Atmosphere Of Venus Research Articles

The Venusian Insolation Atmospheric Topside Thermal Heating Pool

A 1 metre increment modelled pressure profile is used to study the troposphere of Venus from the surface to the lower stratosphere. Using a troposphere model lapse rate profile as the constraint on cooling by vertically convecting air, the modelled height of the tropopause convection limit is a close match to the level of the observed static atmosphere height for the 250 Kelvin freezing point level of 75% by weight of concentrated sulphuric acid, the primary condensing volatile in the Venusian atmosphere. This relationship suggests that the observed albedo of Venus is a response to and not a cause of planetary atmospheric solar radiant forcing.Using the thermal lapse rate for the troposphere of Venus in its top-down mode of application, the depth below the tropopause that solar irradiance is able to achieve effective heating of the Venusian atmosphere is established. This radiant quenching depth delineates a pool of upper tropospheric air that both captures and responds to solar radiant forcing. Consequently, this top of the troposphere insolation forcing induces a process of full troposphere adiabatic convective overturn and delivers solar heated air to the ground via the action of forced air descent in the twin polar vortices of Venus.

Absorption Line Oscillator Strengths for the C 2Π(0)-A 2Σ+(0) Band of Nitric Oxide

We have determined absorption oscillator strengths for rotational transitions of the C 2Π(0)-A 2Σ+(0) band of NO, which has been detected in the upper atmosphere of Venus. The molecular quantum defect orbital method has been used in the calculation of the electronic transition moment and the Rydberg–valence interaction between the C 2Π(v = 0) and the B 2Π (v = 7) states has been considered. Considerable deviations from normal intensity distribution of the rotational lines have been found at J ≤ 5.5. As far as we know, the present line f-values are reported here for the first time. These data may be useful in the interpretation of the observations obtained by the Visible and Infrared Thermal Imaging Spectrometer instrument on the Venus Express spacecraft.

Meteors May Masquerade as Lightning in the Atmosphere of Venus

AbstractLightning in the atmosphere of Venus is either ubiquitous, rare, or non‐existent, depending on how one interprets diverse observations. Quantifying when and where, or even if lightning occurs, would provide novel information about Venus' atmospheric dynamics and chemistry. Lightning is also a potential risk to future missions, which could float in the cloud layers (∼50–70 km above the surface) for up to an Earth‐year. Over decades, spacecraft and ground‐based telescopes have searched for lightning at Venus using many instruments, including magnetometers, radios, and optical cameras. Two optical surveys (from the Akatsuki orbiter and the 61‐inch telescope on Mt. Bigelow, Arizona) observed several flashes at 777 nm (the unresolved triplet emission lines of excited atomic oxygen) that have been attributed to lightning. This conclusion is based, in part, on the statistical unlikelihood of so many meteors producing such energetic flashes, based in turn on the presumption that a low fraction (<1%) of a meteor's optical energy is emitted at 777 nm. We use observations of terrestrial meteors and analogue experiments to show that a much higher conversion factor (∼5%–10%) should be expected. Therefore, we calculate that smaller, more numerous meteoroids could have caused the observed flashes. Lightning is likely too rare to pose a hazard to missions that pass through or dwell in the clouds of Venus. Likewise, small meteoroids burn up at altitudes of ∼100 km, roughly twice as high above the surface as the clouds, and also would not pose a hazard.

Mass Transfer Theory Based Analysis of Influencing Factors on Component Gradient of Near-surface Atmosphere on Venus

The atmosphere of Venus differs completely from that of Earth despite the planets’ similarity in size and mass. At Venus's surface, the atmosphere is hot and dense, with a temperature of approximately 735 K and a pressure of approximately 92 bar. The temperature profile from the Soviet VeGa-2 probe shows high instability of the near-ground potential temperature, which, according to relevant research, can be explained by the vertical gradient of N2 mole fraction. Based on the Maxwell–Stefan mass transfer theory, we propose a theoretical model of binary gas component for a quantitative discussion of influencing factors for the N2 vertical concentration gradient, which consist of temperature, gravity, specific heat ratio, mass relative factor, thermal diffusion factor, and CO2 flux. Our model shows that the 0%–3.5% N2 concentration gradient cannot be generated without CO2 flux in the near-ground atmosphere of Venus. And the result with CO2 source indicates that the 0.000001%–3.5% N2 concentration gradient at 0–7 km atmosphere can be generated by the 2.7 × 10−6 mol m−2 s−6 CO2 flux on Venusian surface, which is in agreement of gradient reckoned by VeGa-2's data. This magnitude of CO2 flux is close to the one produced by volcanic eruptions on Earth, indicating possible existence of volcanic activities on the surface of Venus. This work has provided the community a new vision to understand the influencing factors of Venusian atmospheres composition distribution.

Uncertainty in phosphine photochemistry in the Venus atmosphere prevents a firm biosignature attribution

Context. The possible detection of phosphine (PH3) in the clouds of Venus has raised the question as to which processes could produce such large abundances of PH3. Previous studies suggested that abiotic processes including photochemical production cannot explain the claimed PH3 concentrations. However, the photochemistry of phosphorus-bearing species in the atmosphere of Venus is not well known. Aims. We aim to assess the abiotic production of PH3 considering the effect of uncertainties in the chemical rate coefficients of phosphorus-containing reactions. Methods. Using a photochemical column model, we simulated Venus-like conditions and varied the chemical rate coefficients with a Monte Carlo (MC) approach in order to estimate the associated error in the PH3 abundances throughout the atmosphere. Results. Current uncertainties and missing data in photochemical rate coefficients lead to a variation of about six orders of magnitude in the modelled PH3 abundance on Venus, assuming photochemical production of PH3 from tetraphosphorus hexoxide (P4O6) pathways. Our results suggest an abiotically produced upper limit of 2 ppb PH3 between 50 and 60 km. These concentrations are in the range of a recent reanalysis of Atacama Large Millimeter Array (ALMA) data, suggesting planet-averaged abundances in PH3 of 1–4 ppb above 55 km. Future observations of phosphorus monoxide (PO) on Venus would be beneficial for increasing our confidence in assessing PH3 as a biosignature. Conclusions. We conclude that due to the large uncertainties in phosphorus chemistry, even a firm detection of several ppb PH3 in the Venus atmosphere would not necessarily mean a biological origin.

High temperature atomic oxygen testing for ESA’s Envision mission to Venus

EnVision will be ESA’s next Venus orbiter, providing a holistic view of the planet from its inner core to upper atmosphere to determine how and why Venus and Earth evolved so differently. The spacecraft will be equipped with a suite of instruments including a sounder to reveal underground layering, and spectrometers to study the atmosphere and surface. The thermal fluxes in orbit around Venus are high, the solar flux at Venus distance is twice its value on Earth (around 2600 W/m2), and the reflected sunlight flux has a similar order of magnitude due to the albedo. Besides, there will also be an aerobraking phase, when a third thermal flux, the aerothermal flux, needs to be considered, with a similar order of magnitude as the two others. These high total thermal fluxes, together with the cold instruments’ requirements and high-power dissipation make the thermal environment a design driver for the mission. The chemistry of the atmospheric environment during aerobraking needs also to be taken into account. Atomic oxygen exists in Venus atmosphere at the altitude range foreseen for aerobraking, with densities of up to 1017 oxygen atoms per cubic metres at aerobraking altitudes. Though the concentrations are small, their accumulation over up to 2000 atmospheric passes lead to total atomic oxygen fluences on the exposed spacecraft surfaces which are comparable to those encountered on typical Low Earth orbiting satellites (upwards of 1021 atomscm-2). This drives the selection of spacecraft materials on the most exposed surfaces. Whilst significant data exists about atomic oxygen erosion effects on materials for Low Earth Orbit, there is little knowledge about high temperature atomic oxygen effects on materials under environmental conditions representative of the Venus atmosphere. To analyse the potential risks for the Envision mission, and to assist the designers in selecting the best materials, an atomic oxygen test campaign is being performed in the ESA ESTEC atomic oxygen ground-based simulator (LEOX facility). The facility has been adapted so that material samples can be simultaneously exposed to atomic oxygen and high temperatures up to at least 200°C. For the test campaign, the Envision instrument teams and designers of the prospective satellite systems are providing candidate materials to be exposed. This includes a variety of materials to be utilised on the outside of the satellite such as thermal control coatings, optical materials, coatings for appendages and antennas and multi-layer insulation. The paper describes the modifications to the facility and the first results of the testing which has been performed.

Evaluation of new radio occultation observations among small satellites at Venus by data assimilation

We conducted observing system simulation experiments (OSSEs) for radio occultation measurements (RO) among small satellites, which are expected to be useful for future Venus missions. The effectiveness of the observations based on realistic orbit calculations was evaluated by reproduction of the “cold collar”, a unique thermal structure in the polar atmosphere of Venus. Pseudo-temperature observations for the OSSEs were provided from the Venus atmospheric GCM in which the cold collar was reproduced by the thermal forcing. The vertical temperature distributions between 40 and 90 km altitudes at observation points were assimilated. The result showed that the cold collar was most clearly reproduced in the case where the temperature field in high-latitudes was observed twice a day, suggesting that the proposed observation is quite effective to improve the polar atmospheric structure at least. Although the cold collar was also reproduced in the OSSEs for Longwave Infrared Camera (LIR) observations, the result seemed unrealistic and inefficient compared to that obtained in the RO OSSEs. The present study shows that the OSSEs can be used to evaluate observation plans and instruments in terms of reproducibility of specific atmospheric phenomena, and applied to future missions targeting planetary atmospheres.

Minor species in Venus’ night side troposphere as observed by VIRTIS-H/Venus Express

The 2.3μm spectral window has been used to constrain the composition of the lower atmosphere (in the 30–40 km altitude range) on the night side of Venus for more than thirty years. Here, we present a follow-up study of Marcq et al. (2008), but using the full VIRTIS-H/Venus Express data archive as well as an updated radiative transfer forward model. We are able to confirm a latitudinal increase of CO of about 30% between 0° and 60°N, as well as an anti-correlated vertical shift of OCS profile by about −1km in the same latitude range. Both variations are about twice smaller in the southern hemisphere. Correlations of low latitude CO and OCS variations with zonally shifted surface elevation is tentatively found. These results are consistent with CO and OCS variations resulting from the competition between local thermochemistry and a Hadley-cell-like general circulation, albeit influenced by the orography. Finally, no evidence for spatial variations of water vapor (combined H2O and HDO) or sulfur dioxide could be evidenced in this data set; better constraining possible variations of these species would require future missions to include infrared spectrometers operating at a spectral resolving power higher than ∼104, such as VenSpec-H onboard EnVision. *Plain Language Summary Remotely measuring the composition of the Venusian atmosphere below the clouds is challenging, yet yields invaluable insights about the atmospheric chemistry, circulation and interaction with the surface and interior of the planet. The VIRTIS-H instrument on board ESA’s Venus Express orbiter (2006–2014) provides a rich data set in this regard, thanks to its ability to observe and analyze, on the night side of the planet, the infrared radiation emitted by the deep atmospheric layers. The results of our analyses confirm the previously observed trends for the variations of two trace gases (carbon monoxide and carbonyl sulfide) with latitude, explained by the combined effects of chemical reactions and transport by the atmospheric circulation. Variations of carbon monoxide may also be linked to the variations of ground elevation, confirming the link between surface topography and atmospheric circulation. However, we were unable to separate the signature of heavy water vapor from ordinary water vapor or to detect any variations in sulfur dioxide, both of which require more powerful infrared instruments such as those planned on future Venus orbiters such as ESA’s EnVision.

Measurements of material erosion in space by atomic oxygen using the on-orbit material degradation detector

In recent years atomic oxygen (AO) has become a major challenge for the space community. AO is the most dominant species of the residual atmosphere in low Earth orbit (LEO). In addition, AO was found at the top of the Venusian and Martian atmospheres. As a result of exposure to AO, organic space-facing materials erode, leading to changes in their roughness, thermo-optical properties, and mass loss. In the past years, there has been a growing interest in very low Earth orbit missions, below an altitude of 350 km, where AO density and thus, AO flux, are extremely high. At these low altitudes, material degradation by AO erosion poses a great risk to the integrity of any space-facing material, unless well protected. As such, measuring the AO flux and the consequential material erosion by AO, in real-time while under actual space conditions, are of great interest to the space community.Thus, in this work we present real-time AO material erosion measurements that were conducted, for the first-time in LEO, using the on-orbit material degradation detector (ORMADD). The ORMADD is a low-cost and simple to operate detector, comprised of photovoltaic cells coated with semi-transparent AO sensitive coatings. Two ORMADDs were integrated on TAUSAT-1, a 3U CubeSat, deployed into LEO from the international space station. The first ORMADD was coated with a thin amorphous-carbon coating and the second was covered with a thick pyrolytic Kapton film. Using ORMADD, we were able to follow the erosion of the coatings in real-time conditions and calculate the AO flux in TAUSAT-1 orbit. The average in-orbit flux, derived from ORMADD data, was found to be comparable to the theoretical average AO flux calculated by the space environment information system (SPENVIS) software. This work demonstrates the abilities of ORMADD as a space environment detector, as well as a space material degradation research instrument.

Linear and nonlinear kinetic Alfvén waves at Venus

Space observations show that Venus suffers significant atmospheric erosion caused by the solar wind forcing. Plasma acceleration is found to be one of the main mechanisms contributing to the global atmospheric loss at Venus through its magnetotail. Motivated by these observations, we propose that kinetic Alfvén waves (KAW) may be a possible candidate for charged particle energization at the upper atmosphere of Venus. To test this hypothesis, we explored the basic features of both linear and nonlinear KAW structures at Venus. We considered a low-but-finite β plasma consisting of ionospheric populations (consisting of hydrogen H+, oxygen O−, and isothermal ionospheric electrons) and solar wind populations (protons and isothermal electrons). In the linear regime, we obtain a linear dispersion relation that exhibits a dependence on the intrinsic plasma configuration at Venus. The linear analysis predicts wave structures with wavelengths of ~10–102 km and frequencies of up to ~5 Hz. In the nonlinear regime, small-but-finite-amplitude solitary excitations with their corresponding bipolar electric field are obtained through the reductive perturbation technique. We discuss the influence of the intrinsic plasma parameters (the ionic concentration, solar wind electron temperature, magnetic field strength, and obliqueness) on the nature of the structures of the solitary KAWs and their corresponding electric field. We find that the ambipolar field is amplified with increasing propagation angle, magnetic field strength, and relative temperature of electrons. Our theoretical analysis predicts the propagation of elliptically polarized ultra-low-frequency (ULF) solitary structures with a maximum magnitude of ~0.01–0.034 mV m−1 and a time duration of 20–30 s. The result of the fast Fourier transform (FFT) power spectra of the ambipolar parallel electric field is broadband electromagnetic noise in the frequency range of ~0.5–2 Hz.

Feasibility of power beaming through the Venus atmosphere

Despite great interest by the planetary science community in the robotic exploration of Venus, solutions for operating in this extreme environment present significant challenges to mission architects. A particular challenge in designing any in situ Venus mission of reasonable duration is the selection of a suitable power source. State-of-the-art space power technologies comprising solar arrays, batteries and radioisotope thermoelectric generators are not capable of operating on the surface of Venus, limited by the high temperatures, high pressures and corrosive environment. Despite its proximity to the Sun, the solar resource on the surface is limited by the dense cloud layers. One potential approach for circumventing this limitation includes collecting the abundant visible solar energy above the Venus atmosphere, and wirelessly transferring this power to the surface at a wavelength that can more effectively penetrate the dense cloud layer. The feasibility of such an approach and other related mission concepts are discussed herein from a perspective of atmospheric absorption and scattering of the beamed energy.

Conceptual Design of Hybrid Aerial Vehicle for Venus Exploration

The conceptual design of a hybrid aerial vehicle for the exploration of the upper Venus atmosphere is presented. The vehicle will float like a balloon and harvest solar energy which is stored in batteries. The neutral buoyancy reduces the energy consumption and makes the vehicle robust and durable. Energy stored in the batteries can be used for powered flight with good horizontal and vertical mobility to explore aspects of the atmosphere. The vehicle is intended to operate near 55.3 km altitude and to explore the cloud layer of the planet. The vehicle takes its inspiration from the Stingray inflatable wing by Prospective Concepts. Based on a trade study, the wing span was set to 25 m. Equations are developed for the altitude, gas and skin temperature, and skin stress during neutrally buoyant flight. To keep the equations in a simplified analytical form, the complex compartmentalized gas pockets of the vehicle are lumped into a single gas sphere. The equations take into account the volumetric expansion of the structure and the requirement that the differential pressure needs to be large enough to allow for brief periods of powered flight without significant structural deformation. An aerodynamic analysis provides the lift and drag coefficient curves and indicates that the vehicle is pitch-stable. A powered flight analysis shows that an airspeed of 30 m/s can be maintained for 31 min at 55 km and 69 min at 69 km altitude.

Large Uncertainties in the Thermodynamics of Phosphorus (III) Oxide (P4O6) Have Significant Implications for Phosphorus Species in Planetary Atmospheres

Phosphorus (III) oxide (P$_4$O$_6$) has been suggested to be a major component of the gas phase phosphorus chemistry in the atmospheres of gas giant planets and of Venus. However, P$_4$O$_6$'s proposed role is based on thermodynamic modeling, itself based on values for the free energy of formation of P$_4$O$_6$ estimated from limited experimental data. Values of the standard Gibbs free energy of formation ($\Delta$Go(g)) of P$_4$O$_6$ in the literature differ by up to ~656 kJ/mol, a huge range. Depending on which value is assumed, P$_4$O$_6$ may either be the majority phosphorus species present or be completely absent from modeled atmospheres. Here, we critically review the literature thermodynamic values and compare their predictions to observed constraints on P$_4$O$_6$ geochemistry. We conclude that the widely used values from the NIST/JANAF database are almost certainly too low (predicting that P$_4$O$_6$ is more stable than is plausible). We show that, regardless of the value of $\Delta$Go(g) for P$_4$O$_6$ assumed, the formation of phosphine from P$_4$O$_6$ in the Venusian atmosphere is thermodynamically unfavorable. We conclude that there is a need for more robust data on both the thermodynamics of phosphorus chemistry for astronomical and geological modeling in general and for understanding the atmosphere of Venus and the gas giant planets in particular.

Dependency of the vertical propagation of mountain waves on the zonal wind and the static stability in the lower Venusian atmosphere

Long-Infrared camera (LIR) onboard Akatsuki have detected bow-shaped features over mountain regions, suggesting that mountain waves propagate upward to reach the cloud top level. In this study, we investigated how the vertical propagation characteristics of the mountain waves depend on the thickness and static stability of the planetary boundary layer and the zonal wind near the surface by using a two-dimensional non-hydrostatic model. The obtained results were compared with the observations mainly at the cloud top level. The amplitude of waves reproduced in the model is comparable to the observations at the cloud top level when the zonal wind near the surface is relatively fast and the top of the planetary boundary layer is lower than the top of the mountain. The wave amplitude also becomes comparable to the observations when the top of the planetary boundary layer is higher than the top of the mountain, while it depends also on the zonal wind speed near the surface and the static stability in the planetary boundary layer. Our results suggest that the zonal wind speed and the atmospheric structure near the surface vary with local time and might be able to explain why the bow-shaped structure is often seen in the evening time.

Spectroscopic characterization of [H, Cl, S, O] molecular system: Potential candidate for detection in Venus atmosphere.

Accurate spectroscopic parameters have been obtained for the identification of the [H, Cl, S, O] molecular system in the Venus atmosphere using computational methods. These calculations employed both standard and explicitly correlated coupled cluster techniques. All isomers possess C1 symmetry, with HOSCl being the most stable isomer. Only HOSCl and trigonal-HSOCl isomers are thermodynamically stable relative to the first dissociation limit HCl + SO. Fundamental modes of the lowest three isomers exhibit many anharmonic resonances, resulting in complex spectra. All isomers are found to be stable in the visible region as the calculation of vertical energy transition indicates. No electronic states were found to strongly absorb in the near UV-vis region.

O2 (а1Δg) Airglow at 1.27 μM and upper Mesosphere Dynamics on the Night Side of Venus

This research studies the O2 (a1 Δg) nightglow distribution in 1.27 μm to understand the dynamics of the atmosphere of Venus. Several factors were considered in the retrieval process, such as thermal emission of the lower atmosphere, reflection by the clouds. Results show deviation from SS-AS circulation mode: the area where horizontal flows from the dayside converge and where oxygen recombines and emits shifts from the midnight to 22–23 hours local time. This shift is caused by solar-induced thermal tide on Venus nightside. Some conclusions about the upper mesosphere dynamics are also presented.

Simulation of Venus Lightning‐I: Characterization of Free Radicals Generated in Venus Major Gas Mixture

AbstractA new Venus‐ESD‐Chamber (VEC) and peripheral systems were designed and built to simulate Venus lightning. It consists of three subsystems (a) electrostatic discharge (ESD) generation, (b) environmental pressure, temperature, gas composition control & monitoring, and (c) optical and non‐optical sensors. We conducted arc discharge experiments in air, in CO2, and in Venus major gas mixture (CO2‐N2, 96.5% ± 1.5%:3.5% ± 1.5%) under 10, 350, 700, and 1,000 mbar pressures, that correspond to the 50–75 km altitude range in the cloud layer of Venus. Plasma and Raman spectra, plus gas sensors, and GC‐MS were used to identify the ESD products and to semi‐quantify CO and O3 generated by ESD. We have found all species of free radicals that have been found in previous simulation studies using different discharge technologies, including some important species in CO2‐N2 system, nitrogen oxides and CN. In addition, we found three species (O3, N2+, and C2) that have not been previously reported. Our results suggest that electron flux and kinetic energy are the determining factors for the type of generated free radical species and gas pressure plays a less important role. We found that the quantity of CO changes with the type of ESD. The detection of O3 in this study suggests that lightning might be one of the sources of O3 observed in the Venusian atmosphere. OI emission line at 777.4 nm is the most prominent line in our plasma spectra of FD, consistent with the intense optical flash observed by the Lightning and Airglow Camera (LAC) on the Akatsuki mission.

Characterization of a 2700 ​km long bolide airburst chain, Phoebe Regio, Venus

Detailed geological mapping of Phoebe Regio on Venus, located near 10°S, 282°W, at a scale of 1:500,000, provided the basis for the discovery of a linear trend with 12 splotches, herein termed the Phoebe Regio Splotch Chain. The formation of splotches on the surface is associated with an explosion that occurs as a result of the interaction of a cosmic body penetrating through the dense atmosphere of Venus. The shockwave from such an air-blast could affect the surface in different ways, leading to both radar darkening and brightening. It was found that the 12 splotches differ in size but have a similar morphology and include a dark center and a radar-bright ring. The presence of such characteristics makes it possible to distinguish splotches from other geological features such as volcano-tectonic features (volcanic edifices, pyroclastic mantles, portions of lava flows and associated structures), which, when analyzed on a broad scale, can look similar. Splotches are known to be among the youngest geological features on the surface of Venus, and the elongated distribution of 12 splotches is suggested to have been formed by a stream of individual fragments of a parent body that disrupted well before entering the atmosphere of Venus.

The Effects of the Upper Atmosphere and Corona on the Solar Wind Interaction With Venus

AbstractSince Venus has no substantial planetary magnetic field, the fast‐flowing solar wind plasma interacts directly with its ionosphere, upper atmosphere, and corona. The thermal atmosphere and hot oxygen corona of Venus are expected to play essential roles in the interaction process. To quantify their effects, we combine three major state‐of‐the‐art three‐dimensional numerical models, including (a) The Venus thermosphere general circulation model (VTGCM), (b) The adaptive mesh particle simulator (AMPS), and (c) A multi‐species Magnetohydrodynamics (MHD) model of Venus based on Block Adaptive Tree Solar‐wind Roe Upwind Scheme. The global multi‐species MHD model is used to simulate the planet's interaction with the ambient solar wind, where the background neutral densities are provided by VTGCM and AMPS. Using the above‐mentioned numerical models, the effect of the upper atmosphere and corona on solar wind driven ion escape rates are examined for three typical solar cycle conditions, including solar maximum, solar median, and solar minimum conditions. The model results suggest that even though the hot oxygen corona only has a minor effect on the ion density profiles in the ionosphere, it can enhance ion loss rate up to ∼25% for high solar activity.

Venusian Ionosphere During Deep Solar Minima: Some New Insights Using Akatsuki Radio Science Experiment

AbstractThe characteristic features of different layers in the Venus ionosphere during the deep solar minimum of the solar cycle 24 have been studied using a radio science experiment onboard the Akatsuki spacecraft. Radio signals from the spacecraft were tracked at the Indian deep space network, Bangalore; Usuda Deep Space Center, Japan; and DLR Ground station, Weilheim, Germany. The orbital geometry of the spacecraft provides rare opportunities to probe the Venusian ionosphere and atmosphere in the equatorial region at low solar zenith angles (SZAs). The height of the peak plasma density of the V2 layer (∼141 km) was seen to remain almost constant for the SZA ≤ 90° while the peak density was the least among the published results. Features of the V1 layer (∼125 km) agree well with the Venus Express radio occultation measurements. All three types of V1 layers were observed in Akatsuki observations. The V0 layer (∼110 km) was observed in about 15% of cases and was seen to occur irrespective of SZA and geographical constraints. Nighttime occurrence of the ionosphere was very limited despite regular observations.