Change in the Wind and Climate at the ExoMars 2022 Landing Site in Oxia Planum (Mars).

<p>The ESA/ROSCOSMOS ExoMars 2022 will land in Oxia Planum an area that shows outcrops of clay-rich Noachian-aged phyllosilicates overlaid by an Early Amazonian volcanic dark resistant unit (Adru) [1]. Using HiRISE images, we identified NE-SW (53.9 ± 13.2°) oriented TARs overlying an enigmatic ~EW (95.4 ± 10°) oriented ridge pattern that we interpreted as periodic bedrock ridges (PBRs) [2]. Ridges (~ 38 m spaced) display Y-junctions, show cross-cutting fractures and share the same blocky texture of the bedrock they are associated with. Ridge crestlines are locally found in continuity outside and inside heavily eroded impact craters around the dark upstanding material (Adru) exposed in the center of many craters. These stratigraphic relationships suggest that the ridges (PBRs) formed after the event(s) that eroded the crater rims and thus after deposition of the Adru (2.6 Ga). Ridges are even visible in association with impact crater ejecta and are superimposed by 10-25 m craters and boulders, so they pre-date these impact events. When associated with crater ejecta, ridges locally show two different crests. Both crests are truncated by craters suggesting they were emplaced before the impacts. We interpret this double crest arrangement as megaripples detaching from PBRs. The ejecta deposited over the megaripple-PBRs favored the preservation of the megaripple crests from a subsequent episode/s of erosion that led to the complete exposure of the PBRs on the plain. Because the preserved megaripples are locally visible on the southern edges of the PBRs, the wind that formed the megaripple-PBR system should have blown from N-NNE because the megaripples are located at the downwind side of PBRs [3]. To better understand the relative age of the ridges, we mapped their occurrence on 316 craters in the study area that we qualitatively classified as relatively degraded/old and pristine/young. Results show that ridges are only found in degraded/old craters but are never found inside pristine/young craters. Thus, the ridge forming process was only active in-between the formation of degraded/old and pristine/young craters. A major change in the wind regime occurred during or after the event that exposed the PBRs: N-NNE winds that shaped the PBRs changed into dominant SE winds that led to the deposition of the TARs above the PBR/megaripples. This work unveils a complex history of aeolian erosion and deposition in Oxia Planum during the Amazonian. By visiting PBRs for the first time, the ExoMars 2022 mission will provide further constraints on PBR formation and paleo-winds, shedding light on a past Amazonian environment.</p><p>This work is a summary of a manuscript that is currently in press on Geophysical Research Letters: Silvestro et al. 2021, Periodic Bedrock Ridges at the ExoMars 2022 Landing Site: Evidence for a Changing Wind Regime. DOI: 10.1029/2020GL091651.</p><p>[1] Quantin-Nataf C. et al. (2021). Astrobiology, 21, N.3.</p><p>[2] Silvestro S. et al. (2020). 6th Int. Planet. Dunes Work. 12-15 May, 2020. LPI No. 2188, id.3009.</p><p>[3] Hugenholtz C. H. et al. (2015). Aeolian Res. 18, 135–144.</p>

Role of Equatorial Cold Tongue in Central Pacific Double-ITCZ Bias in the NCAR CESM1.2

Warm SST bias underlying the spurious southern ITCZ has long been recognized as one of the main causes for double-ITCZ bias in coupled GCMs in the central Pacific. This study demonstrates that the NCAR CESM1.2 can still simulate significant double-ITCZ bias even with cold SST bias in the southern ITCZ region, indicating that warm SST bias is not a necessary condition for double-ITCZ bias in the central Pacific. Further analyses suggest that the equatorial cold tongue (ECT) biases play important roles in the formation of double-ITCZ bias in the central Pacific. The severe cold SST biases in the ECT region in the central Pacific may enhance the SST gradient between the ECT and southern ITCZ region, strengthening the lower-troposphere dynamical convergence and hence convection in the southern ITCZ region. The formation mechanism of excessive ECT bias is further investigated. It is shown that the cold SST biases in the ECT region can be largely attributed to the anomalous cooling tendency produced by the upper-ocean zonal advection due to overly strong zonal currents. In the ECT region, the westward ocean surface zonal current is driven by the equatorial easterly surface winds. It is shown that convection bias simulated by the atmospheric model in the equatorial Amazon region may lead to easterly wind bias in the downwind side (west) of convection region. The mean Walker circulation transports these easterly wind momentum anomalies downward and westward to the surface, resulting in the overly strong surface easterly wind in the central equatorial Pacific.

Potential Vorticity Dynamics of the Arctic Halocline

An idealized two-layer shallow water model is applied to the study of the dynamics of the Arctic Ocean halocline. The model is forced by a surface stress distribution reflective of the observed wind stress pattern and ice motion and by an inflow representing the flow of Pacific Water through Bering Strait. The model reproduces the main elements of the halocline circulation: an anticyclonic Beaufort Gyre in the western basin (representing the Canada Basin), a cyclonic circulation in the eastern basin (representing the Eurasian Basin), and a Transpolar Drift between the two gyres directed from the upwind side of the basin to the downwind side of the basin. Analysis of the potential vorticity budget shows a basin-averaged balance primarily between potential vorticity input at the surface and dissipation at the lateral boundaries. However, advection is a leading-order term not only within the anticyclonic and cyclonic gyres but also between the gyres. This means that the eastern and western basins are dynamically connected through the advection of potential vorticity. Both eddy and mean fluxes play a role in connecting the regions of potential vorticity input at the surface with the opposite gyre and with the viscous boundary layers. These conclusions are based on a series of model runs in which forcing, topography, straits, and the Coriolis parameter were varied.

Analysis of Influence of Floating-Deck Height on Oil-Vapor Migration and Emission of Internal Floating-Roof Tank Based on Numerical Simulation and Wind-Tunnel Experiment

Internal floating-roof tanks (IFRTs) are widely used to store light oil and chemical products. However, if the annular-rim gap around the floating deck becomes wider due to abrasion and aging of the sealing arrangement, the static breathing loss from the rim gap will be correspondingly aggravated. To investigate the oil-vapor migration and emissions from an IFRT, the effects of varying both the floating-deck height and wind speed on the oil-vapor diffusion were analyzed by performing numerical simulations and wind-tunnel experiments. The results demonstrate that the gas space volume and the wind speed of an IFRT greatly influence the vapor-loss rate of the IFRT. The larger the gas space volume, the weaker the airflow exchange between the inside and outside of the tank, thereby facilitating oil-vapor accumulation in the gas space of the tank. Furthermore, the loss rate of the IFRT is positively correlated with wind speed. Meanwhile, negative pressures and the vortexes formed on the leeward side of the tank. In addition, the higher concentration areas were mainly on the three vents on the downwind side of the IFRT. The results can provide important theoretical support for the design, management, and improvement of IFRTs.

Airflow Characteristics Downwind a Naturally Ventilated Pig Building with a Roofed Outdoor Exercise Yard and Implications on Pollutant Distribution

The application of naturally ventilated pig buildings (NVPBs) with outdoor exercise yards is on the rise mainly due to animal welfare considerations, while the issue of emissions from the buildings to the surrounding environment is important. Since air pollutants are mainly transported by airflow, the knowledge on the airflow characteristics downwind the building is required. The objective of this research was to investigate airflow properties downwind of a NVPB with a roofed outdoor exercise yard for roof slopes of 5°, 15°, and 25°. Air velocities downwind a 1:50 scaled NVPB model were measured using a Laser Doppler Anemometer in a large boundary layer wind tunnel. A region with reduced mean air velocities was found along the downwind side of the building with a distance up to 0.5 m (i.e., 3.8 times building height), in which the emission concentration might be high. Additional air pollutant treatment technologies applied in this region might contribute to emission mitigation effectively. Furthermore, a wake zone with air recirculation was observed in this area. A smaller roof slope (i.e., 5° slope) resulted in a higher and shorter wake zone and thus a shorter air pollutant dispersion distance.

Airflow Characteristics Downwind a Naturally Ventilated Pig Building with a Roofed Outdoor Exercise Yard and Implications on Pollutant Distribution

The application of naturally ventilated pig buildings (NVPBs) with outdoor exercise yards is on the rise mainly due to animal welfare considerations, while the issue of emissions from the buildings to the surrounding environment is important. Since air pollutants are mainly transported by airflow, the knowledge on the airflow characteristics downwind the building is required. The objective of this research was to investigate airflow properties downwind of a NVPB with a roofed outdoor exercise yard for roof slopes of 5°, 15°, and 25°. Air velocities downwind a 1:50 scaled NVPB model were measured using a Laser Doppler Anemometer in a large boundary layer wind tunnel. A region with reduced mean air velocities was found along the downwind side of the building with a distance up to 0.5 m (i.e. 3.8 times building height), in which the emission concentration might be high. It was found that a smaller roof slope (i.e. 5° slope) resulted in a higher and shorter wake zone and thus a shorter air pollutant dispersion distance. It was concluded that a smaller roof slope could contribute to the dilution of air pollutants and a lower air pollutant concentration near the ground.

Modelling the transfer of road transport emissions in a street canyon

Работа посвящена построению и апробации микромасштабной математической модели и численного метода ее решения для исследования турбулентных течений и переноса пассивной газообразной примеси в уличных каньонах. Представлены результаты исследования структуры течения в уличном каньоне в зависимости от соотношения ширины улицы и высоты зданий, а также результаты расчета неизотермического турбулентного течения в условиях влияния естественной конвекции. The study is focused on developing and testing a microscale mathematical model for the analysis of turbulent flow and passive gaseous admixture transfer in street canyons. Mathematical model is based on Reynolds-averaged NavierStokes and continuity equations. Boussinesq approximation and two-parameter k-epsilon turbulence model is used to close the equations. Numerical solution of the system of differential equations is obtained with the finite volume method on a staggered mesh. Convective terms of the NavierStokes equations are approximated with MLU numerical scheme. SIMPLE computational algorithm is used to couple velocity and pressure fields. Laminar flow on the inlet section of the 2D channel was modelled to test the computational algorithm. Turbulent flow and emission transport in a wind tunnel was modelled to verify the mathematical model. Series of computations of the flow influenced by natural convection in an ideal model of street canyon were performed using the presented mathematical model. Computations were performed for a 24 m height and 20 m wide street canyon. The constant emission source was placed in the center of the canyon near the floor. Analysis of the results has showed that in cases of heating the upwind side or the bottom of the canyon emissions are transported out of the canyon more intensively and maximal concentrations decrease by 1015 from the isothermal case. In case of heating the downwind side the structure of the flow changes significantly and maximal concentrations increase by 33.5 times. The structure of the flow in the street canyon was investigated depending on the ratio of the street width to the height of the buildings. Both width of the street and height of the building varied from 5 to 40 m. The results show that increase in the height of the canyon decrease ventilation of the street canyon and increases local maximal concentrations of adverse emissions.

Estimating real driving emissions from MAX-DOAS measurements at the A60 motorway near Mainz

<p>Nitrogen oxides (NO<sub>x</sub> = NO + NO<sub>2</sub>) have a direct and indirect impact on human health. Therefore, the World Health Organization recommends limiting the concentration of nitrogen dioxide (NO<sub>2</sub>) in the atmosphere. Nevertheless, these limits are regularly exceeded. Especially, fossil fuel combustion from road traffic is a major contributor to the emission of NO<sub>x</sub>.</p><p>Multi Axis-Differential Optical Absorption Spectroscopy (MAX-DOAS) is able to measure trace gases in the lower troposphere. Here, this remote sensing method was used to measure NO<sub>x</sub> emissions at a highly frequented motorway. Two MAX-DOAS instruments were set up on both sides of the A60 motorway close to Mainz, Germany. The parallel viewing direction allows measuring the background signal at the upwind side and the background plus traffic emissions on the downwind side. Together with the effective wind speed perpendicular to the motorway, it is thus possible to retrieve the total traffic emissions. Compared to the expected emissions calculated from the European emission standards, the derived emissions of NO<sub>x</sub> are by a factor 7±4 higher.</p><p>In this study, first measurement results are presented and the method is evaluated with regard to the practicability and error margin.</p>

Living snow fences for protection of roads: case study crest Čestobrodica

Snowdrifts caused by wind gusts reduce visibility on the road which endangers traffic safety, increases travel time and road maintenance costs. Based on previous experience and research it has been proven that living snow fence is an economical, ecological and efficient solution for protection of roads from snowdrifts. Living snow fences with their above-ground part, reduce the wind speed, act as a mechanical barrier for the snow and accumulate a certain amount of snow. This study presented use and efficiency of living snow fence in controlling snowdrifts on the road section Paraćin-Zaječar, locality – crest Čestobrodica. Analysis of environmental conditions, which are resented main endangering factor for snowdrifts, included the determination of indicators of possibility of snowdrifts: snowfall water equivalent (Swe), snow transport (Q) and ability of living snow fence to prevent snowdrifts: snow storage capacity of the fance (Qc). Snow storage capacity for living snow fence is analyzed for ten year period. Using equation for estimation of length of snowdrifts on downwind side of fance, a change in length of snowdrifts during the analyzed period are determin, and the efficiency of living snow fence in protection of the road from snowdrifts with increasing age.The results of this study represent a contribution to using living snow fence in solving the problem of roads protection from snowdrifts and increasing traffic safety during winter conditions.

Subsiding shells and the distribution of up- and downdraughts in warm cumulus clouds over land

The mass flux of air lifted within the updraughts (updraft in American English) of shallow convection is usually thought to be compensated outside the cloud through either large-scale subsidence or stronger downdraughts in a thin shell surrounding the cloud. Subsiding shells were postulated based on large eddy simulation and are experimentally tested in this study for shallow convection over land. Isolated cumulus clouds were probed with a small research aircraft over flat land and mountainous terrain, in different wind situations and at different levels of the clouds. The average of the 191 cloud transects shows the subsiding shell as a narrow downdraught region outside the cloud boundaries. The ensemble-mean subsiding shell is narrower on the upwind side of the cloud, while it is at least half a cloud diameter wide and more humid on the downwind side. At least half of the upward mass transport in the cloud is compensated within a distance of 20 % of the cloud diameter. However, this shell is not uniform. Distinct regions of downdraughts and updraughts with high variability in the vertical wind are frequent and randomly distributed in the vicinity and also within the cloud. The median diameter of the draughts directly at the cloud boundary is at least 4 times as large as inside the clouds and in the environment. Downdraughts at the cloud boundary are twice as frequent as updraughts. In contrast to the updraughts the major part of the downdraughts is situated outside of the cloud. The subsiding shell results from the distribution of these up- and downdraughts.