basics & motivation technique & observations fits & measurements summary & outlook...

Atmospheric Wave Workshop ESTEC11/10/2011

Tobias StangierIst Physics InstituteUniversity of Cologne

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Basics & Motivation Technique & Observations Fits & Measurements Summary & OutlookBasics & Motivation Technique & Observations Fits & Measurements Summary & Outlook

Variation of CO2 Absorption Features at

10µm in Venus Upper Atmosphere

Wave Workshop ESTEC / Nordwijk

Tobias Stangier

November 10th 2011

Ist Physics Institute

University of Cologne



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Overview

• Basics and Motivation

• Data Reduction and Observing Condition

• Fits and Measurements

• Summary and Outlook



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Motivation

State of the art:

› Determination out of the non-LTE line profile→Line-of-sight wind speeds

→Kinetic temperatures

› But we can do better more than that!→Non-LTE solar induced => only present on Venusian day side

› Measurements on night side→No non-LTE emission features overlaying the absorption



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Absorption of CO2 on Venus

› High abundances of CO2

› Low pressure => non-LTE emission features @ 110km

› Vertical temperature gradient defines pressure induced line broadening

› Probing the atmosphere between ~60km and 110km



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Heterodyne – the unique technique

› Ultra high frequency resolution enables to resolve single line profiles

› Probing the mid-Infrared spectral region 7-11µm

› Higher spatial resolution than at radio-frequency→Beam size many times smaller than planetary disc

→Longitudinal and latitudinal profiling possible



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Instruments and Telescopes

› Cologne's→ TTuneable uneable HHeterodyne eterodyne

IInfrared nfrared SSpectrometerpectrometer (THIS)

@

› NASA GSFC's → HHeterodyne eterodyne IInstrument for nstrument for

PPlanetary lanetary WWinds and inds and CComposition omposition (HIPWAC)

@

Data acquisition during 7 different observing runs between 2007 and 2011 using

McMath-Pierce Solar TelescopeKitt Peak, AZ

NASA InfraRed Telescope FacilityMauna Kea, HI



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Observing Geometry

x

June 2009Nov. 2007May 2007

› Planetary disc ~ 50% illuminated

› FoV = 1.7”, Angular size ~ 20”

› Investigation of south polar region



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› Observing geometry March 2009

› Angular size 33 x 1.7” ~ 56”

› Many night-side measurements

› Observing CO

2(P16) line

› Latitudinal and longitudinal variation

› Non-LTE features immediately to observe



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Radiative Transfer Model CODAT

State of atmosphere - Kind and abundances of

most prominent gases

- On Venus CO2

→Temperature profile- In dependence on the

pressure level/altitudes

Observing Geometry- Sub-Solar point- Sub-Earth Point etc.- Beam-size on Planet- Transmission of Earth

atmosphere

› Initial conditions for model

Only temperature profile variable!Only temperature profile variable!



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Influence of Temperature Profile

› South pole measurement

› Freq. res. of 10MHz

› Divergence of fits to observe

› LTE model seems to be offset



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Temperature Profile

› VIRA profile for 85 deg latitude used for model Seiff et. al

› Tilted profile by T~10K at 300 mbar

› Warmer atmosphere at lower layers



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Influence of Temperature Profile

› Tilted temperature profile increases fit quality

› Ttilt = 10 K

› Higher SNR improves fit => longer integration time



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Summary

› Preliminary analysis of CO2 absorption lines at 10 micron

› Strong variation of absorption profile detected

› Pressure induced broadening effects give hint on temperature

› Influence of vertical temperature profile under investigation

› Fit results improved if profile is slightly tilted→Strong effect even for small changes



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Outlook

› Coordination with RadioScienceExperiment

› Ground-based measurements of a vertical temperature profile→High spatial resolution in the mid-IR

→Longer integration time to achieve higher SNR

› Vertical wind profiles→ Wind shear between atmospheric layers

- Transition between super-rotation and SS-AS flow dominated regions- Wave propagation

› Detailed investigation of longitudinal and latitudinal variation

› Continuous long-term observation →Seasonal behavior?

→Especially at south-pole



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Thank you for your attention!Thank you for your attention!



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Temperature Profiles

› First step: influence of the temperature profiles→VEX:RadioScience

Experiment on board of VenusExpress (Tellmann et al.)

→VIRA from Seiff et al. and Keating et al.

→VEX temperature lower



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Resulting Fits

› south pole measurement @ 10MHz resolution

› slight difference between fits to observe

› absorption depth of LTE model dependent of temp. profile

› poor signal to noise ratio→ longer integration

time required

basics & motivation technique & observations fits & measurements summary & outlook...

Documents

outlook slide

absorption slide

hi slide

motivation state

condition fits

divergence of fits

unique technique

overview basics