind rotation is distributed, what can influence the level of energy deposited and how is energy and angular momentum exchanged between the surface and the atmosphere. This newly discovered phenomenon directly traces the interaction and angular momentum exchange between Venus solid body with the atmosphere A in-depth study of this phenomenon can be a game changer in Venus atmosphere science

6 REFLECTANCE VCO/LIR image VCO LIR 8-12 um Brightness T IR spectra from TEXES directly over or other grd obs. would add value GW HST/STIS G230LB spectrum: 290 nm Anticipated FOV from Jessup et al VCO/UVI 283 nm bandpass WFC3 280 nm Anticipated FOV 365 nm WFC3 373 nm VCO/UVI 283 nm HST/WFC3 280 nm HST/STIS nm (5 km/pixel at periapsis) 20±3 km/pixel 45 km/pixel full disk limb-to-limb VCO UVI/365 nm (5 km/pixel at periapsis) HST/WFC3 373 nm 20±3 km/pixel HST/STIS nm 45 km/pixel limb-to-limb HST/STIS G230LB HST/STIS G430L

7 HST/STIS spectra maps latitude and LT: Photochemical modeling: the SO 2 and SO cloud top abundances H 2 SO 4 profile cloud top altitude Vertical mixing profile 245 nm albedo (haze opacity )and abundance --convective activity Conditions within and outside of the GW well defined from spectra WFC3 images provides cloud tracking and wind speeds Inclusion of empirically retrieved atmospheric and cloud conditions helps us to Refine models developed by the Akatsuki team - of the sensitivity of the wave structure to thermal stability. Advance our ability to constrain the stability conditions at each local time and latitude Ultimately improve our understanding of how the atmospheric structure changes with local time and its impact on the and energy/momentum exchange within the atmosphere as a whole These studies will advance the development of empirically constrained (thus more rigorous) models of Venus super-rotation mechanism

8 ENIGMA II

9 The climate enigma Venus clouds are composed of H 2 SO 4 gas and aerosols. The thickness and distribution of these clouds determines the percentage of solar light reflected and absorbed at the cloud top level particularly between 240 and 260 nm; it also interferes with absorption from the unnamed UV absorber at wavelengths longward of 300 nm. Studying and defining the mechanisms that drive H 2 SO 4 variation is key for modeling Venus climate Photolysis of the SO 2, SO gases leads to the formation of the dominant component of Venus clouds the H 2 SO 4 aerosol absorption by the SOx species occurs primarily between nm. Tracing Venus nm cloud top albedo latitude and local time variation, is the most definitive way to define the what controls systematic changes in the H 2 SO 4 density it also provides the most realistic basis to project its expected long term evolution from the past and for the future.

10 Tracing Venus nm cloud top albedo latitude and local time variation provides the most reliable data from which to define the characteristics of the unnamed UV absorber change relative to systematic changes in the H 2 SO 4 density this is crucial for defining the expected impact on climate relative to longterm changes in both the H 2 SO 4 and unnamed UV absorber properties HST-UVI HST-UVI-LIR COORINATED COORDINATED STUDY OF STUDY VENUS OF CLOUD TOPS The climate enigma Venus clouds are composed of H 2 SO 4 gas and aerosols. The thickness and distribution of these clouds determines the percentage of solar light reflected and absorbed at the cloud top level particularly between 240 and 260 nm; it also interferes with absorption from the unnamed UV absorber at wavelengths longward of 300 nm. Studying and defining the mechanisms that drive H 2 SO 4 variation is key for modeling Venus climate 365 nm The observable distribution of the cloud top absorber at 365 nm is dependent on the H 2 SO 4 haze abundance, the movement of the absorber with winds and coriolis forces, and the state (gas, aerosol, aged aerosol, etc.) of the absorber.