Morphology of the cloud tops as observed by the Venus Express Monitoring Camera

Since the discovery of ultraviolet markings on Venus, their observations have been a powerful tool to study the morphology, motions and dynamical state at the cloud top level. Here we present the results of investigation of the cloud top morphology performed by the Venus Monitoring Camera (VMC) during more than 3 years of the Venus Express mission. The camera acquires images in four narrow-band filters centered at 365, 513, 965 and 1010 nm with spatial resolution from 50 km at apocentre to a few hundred of meters at pericentre. The VMC experiment provides a significant improvement in the Venus imaging as compared to the capabilities of the earlier missions. The camera discovered new cloud features like bright “lace clouds” and cloud columns at the low latitudes, dark polar oval and narrow circular and spiral “grooves” in the polar regions, different types of waves at the high latitudes. The VMC observations revealed detailed structure of the sub-solar region and the afternoon convective wake, the bow-shape features and convective cells, the mid-latitude transition region and the “polar cap”. The polar orbit of the satellite enables for the first time nadir viewing of the Southern polar regions and an opportunity to zoom in on the planet. The experiment returned numerous images of the Venus limb and documented global and local brightening events. VMC provided almost continuous monitoring of the planet with high temporal resolution that allowed one to follow changes in the cloud morphology at various scales.We present the in-flight performance of the instrument and focus in particular on the data from the ultraviolet channel, centered at the characteristic wavelength of the unknown UV absorber that yields the highest contrasts on the cloud top. Low latitudes are dominated by relatively dark clouds that have mottled and fragmented appearance clearly indicating convective activity in the sub-solar region. At ～50° latitude this pattern gives way to streaky clouds suggesting that horizontal, almost laminar, flow prevails here. Poleward from about 60°S the planet is covered by almost featureless bright polar hood sometimes crossed by dark narrow (～300 km) spiral or circular structures. This global cloud pattern can change on time scales of a few days resulting in global and local “brightening events” when the bright haze can extend far into low latitudes and/or increase its brightness by 30%. Close-up snapshots reveal plenty of morphological details like convective cells, cloud streaks, cumulus-like columns, wave trains. Different kinds of small scale waves are frequently observed at the cloud top. The wave activity is mainly observed in the 65–80° latitude band and is in particular concentrated in the region of Ishtar Terra that suggests their possible orographic origin. The VMC observations have important implications for the problems of the unknown UV absorber, microphysical processes, dynamics and radiative energy balance at the cloud tops. They are only briefly discussed in the paper, but each of them will be the subject of a dedicated study.     

Regional geomorphology of the continental slope of NW India: Delineation of the signatures of deep‐seated structures

Geomorphological features (derived from 16,000 lkm of echo‐sounding and bathymetric data) and deep‐seated tectonic structures of the continental margin off NW India are presented. The shelf break over the entire region occurs between 80 to 154 m water depth, and adjacent to Saurashtra and Bombay High the depth and orientation of the shelf edge show marked variations. The boundary of the slope is shallower in the northern portion (about 1450 m in the vicinity of the Indus) than in the southern region (2900 m off Bombay).

The steep slope off the Gulf of Kachchh has relatively smooth physiography due to higher input of fluvial sediment and burial of structures. The gentler slope off Saurashtra and the Bombay High area has numerous complex features, the most prominent among them being benches at depths of 180–230 m (width 2–10 km) and 650–780 m and a series of bathymetric highs and lows. Slope breaks are also observed between 400 and 600 m off Bombay and between 560 and 960 m off Saurashtra. These features are surface manifestations of the anticlinal features extending along the shelf in this region. Unevenness (order of 100–300 m) due to slumping is also observed at the base of the slope.

Based on the correlation between tectonic structures of this area and these subphysiographic features, extension of the Saurashtra Anticline onto the slope, a new strike slip fault (the southern boundary fault of Narmada graben) and an along‐shelf anticlinal structure off Saurashtra are delineated.     

New active galactic nuclei science cases with interferometry

Infrared (IR) interferometry has made widely recognised contributions to the way we look at the dusty environment of supermassive black holes on parsec scales. It finally provided direct evidence for orientation-dependent unification of active galaxies, however it also showed that the classical “torus” picture is oversimplified. New scientific opportunities for AGN have been suggested, and will soon be carried out, focusing on the dynamical aspects of spectrally and spatially resolved interferometry, as well as the potential to employ interferometry for cosmology. This will open interferometry to new scientific communities.     

Studying the errors in the estimation of the variation of energy by the “patched-conics” model in the three-dimensional swing-by

The swing-by maneuver is a technique used to change the energy of a spacecraft by using a close approach in a celestial body. This procedure was used many times in real missions. Usually, the first approach to design this type of mission is based on the “patched-conics” model, which splits the maneuver into three “two-body dynamics.” This approach causes an error in the estimation of the energy variations, which depends on the geometry of the maneuver and the system of primaries considered. Therefore, the goal of the present paper is to study the errors caused by this approximation. The comparison of the results are made with the trajectories obtained using the more realistic restricted three-body problem, assumed here to be the “real values” for the maneuver. The results shown here describe the effects of each parameter involved in the swing-by. Some examples using bodies in the solar system are used in this part of the paper. The study is then generalized to cover different mass parameters, and its influence is analyzed to give an idea of the amount of the error expected for a given system of primaries. The results presented here may help in estimating errors in the preliminary mission analysis using the “patched-conics” approach.     

Spartina maritima (cordgrass) rhizosediment extracellular enzymatic activity and its role in organic matter decomposition processes and metal speciation

Seasonal monitoring was carried out to investigate the influence of extracellular enzymatic activity (EEA) on metal speciation and organic matter cycling in the rhizosediment of Spartina maritima . Heavy metal speciation was achieved by the Tessier scheme, and showed a similar pattern of variation of the organic-bound fraction, indicating a decomposition process in progress. Both humic acid and organic matter showed the same seasonal pattern. The basal respiration of the rhizosediments also presented a similar seasonal pattern, indicating a microbial degradation of organic matter. The high organic-bound fraction found in the summer gradually decreased towards the winter. This decrease was found to be related to the increase of activity of peroxidase, β- N -acetylglucosaminidase and protease. Also the activity of sulphatase was found to be related to the depletion on the exchangeable fraction, probably due to sulphide formation and consequent mobilization. The results show an interaction between several microbial activities, affecting metal speciation.     

Hydraulic response of a tidally forced coastal aquifer, Pontal do Paraná, Brazil

The unconfined aquifer supported by the extensive Holocene coastal plain of southern Brazil is found dissected at several places by tidally forced streams. One such unit of coastal plain, falling within the watershed limits of Perequê Stream in Paraná state, was analyzed using MODFLOW to assess the surface and subsurface water components under different stress conditions. The steady-state simulation suggests that ~23,000 m³/day of water forms the total budget of the designated aquifer zone and this zone discharges ~16,000 m³/day across the interface between the freshwater aquifer zone and the sea as direct submarine discharge. The maximum evaporation loss was assumed to be 2,700 m³/day. Any change in effective aquifer storage was insignificant, as there is no large-scale exploitation of local groundwater reserves. A calibration exercise, based on field measurements lasting 1 year, supports validity of the model considered. Simulations representing two different transient conditions point to the dynamic hydraulic response exhibited by the aquifer. A schematic map, showing directions and velocity of subsurface flows, and a three-dimensional model of the groundwater reserve helped to visualize the hydrogeologic changes and to formulate management plans.