Title: Ground Based Venusian Thermal Structure and Dynamics Observations in Support of In-
Situ Measurements

Abstract:
We will discuss Venus observations from ground based observatories that span a 4-decade 
period. Infrared Heterodyne Spectroscopy provides sub-Doppler resolution measurements of 
molecular transitions of atmospheric species above the Venusian cloud tops. The high spectral 
resolution of instruments such as Heterodyne Instrument for Planetary Winds and Composition 
(HIPWAC – NASA Goddard Space Flight Center) and Tunable Heterodyne Infrared 
Spectrometer (THIS – University of Cologne) measure rotation-vibration line shapes free of 
contamination from other molecular and continuum opacity sources. Such studies compliment 
high spatial resolution observations of dedicated Venusian missions such as Venus Express. In 
example, we will focus on Venus observations from 19-23 Aug 2010 (UT) to investigate 
equatorial wind velocities from above the cloud tops through the lower thermosphere. These 
measurements were made from the NASA Infrared Telescope Facility using HIPWAC. High-
resolution spectra were acquired on a CO2 pressure-broadened absorption feature that probes 
the lower mesosphere (70 km altitude) with a non-LTE core emission of the same transition that 
probes the lower thermosphere (110 km). The resolving power of λ/Δλ=2.5E7 determines line-
of-sight velocity from Doppler shifts to high precision. The altitude differential between the 
features enables investigating the transition from zonal wind flow near the cloud tops to 
subsolar-to-antisolar flow in the thermosphere. The fully-resolved carbon dioxide transition was 
measured near 952.8808 cm-1 (10.494 µm) rest frequency at the equator with 1 arcsec field-
of-view on Venus (24 arcsec diameter) distributed about the central meridian and across the 
terminator at ±15-degree intervals in longitude. The non-LTE emission is solar-pumped and 
appears only on the daylight side, probing subsolar-to-antisolar wind velocity vector flowing 
radially from the subsolar point through the terminator, which was near the central meridian in 
these observations and had zero line-of-sight wind projection at the terminator. The velocity of 
the zonal flow is approximately uniform, with maximum line-of-sight projection at the limb, and 
can be measured by the frequency of the absorption line on both the daylight and dark side. 
Variations in Doppler shift between the observable features and the differing angular dependence 
of the contributing wind phenomena thus provide independent mechanisms to distinguish the 
dynamical processes at the altitude of each observed spectral feature. Winds up to >100 m/s 
were determined in previous investigations with uncertainties of order 10 m/s or less. This work 
was supported by the NASA Planetary Astronomy Program.



Co-authors:
T. Kostiuk
T. A. Livengood
T. Stangier
M. Sornig
G. Sonnabend
K. Fast
J. Annen