Production of ammonia makes Venusian clouds habitable and explains observed cloud-level chemical anomalies

The atmosphere of Venus remains mysterious, with many outstanding chemical connundra. These include the unexpected presence of ∼10 ppm O2 in the cloud layers, an unknown composition of large particles in the lower cloud layers, and hard to explain measured vertical abundance profiles of SO2 and H2O. We propose a hypothesis for the chemistry in the clouds that largely addresses all of the above anomalies. We include ammonia (NH3), a key component that has been tentatively detected both by the Venera 8 and Pioneer Venus probes. NH3 dissolves in some of the sulfuric acid cloud droplets, effectively neutralizing the acid and trapping dissolved SO2 as ammonium sulfite salts. This trapping of SO2 in the clouds, together with the release of SO2 below the clouds as the droplets settle out to higher temperatures, explains the vertical SO2 abundance anomaly. A consequence of the presence of NH3 is that some Venus cloud droplets must be semisolid ammonium salt slurries, with a pH of ∼1, which matches Earth acidophile environments, rather than concentrated sulfuric acid. The source of NH3 is unknown but could involve biological production; if so, then the most energy-efficient NH3-producing reaction also creates O2, explaining the detection of O2 in the cloud layers. Our model therefore predicts that the clouds are more habitable than previously thought, and may be inhabited. Unlike prior atmospheric models, ours does not require forced chemical constraints to match the data. Our hypothesis, guided by existing observations, can be tested by new Venus in situ measurements.

Climatic conditions of the development of tourism and leisure on the Żuławy Alluvial Plain

Based on the data for the years 1981–2014 from two meteorological stations located in the central and northern part of the Żuławy Alluvial Plain, the climatic conditions for the development of tourism and recreation in this area were analyzed. The factors contributing to this type of activity are the average temperatures in the fall and winter months higher than in central Poland and lower temperatures in the summer months, a relatively small number of hot and very hot days, as well as ice and very ice days. The central part of the analyzed area is characterized by lower precipitation totals, lower relative humidity, lower number of steamy days, lower cloud cover, and a high number of days with less than 50% cloudiness than the northern part, which is favorable to tourism in this area. Due to the small number of days with snowfall and snow cover over 8 cm thick, the possibility of skiing here is limited.

Improved monitoring of shipping NO₂ with TROPOMI: decreasing NO_x emissions in European seas during the COVID-19 pandemic

TROPOMI measurements of tropospheric NO2 columns provide powerful information on emissions of air pollution by ships on open sea. This information is potentially useful for authorities to help determine the (non-)compliance of ships with increasingly stringent NOx emission regulations. We find that the information quality is improved further by recent upgrades in the TROPOMI cloud retrieval and an optimal data selection. We show that the superior spatial resolution of TROPOMI allows the detection of several lanes of NO2 pollution ranging from the Aegean Sea near Greece to the Skagerrak in Scandinavia, which have not been detected with other satellite instruments before. Additionally, we demonstrate that under conditions of sun glint TROPOMI's vertical sensitivity to NO2 in the marine boundary layer increases by up to 60 %. The benefits of sun glint are most prominent under clear-sky situations when sea surface winds are low, but slightly above zero (±2 m/s). Beyond spatial resolution and sun glint, we examine for the first time the impact of the recently improved cloud algorithm on the TROPOMI NO2 retrieval quality, both over sea and over land. We find that the new FRESCO+wide algorithm leads to 50 hPa lower cloud pressures, correcting a known high bias, and produces 1–4·1015 molec/cm2 higher retrieved NO2 columns, thereby at least partially correcting for the previously reported low bias in the TROPOMI NO2 product. By training an artificial neural network on the 4 available periods with standard and FRESCO+wide test-retrievals, we develop a historic, consistent TROPOMI NO2 data set spanning the years 2019 and 2020. This improved data set shows stronger (35–75 %) and sharper (10–35 %) shipping NO2 signals compared to co-sampled measurements from OMI. We apply our improved data set to investigate the impact of the COVID-19 pandemic on ship NO2 pollution over European seas and find indications that NOx emissions from ships reduced by 20–25 % during the pandemic. The reductions in ship NO2 pollution start in March–April 2020, in line with changes in shipping activity inferred from AIS data.

Final Results on Atmospheric Wave Characterisation on the Nightside Lower Clouds of Venus

<p>An atmospheric internal gravity wave is a oscillatory disturbance on an atmospheric layer in which buoyancy acts as the restoring force. As such, they can only exist in a continuously stably stratified atmosphere, that is, a fluid in which the static stability is positive and horizontal variations in pressure are negligible when compared to the vertical variations (in altitude) [Gilli et al. 2020; Peralta et al. 2008]. These waves are of particular interest because they represent an effective means of energy and momentum transport across various layers of a planetary atmosphere, as these waves can form on one atmospheric region and travel through the atmosphere, sometimes over great distances, and dump their contained energy upon wave dissipation or breaking [Alexander et al. 2010]. Given these properties, study of atmospheric waves on Venus becomes important as another tool to answer some of the fundamental question surrounding its atmosphere dynamics, mainly the origin and support mechanism of the remarkable superrotation of the atmosphere.<br>We present here the final results on a study conducted on the nightside lower cloud of Venus to detect and characterise mesoscale waves. This analysis was conducted with infrared imaging data from both the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) onboard Venus Express (Vex) [Svedhem et al. 2007] and the 2-micron camera (IR2) onboard Akatsuki [Nakamura et al. 2011, Satoh et al. 2016] space missions. We covered the entire VIRTIS-M-IR archive selecting the 1.74- and 2.25-micron wavelengths as well as all available images from the IR2 camera at 2.26 microns to ensure a most comprehensive survey and through image navigation and processing we were able to characterise approximately 300 wave packets across more than 5500 images over a broad range of latitudes on Venus. From these waves we retrieved basic morphological properties such as horizontal wavelength, number of crests and the full extent of the wave. Additionally, we were able to track the evolution of waves as they moved on the atmosphere, enabling some dynamical characterisation. The panel below shows examples of atmospheric waves observed in this study. Figures A-C show VIRTIS-M-IR images while figures D-F show IR2 data. All images have been subject to contrast enhancement techniques to improve observability of waves.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.664bc41e16a062149941261/sdaolpUECMynit/1202CSPE&app=m&a=0&c=4d76fa87765c4d96de6f9a4578649e21&ct=x&pn=gnp.elif&d=1" alt=""></p><p>Our goal was to provide a survey on atmospheric waves in the lower cloud as complete as possible, using two different instruments which cover in detail different sections of the globe of Venus over a long-time span, expanding on other studies performed by Peralta et al. (2008), (2019). With the larger data base, we discuss the nature of these waves, possible forcing mechanisms, and their relationship with the background atmosphere. Several questions remain however, such as how much energy do these waves transport in the cloud layer and how much do they contribute to Venus’ superrotation and if there is a dominant source of excitation for these waves. Full details of these results can be found in Silva et al. (2021) and we hope that these updated results can prove useful to recent and future models of Venus atmosphere as well as atmosphere of other slow rotators in the Solar System.</p><p><br><strong>References</strong></p><ul><li>Alexander M.J. et al, Quarterly Journal of the Royal Meteorological Society, vol. 136, pp. 1103-1124, 2010;</li> <li>Gilli G. et al, Journal of Geophys. Research – Planets, ID. e05873, 2020;</li> <li>Nakamura M. et al, Earth, Planets and Space, vol. 63, pp. 443-457, 2011;</li> <li>Peralta J. et al, Journal of Geophysical Research, vol. 113, ID. E00B18, 2008;</li> <li>Peralta J. et al, Icarus, vol. 333, pp. 177-182, 2019;</li> <li>Satoh T. et al, Earth, Planets and Space, vol. 68, ID. 74, 2016;</li> <li>Silva J. et al, A&A, vol. 649, ID. A34, 2021;</li> <li>Svedhem H. et al, Planetary and Space Science, vol. 55, pp. 1636-1652, 2007;</li> </ul>

Statistical Characteristics of Mesoscale Convective Systems Initiated over the Tibetan Plateau in Summer by Fengyun Satellite and Precipitation Estimates

In order to investigate the key characteristics of mesoscale convective systems (MCSs) initiated over the Tibetan Plateau (TP) in recent years and the main differences in circulation and environmental factors between different types of MCSs, an automatic MCS identification and tracking method was applied based on the data from China’s Fengyun satellite and precipitation estimates. In total, 8820 MCSs were found to have been initiated over the TP during the summers from 2013 to 2019, and a total of 9.3% of them were able to move eastward out of the TP (EO). The number of MCSs showed a monthly variation, with a maximum in July and a minimum in June, while most EOs occurred in June. Compared with other types of MCSs, EOs usually had a lower cloud-top temperature, a greater rainfall intensity, a longer life duration, more rapid development, larger areas of rainfall and convective clouds, longer tracks and a wider influence range, indicating that EOs are more vigorous than the other types of MCSs. The movement of MCSs is mainly due to the mid- to high-level dynamic conditions, and moisture is an essential factor in their development and maintenance.

Color changes and dynamics of the third largest oval on Jupiter

<p>Because of its large size, fast rotation and multiple atmospheric jets, Jupiter’s atmosphere holds a large variety of vortices. A large anticyclone at 19ºN planetographic latitude persists since at least 2006 after a complex dynamic history. This North Tropical Oval (NTrO) is located in the transition region between the North Equatorial Band (NEBn) and North Tropical Zone (NTrZ) and it is one of the longest-lived anticyclonic oval in the planet, following the Great Red Spot and oval BA. The region where it is located has a strong latitudinal shear, which allows the formation of dark cyclones and usually white anticyclones that stay stable in latitude. The NTrO has survived for years after mergers and disturbances: in February 2013, it merged with another oval and some months later, in September 2013, its color changed from white to red and then, in December 2014, back to white with an external red ring. The oval also survived the North Temperate Belt Disturbance (October 2016) which fully covered the oval, leaving it unobservable for a short time. It reappeared at its expected longitude as a white large oval keeping the same color and morphology from 2017 to 2020. Using JunoCam, Hubble Space Telescope (HST) and PlanetCam-UPV/EHU multi-wavelength observations, we describe the historic evolution of this oval’s properties. We used JunoCam and HST images to measure its size and its internal rotation obtaining a mean value of (10,500±1,000) x (5,800±600) km for the size and a mean relative vorticity of -(2±1)·10<sup>-5</sup>s<sup>-1</sup>. Contrarily to GRS and BA, which have higher vorticity values than their surroundings, the NTrO’s vorticity is nearly the same as the ambient vorticity of the area, which suggests that this oval is probably sustained by the zonal jets confining it. We also used HST and PlanetCam observations to characterize its color changes. The color and the altitude-opacity indices show that the oval is higher and has redder clouds than its environment but has lower cloud tops than other large ovals like the GRS, and it is less red than the GRS and oval BA. Despite the changes, mergers and disturbances experienced by the oval, its main characteristics remain unaltered and this suggests a vertically extended vortex with properties that could be related with the atmospheric dynamics below the observable cloud deck.</p>

Winds in the Lower Cloud Level on the Nightside of Venus from VIRTIS-M (Venus Express) 1.74 μm Images

The horizontal wind velocity vectors at the lower cloud layer were retrieved by tracking the displacement of cloud features using the 1.74 µm images of the full Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS-M) dataset. This layer was found to be in a superrotation mode with a westward mean speed of 60–63 m s−1 in the latitude range of 0–60° S, with a 1–5 m s−1 westward deceleration across the nightside. Meridional motion is significantly weaker, at 0–2 m s−1; it is equatorward at latitudes higher than 20° S, and changes its direction to poleward in the equatorial region with a simultaneous increase of wind speed. It was assumed that higher levels of the atmosphere are traced in the equatorial region and a fragment of the poleward branch of the direct lower cloud Hadley cell is observed. The fragment of the equatorward branch reveals itself in the middle latitudes. A diurnal variation of the meridional wind speed was found, as east of 21 h local time, the direction changes from equatorward to poleward in latitudes lower than 20° S. Significant correlation with surface topography was not found, except for a slight decrease of zonal wind speed, which was connected to the volcanic area of Imdr Regio.

Tropical Cyclone Temperature Profiles and Cloud Macro-/Micro-Physical Properties Based on AIRS Data

We used the observations from Atmospheric Infrared Sounder (AIRS) onboard Aqua over the northwest Pacific Ocean from 2006–2015 to study the relationships between (i) tropical cyclone (TC) temperature structure and intensity and (ii) cloud macro-/micro-physical properties and TC intensity. TC intensity had a positive correlation with warm-core strength (correlation coefficient of 0.8556). The warm-core strength increased gradually from 1 K for tropical depression (TD) to >15 K for super typhoon (Super TY). The vertical areas affected by the warm core expanded as TC intensity increased. The positive correlation between TC intensity and warm-core height was slightly weaker. The warm-core heights for TD, tropical storm (TS), and severe tropical storm (STS) were concentrated between 300 and 500 hPa, while those for typhoon (TY), severe typhoon (STY), and Super TY varied from 200 to 350 hPa. Analyses of the cloud macro-/micro-physical properties showed that the top of TC cloud systems mainly consisted of ice clouds. For TCs of all intensities, areas near the TC center showed lower cloud-top pressures and lower cloud-top temperatures, more cloud fractions, and larger ice-cloud effective diameters. With the increase in TC intensity, the levels of ice clouds around the TC center became higher and the spiral cloud-rain bands became larger. When a TC developed into a TY, STY, or Super TY, the convection in the clouds was stronger, releasing more heat, thus forming a much warmer warm core.

Extensive layer clouds in the global electric circuit: their effects on vertical charge distribution and storage

A fair-weather electric field has been observed near the Earth's surface for over two centuries. The field is sustained by charge generation in distant disturbed weather regions, through current flow in the global electric circuit. Conventionally, the fair-weather part of the global circuit has disregarded clouds, but extensive layer clouds, important to climate, are widespread globally. Such clouds are not electrically inert, becoming charged at their upper and lower horizontal boundaries from vertical current flow, in a new electrical regime—neither fair nor disturbed weather; hence it is described here as semi-fair weather . Calculations and measurements show the upper cloud boundary charge is usually positive, the cloud interior positive and the lower cloud boundary negative, with the upper charge density larger, but of the same magnitude (∼nC m −2 ) as cloud base. Globally, the total positive charge stored by layer clouds is approximately 10 5 C, which, combined with the positive charge in the atmospheric column above the cloud up to the ionosphere, balances the total negative surface charge of the fair-weather regions. Extensive layer clouds are, therefore, an intrinsic aspect of the global circuit, and the resulting natural charging of their cloud droplets is a fundamental atmospheric feature.

The Characteristics of Multi-layer Clouds in Summer over Tibetan Plateau Based on CloudSat Measurements

<p>The characteristics including cloud occurrence frequencies, vertical structure, configuration of cloud type, and microphysical structure of single-layer and multi-layer clouds in Tibetan Plateau (TP) in summer (June-August) during 2007-2010 are investigated based on the CloudSat merged data. The results indicate that cloud over the TP is mainly in the form of single-layer cloud with occurrence frequency of 56.86%, and then followed by the form of double-layer cloud with 24.47%. The spatial distribution of occurrence frequency shows that the single-layer cloud is mainly located in the northern plateau, and fraction of multi-layer cloud decrease gradually from the southeast to the northwest. Single-layer clouds mainly consist of stratocumulus (22.71%), and then followed by altostratus (19.98%) and nimbostratus (19.42%). As for the multi-layer clouds, the upper layers mainly consist of cirrus and altostratus, and the middle layers are mainly dominated by altostratus, cirrus and altocumulus. The lower layers mainly consist of stratocumulus, altocumulus and cumulus. The vertical structure indicates that the averaged cloud thicknesses of single-layer are larger compared with multi-layer clouds. The distributions of microphysical characteristics of multi-level clouds and single-layer clouds are similar, while the averaged values of microphysical characteristics including particle number concentration, cloud water content and effective radius of single-layer are larger. Moreover, the microphysical variable values of upper cloud are lower compared with lower cloud, which are related to the cloud types. The precipitation is mainly in the form of liquid precipitation, and then followed by the solid precipitation, and the drizzle. Furthermore, the drizzle occurs mainly in the multi-layer clouds. The single-layer fraction in the daytime (62.99%) is larger than that at night (51.00%), whereas, multi-layer clouds are opposite. The fraction of liquid precipitation and deep convection are larger during the daytime than those at night. Conversely, the fractions of drizzle and nimbostratus are larger at night. In addition, higher surface temperature, larger surface specific humidity and higher surface pressure is found to be contributed to the formation of multi-layer clouds.</p>