Data selection using support vector regression

Geophysical data sets are growing at an ever-increasing rate, requiring computationally efficient data selection(thinning)methods to preserve essential information. Satellites, such as Wind Sat, provide large data sets for assessing the accuracy and computational efficiency of data selection techniques. A new data thinning technique, based on support vector regression(SVR), is developed and tested. To manage large on-line satellite data streams, observations from Wind Sat are formed into subsets by Voronoi tessellation and then each is thinned by SVR(TSVR). Three experiments are performed. The first confirms the viability of TSVR for a relatively small sample, comparing it to several commonly used data thinning methods(random selection, averaging and Barnes filtering), producing a 10% thinning rate(90% data reduction), low mean absolute errors(MAE) and large correlations with the original data. A second experiment, using a larger dataset, shows TSVR retrievals with MAE < 1 m s-1and correlations 0.98. TSVR was an order of magnitude faster than the commonly used thinning methods. A third experiment applies a two-stage pipeline to TSVR, to accommodate online data. The pipeline subsets reconstruct the wind field with the same accuracy as the second experiment, is an order of magnitude faster than the nonpipeline TSVR. Therefore, pipeline TSVR is two orders of magnitude faster than commonly used thinning methods that ingest the entire data set. This study demonstrates that TSVR pipeline thinning is an accurate and computationally efficient alternative to commonly used data selection techniques.     

Assessing the effect of domain size over the Caribbean region using the PRECIS regional climate model

This study investigates the sensitivity of the one-way nested PRECIS regional climate model (RCM) to domain size for the Caribbean region. Simulated regional rainfall patterns from experiments using three domains with horizontal resolution of 50 km are compared with ERA reanalysis and observed datasets to determine if there is an optimal RCM configuration with respect to domain size and the ability to reproduce important observed climate features in the Caribbean. Results are presented for the early wet season (May–July) and late wet season (August–October). There is a relative insensitivity to domain size for simulating some important features of the regional circulation and key rainfall characteristics e.g. the Caribbean low level jet and the mid summer drought (MSD). The downscaled precipitation has a systematically negative precipitation bias, even when the domain was extended to the African coast to better represent circulation associated with easterly waves and tropical cyclones. The implications for optimizing modelling efforts within resource-limited regions like the Caribbean are discussed especially in the context of the region’s participation in global initiatives such as CORDEX.     

On the use of X-ray and γ-ray telescopes for identifying the origin of electrons and positrons observed by ATIC, Fermi, and PAMELA

X-ray and γ-ray observations can help understand the origin of the electron and positron signals reported by ATIC, PAMELA, PPB-BETS, and Fermi. It remains unclear whether the observed high-energy electrons and positrons are produced by relic particles, or by some astrophysical sources. To distinguish between the two possibilities, one can compare the electron population in the local neighborhood with that in the dwarf spheroidal galaxies, which are not expected to host as many pulsars and other astrophysical sources. This can be accomplished using X-ray and γ-ray observations of dwarf spheroidal galaxies. Assuming the signal detected by Fermi and ATIC comes from dark matter and using the inferred dark matter profile of the Draco dwarf spheroidal galaxy as an example, we calculate the photon spectrum produced by electrons via inverse Compton scattering. Since little is known about the magnetic fields in dwarf spheroidal galaxies, we consider the propagation of charged particles with and without diffusion. Extending the analysis of Fermi collaboration for Draco, we find that for a halo mass ∼10⁹ M_⊙, even in the absence of diffusion, the γ-ray signal would be above the upper limits. This conclusion is subject to uncertainties associated with the halo mass. If dwarf spheroidal galaxies host local magnetic fields, the diffusion of the electrons can result in a signal detectable by future X-ray telescopes.     

EAS Tycho Brahe prize lecture 2011

The Hipparcos satellite was launched in 1989. It was the first, and remains to date the only, attempt at performing large-scale astrometric measurements from space. Hipparcos marked a fundamentally new approach to the field of astrometry, revolutionising our knowledge of the positions, distances, and space motions of the stars in the solar neighbourhood. In this retrospective, I look back at the processes which led to the mission??s acceptance, provide a short summary of the underlying measurement principles and the experiment??s scientific achievements, and a conclude with a brief summary of its principal legacy??the Gaia mission.     

A composite Fe,Ni‐FeS and enstatite‐forsterite‐diopside‐glass vitrophyre clast in the Larkman Nunatak 04316 aubrite: Origin by pyroclastic volcanism

Abstract– We studied the mineralogy, petrology, and bulk, trace element, oxygen, and noble gas isotopic compositions of a composite clast approximately 20 mm in diameter discovered in the Larkman Nunatak (LAR) 04316 aubrite regolith breccia. The clast consists of two lithologies: One is a quench‐textured intergrowth of troilite with spottily zoned metallic Fe,Ni which forms a dendritic or cellular structure. The approximately 30 μm spacings between the Fe,Ni arms yield an estimated cooling rate of this lithology of approximately 25–30 °C s^?1. The other is a quench‐textured enstatite‐forsterite‐diopside‐glass vitrophyre lithology. The composition of the clast suggests that it formed at an exceptionally high degree of partial melting, perhaps approaching complete melting, and that the melts from which the composite clast crystallized were quenched from a temperature of approximately 1380–1400 °C at a rate of approximately 25–30 °C s^?1. The association of the two lithologies in a composite clast allows, for the first time, an estimation of the cooling rate of a silicate vitrophyre in an aubrite of approximately 25–30 °C s^?1. While we cannot completely rule out an impact origin of the clast, we present what we consider is very strong evidence that this composite clast is one of the elusive pyroclasts produced during pyroclastic volcanism on the aubrite parent body ( Wilson and Keil 1991 ). We further suggest that this clast was not ejected into space but retained on the aubrite parent body by virtue of the relatively large size of the clast of approximately 20 mm. Our modeling, taking into account the size of the clast, suggests that the aubrite parent body must have been between approximately 40 and 100 km in diameter, and that the melt from which the clast crystallized must have contained an estimated maximum range of allowed volatile mass fractions between approximately 500 and approximately 4500 ppm.     

Meteorites at Meridiani Planum provide evidence for significant amounts of surface and near‐surface water on early Mars

Abstract– Six large iron meteorites have been discovered in the Meridiani Planum region of Mars by the Mars Exploration Rover Opportunity in a nearly 25 km‐long traverse. Herein, we review and synthesize the available data to propose that the discovery and characteristics of the six meteorites could be explained as the result of their impact into a soft and wet surface, sometime during the Noachian or the Hesperian, subsequently to be exposed at the Martian surface through differential erosion. As recorded by its sediments and chemical deposits, Meridiani has been interpreted to have undergone a watery past, including a shallow sea, a playa, an environment of fluctuating ground water, and/or an icy landscape. Meteorites could have been encased upon impact and/or subsequently buried, and kept underground for a long time, shielded from the atmosphere. The meteorites apparently underwent significant chemical weathering due to aqueous alteration, as indicated by cavernous features that suggest differential acidic corrosion removing less resistant material and softer inclusions. During the Amazonian, the almost complete disappearance of surface water and desiccation of the landscape, followed by induration of the sediments and subsequent differential erosion and degradation of Meridiani sediments, including at least 10–80 m of deflation in the last 3–3.5 Gy, would have exposed the buried meteorites. We conclude that the iron meteorites support the hypothesis that Mars once had a denser atmosphere and considerable amounts of water and/or water ice at and/or near the surface.     

Radiation hydrodynamical instabilities in cosmological and galactic ionization fronts

Ionization fronts, the sharp radiation fronts behind which H/He ionizing photons from massive stars and galaxies propagate through space, were ubiquitous in the universe from its earliest times. The cosmic dark ages ended with the formation of the first primeval stars and galaxies a few hundred Myr after the Big Bang. Numerical simulations suggest that stars in this era were very massive, 25–500 solar masses, with H(II) regions of up to 30,000 light-years in diameter. We present three-dimensional radiation hydrodynamical calculations that reveal that the I-fronts of the first stars and galaxies were prone to violent instabilities, enhancing the escape of UV photons into the early intergalactic medium (IGM) and forming clumpy media in which supernovae later exploded. The enrichment of such clumps with metals by the first supernovae may have led to the prompt formation of a second generation of low-mass stars, profoundly transforming the nature of the first protogalaxies. Cosmological radiation hydrodynamics is unique because ionizing photons coupled strongly to both gas flows and primordial chemistry at early epochs, introducing a hierarchy of disparate characteristic timescales whose relative magnitudes can vary greatly throughout a given calculation. We describe the adaptive multistep integration scheme we have developed for the self-consistent transport of both cosmological and galactic ionization fronts.     

The Maria asteroid family: Genetic relationships and a plausible source of mesosiderites near the 3:1 Kirkwood Gap

We present a mineralogical assessment of 12 Maria family asteroids, using near-infrared spectral data obtained over the years 2000-2009 combined with visible spectral data (when available) to cover the spectral interval of 0.4-2.5 μm. Our analysis indicates the Maria asteroid family, which is located adjacent to the chaotic region of the 3:1 Kirkwood Gap, appears to be a true genetic family composed of assemblages analogous to mesosiderite-type meteorites. Dynamical models by Farinella et al. (Farinella, P., Gunczi, R., Froeschlé, Ch., Froeschlé, C., [1993]. Icarus 101, 174-187) predict this region should supply meteoroids into Earth-crossing orbits. Thus, the Maria family is a plausible source of some or all of the mesosiderites in our meteorite collections. These individual asteroids were most likely once part of a larger parent object that was broken apart and dispersed. One of the Maria dynamical family members investigated, ((695) Bella), was found to be unrelated to the genetic Maria family members. The parameters of (695) Bella indicate an H-chondrite assemblage, and that Bella may be a sister or daughter of Asteroid (6) Hebe.     

Nanometer‐scale anatomy of entire Stardust tracks

Abstract– We have developed new sample preparation and analytical techniques tailored for entire aerogel tracks of Wild 2 sample analyses both on “carrot” and “bulbous” tracks. We have successfully ultramicrotomed an entire track along its axis while preserving its original shape. This innovation allowed us to examine the distribution of fragments along the entire track from the entrance hole all the way to the terminal particle. The crystalline silicates we measured have Mg‐rich compositions and O isotopic compositions in the range of meteoritic materials, implying that they originated in the inner solar system. The terminal particle of the carrot track is a ¹⁶O‐rich forsteritic grain that may have formed in a similar environment as Ca‐, Al‐rich inclusions and amoeboid olivine aggregates in primitive carbonaceous chondrites. The track also contains submicron‐sized diamond grains likely formed in the solar system. Complex aromatic hydrocarbons distributed along aerogel tracks and in terminal particles. These organics are likely cometary but affected by shock heating.