The Clouds of Venus in a Global Context

The two defining characteristics of the planet Venus are its atmospheric super-rotation and the planet-enshrouding cloud layers. The clouds reflect more than 70% of the incident solar flux back into space, but about half of the solar flux that is received by the planet is absorbed at the altitudes occupied by the clouds. But for its massive greenhouse effect, the planet Venus would be even cooler than Earth, despite being located closer to the Sun. The clouds play a pivotal role here, too, as they are the fourth largest contributor to this greenhouse effect, following CO2, H2O, and SO2. Thus, a large fraction of the incident solar flux and a significant fraction of the upwelling infrared flux are absorbed by the Venusian cloud layers. This energy deposition possibly plays a significant role in sustaining the global super-rotation of Venus in which the entire atmosphere circles the planet with periods of as little as four days at the cloud tops. However, these clouds are also highly variable, especially when viewed at ultraviolet and near infrared wavelengths. In this talk, I discuss the value of multispectral analysis of Venus in characterizing the properties of the planet’s clouds and their role in the global energy and momentum budgets; especially when coupled with in situ measurements of the clouds themselves.https://commons.und.edu/ss-colloquium/1051/thumbnail.jp

Measurement of Isothermal Pressure of Lattice Gas by Random Walk

We present a computational random walk method of measuring the isothermal pressure of the lattice gas with and without the excluded volume interaction. The method is based on the discretization of the exact thermodynamic relation for the pressure. The simulation results are in excellent agreement with the theoretical predictions.Comment: 10 Pages, 2 Figures, Teaching Material. To Appear in Physica

Microphysical Modelling of Venus Clouds, Including Radiative Transfer

No abstract availabl

Using VIRTIS on Venus Express to Constrain the Properties of the Giant Dark Cloud Observed in Images of Venus by IR2 on Akatsuki

A cloud opacity contrast feature that has been called a “long-lived sharp disruption” has been seen in the atmosphere of Venus in the near-infrared using Akatsuki’s IR2 camera, most clearly at equatorial latitudes. This feature was found to have a consistent planet-circling period of 4.9 days, and subsequent searches of past imagery revealed that it has probably existed for at least 30 years, the duration of near-infrared investigation of the deep atmosphere of Venus. Guided by the remarkably consistent morphological appearance of this feature, we have identified at least one previous instance of it in the Venus Express Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) data. We take advantage of the spectroscopic capabilities of VIRTIS to retrieve atmospheric parameters in the vicinity of this feature that cannot be retrieved using the limited filter selection on board Akatsuki. We find that the changes in measurable quantities, such as cloud particle acid mass fraction, water vapor, carbon monoxide, cloud base altitude, and particle size, suggest that the changes that take place in the vicinity of this feature are restricted to the lower clouds of Venus (below 50 km). We hypothesize that further evolution of this feature (over timescales of days to weeks) results in measurable variations in these parameters at altitudes in the middle clouds of Venus (50–57 km), lending credence to its identification as a baroclinic trough or Kelvin front

Effects of variation in coagulation and photochemistry parameters on the particle size distributions in the Venus clouds

Abstract This paper explores the effects that variation in the coalescence efficiency of the Venus cloud particles can have on the structure of the Venus cloud. It is motivated by the acknowledgment of uncertainties in the measured parameters—and the assumptions made to account for them—that define our present knowledge of the particle characteristics. Specifically, we explore the consequence of allowing the coalescence efficiency of supercooled sulfuric acid in the upper clouds to tend to zero. This produces a cloud that occasionally exhibits an enhancement of small particles at altitude (similar to the upper hazes observed by Pioneer Venus and subsequently shown to be somewhat transient). This simulated cloud occasionally exhibits a rapid growth of particle size near cloud base, exhibiting characteristics similar to those seen in the controversial Mode 3 particles. These results demonstrate that a subset of the variations observed as near-infrared opacity variations in the lower and middle clouds of Venus can be explained by microphysical, in addition to dynamical, variations. Furthermore, the existence of a population of particles exhibiting less efficient coalescence efficiencies would support the likelihood of conditions suitable for charge exchange, hence lightning, in the Venus clouds. We recommend future laboratory studies on the coalescence properties of sulfuric acid under the range of conditions experienced in the Venus clouds. We also recommend future in situ measurements to better characterize the properties of the cloud particles themselves, especially composition and particle habits (shapes)

The Influence of Cloud Condensation Nucleus Coagulation on the Venus Cloud Structure

We present the Venus version of PlanetCARMA and demonstrate the significance of coagulation properties on the structure of the Venus cloud system. The composition of the smallest mode of particles in the Venus atmosphere, which likely serve as cloud condensation nuclei (CCN), is unknown. Here we demonstrate that a change in the ability of CCN to grow via coagulation in the Venus atmosphere can produce measurable short-term and long-term signatures in the Venus cloud structure. Specifically, we find that the existence of a population of CCN that is prevented from growing via coagulation will result in an overall reduced total cloud opacity and can, under some conditions, produce long-term (on the order of several hundred days) variations in both the photochemical cloud opacity (above 57 km) and the condensational cloud opacity (below 57 km). While we show that these variations do not appear to be the source of the short-timescale cloud opacity variations seen on the nightside near-infrared emission of Venus, it is possible that they may contribute to the longer-term variations seen over the 2.5 yr lifetime of the VIRTIS-M-IR instrument on Venus Express. We recommend further modeling studies to investigate wider ramifications of this behavior, as well as further laboratory studies to better constrain the microphysical properties of the aerosols that can make up the Venus clouds

Special issue “Akatsuki at Venus: The First Year of Scientific Operation”

International audienc

Microphysical modeling of the Venusian clouds with the IPSL Venus GCM

International audienceTo understand the Venus atmosphere, LMD and LATMOS laboratories have developed a 3D IPSL Venus Global Climate Model (Lebonnois et al. 2010). In this GCM, the cloud description is simplified. As clouds play a crucial role in radiative transfer, dynamics and generally the climate of Venus, it is necessary to improve the VGCM with a microphysical representation