Venus Express Research Articles

Impact of Data Assimilation on Thermal Tides in the Case of Venus Express Wind Observation

AbstractImpacts of horizontal winds assimilation on thermal tides are investigated by using the Venus atmospheric general circulation model for the Earth Simulator local ensemble transform Kalman filter data assimilation system. The assimilated data are horizontal winds derived from Venus ultraviolet images taken by the Venus Monitoring Camera onboard the Venus Express orbiter. The results show that three‐dimensional structures of the thermal tides are significantly improved not only in the horizontal winds but also in the temperature field, even though the observations are available only at the cloud top level on the southern dayside hemisphere approximately once an Earth day. The reproduced temperature fields agree well with recent radio occultation measurements of the Venus Climate Orbiter Akatsuki. The zonal mean fields of the zonal wind and temperature are also improved globally. This study would enable reanalysis of past Venus observations.

Formation of the Y Feature at the Venusian Cloud Top by Planetary‐Scale Waves and the Mean Circulation: Analysis of Venus Express VMC Images

AbstractThe relationship between the planetary‐scale ultraviolet contrast known as the Y feature and the wind field at the Venusian cloud top was investigated by using images obtained by Venus Monitoring Camera (VMC) on ESA's Venus Express. Spectral analyses of the ultraviolet reflectivity and the wind field revealed common periodicities of 4–5 Earth days, which are attributed to Kelvin and Rossby waves with a zonal wave number of unity. Combined with the morphological relationship between the dark streaks and the enhancement of poleward flow, we propose a mechanism for the formation of the Y feature: The dark materials are supplied to the cloud top in the equatorial region by a Kelvin wave, subsequently advected poleward by the mean meridional circulation and a Rossby wave, and then stretched by the midlatitude jet to the tilted band structures. A simplified transport model was developed to demonstrate the scenario.

Observations of the Venus Dramatic Response to an Extremely Strong Interplanetary Coronal Mass Ejection

Abstract On 2011 November 5, Venus Express observed the impact of an extremely strong interplanetary coronal mass ejection (ICME) on Venus. As a result, the Venusian induced magnetosphere dramatically fluctuated during the ICME passage: the bow shock was compressed and broadened by the sheath and the body of the ICME, respectively; an atypically strong magnetic barrier (over 250 nT) of Venus was detected; and the plasma sheet in the magnetotail flapped so rapidly that it was crossed by Venus Express 5 times within 1.5 minutes. The ionosphere was totally magnetized because of the very high magnetic pressure of the induced magnetosphere. However, the altitude of the ionopause did not decrease with respect to those in neighboring orbits, which is inconsistent with the ionopause descents reported by previous studies. We found that the ionosphere was greatly excited by the ICME as evidenced by the much higher heavy ion density. That is why the balance between the ionospheric thermal pressure and the strong magnetic pressure can be maintained at a relatively high altitude. We propose that a much stronger massloading effect resulting from the excited ionosphere is responsible for the anomalously high magnetic barrier because much more magnetic field lines were anchored. Our results also suggest that such ICMEs that can excite the ionosphere are substantially efficient in enhancing the atmospheric loss of Venus.

Proton Temperature Anisotropies in the Plasma Environment of Venus

AbstractVelocity distribution functions (VDFs) are a key to understanding the interplay between particles and waves in a plasma. Any deviation from an isotropic Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer (MAG) onboard Venus Express, we study proton distributions in the plasma environment of Venus. We focus on the temperature anisotropy, that is, the ratio between the proton temperature perpendicular (T⊥) and parallel (T‖) to the background magnetic field. We calculate average values of T⊥ and T‖ for different spatial areas around Venus. In addition we present spatial maps of the average of the two temperatures and of their average ratio. Our results show that the proton distributions in the solar wind are quite isotropic, while at the bow shock stronger perpendicular than parallel heating makes the downstream VDFs slightly anisotropic (T⊥/T‖ > 1) and possibly unstable to generation of proton cyclotron waves or mirror mode waves. Both wave modes have previously been observed in Venus's magnetosheath. The perpendicular heating is strongest in the near‐subsolar magnetosheath (T⊥/T‖≈3/2), which is also where mirror mode waves are most frequently observed. We believe that the mirror mode waves observed here are indeed generated by the anisotropy. In the magnetotail we observe planetary protons with largely isotropic VDFs, originating from Venus's ionosphere.

Venus Express radio occultation observed by PRIDE

Context. Radio occultation is a technique used to study planetary atmospheres by means of the refraction and absorption of a spacecraft carrier signal through the atmosphere of the celestial body of interest, as detected from a ground station on Earth. This technique is usually employed by the deep space tracking and communication facilities (e.g., NASA’s Deep Space Network (DSN), ESA’s Estrack). Aims. We want to characterize the capabilities of the Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique for radio occultation experiments, using radio telescopes equipped with Very Long Baseline Interferometry (VLBI) instrumentation. Methods. We conducted a test with ESA’s Venus Express (VEX), to evaluate the performance of the PRIDE technique for this particular application. We explain in detail the data processing pipeline of radio occultation experiments with PRIDE, based on the collection of so-called open-loop Doppler data with VLBI stations, and perform an error propagation analysis of the technique. Results. With the VEX test case and the corresponding error analysis, we have demonstrated that the PRIDE setup and processing pipeline is suited for radio occultation experiments of planetary bodies. The noise budget of the open-loop Doppler data collected with PRIDE indicated that the uncertainties in the derived density and temperature profiles remain within the range of uncertainties reported in previous Venus’ studies. Open-loop Doppler data can probe deeper layers of thick atmospheres, such as that of Venus, when compared to closed-loop Doppler data. Furthermore, PRIDE through the VLBI networks around the world, provides a wide coverage and range of large antenna dishes, that can be used for this type of experiments.

The upper atmosphere of Venus: Model predictions for mass spectrometry measurements

Venus is the closest and most similar planet to Earth in the whole solar system, yet, basic measurements are missing. The atmospheric composition has been studied to some extent with the Pioneer Venus Orbiter mission and the more recent Venus Express, however, the concentration of many species and their isotopic ratios are not yet known with satisfying accuracy. Especially when it comes to the heavy noble gases as Kr and Xe, there is little to no collected data in this field. These elements form a key link to the reconstruction of the atmospheric evolution, which would deliver crucial information on the formation of Earth-like bodies. Knowing the abundances of the noble gases may allow us to answer the question why Venus did not evolve to a potentially habitable planet like its neighbour Earth.This paper presents a meta-study of existing observations of Venus' upper atmosphere and exosphere and an exospheric model of the thermal and hot atmosphere of Venus above the homopause. Mass spectra for possible future Venus missions are predicted, as for example the EnVision mission of ESA. The main focus are the heavy noble gases and requirements for the trajectories are proposed. In addition, mass spectra and recommended integration times for the Venus flyby of ESA's JUICE mission are derived.

Public “Cloud” Provisioning for Venus Express VMC Image Processing

In this paper, we consider the implementation of the “cloud” computing strategy to study data sets associated to the atmospheric exploration of the planet Venus. More concretely, the Venus Monitoring Camera (VMC) onboard Venus Express orbiter provided the largest and the longest so far set of ultraviolet (UV), visible and near-IR images for investigation of the atmospheric circulation. To our best knowledge, this is the first time where the analysis of data from missions to Venus is integrated in the context of the “cloud” computing. The followed path and protocols can be extended to more general cases of space data analysis, and to the general framework of the big data analysis.

Morphology and Dynamics of Venus's Middle Clouds With Akatsuki/IR1

AbstractThe Venusian atmosphere is covered by clouds with superrotating winds whose accelerating mechanism is still not well understood. The fastest winds, occurring at the cloud tops (∼70‐km height), have been studied for decades, thanks to their visual contrast in dayside ultraviolet images. The middle clouds (∼50–55 km) can be observed at near‐infrared wavelengths (800–950 nm), although with very low contrast. Here we present the first extensive analysis of their morphology and motions at lower latitudes along 2016 with 900‐nm images from the IR1 camera onboard Akatsuki. The middle clouds exhibit hemispherical asymmetries every 4–5 days, sharp discontinuities in elongated “hook‐like” stripes, and large contrasts (3–21%) probably associated with large changes in the optical thickness. Zonal winds obtained with IR1 images and with ground‐based observations reveal mean zonal winds peaking at the equator, while their combination with Venus Express unveils long‐term variations of 20 m/s along 10 years.

Generic Magnetic Field Intensity Profiles of Interplanetary Coronal Mass Ejections at Mercury, Venus, and Earth From Superposed Epoch Analyses

AbstractWe study interplanetary coronal mass ejections (ICMEs) measured by probes at different heliocentric distances (0.3–1 AU) to investigate the propagation of ICMEs in the inner heliosphere and determine how the generic features of ICMEs change with heliospheric distance. Using data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER), Venus Express and ACE spacecraft, we analyze with the superposed epoch technique the profiles of ICME substructures, namely, the sheath and the magnetic ejecta. We determine that the median magnetic field magnitude in the sheath correlates well with ICME speeds at 1 AU, and we use this proxy to order the ICMEs at all spacecraft. We then investigate the typical ICME profiles for three categories equivalent to slow, intermediate, and fast ICMEs. Contrary to fast ICMEs, slow ICMEs have a weaker solar wind field at the front and a more symmetric magnetic field profile. We find the asymmetry to be less pronounced at Earth than at Mercury, indicating a relaxation taking place as ICMEs propagate. We also find that the magnetic field intensities in the wake region of the ICMEs do not go back to the pre‐ICME solar wind intensities, suggesting that the effects of ICMEs on the ambient solar wind last longer than the duration of the transient event. Such results provide an indication of physical processes that need to be reproduced by numerical simulations of ICME propagation. The samples studied here will be greatly improved by future missions dedicated to the exploration of the inner heliosphere, such as Parker Solar Probe and Solar Orbiter.

Female-biased sexual dimorphism of corticotropin-releasing factor neurons in the bed nucleus of the stria terminalis

BackgroundThe bed nucleus of the stria terminalis (BNST) contains the highest density of corticotropin-releasing factor (CRF)-producing neurons in the brain. CRF-immunoreactive neurons show a female-biased sexual dimorphism in the dorsolateral BNST in the rat. Since CRF neurons cannot be immunostained clearly with available CRF antibodies in the mouse, we used a mouse line, in which modified yellow fluorescent protein (Venus) was inserted to the CRF gene, and the Neo cassette was removed, to examine the morphological characteristics of CRF neurons in the dorsolateral BNST. Developmental changes of CRF neurons were examined from postnatal stages to adulthood. Gonadectomy (GDX) was carried out in adult male and female mice to examine the effects of sex steroids on the number of CRF neurons in the dorsolateral BNST.MethodsThe number of Venus-expressing neurons, stained by immunofluorescence, was compared between male and female mice over the course of development. GDX was carried out in adult mice. Immunohistochemistry, in combination with Nissl staining, was carried out, and the effects of sex or gonadal steroids were examined by estimating the number of Venus-expressing neurons, as well as the total number of neurons or glial cells, in each BNST subnucleus, using a stereological method.ResultsMost Venus-expressing neurons co-expressed Crf mRNA in the dorsolateral BNST. They constitute a group of neurons without calbindin immunoreactivity, which makes a contrast to the principal nucleus of the BNST that is characterized by calbindin immunostaining. In the dorsolateral BNST, the number of Venus-expressing neurons increased across developmental stages until adulthood. Sexual difference in the number of Venus-expressing neurons was not evident by postnatal day 5. In adulthood, however, there was a significant female predominance in the number of Venus expressing neurons in two subnuclei of the dorsolateral BNST, i.e., the oval nucleus of the BNST (ovBNST) and the anterolateral BNST (alBNST). The number of Venus-expressing neurons was smaller significantly in ovariectomized females compared with proestrous females in either ovBNST or alBNST, and greater significantly in orchiectomized males compared with gonadally intact males in ovBNST. The total number of neurons was also greater significantly in females than in males in ovBNST and alBNST, but it was not affected by GDX.ConclusionVenus-expressing CRF neurons showed female-biased sexual dimorphism in ovBNST and alBNST of the mouse. Expression of Venus in these subnuclei was controlled by gonadal steroids.

Venus crater-related radar-dark parabolas and neighboring terrains: A comparison of 1-μm emissivity and microwave properties

This work presents a comparative study of microwave properties and 1-μm emissivity for five Venus crater-associated radar-dark parabolas along with neighboring plains and some other geologic units. Craters of interest are Adivar, Bassi, Bathsheba, Sitwell, and du Chatelet with nearby crater Caccini having non-parabolic radar-dark halo. Microwave properties under study include emissivity, Fresnel reflectivity, decameter-scale surface roughness, and radar cross-section from the Magellan mission. 1-μm emissivity was derived using Venus Monitoring Camera (VMC) measurements on board of Venus Express (VEx). Results of our analysis show that 1-μm emissivity which characterizes the uppermost hundreds microns-thick layer of parabola mantles usually relates to microwave properties as following: the lower 1-μm emissivity, the lower Fresnel reflectivity, the higher microwave emissivity. For loose mantles having the same composition, lower 1-μm emissivity indicates smaller particles. Differences in bulk properties of parabola units showing the same 1-μm emissivity appear to reflect differences in a packing style of mantles consisting of particles having similar sizes. Properties of radar bright inner parabola parts, observed within the three of five studied parabolas possibly indicate more turbulent (comparing to radar-dark parts) deposition environment, thinner parabola mantles and/or partial coverage of the underlying surface. The non-parabolic halo of the crater Caccini exhibits characteristics close to dark parabolas suggesting that in a process of shrinking of a parabolic-like deposit into non-parabolic one parabola mantle properties remain mainly unchanged. Observed differences in microwave emissivity and Fresnel reflectivity between parabolas and adjacent plains may indicate highly weathered loose parabola material (with oxidation of their iron into hematite) that is more easily accessible for atmospheric gases. Studied properties of tessera terrains confirmed suggestions of earlier works for a possible non-basaltic composition of tesserae material. The distinctive (from plains) composition of tesserae also could indicates an effective down-slope movement of these material uncovering new portions of pristine tessera material. Otherwise considered in this work horizontal transportation of the very thin layer of surface material would equalize the observed properties.

Nightside Winds at the Lower Clouds of Venus with Akatsuki/IR2: Longitudinal, Local Time, and Decadal Variations from Comparison with Previous Measurements

Abstract We present measurements of the wind speeds at the nightside lower clouds of Venus from observations by JAXA’s mission Akatsuki during 2016, complemented by new wind measurements from ground-based observations acquired with the TNG/Near Infrared Camera Spectrometer (NICS) in 2012 and IRTF/SpeX in 2015 and 2017. The zonal and meridional components of the winds were measured via cloud tracking on a total of 466 Akatsuki images of Venus acquired by the camera IR2 using the 2.26 μm filter, with spatial resolutions ranging from 10 to 80 km per pixel and covering 2016 March 22 to October 31. More than 149,000 wind vectors were obtained using an automatic template-matching technique, and 2947 wind vectors were inferred using a manual procedure. The meridional profiles for both components of the winds are found to be consistent with results from the Venus Express mission during 2006–2008, although stronger wind variability is found for the zonal component at equatorial latitudes where Akatsuki observations have better viewing geometry than Venus Express. The zonal winds at low latitudes also suggest a zonal variability that could be associated with solar tides or vertically propagating orographic waves. Finally, the combination of our wind measurements from TNG/NICS, IRTF/SpeX, and Akatsuki images with previously published data from 1978 to 2017 suggests variations of up to 30 m s−1 in the winds at the nightside lower clouds of Venus.

Effects of the solar wind and the solar EUV flux on O+ escape rates from Venus

We investigate dependences of O+ escape rates from Venus both on the solar wind and the solar extreme ultraviolet (EUV) flux by using the 8.5-year dataset (May 2006 to December 2014) of the Ion Mass Analyzer and the magnetometer aboard Venus Express. We examine the O+ escape rates for 8 different conditions depending on the solar wind's dynamic pressure, the magnitude of the motional electric field, and the solar F10.7 index which is a good indicator for the solar EUV flux. We find that the O+ escape rates are mainly controlled by the motional electric field and the solar EUV flux in the magnetosheath. We suggest that the ion pickup by the motional electric field is the main ion escape process in the magnetosheath. On the other hand, in the induced magnetosphere, the O+ escape rates are controlled by not only the solar wind and the solar EUV flux but also return flows. We find that the return flows become dominant in the magnetotail in the solar maximum period, which results in reducing the net escape rates in the induced magnetosphere. As a result, net escape rates tend to become larger in the solar minimum period than those in the solar maximum period. Further analysis of the magnetic field shows that the return flows are preferably observed when the magnetic field component along the Venus-Sun line reverses multiple times in the magnetotail. We suggest that ionospheric irregular structures or IMF sector boundary crossings form the fine scale anti-parallel draping pattern of the interplanetary magnetic field (IMF), and this causes ion acceleration towards Venus due to the magnetic tension force or magnetic reconnections. Another possibility is precipitations of O+ pickup ions on the nightside of Venus under the fine structure of IMF. Since the return flows significantly affect the O+ escape rates from Venus, it is important to study not only long-term transition of ion outflow from Venus but also return flows to estimate the net ion loss from Venus over the long history of the solar system.

H+/O+ Escape Rate Ratio in the Venus Magnetotail and its Dependence on the Solar Cycle

AbstractA fundamental question for the atmospheric evolution of Venus is how much water‐related material escapes from Venus to space. In this study, we calculate the nonthermal escape of H+ and O+ ions through the Venusian magnetotail and its dependence on the solar cycle. We separate 8 years of data obtained from the ion mass analyzer on Venus Express into solar minimum and maximum. The average escape of H+ decreased from 7.6 · 1024 (solar minimum) to 2.1 · 1024 s−1 (solar maximum), while a smaller decrease was found for O+: 2.9 · 1024 to 2.0 · 1024 s−1. As a result, the H+/O+ flux ratio decreases from 2.6 to 1.1. This implies that the escape of hydrogen and oxygen could have been below the stoichiometric ratio of water for Venus in its early history under the more active Sun.

Author Correction: Atmospheric mountain wave generation on Venus and its influence on the solid planet’s rotation rate

In the version of this Article originally published, a statement regarding past measurements of the length of day and rotation rate of Venus was potentially misleading. The original statement has now been replaced in the online versions of this Article, to acknowledge that neither Magellan nor Venus Express measured an instantaneous rotation rate.

Measurement of plasma channels in the Venus wake

Plasma channels have been suggested to account for the observation of ionospheric holes in the Venus nightside ionosphere. They are produced by the erosion of the solar wind on the magnetic polar regions of the Venus ionosphere, and are related to a sharp plasma transition that extends along the flanks of the wake and that is located downstream from the bow shock. The sharp plasma (intermediate) transition is a feature that has been detected with instruments onboard all the main spacecraft that have probed the Venus wake. From the early flyby transit of the Mariner 5 spacecraft to the later orbit crossings of the Venera 10, the Pioneer Venus and more recently the Venus Express there has been accumulated evidence of the presence of that transition by the flanks of the Venus wake. We report here measurements made with the ASPERA-4 instrument of the Venus Express that were conducted in orbit crossings by the midnight plane over a 4 year period (between 2006 and 2009), and that show different positions of the intermediate transition in the Venus wake at locations closer to the sun-Venus axis near solar minimum conditions by 2009. Measurements conducted in this latter time period also indicate that the intermediate transition by the midnight plane derives from the plasma channels and that is replaced by a broad velocity layer in orbits that probed farther away from that plane. It is argued that changes in the position of the intermediate transition with respect to the plasma channels are related to processes produced by the transport of solar wind momentum to the Venus polar ionosphere. The energy spectra of planetary ions measured in VEX orbits that probed by the midnight plane show momentum transport from the solar wind protons. This result is contrary to the conclusions reported by Collinson et al. (2014) in the sense that there is ¨no difference in the peak energy of the ionospheric outflow¨ when measured inside and outside an ionospheric hole.

Three‐Dimensional Turbulence‐Resolving Modeling of the Venusian Cloud Layer and Induced Gravity Waves: Inclusion of Complete Radiative Transfer and Wind Shear

AbstractVenus' convective cloud layers and associated gravity waves strongly impact the local and global budget of heat, momentum, and chemical species. Here we use for the first time three‐dimensional turbulence‐resolving dynamical integrations of Venus' atmosphere from the surface to 100‐km altitude, coupled with fully interactive radiative transfer computations. We show that this enables to correctly reproduce the vertical position (46‐ to 55‐km altitude) and thickness (9 km) of the main convective cloud layer measured by Venus Express and Akatsuki radio occultations, as well as the intensity of convective plumes (3 m/s) measured by VEGA balloons. Both the radiative forcing in the visible and the large‐scale dynamical impact play a role in the variability of the cloud convective activity with local time and latitude. Our model reproduces the diurnal cycle in cloud convection observed by Akatsuki at the low latitudes and the lack thereof observed by Venus Express at the equator. The observed enhancement of cloud convection at high latitudes is simulated by our model, although underestimated compared to observations. We show that the influence of the vertical shear of horizontal superrotating winds must be accounted for in our model to allow for gravity waves of the observed intensity (>1 K) and horizontal wavelength (up to 20 km) to be generated through the obstacle effect mechanism. The vertical extent of our model also allows us to predict for the first time a 7‐km‐thick convective layer at the cloud top (70‐km altitude) caused by the solar absorption of the unknown ultraviolet absorber.

Fbxo2VHC mouse and embryonic stem cell reporter lines delineate in vitro-generated inner ear sensory epithelia cells and enable otic lineage selection and Cre-recombination

While the mouse has been a productive model for inner ear studies, a lack of highly specific genes and tools has presented challenges. The absence of definitive otic lineage markers and tools is limiting in vitro studies of otic development, where innate cellular heterogeneity and disorganization increase the reliance on lineage-specific markers. To address this challenge in mice and embryonic stem (ES) cells, we targeted the lineage-specific otic gene Fbxo2 with a multicistronic reporter cassette (Venus/Hygro/CreER = VHC). In otic organoids derived from ES cells, Fbxo2VHC specifically delineates otic progenitors and inner ear sensory epithelia. In mice, Venus expression and CreER activity reveal a cochlear developmental gradient, label the prosensory lineage, show enrichment in a subset of type I vestibular hair cells, and expose strong expression in adult cerebellar granule cells. We provide a toolbox of multiple spectrally distinct reporter combinations for studies that require use of fluorescent reporters, hygromycin selection, and conditional Cre-mediated recombination.

A Statistical Study of Ionospheric Boundary Wave Formation at Venus

AbstractPrevious missions to Venus have revealed that encounters with plasma irregularities of atmospheric origin outside the atmosphere are not uncommon. A number of mechanisms have been proposed to discuss their origins as well as their roles in the atmospheric evolution of Venus. One such mechanism involves an ionopause with a wavelike appearance. By utilizing the magnetic field and plasma data from Venus Express, we present the first observational statistical analysis of the ionospheric boundary wave phenomena at Venus using data from 2006 to 2014. Results from the minimum variance analysis of all the photoelectron dropout events in the ionosphere reveal that the ionopause of Venus does not always appear to be smooth but often exhibits a wavelike appearance. In the northern polar region of Venus, the normal directions of the rippled ionospheric boundary crossings lie mainly in the terminator plane with the largest component predominantly along the dawn‐dusk (YVSO) direction. The average estimated wavelength of the boundary wave is 212 ± 12 km, and the average estimated velocity difference across the ionopause is 104 ± 6 km/s. The results suggest that the rippled boundary is a result of Kelvin‐Helmholtz instability. Analysis reveals a correlation between the normal directions and the locations of the boundary wave with respect to Venus. This indicates that the draping of magnetic field lines may play a role in enhancing the plasma flow along the dawn‐dusk direction, which could subsequently set up a velocity shear that favors the excitation of ionospheric boundary wave by the Kelvin‐Helmholtz instability along the dawn‐dusk direction.

Fine Vertical Structures at the Cloud Heights of Venus Revealed by Radio Holographic Analysis of Venus Express and Akatsuki Radio Occultation Data

AbstractRadio occultation (RO) is one of the most efficient techniques for studying fine vertical structures in planetary atmospheres. However, the geometrical optics (GO) method, which has been used for the analysis of RO data, suffers blurring by the finite width (Fresnel scale) of the radio ray and cannot decipher multipath propagation, which also prevents retrieval of fine structures. Here we apply Full Spectrum Inversion (FSI), which is one of the radio holographic methods, to RO data taken in Venus Express and Akatsuki missions to retrieve fine structures in Venus' cloud‐level atmosphere. The temperature profiles obtained by FSI achieve vertical resolutions of ~150 m, which is much higher than the typical resolution of 400–700 m in GO, and resolve structures in multipath regions. Thin, near‐neutral layers are found to be ubiquitous at cloud heights; we suggest here that those layers are caused by the mixing associated with the breaking of short‐wavelength gravity waves. The wavenumber spectra of small‐scale structures are consistent with the semiempirical spectrum of saturated gravity waves and show larger amplitudes at higher latitudes. Temperature profiles in the high latitudes frequently show a sharp temperature minimum near the cloud top, below which the vertical temperature gradient is near adiabat, implying that the sharp temperature minimum is created by adiabatic cooling associated with convective plumes that impinge on the overlying stable layer.