In situ observations of waves in Venus’s polar lower thermosphere with Venus Express aerobraking

Abstract

Waves are ubiquitous phenomena found in oceans and atmospheres alike. From earliest formal studies of waves in the Earth's atmosphere to more recent studies on other planets, waves have been shown to play a key role in shaping atmospheric bulk structure, dynamics and variability [1][2][3][4] . Yet, waves are difficult to characterise as they ideally require in-situ measurements of atmosphere properties which are difficult to obtain away from Earth. Thereby, we have incomplete knowledge of atmospheric waves on planets other than our own, and we are thereby limited in our ability to understand and predict planetary atmospheres. We report on the first ever in-situ observations of atmospheric waves in Venus' thermosphere (130-140 km) at high latitudes (71.5-79.0 ). These were made by the Venus Express Atmospheric Drag Experiment (VExADE) 5 during aerobraking from June 24-July 11, 2014. As the spacecraft flew through Venus' atmosphere, deceleration by atmospheric drag was sufficient to obtain from accelerometer readings a total of 18 vertical density profiles. We infer an average temperature of T=114±23 K and findhorizontal wave-like density perturbations and mean temperatures being modulated at a quasi-5-day period.

Atmospheric Waves and Their Possible Effect on the Thermal Structure of Saturn's Thermosphere

“…Figure shows H 2 density perturbations with respect to a hydrostatic fit to the densities observed by the INMS during “Deep Dip” orbits 288, 290, 291, and 292. During these orbits, the spacecraft reached down to 1,630‐km altitude above the 1‐bar level near latitude 5° S. In producing the hydrostatic fit, densities along an entire pass through Saturn's atmosphere were initially fit with a curve that assumed the exponential change of density with height, following the procedure previously applied to data from the Venus Express spacecraft (Müller‐Wodarg et al, ). The reader is referred to the supporting information for a description of our technique for extracting perturbations from the density data set.…”

Determination of Venus’ Interior Structure with EnVision

“…The radiation forces are perturbed with a 0.03 standard deviation to consider possible inaccuracies in the spacecraft modeling (e.g., attitude, thermo-optical coefficients of the spacecraft panels) and in the radiation models. The standard deviation for the atmospheric drag is 0.3, which is representative of the average fluctuations of the Venusian thermosphere density observed on the day side (~5%) and night side (~50%) and is also representative of its day-to-day variability at 130-140 km [40]. This standard deviation is a worse case since the atmospheric density is lower at the EnVision orbital altitudes (>220 km).…”

Gravity Wave Packets in the Venusian Atmosphere Observed by Radio Occultation Experiments: Comparison With Saturation Theory

“…The evaluation of radiative damping requires information on the wave's frequency, which cannot be obtained by radio occultation. Gravity wave‐like oscillations have been observed in the thermosphere (Garcia et al., 2009; Müller‐Wodarg et al., 2016); the change in wave characteristics associated with upward propagation into the thermosphere when subjected to radiative damping will be a subject of a future study.…”