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In this study we present the behaviour of sporadic E-layer during a total solar eclipse (TSE) which occurred during the dawn/sunrise hours over a site located in the path of totality. A Canadian Advanced Digital Ionosonde (CADI) was operated at Allahabad (25.4° N, 81.9° E), a low latitude station located near the crest of equatorial ionization anomaly (EIA) in the Indian subcontinent to study the ionospheric effects of 22 July 2009 TSE. Corresponding to the eclipse period, a gradual increase of ftEs (top frequency of Es layer) in the 4–5 MHz range was seen on the control days. On 22 July (the TSE day), correlated changes in ftEs coinciding with the TSE progression was noted – (i) sharp decrease near first and second contact of TSE, (ii) an increase after first and second contact, and (iii) wavelike fluctuations in ftEs variation during eclipse hours and beyond. Much higher ftEs values were noted during the TSE hours in comparison to that seen on usual days. Strong blanketing Es layer developed during the TSE hours and persisted for slightly longer duration than its usual occurrence time. Near the TSE totality, slight lowering of the base height of Es layer was also noted.

The conventional use of ‘globally averaged temperatures’ causes ambiguity in our perception of human climate effects. Satellite images show distinct clusters or 'nodes' of population, light, CO2, heat, and likely water vapour. These urban nodes juxtaposed with the intervening rural dark areas form a 'mosaic' perspective of the anthropogenic effects on climate. Over-averaging of these nodes to indicate a 'blanketing' effect and hiding the mosaic is likened to mis-diagnosing sharp appendicitis pain.

This work analysis the blanketing sporadic layers (Es b ) behavior over Sao Luis, Brazil (2° 31′ S, 44° 16′ W, dip: −4.80) which is classified as a transition region between equatorial and low-latitude. Hence, some peculiarities can appear as Es b occurrence instead of the common Es q , which is a non-blanketing irregularity layer. The analysis presented here was obtained using a modified version of a theoretical model for the E region (MIRE), which computes the densities of the metallic ions (Fe + and Mg + ) and the densities of the main molecular ions (NO + , O 2 + , N 2 + ) by solving the continuity and momentum equations for each one of them. In that model, the Es layer physics driven by both diurnal and semidiurnal tidal winds are taken into account and it was extended in height coverage by adding a novel neutral wind model derived from the all-sky meteor radar measurements. Thus, we provide more trustworthy results related to the Es layer formation in the equatorial region. We verified the contribution of each tidal wind component to the Es b layer formation in this equatorial region. Additionally, we compared the Es layer electron density computed by MIRE with the data obtained by using the blanketing frequency parameter ( fb Es) deduced from ionograms. The results show that the diurnal component of the tidal wind is more important in the Es b layer formation whereas the semidiurnal component has a little contribution in our simulations. Finally, it was verified that the modified MIRE presented here can be used to study the Es b layers occurrence over the equatorial region in the Brazilian sector.

The tallest volcano in the solar system, Olympus Mons on Mars, is bordered by at least ten enormous sub-circular hummocky deposits forming a welded halo, termed the aureole. The aureole units (or simply aureoles), which are the deposits of landslides from Olympus Mons, have dramatically transformed the pristine size and shape of the volcanic edifice. Topographic data are used to determine the amount of collapsed material, and so reconstruct the original outline of Olympus Mons before the landslides took place, under the assumption that the edifice did not start failing until it had reached this maximum size. Due to post-aureole deposition on the eastern and southern flanks and to the uncertainty of the slippage level on the northern side, the reconstruction is sufficiently precise along the western and north-western Olympus Mons flank, it is more uncertain for the northern flank, while it is not feasible around the rest of the volcano. It appears that the radius along the western and north-western Olympus Mons before the collapse of the aureole landslides was approximately 200 km longer or more. The results show that the volume of the aureoles, even if enormous, is insufficient to fill the ideal conical edifice which would be obtained prolonging the Olympus Mons flanks with present slope angles. Thus, an overhang remains in the pre-aureole reconstructed Olympus Mons, which would also explain the onset of instability that led to the aureole collapse. Further, a drape deposit blanketing the southern Acheron Fossae ridge just at the front of the western (W) aureole landslide deposit and a fan-channel system carved on the same W aureole are investigated, and it is suggested that these morphologies have been emplaced in subaqueous setting. While the drape may indicate a landslide-thrust water splash akin to a tsunami deposit caused by the fast travelling W aureole landslide, the fan-channel system is similar to certain morphologies in the terrestrial oceans. A numerical model of the collapse of the western aureole unit in water shows final runouts on both Acheron ridge and Amazonis Planitia compatible with observations provided that the friction angle is extremely small, of the order of a tenth of degree. Simulations indicate that the W aureole could have reached Acheron Fossae ridge with velocities in excess of 100 m/s, which would explain the several tens of km long distance reached by the landslide-thrust tsunami deposit. In short, morphological and numerical lines of evidence would indicate a subaqueous origin for the largest, W aureole landslide.

This work presents new results about simulations of blanketing sporadic E-layers, Esb, using a modified version of a theoretical model for the E region (MIRE) for a Brazilian region: Cachoeira Paulista, a low latitude station. MIRE computes the densities of the metallic ions (Fe+ and Mg+) and of the main molecular ions (NO+, O2+, N2+) by solving the continuity and momentum equations for each one of them. Additionally, this model includes the physics of Es layer development driven by tidal winds. In this study, we extend MIRE adding a novel neutral wind model derived from the all-sky meteor radar measurements, which provides more trustworthy results related to the Es layer formation in the Brazilian sector. Afterwards, this new model is validated comparing the computed electron density for the Es layer with the electron density obtained using the blanketing frequency parameter (fbEs) deduced from ionograms in the analyzed region. The results show that the values computed by the extended MIRE are in good agreement with the observational data for the Es layers formed by the wind shear mechanism. Therefore, the extended MIRE presented in this work is the only available model that allows simulating Esb layers with a much higher confidence level for the low-latitude in the Brazilian sector.

Dead-ended anode operation has a number of practical advantages that simplify system complexity and lower cost for polymer electrolyte fuel cells. However, dead-ended mode leads to performance loss over time which can only be reversed by performing intermittent purge events. This work applies a combined hydro-electro-thermal analysis to an air-cooled open-cathode fuel cell, presenting experimental functional maps of water distribution, current density and temperature. This approach has allowed the identification of a ‘nitrogen blanketing’ effect due to nitrogen cross-over from the cathode and a ‘bypass’ effect where a peripheral gap between the gasket and the GDL offers a hydrogen flow ‘short circuit’ to the border of the electrode. A consequence of high local current density at the margin of the electrode, and resulting high temperatures, may impact the lifetime of the cell in dead-end mode.

In this work a method has been presented for preparation of sol–gel derived transparent conductive Al-doped zinc oxide (AZO) films. This method is based on rapid cooling of the glass in the presence of a gas blanket and does not require the post annealing step. Rapid cooling is used to kinetically limit the oxygen diffusion to the film and gas blanketing has been used to enhance the effect. Gas blankets have been generated by placing the hot AZO coated glass on a gas evolving material (e.g. ammonium carbonate) which generates gas by endothermic reaction. Rapid cooling has been shown to be only slightly effective and combined rapid cooling and gas blanketing has been shown to be a good combination. AZO films (100 nm thick) prepared by this method show low resistivity (5.4 × 10 − 2 Ω ‐ cm), high transmittance (> 90%), and preferential crystalline orientation [002] comparable with conventionally post-annealed AZO film in forming gas atmosphere.

The ordinary wave critical frequency foEs is measured routinely by ionosondes and used widely in estimating the intensity and occurrence of sporadic E (Es) metal ion layers. Recently, however, it was realized that foEs overestimates Es intensities because it corresponds to the sum of both the layer metal ion plasma and the regular E region plasma densities. To account for this, a new parameter, foμEs, was introduced that corresponds to the Es layer metal plasma density only, and a method was proposed for its calculation. In the present work, an ionosonde data set is analyzed to assess the importance of replacing foEs by foμEs in Es studies. To this objective, the diurnal and seasonal variability of sporadic E is re-examined. It turns out that the Es mean diurnal and seasonal variations estimated by means of using foμEs, differ substantially from those based on foEs, implying that the use of foEs leads to biased results and wrong physical inferences. It is therefore urged that foμEs is adopted and used instead of foEs, in future ionosonde sporadic E studies. The same applies for the case of satellite radio occultation (RO) sporadic E investigations as well, where foμEs should be used, instead of foEs, for calibration and validation purposes. All this is equally valid in the case of the blanketing sporadic E frequency fbEs and the corresponding new parameter fbμEs that needs also to be adopted and used.

The tritium storage bed receives and supplies tritium gas for fusion facilities. Inert gases, such as helium-3, which is produced by tritium beta decay, disturb the absorption behavior of tritium in the bed and this is called the Helium Blanketing Effect (HBE). This study focused on the HBE and gas circulation as a way of breaking the HBE for the hydriding reaction with ZrCo. The hydriding reaction with the application of 100 % hydrogen without helium-4 was completed within five minutes under 120 kPa initial hydrogen partial pressure and 20 °C reactor temperature. With 5% helium-4 in the hydrogen, it took more than 1000 min for the hydriding reaction to be completed under the same conditions. The HBE was broken with the application of a gas-circulation process. Even with 50 % helium-4 in the hydrogen, the hydriding reaction was completed in five minutes under the same conditions. In an experiment conducted at various flow rates of gas circulation, breaking the HBE was observed even at a small flow rate. The gas circulation process can efficiently break the HBE and separate the helium-3 produced in the tritium storage bed.

A multi-year global comparison between mid-latitude and equatorial sporadic-E ( E s ) height and intensity derived from COSMIC GPS radio occultation (GPS-RO) data and blanketing E frequency (fbEs) from ground-based Digisonde measurements is performed. The E s layer intensity from GPS-RO measurements was estimated using the S2 scintillation index and total electron content (TEC) assuming constant and variable E s cloud thicknesses individually. GPS-RO crossings were limited to within 150 km and 30 min of fbEs occurrences at each Digisonde. Intensities derived from the TEC with constant thickness method agreed more closely with the Digisonde fbEs measurements in terms of relative error and spread. E s path lengths estimated from the variable thickness method were also significantly larger than the average E s cloud length indicating that tube geometry assumptions between thickness and length do not apply to sporadic-E. Furthermore, intensities calculated from the S2 technique generally placed the frequency of fbEs between 2.7 and 5.3 MHz. Mean fbEs predictions from the S2 and constant thickness TEC methods are found to be statistically similar to the mean Digisonde fbEs. Both TEC and S2 methods underestimated the altitude of the fbEs events, but the S2 technique performed better overall. The mean heights calculated from both of the GPS-RO methods show a statistically significant difference with the mean Digisonde calculated heights, suggesting a bias in the height estimates.

We present a seismic- and 3D-gravity-constrained lithospheric-scale 3D structural model of Hessen that differentiates 7 sedimentary units, 5 Variscan upper crustal bodies, the lower crystalline crust and the lithospheric mantle. To predict the present- day subsurface temperatures, we solve the steady-state conductive heat equation by using a 3D FE method and assigning lithology-dependent thermal properties. We show that the thermal field is mainly controlled by the varying radiogenic heat production in the crystalline crust, which results in a colder NW and a warmer SE domain. Locally, this regional trend is superimposed by thermal blanketing of low-conductive sediments leading to higher temperatures.

This study is to know how the characteristics of sporadic E-layer (E s -layer) affect the generation of spread-F in the nighttime ionosphere near the crest of equatorial ionization anomaly during solar minimum. The data of E s -layer parameters and spread-F are obtained from the Chungli ionograms of 1996. The E s -layer parameters include foE s (critical frequency of E s -layer), fbE s (blanketing frequency of E s -layer), and Δ f (≡foE s −fbE s ). Results show that the nighttime variations of foE s and fbE s medians (Δ f medians) are different from (similar to) that of the occurrence probabilities of spread-F. Because the total number of E s -layer events is greater than that of spread-F events, the comparison between the medians of E s -layer parameters and the occurrence probabilities of spread-F might have a shortfall. Further, we categorize the E s -layer and spread-F events into each frequency interval of E s -layer parameters. For the occurrence probabilities of spread-F versus foE s , an increasing trend is found in post-midnight of all three seasons. The increasing trend also exists in pre-midnight of the J-months and in post-midnight of all seasons, for the occurrence probabilities of spread-F versus Δ f . These demonstrate that the spread-F occurrence increases with increasing foE s and/or Δ f . Moreover, the increasing trends indicate that polarization electric fields generated in E s -layer assist to produce spread-F, through the electrodynamical coupling of E s -layer and F-region. Regarding the occurrence probabilities of spread-F versus fbE s , the significant trend only appears in post-midnight of the E-months. This implies that fbE s might not be a major factor for the spread-F formation.

International audience; We report on the physical properties of the craters of Achaia region of the main-belt asteroid (21) Lutetia, based on images obtained with the OSIRIS instrument during the Rosetta flyby that took place on 10 July 2010. Images of the surface were acquired with its Narrow Angle Camera, from which Digital Terrain Models (DTM) of the surface were constructed. These DTMs give access to the geometrical properties of the craters of the asteroid. On a complex asteroid shape, slopes and depth-to-diameter ratios (d/D) of craters should be carefully measured taking into account the local topography to obtain a value that is physically related to the work of forces resisting to mass displacement (associated with gravity and/or material strength) occurring in either excavation or degradation processes. We present new measurements of d/D and internal slopes of impact craters of the Achaia region, which offers optimal conditions of observations and a large population of craters. We find that d/D values for Achaia craters differ from previous works on Lutetia and are consistent with the values found on other asteroids such as (243) Ida or (951) Gaspra. The Achaia region may be divided into three units based on geomorphological analysis. The mean d/D values of the three units are different, revealing differences in resurfacing history by impact-related ejecta blanketing and seismic shaking. Some of these geological events may be recent compared to the age of the region since several lineaments intersect most craters of one of the three units. Independent evidence for ejecta blanket have been given for the unit associated with low d/D values confirming the contribution of this process to crater modification. Moreover, we suggest that displacements along faults identified as surface lineaments may have been responsible for the erasure of small craters. Our results are finally integrated into a chronology sequence of events explaining the present characteristics of the Achaia region.

We have analyzed the behavior of blanketing frequency of the Es layer (fb Es) occurring at an equatorial station covering the days before, during and subsequent to 24 intense and very intense magnetic storms ( Dst ≤ − 100 nT ) that occurred during the solar cycle 23. The fb Es was measured by digital ionosonde over Sao Luis, Brazil (2.33° S, 44.2° W, dip: −4.5°). Our analysis shows that there are significant changes in the fb Es, mainly during the recovery phase of magnetic storms, characterized by occurrence of peaks that exceed the ambient background values. Also, these peaks are associated to other types of sporadic E layer than the Esq (a non-blanketing layer detected due the plasma irregularities in the equatorial electrojet), which in turn means competing mechanisms. The results are discussed in terms of the statistics of the abnormal enhancement taking into account the phase of the magnetic storm.

One of the recent developments in the form of a novel probe for simultaneous in-situ measurements of Electron density and Neutral Wind (ENWi) parameters was extensively made use of during the annular solar eclipse that passed right over the magnetic dip equatorial station, Trivandrum in India. The response of the equatorial ionosphere to the annular solar eclipse of January 2010 is investigated using the data from ENWi and other ground based instruments like digital Ionosonde, HF radar, magnetometer etc. Significant effects on the neutral wind components and electron densities during the peak phase of the eclipse are brought out by the ENWi data. A clear reversal in the zonal neutral wind is observed during the rocket flights at the peak phase of the eclipse as well as in the flight conducted 3 h later. The ground magnetic field measurements revealed the reversal of electrojet during the eclipse alongwith blanketing Es layers vindicating the earlier hypothesis that blanketing Es layers manifest over magnetic equatorial regions only during periods of either weak or reversed electrojet (counter electrojet). The HF radar results independently substantiate the in situ measurements with regard to the location of the irregularities and their Doppler velocities. The regional scale changes that have been brought about by the Solar eclipse both in the neutral and ionized medium and the consequent electrodynamics are highlighted.

Due to mechanisms such as impact heating, early atmospheric thermal blanketing, and radioactive heating, the presence of at least one global magma ocean stage in the early histories of terrestrial planets seems unavoidable. In such a context, a key question to constrain the early thermo–chemical evolution of the Earth is how much iron diapirs provided by differentiated impactors emulsified during their sinking towards the bottom of an early magma ocean. In the past years, several workers have focused on this question, using however various approaches and making different assumptions. While most studies favor rapid breakup and equilibration of iron bodies during their sinking through the magma ocean, recent work suggests that iron bodies of size comparable or greater than a few tens of kilometers may preserve most of their initial volume as they reach the bottom of a magma ocean, therefore leading to metal–silicate disequilibrium. To clarify the discrepancies and the differences among studies I have conducted a series of numerical simulations and theoretical calculations to derive the conditions and the timing for the breakup of metal diapirs of any size, sinking through a silicate magma ocean, with a large range of plausible viscosity values. The obtained breakup criterion is used to derive stable diapir sizes and their ability to equilibrate with the surrounding silicates. I show that for plausible magma ocean viscosities, diapirs with initial radii smaller than the thickness of a magma ocean rapidly break up into stable diapir sizes smaller than 0.2 m, at which metal–silicate equilibration is rapidly achieved.

A new model is presented on how chemically driven cryovolcanism might contribute to episodic outgassing at the icy moon Enceladus and potentially elsewhere including Europa and Kuiper Belt Objects. Exposed water ices can become oxidized from radiolytic chemical alteration of near-surface water ice by space environment irradiation. In contact with primordially abundant reductants such as NH3, CH4, and other hydrocarbons, the product oxidants can react exothermically to produce volatile gases driving cryovolcanism via gas-piston forces on any subsurface liquid reservoirs. Radiolytic oxidants such as H2O2 and O2 can continuously accumulate deep in icy regoliths and be conveyed by rheological flows to subsurface chemical reaction zones over million-year time scales indicated by cratering ages for active regions of Enceladus and Europa. Surface blanketing with cryovolcanic plume ejecta would further accelerate regolith burial of radiolytic oxidants. Episodic heating from transient gravitational tides, radioisotope decay, impacts, or other geologic events might occasionally accelerate chemical reaction rates and ignite the exothermic release of cumulative radiolytic oxidant energy. The time history for the suggested "Old Faithful" model of radiolytic gas-driven cryovolcanism at Enceladus and elsewhere therefore consists of long periods of chemical energy accumulation punctuated by much briefer episodes of cryovolcanic activity. The most probable sequence for detection of activity in the current epoch is a long evolutionary phase of slow but continuous oxidant accumulation over billions of years followed by continuous but variable high activity over the past 10(exp 7)-10(exp 8) years. Detectable cryovolcanic activity could then later decline due to near-total oxidation of the rheologically accessible ice crust and depletion the accessible reductant abundances, as may have already occurred for Europa in the more intense radiation environment of Jupiter's magnetosphere. Astrobiological potential of Enceladus could correspondingly be higher than at Europa due to a less extreme state of oxidation and greater residual abundance of organics.

Sporadic-E is a problem in high latitude HF communications because of its irregular and as yet unpredictable behaviour. This paper characterises the change in E-layer critical frequency (foE) that occurs in the four hours following a storm sudden commencement (SSC) event which is a precursor to magnetospheric storms which adversely affect ionospheric communications. Following checks for any seasonal or solar activity dependency in the data, further analysis determines the occurrence of full blanketing (screening) Sporadic-E layer formation at high latitudes as seen on vertical ionosondes in Northern Finland (671 Latitude). An appropriate threshold value of foE is proposed that could be used following the commencement of ionospheric storms, indicating that there is a high probability that F-layer screening will occur. As far as the authors are aware this is the first statistical analysis of the onset of Sporadic-E following SSC.

During an equatorial campaign called COPEX (Conjugate Point Equatorial Experiment) ionosondes at a pair of conjugate stations in Brazil were operated for 2 months in 2002. One expected the sporadic-E (E s ) layers to be rather similar at the conjugate locations. However, there were significant differences in the E s , particularly in the part of the E s trace that extends above the blanketing frequency. Considerations of the ambient conditions at the conjugate locations indicate that relatively small differences in parameters such as the tidal winds, electric fields, and background density gradients can significantly affect the structuring of the E s layer.

Geochronological evidence for and against a late heavy bombardment (LHB) spike in impact rates on the Moon and meteorite parent bodies is re-examined. In particular, we find that the sampling of impact melts on the Moon is strongly biased against older examples, possibly due to preferential surface deposition of such melts and/or blanketing and burial by basin ejecta (arguments that the bias might be due to pulverization of old impact melts at depth are incorrect). The apparent absence of melts older than 4 Ga thus provides much weaker evidence for a pre-nectarian lull in bombardment (which would define a post-nectarian cataclysm) than has been argued, although their absence compared with other rocks from depth may remain a weak constraint. Differences in rock-age histograms between meteorite parent bodies and the Moon may imply that different sampling biases exist for bodies in the asteroid belt; otherwise, the more straightforward interpretation is that the bombardment that affected the asteroids was more long-lasting than the lunar LHB. Since the strongest constraint on the dynamics of source populations for the LHB remains the very rapid decline in rate of basin formation from 3.90 to 3.85 Ga, we must re-establish that the associations of dated samples with particular basins are robust. Further studies of processes that can bias sampling are warranted, in particular more quantitative modeling of regolith and megaregolith evolution. In summary, we find that constraints either for or against the lunar cataclysm as a spike in the bombardment rate that commenced shortly before the formation of Nectaris are very weak. There may or may not have been a lull in bombardment before 3.9 Ga. Only the rapid decline in bombardment rate after Imbrium is fairly secure and can be adopted as a constraint to be matched by various dynamical scenarios for the impact history of the Moon.

The treatment of zirconium oxidation kinetics in severe accident (SA) codes has been the subject of many discussions and controversies in recent years. The main problem was the existence of several correlations which could lead to large differences in the calculated results. It appeared clearly that there was a need to converge towards a common understanding of the physical processes that must be modeled (oxygen diffusion, blanketing effect, etc.) and an agreed database among code developers and users. It would help reducing an important source of uncertainties in SA calculations. The kinetic correlation database, obtained as a result of examination of complementary experimental data in Parts I and II, is applied here to analyze a few high-temperature separate-effects tests and bundle experiments where Zry oxidation reaction played a dominant role. The ICARE/CATHARE computer code developed by IRSN is used to check the validity of the high-temperature correlations derived in Parts I and II. The physical modeling provided by the code includes detailed account of specific features of chemical interactions between fuel rod cladding and steam. In particular, high reaction rates at T > 2000 K are moderated by two effects, examined in Part I: steam blanketing during thin oxide layers growth and transition to oxidation of α-Zr(O) phase after total consumption of primary β-Zr in cladding metallic part. When applied to separate-effects tests, the evaluated parabolic correlations have shown their applicability to different types of temperature transients taking into account Zry oxidation specifics in rod geometry. The bundle integral experiments QUENCH-06 and PHEBUS B9+ did not lead to extremely large temperature excursions. Calculated temperatures, hydrogen production and oxide thickness, as well as parameters of melt relocation were found to agree well with experimentally measured values. As a result of this study, we believe that the new best-fitted correlations, obtained in agreement with available experimental data, can be used in further studies and can improve predictive power of the codes. The continuation of the current work will be the application of ICARE/CATHARE code with best-fitted Zry oxidation correlations to NPP accident scenarios.

Significant influence of diurnal and interdiurnal variations of irregular movements at heights of the lower thermosphere on the frequency parameters of ionospheric sporadic E-layer, characterizing its intensity, was fount out. Common periodicities with time scales of planetary waves, having significant coherence, were revealed in variations of mesocale turbulence intensity and critical frequency foEs, blanketing frequency fbEs.

To assess the uncertainties in primordial helium abundance determination by nebular codes, we calculate a grid of OB stellar atmospheres at low metallicities, including both non-local thermodynamic equilibrium (NLTE) and metal line blanketing effects. The more sophisticated stellar atmosphere models we use can differ from LTE models by as much as 40% in the ratio of He to H-ionizing photons.

We present a finite-element model for the prediction of the subsidence history and thermal evolution of extensional basins. The model takes into account the inhomogeneity of the lithosphere, and allows the space formed by lithospheric extension to be filled with sediments or water or both. Local isostatic compensation is assumed. The stability and accuracy of the algorithm are investigated. Time increments of 0.05–0.1 Ma are most appropriate for triangular elements of size 13 km 2 . For an initially old continental lithosphere (thickness: 130 km), thermal equilibrium is reached in approximately 100 Ma for a basin of initial width 100 km with a maximum β-factor of 2.0. The duration of extension for a given β-factor affects the heat flow and subsidence. For extension periods of 10 and 20 Ma, faster extension results in less subsidence and more prolonged high heat flow after the cessation of extension. If the basin is filled with sediments (as opposed to water), thermal blanketing effects are significant. The algorithm can be used to complement our understanding of the effects of thermal blanketing, lateral heat conduction, and sediment loading on the subsidence and thermal evolution of extensional basins.

A pall of aerosols and trace gases frequently occurs over southern Africa to a depth of ∼500 hPa, blanketing vast areas, particularly in the austral winter and spring. Large-scale offshore transport of these aerosols and trace gases in extremely large plumes from interior continental areas of the subcontinent to the Indian and Atlantic Oceans is a common occurrence. The nature of the transport plumes, their climatology, chemical composition and morphology are discussed. In the vertically integrated, surface-to-500 hPa layer, poleward of about 15° S, transport into the Indian Ocean is shown to be about 60% greater into the Indian Ocean than into the Atlantic Ocean. Recirculation of atmospheric constituents is considered and estimates of aerosol mass fluxes over central southern Africa are presented. Of the total of about 50 Mt yr -1 of aerosols being transported at the central meridian, 44% is shown to be recirculated material. The rest exits the subcontinent directly without recirculation. Preferred plume corridors of exit and entry are postulated for different localities on the east and west coasts. Two case studies of east- and west-coast plumes apparently flowing uniformly out of southern Africa are examined. The illusion of uniformity in plume structure is shown to be misleading. Both plumes are shown to be above and separated from the marine boundary layer. Each is over 1500 km in width and 3–5 km deep. Likewise, both are capped by absolutely stable layers at ∼500 hPa and exhibit a complex structure of both outflowing aerosols and trace gases and inflowing, recycled and recirculated material. Indications of the composition of the recirculated material are given and implications of the plume transports are considered.

A RH-560 rocket instrumented with a Langmuir Probe and two pairs of double probes was launched from SHAR (dip 14 ° N) at 2130 hr LT (1ST) on 4 October 1988 during spread-F conditions. As a part of this campaign VHF scintillations at 136.1 MHz were also recorded, using the beacon onboard the geostationary satellite ETS-II (130 ° E). A new digital ionosonde (KEL) installed at SHAR during the first week of September 1988 provided the basic ionospheric information. Ionosonde and scintillation data during this campaign (15 September–4October), along with the Langmuir probe data, are described. The occurrence of scintillations and spread-F during the campaign period was very high, with maximum hourly percentage occurrences of about 80 and 70%, respectively. Generally the onset of spread-F occurred slightly before 1900 hr LT when scintillations in the satellite signal also start appearing. This is followed soon by the range spreading on the ionosonde trace. On days with spread-F the minimum virtual height of the F-layer, h′F, rose to about 400 km in the post-sunset period while on days without spread-F it rose to only about 300–320 km. The electric field reversal, as inferred from the h′F variations, occurred around 1930 hr LT on spread-F days and around 1900 hr LT on days without spread-F. The ionograms, taken at 5 min interval on several nights, were used to determine the vertical drift velocities and these exceeded 50 m/s on spread-F days in the post-sunset period. At the time of the rocket launch, a strong blanketing type of sporadic-E with several multiple reflections appeared around 105 km. The electron density profile obtained from the Langmuir probe data also showed an extremely sharp layer at 105 km and another prominent layer at 130 km, both during the ascent and the descent. The electron density irregularities associated with spread-F were seen in different altitude regions, the most prominent being from 210 to 250 km and from 300 to 320 km. The power spectra of the electron density fluctuations have been obtained both from the in situ probe data and the scintillation data.

By dividing the total energy radiated from the photosphere of a supernovae into a large number of photon packets and then following them in their outward journey, we overcome the problem of line blanketing encountered in usual simulation work. With supporting programs providing the density and abundance distributions in the envelope, our software package can be effectively used for a study of the early spectrum of supernovae. We give an application to the observed spectrum of SN 1993J on 1993-04-13.

Among the well-imaged small satellites and asteroids, Deimos displays a unique surface: very smooth with global-scale albedo features. We have examined the disk-resolved photometry of Deimos using Viking Orbiter images for clues to its distinctive appearance. Hapke parameters were fit to characterize the phase behavior and to compute normal reflectance. The opposition surge amplitude (B0) is smaller for Deimos than for Phobos. Outside the range of the opposition effect the two martian satellites have similarly shaped phase curves, but Deimos is about 20–30% brighter than Phobos from 10°–80° phase. The calculated mean normal reflectance of Deimos (λeff= 0.54 μm) is 0.068 ± 0.007. The brighter and darker areas on Deimos exhibit constant contrast between 0.6° and 81° phase; this characteristic allows a calculation of the range of normal reflectances over most of its surface, nearly all of which values are between 0.06 and 0.09. The trailing side of Deimos has a larger relative distribution of the brighter material, and is on average about 10% brighter than the leading side. The mean normal reflectance cannot be formally distinguished from that of Phobos (0.071 ± 0.012; Simonelli, D. P., M. Wisz, A. Switala, D. Adinolfi, J. Veverka, P. C. Thomas, and P. Helfenstein 1996. Submitted toIcarus). Although the statistical distribution of normal reflectances on the two satellites is similar, the geography of the albedo variations is very different. Deimos has gradational changes in albedo downslope from ridge crests, primarily manifested in long albedo “streamers.” On Phobos there is a more patchy global distribution of albedos, apparently related to ejecta from the large crater Stickney. Because of the similarity of mean density, spectral properties, mean normal reflectance, the range of normal reflectance, and phase function outside the opposition effect, Deimos appears to be made of materials with compositions very similar to those on Phobos, although the apparent wider distribution of ejecta on Deimos has been cited as indicating a greater role for strength scaling in cratering on Deimos (Lee, S. W., P. Thomas, and J. Veverka 1986.Icarus68, 77–86). Simple modeling of the formation of the albedo patterns by gardening, creep, and “weathering” of bright material from crater rims suggests that impact gardening contributes very little to the motion of the material downslope, and that vertical mixing and/or “weathering” must be important in addition to an unspecified creep process. The distinction of Deimos is primarily in the smooth surface that allows a particularly large scale of downslope movement of regolith on very gentle slopes. This smoothness is most easily explained by the effects from impact formation of a 10-km concavity at high southern latitudes in the latter half of Deimos' surface history. This impact scar is relatively much larger than is the crater Stickney on Phobos. The effects of this large impact probably include blanketing by an average of nearly 200 m of ejecta, but also may include seismic erasing of craters similar to that proposed for Ida by Asphauget al. (Asphaug, E., J. M. Moore, D. Morrison, W. Benz, and R. A. Sullivan 1996.Icarus120, 158–184).

This paper presents simultaneous observations made near the magnetic equator during counter electrojet events using a coherent VHF backscattcr radar, magnetometer and digital ionosonde to understand the physical processes that generate the counter electrojet conditions. The VHF backscatter radar gives the height structure of the drift velocity or the ionization irregularities, the equatorial electrojet current variations are obtained from the magnetometer and the digital ionosonde provides the presence of blanketing E-layers at the F-region heights which give rise to the backscatter signals. These observations have provided direct experimental evidence for the theoretically predicted distortions in the height structure of the polarization electric field in the equatorial electrojet due to the local effects of shearing zonal neutral winds.

The Bribie Island HF radar array (27°S, 153° E) can be set up to make angle of arrival and Doppler shift measurements throughout the range of spread-Es, layers. Results of this experiment show that the range spread seen on ionograms is not due to multiple reflection with varying obliquity, but rather a genuine height spread exists. Where velocity measurements can be reliably made, reflector velocity appears to be a slowly varying function of height. Spread-Es, can be blanketing or non-blanketing, sequential or non-sequential and at first impression it seems that the chief difference between spread-Es, and normal Es, is a small scale, partially transparent structure in lower regions that allows higher regions to be observed. It is suggested that on occasion spread-Es, irregularities are further modulated by the passage of gravity waves.

This study has used ionospheric and magnetic observational data obtained at a meridional chain of stations during the high latitude geophysical experiment ‘Taimir-82’ in the winter of 1982–1983. Mean statistical latitude-time distributions of the occurrence probability of various types of E s , their blanketing frequency and of the amplitude of geomagnetic field H -variations have been constructed. Based on these distributions and taking the E s properties into account, an analysis is made of the mutual correspondence of large-scale structures of the auroral ionosphere and ionospheric currents. Ionospheric currents flow mainly in the region of high E -layer ionization. With increasing magnetic activity, the zone of currents and the zone of ionization expand simultaneously toward lower latitudes. The evening eastward electrojet and the morning westward electrojet are localized inside the zone of diffuse auroral precipitation which is responsible for the formation of E s type r . The equatorial part of the midnight westward electrojet is also located in the zone of diffuse precipitation which coincides also with the region of maximum ionization of the E -layer. The polar part of this electrojet, which extends far into the dusk sector, is located in the zone of discrete auroral precipitation ( a type E s ). Whereas there exists in the meridional cross-section quite a definite relationship between the Harang discontinuity and ionospheric parameters, such a relationship is not manifested in the zonal cross-section of the Harang discontinuity.

A model using photochemistry and transport due to electric fields and gravity wave winds has been used to explain the formation of ionisation layers observed over an equatorial station Thumba (dip 0°47′S) with rocket-borne Langmuir probes during two daytime counter-electrojet periods. These layers were seen as blanketing E s -layers with an ionosonde at Thumba. Convergence of the metallic ions due to three-dimensional gravity wave winds and a westward electric field appears to be mainly responsible for the observed ionisation layer over the equator.

Intensity scintillations of 40 MHz, 140 MHz and 360 MHz radio beacons on board the geostationary satellite ATS-6, (at 34°E longitude), recorded at Ootacamund (magnetic dip latitude 3°N) during the ATS-6 phase II (1975–1976) are described. The scintillation index S4, which is the normalised RMS value of the intensity fluctuations, is found to be very large at 2100-0200 h associated with equatorial spread-F, and in the forenoon and afternoon hours associated with a blanketing type of sporadic E-layer. At 40 MHz there seems to be a weak scintillation (S4 The frequency exponent, n, (with S 4 ∝ ƒ −1 , whereƒ is the signal frequency), was found to decrease monotonically with increasing intensity of scintillations, approaching a value of zero for saturated scintillations. The relationship between the frequency exponent and the scintillation index was found to be independent of the time of the day or the season, in spite of different kinds of irregularities being involved in the scintillation processes.

In this paper we discuss the influence of mesoscale turbulence in lower thermosphere, measured by radiometeor method, on the characteristics of Es layers, as observed by ionospheric sounding. Mesoscale turbulence has a considerable influence on the average daily values and inter-daily variations of the blanketing frequency fbEs, critical frequency foEs and semi-transparency δfbEs of the Es layer. More intense, probably semi-transparent, Es layers occur during periods of less developed mesoscale turbulence, while weak blanketing Es layers occur when values of turbulence in the lower thermosphere are increased, both in daytime and night-time, for all seasons.

The unique combination of measurements of atmospheric electricity (AE) parameters and ionosphere monitoring by vertical sounding station at the same place (Voeikovo, near St.Petersburg) allowed to analyze mutual influence of two environments divided from each other by atmosphere (Earth-ionosphere interval). It was done for individual events. Consequences of Chernobyl atomic reactor catastrophe appeared near St.Petersburg some days later in AE parameters (negative and positive bearers conductivities, small ion concentration, mobility and electric field intensity changes). Comparison of AE parameters with ionospheric data reveals strong correlation, particularly with E s layer parameters (f b E s — blanketing frequency, h'E s — E s layer height, f min — minimum frequency).

The paper discusses Martian altitudes measured by radar during the oppositions of 1971 and 1973 using the 64-m antenna at Goldstone, Calif. The resultant topographic profiles substantiate a zonal classification of the volanic flows blanketing the south flanks of Arsia Mons, and they confirm the existence of a secondary, parasitic shield, attached from the SSW to the main Arsia shield. The secondary shield is about 400 km in diameter at its base and at least 4 km high at its center. The distribution and orientation of the lunar mare - like ridges in Sinai Planum appear to be independent of the regional gradients. Segments of the chaotic terrain at the eastern terminus of Valles Marineris are located down to 6 km below the level of the surrounding plains.

It is shown that the day-time scintillations of VHF radio waves at the equatorial station, Huancayo, are very small, of the order of 1–2 dB peak, during the equatorial electrojet condition. If the event of complete or partial counter-electrojet occurring either on quiet or during disturbed conditions is followed by the occurrence of blanketing type of Es , then only strong day-time scintillations are observed. Counter-electrojet events followed by only the absence of Es are not found to produce any additional scintillations. Thus the day-time VHF scintillations near the magnetic equatorial regions are due to the sharp plasma gradient associated with blanketing type of sporadic E region.

Measurements of the total mass transfer rate, and of the distributions of mass transfer and pressure, have been made in an instrumented electrochemical pump cell at zero rotation speed, which is equivalent to a capillary gap cell. In the turbulent regime the overall Sherwood number dependence is given by as suggested by Kreith, where Re is the channel Reynolds number, h is the interelectrode gap and r o and r i the outer and inner radii of the disc electrode. Similar relationships are obtained for local Sherwood numbers, but the exponents vary from 0.29 to 0.99. Towards exit the flow relaminarizes, decreasing the exponents, so that the distribution of mass transport coefficient shows a peak, the position and height of height of which depend on hydrodynamic conditions. The measured pressure distributions agree reasonably well with theoretical predictions: it is shown that the flow may experience an adverse or favourable pressure gradient depending on conditions, which may explain gas evolution and gas blanketing effects.

The paper presents E -region drift results at Ibadan using the data for 1964–1965 and 1975. By combining the daytime data for the E -layer with the night-time data for blanketing sporadic- E , it has been possible to examine the tidal components. A brief comparison is also made of E - and F -region velocities observed during the same period in March 1975. The results obtained at Ibadan are then discussed in relation to both the equatorial electroject and other velocity measurements at equatorial and midlatitude stations.

Computerized cratering-obliteration models are developed for use in interpreting planetary surface histories in terms of the diameter-frequency relations for craters classified by morphology. An application is made to a portion of the lunar uplands, revealing several episodes of blanketing, presumably due to the formation of some of the major basins. Application to Martian craters leads to the following picture of Martian cratering and obliteration history. During a probable period of intense early bombardment, craters were degraded by two processes: a depositional-type process connected with the declining cratering rate, and a process tending to flatten the largest craters (e.g., isostatic adjustment). During late stages of the early bombardment, or subsequent to it, there occurred a major relative episode of obliteration (probably atmosphere related), but it ceased concurrently with the massive (presumably volcanic) resurfacing of the cratered plains. Subsequent resurfacing episodes have occurred in the smooth plain terrains, but obliteration processes have been virtually absent in the low-latitude cratered terrains. Recent global Martian cratering interpretations of Hartmann and Soderblom are compared. Absolute cratering chronologies are only so good as knowledge of the absolute cratering flux on Mars. The crater data of Arvidson, Mutch, and Jones do not confirm the basis, whereby Soderblom requires the dominant Martian crater obliteration process to be coincident in time with the early bombardment. If the asteroidal-cometary impact flux on Mars has averaged five times the lunar flux during post-lunar-mare epochs, then the obliterative episode lasted about half a billion years and occurred about 1.5 × 10 9 yr ago.

This paper presents the results of fast transient boiling tests using rapidly heated platinum wires immersed in water. Very fast heating resulted in spontaneous nucleation on the wire surface and exceptionally high rates of heat transfer. Vapour blanketing of the wire did not occur under the investigated transient conditions for periods lasting several tens of microseconds and exceeding by two orders of magnitude the associated bubble growth time.

A three-dimensional melting and solidification problem is solved in which a second layer of solid is added at variable rates. The physical properties of the system are position and temperature dependent, and there is heat generation within the system. Each phase has a grid scheme where every grid point travels differently with the effect of phase change or addition. The resulting differential equations are solved through an explicit method where the derivatives are approximated in a non-Cartesian coordinate system. The effect of blanketing by a second solid layer having different thermal conductivities is investigated. Numerical results are generated for a specific melting and solidification problem.

The parallel analysis of the H -component ground-based magnetometer data, registered on quiet days, and the sporadic E vertical ionospheric sounding data for the period 1978–1982, is carried out. The changes in the sporadic E behaviour as well as the Sq current system variability, are both assumed to originate from the perturbation of the existing tidal wind pattern in the dynamo region. A coincidence was found between the phase and amplitude day-to-day changes of the Sq ( H ) variation, and changes in the diurnal distribution of the sporadic E virtual height and blanketing frequency. It was also found that the presence of the extremely intense sporadic E layers ( f b E s , from 10 to 15 MHz), coincides with the appearance of the small size H -component disturbances ( δH about a few nT). These disturbances might be induced by the current flow in the layer. The data used in this analysis were recorded at the geomagnetic and ionospheric observatories, at Grocka (44°38' N, 20°46' E, I = 61°).

A study of Sporadic E-layer phenomena over Cachoeira Paulista (22.6°S, 45°W), located in the vicinity of the Brazilian geomagnetic anomaly centre is presented. Monthly average diurnal behaviour of the Es occurrence presented for summer, winter and equinoctial months shows that the simidiurnal tidal component dominates in some months while others show a single diurnal maximum. The night-to-day ratio in the occurrence rate of Es appears to be greatly enhanced over our station in relation to middle latitude stations. This and the frequent night occurrence of high blanketing frequencies (fbEs) are interpreted as evidence of a regular night-time ionization source in the geomagnetic anomaly. From considerations based upon the theory of redistribution of ionization by neutral winds a lower limit in the ambient ionization needed to produce the observed fbEs is determined and a corresponding precipitating electron flux is estimated.

Several types of sporadic E are observed using the 5.80 and 3.84 MHz Bribie Island pencil beam high frequency radar. Blanketing Es, takes the form of large flat sheets with ripples in them. Non-blanketing Es is observed to be small clouds that drift across the field of view (40°). There is continuous gradation of sporadic E structure between these extremes. There are at least four different physical means by which sporadic E clouds may apparently move. It is concluded that non-blanketing sporadic E consists of separate clouds which follow the movement of the constructive interference between internal gravity waves rather than being blown by the background wind.

Generation and properties of the ionospheric gyroechoes in the presence of a thin sporadic E-layer are theoretically investigated. The intensification of the echo and the decrease of its virtual height occurring at the onset of an Es-layer are explained in terms of mode coupling. A mechanism is found capable of producing gyroechoes when an otherwise totally blanketing flat-type Es-layer is present.

In this review, the recent additional knowledge about the physical processes in two broad areas of the equatorial electrojet are emphasized 1. (i) the local interactions of the neutral winds with the electrojet plasma which result in diverse but physically inter-related effects on the altitude structure of electric fields and currents, ionization convergences and the formation of blanketing E s layers and F -region ionization dynamics 2. (ii) the very sensitive responses of the equatorial electrojet to the complex auroral ionosphere-magnetosphere interaction processes. On both the aspects, a synthesis of the observational results and theoretical models and ideas is attempted. The factors which contribute to apparent contradictions in the morphological results on the equatorial ‘counter-electrojet’ are discussed along with the possible physical processes causing the ‘counter-electrojet’.

The very large overabundances of rare earth elements found in Ap stars (>103 − 105) usually arise in cases where the observable second spectra does not represent the dominant ionization stage. The extreme overabundance factors are highly correlated with effective temperature in a way that is regarded with suspicion. In cool Ap stars, where one does observe the dominant ionization state, more modest overabundances (∼ 102) occur. The typical cool Ap and Am stars must have comparable abundances of the lighter lanthanides. It is argued that the sharp rise in typical Ap star abundances that parallels the predicted degree of ionization may be due to a breakdown in the Saha Equation or possibly to the existence of a cool upper photosphere caused by line blanketing in the hotter Ap stars. Attention is called to the observational fact that the cool Am stars have deeper line cores than chemically normal main sequence stars or cool Ap stars. These line cores resemble those of more luminous stars, a fact which comports well with some (though not all) low dispersion similarities between Am stars and evolved objects. While various studies (e.g. by Conti and Van't Veer Menneret) have shown that reduced gravity models cannot remove the abundance anomalies in the Am stars, some modification of the traditional models and/or line formation theory is indicated in order to explain the observations.

The methods of constructing a model atmosphere and computing its theoretical spectrum are reviewed, attention being directed to the restrictions which are imposed and to the simplifications which are made in representing the interactions between radiation and matter. One important restriction is that it is assumed that Boltzmann's, Saha's and Kirchhoff's laws are valid throughout the atmosphere. However, observation indicates that these relationships are certainly not valid in those parts of the atmosphere where many of the strong lines which are used for classifying O B stars are formed. More accurate theories of line formation are required to predict the strengths and shapes of lines from the lowest levels and from metastable levels or levels connected to the metastable levels by strong transitions in the spectra of the light elements. It is pointed out that the constraints radiative equilibrium and hydrostatic equilibrium do not define sufficiently accurately the parts of the atmosphere where many empirically selected classification lines are formed. Here the motion of the gases seems to play a significant role in determining the shape and strength of the absorption lines. Some examples are given of the differences between the line profiles predicted from blanketed and unblanketed early-type models and it is shown that these differences would not be readily detected from the usually observed spectrum in the range 3500 A to 5000 a. Although line blanketing lowers the effective temperatures of O B models by 2500° to 3000° from the values estimated by means of unblanketed models, the unblanketed models are adequate for interpreting the spectrum between 3500 A and 5000 A and deducing abundances from weak lines.