Solution of Earth orientation parameters in the frame of new Earth orientation Catalogue

The new Earth Orientation Catalogue was recently derived, based mostly on the ARIHIP and Tycho-2 Catalogues that were combined with ground-based optical observations of latitude and Universal Time variations in the 20th century. The solution of Earth orientation parameters, based on this new star catalogue and the new IAU model of precession-nutation, is presented

The Enigma of Lunar Dust Transport

We will review the highly contrasting points of view regarding the ability of fine dust grains to become transported in the near-space lunar environment. While Surveyor and Apollo camera images suggest the presence of a horizon glow that has been provocatively interpreted as levitated and/or lofted dust, there is contrasting geological evidence to indicate that surface regolith has not been moved in a substantial way. While electric forces have been suggested as a driver for grain dynamics, recent detailed modeling of near-surface non-monotonic potentials would suggest grains could not get to large heights. While lofting models require submicron grains to hold/contain 100's of elementary charges, it can be shown analytical1y that a grain residing on a flat surface would have an extremely low probability of having even a single electron on its surface, Can these diametrically opposing viewpoints be reconciled? We will review the pros and cons on both sides. and suggest that the UVS and LDEX instrument on LADEE will provide key new insights on dust transport at the Moon

Review—Recent Progress in Electrocatalysts for Oxygen Reduction Suitable for Alkaline Anion Exchange Membrane Fuel Cells

Alkaline fuel cell technology has been reinvigorated since the recent rapid development and deployment of anion exchange membranes. Without the "acid-stability" requirement in low pH environments such as that of proton exchange membrane fuel cells, a much wider range of materials including noble metals, non-noble transition metals, and even metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media have been developed due to both thermodynamic and kinetic reasons. As compared to the rapidly increasing number of reports on the development of novel catalyst materials, the understanding of the reaction mechanisms of the various ORR electrocatalysts is quite insufficient, and the application and investigation in real alkaline anion exchange membrane fuel cells (AAEMFCs) is even scarcer. By reviewing the compositions, preparation methods, physiochemical properties and ORR performance of different categories of cathodic electrocatalysts that have emerged in the past few years, some common and intrinsic properties and factors that account for the superior activity of these materials may be extracted and summarized, which may further help to identify the reasons for the kinetic facility of the ORR in alkaline media. Some practical issues of utilization of the promising novel replacement materials for the state-of-the-art Pt-based cathodic electrocatalysts in AAEMFCs are pointed out. In addition to the progress on the development of novel materials with outstanding ORR activity, many and varied compositions and morphologies in one, two and three dimensions, scalable preparation technologies, low cost, and other unique properties, some feedback on the performance and especially the problems of their use as cathodes in AAEMFCs is urgently needed. Such feedback should provide guidelines for the design and manufacture of next-generation electrocatalysts and accelerate the application of AAEMFCs

The Combined Solution C04 for Earth Orientation Parameters Consistent with International Terrestrial Reference Frame 2005

The Earth Orientation Center of the IERS, located at Paris Observatory, SYRTE, has the task to provide to the scientific community the international reference time series for the Earth Orientation Parameters (EOP), referred as ”IERS C04 ” (Combined 04), resulting from a combination of operational EOP series, each of them associated with a given geodetic technique. The procedure developed to derive the C04 solution was recently upgraded back to 1993. The main objective is to insurre its consistency with respect to the newly release ITRF 2008. Due to the separate determination of both terrestrial reference frames and EOP, there has been a slow degradation of the overall consistency since the least ITRF release in 2005, and discrepancies at the level of 50 micoarseconds for x pole coordinate exists between the current IERS C04 and the ITRF realization. We have taken this opportunity to upgrade the numerical combination procedure. Now there are better estimates of the errors of combined values. Individual EOP series have been reprocessed since 1993. Pole coordinates are now fully consistent with ITRF. The new C04 solution, referred as 08 C04, updated two times per week became the official C04 solution since february 2010

Could Lunar Polar Ice be a "Fountain" Source for the Dayside Water Veneer?

We discuss the possibility that the lunar polar regions are a source of a lunar 'rain' which provides a light coating (veneer) of water at mid-latitudes

Instantaneous ionospheric global conductance maps during an isolated substorm

International audienceData from the Polar Ionospheric X-ray Imager (PIXIE) and the Ultraviolet Imager (UVI) on board the Polar satellite have been used to provide instantaneous global conductance maps. In this study, we focus on an isolated substorm event occurring on 31 July 1997. From the PIXIE and the UVI measurements, the energy spectrum of the precipitating electrons can be derived. By using a model of the upper atmosphere, the resulting conductivity values are generated. We present global maps of how the 5 min time-averaged height-integrated Hall and Pedersen conductivities vary every 15 min during this isolated substorm. The method presented here enables us to study the time development of the conductivities, with a spatial resolution of ~ 700 km. During the substorm, a single region of enhanced Hall conductance is observed. The Hall conductance maximum remains situated between latitudes 64 and 70 corrected geomagnetic (CGM) degrees and moves eastward. The strongest conductances are observed in the pre-midnight sector at the start of the substorm expansion. Toward the end of the substorm expansion and into the recovery phase, we find the Hall conductance maximum in the dawn region. We also observe that the Hall to Pedersen conductance ratio for the regions of maximum Hall conductance is increasing throughout the event, indicating a hardening of the electron spectrum. By combining PIXIE and UVI measurements with an assumed energy distribution, we can cover the whole electron energy range responsible for the conductances. Electrons with energies contributing most to the Pedersen conductance are well covered by UVI while PIXIE captures the high energetic component of the precipitating electrons affecting the Hall conductance. Most statistical conductance models have derived conductivities from electron precipitation data below approximately 30 keV. Since the intensity of the shortest UVI-wavelengths (LBHS) decreases significantly at higher electron energies, the UVI electron energy range is more or less comparable with the energy ranges of the statistical models. By calculating the conductivities from combined PIXIE and UVI measurements to compare with the conductivities from using UVI data only, we observe significant differences in the Hall conductance. The greatest differences are observed in the early evening and the late morning sector. We therefore suggest that the existing statistical models underestimate the Hall conductance

Ionospheric conductances derived from satellite measurements of auroral UV and X-ray emissions, and ground-based electromagnetic data: a comparison

International audienceGlobal instantaneous conductance maps can be derived from remote sensing of UV and X-ray emissions by the UVI and PIXIE cameras on board the Polar satellite. Another technique called the 1-D method of characteristics provides mesoscale instantaneous conductance profiles from the MIRACLE ground-based network in Northern Scandinavia, using electric field measurements from the STARE coherent scatter radar and ground magnetometer data from the IMAGE network. The method based on UVI and PIXIE data gives conductance maps with a resolution of ~800km in space and ~4.5min in time, while the 1-D method of characteristics establishes conductances every 20s and with a spatial resolution of ~50km. In this study, we examine three periods with substorm activity in 1998 to investigate whether the two techniques converge when the results from the 1-D method of characteristics are averaged over the spatial and temporal resolution of the UVI/PIXIE data. In general, we find that the calculated conductance sets do not correlate. However, a fairly good agreement may be reached when the ionosphere is in a state that does not exhibit strong local turbulence. By defining a certain tolerance level of turbulence, we show that 14 of the 15 calculated conductance pairs during relatively uniform ionospheric conditions differ less than ±30%. The same is true for only 4 of the 9 data points derived when the ionosphere is in a highly turbulent state. A correlation coefficient between the two conductance sets of 0.27 is derived when all the measurements are included. By removing the data points from time periods when too much ionospheric turbulence occurs, the correlation coefficient raises to 0.57. Considering the two very different techniques used in this study to derive the conductances, with different assumptions, limitations and scale sizes, our results indicate that simple averaging of mesoscale results allows a continuous transition to large-scale results. Therefore, it is possible to use a combined approach to study ionospheric events with satellite optical and ground-based electrodynamic data of different spatial and temporal resolutions. We must be careful, though, when using these two techniques during disturbed conditions. The two methods will only give results that systematically converge when relatively uniform conditions exist

Anticipated Electrical Environment Within Permanently Shadowed Lunar Craters

Shadowed locations ncar the lunar poles arc almost certainly electrically complex regions. At these locations near the terminator, the local solar wind flows nearly tangential to the surface and interacts with large-scale topographic features such as mountains and deep large craters, In this work, we study the solar wind orographic effects from topographic obstructions along a rough lunar surface, On the leeward side of large obstructions, plasma voids are formed in the solar wind because of the absorption of plasma on the upstream surface of these obstacles, Solar wind plasma expands into such voids) producing an ambipolar potential that diverts ion flow into the void region. A surface potential is established on these leeward surfaces in order to balance the currents from the expansion-limited electron and ion populations, Wc find that there arc regions ncar the leeward wall of the craters and leeward mountain faces where solar wind ions cannot access the surface, leaving an electron-rich plasma previously identified as an "electron cloud." In this case, some new current is required to complete the closure for current balance at the surface, and we propose herein that lofted negatively charged dust is one possible (nonunique) compensating current source. Given models for both ambipolar and surface plasma processes, we consider the electrical environment around the large topographic features of the south pole (including Shoemaker crater and the highly varied terrain near Nobile crater), as derived from Goldstone radar data, We also apply our model to moving and stationary objects of differing compositions located on the surface and consider the impact of the deflected ion flow on possible hydrogen resources within the crater