ALBERT

Beschreibung: We observe two near-limb solar filament eruptions, one of 2000 February 26 and the other of 2002 January 4. For both we use 195 A Fe XII images from the Extreme-Ultraviolet Imaging Telescope (EIT) and magnetograms from the Michelson Doppler Imager (MDI), both of which are on the Solar and Heliospheric Observatory (SOHO). For the earlier event we also use soft X-ray telescope (SXT), hard X-ray telescope (HXT), and Bragg Crystal Spectrometer (BCS) data from the Yohkoh satellite, and hard X-ray data from the BATSE experiment on the Compton Gamma Ra.v Observatory (CGRO). Both events occur in quadrupolar magnetic regions, and both have coronal features that we infer belong to the same magnetic cavity structures as the filaments. In both cases, the cavity and filament first rise slowly at approx.10 km/s prior to eruption and then accelerate to approx.100 km/s during the eruption, although the slow-rise movement for the higher altitude cavity elements is clearer in the later event. We estimate that both filaments and both cavities contain masses of approx.10(exp 14)-10(exp 15) and approx.10(exp 15)-10(exp 16) g, respectively. We consider whether two specific magnetic reconnection-based models for eruption onset, the "tether cutting" and the "breakout" models, are consistent with our observations. In the earlier event, soft X-rays from SXT show an intensity increase during the 12 minute interval over which fast eruption begins, which is consistent with tether- cutting-model predictions. Substantial hard X-rays, however, do not occur until after fast eruption is underway, and so this is a constraint the tether-cutting model must satisfy. During the same 12 minute interval over which fast eruption begins, there are brightenings and topological changes in the corona indicative of high-altitude reconnection early in the eruption, and this is consistent with breakout predictions. In both eruptions, the state of the overlying loops at the time of onset of the fast-rise phase of the corresponding filament can be compared with expectations from the breakout model, thereby setting constraints that the breakout model must meet. Our findings are consistent with both runaway tether-cutting-type reconnection and fast breakout-type reconnection, occurring early in the fast phase of the February eruption and with both types of reconnection being important in unleashing the explosion, but we are not able to say which, if either, type of reconnection actually triggered the fast phase. In any case, we have found specific constraints that either model, or any other model, must satisfy if correct.

Beschreibung: Bangui anomaly is the name given to one of the Earth s largest crustal magnetic anomalies and the largest over the African continent. It covers two-thirds of the Central African Republic and therefore the name derives from the capitol city-Bangui that is also near the center of this feature. From surface magnetic survey data Godivier and Le Donche (1962) were the first to describe this anomaly. Subsequently high-altitude world magnetic surveying by the U.S. Naval Oceanographic Office (Project Magnet) recorded a greater than 1000 nT dipolar, peak-to-trough anomaly with the major portion being negative (figure 1). Satellite observations (Cosmos 49) were first reported in 1964, these revealed a 40nT anomaly at 350 km altitude. Subsequently the higher altitude (417-499km) POGO (Polar Orbiting Geomagnetic Observatory) satellite data recorded peak-to-trough anomalies of 20 nT these data were added to Cosmos 49 measurements by Regan et al. (1975) for a regional satellite altitude map. In October 1979, with the launch of Magsat, a satellite designed to measure crustal magnetic anomalies, a more uniform satellite altitude magnetic map was obtained. These data, computed at 375 km altitude recorded a -22 nT anomaly (figure 2). This elliptically shaped anomaly is approximately 760 by 1000 km and is centered at 6%, 18%. The Bangui anomaly is composed of three segments; there are two positive anomalies lobes north and south of a large central negative field. This displays the classic pattern of a magnetic anomalous body being magnetized by induction in a zero inclination field. This is not surprising since the magnetic equator passes near the center of this body.

Beschreibung: Recent studies have shown that strong correlations are observed between the low frequencies (1-10 Hz) of quasiperiodic oscillations (QPOs) and the spectral power law index of several Black Hole (BH) candidate sources, in low hard states, steep power-law (soft) states and in transition between these states. The observations indicate that the X-ray spectrum of such state (phases) show the presence of a power-law component and are sometimes related to simultaneous radio emission indicated the probable presence of a jet. Strong QPOs (less than 20% rms) are present in the power density spectrum in the spectral range where the power-law component is dominant ( i.e. 60-90% ). This evidence contradicts the dominant long standing interpretation of QPOs as a signature of the thermal accretion disk. We present the data from the literature and our own data to illustrate the dominance of power-law index-QPO frequency correlations. We provide a model, that identifies and explains the origin of the QPOs and how they are imprinted on the properties of power-law flux component. We argue the existence of a bounded compact coronal region which is a natural consequence of the adjustment of Keplerian disk flow to the innermost sub-Keplerian boundary conditions near the central object and that ultimately leads to the formation of a transition layer (TL) between the adjustment radius and the innermost boundary. The model predicts two phases or states dictated by the photon upscattering produced in the TL: (1) hard state, in which the TL is optically thin and very hot (kT approx. greater than 50 keV) producing photon upscattering via thermal Componization; the photon spectrum index Gamma appprox.1.5 for this state is dictated by gravitational energy release and Compton cooling in an optically thin shock near the adjustment radius; (2) a soft state which is optically thick and relatively cold (approx. less than 5 keV); the index for this state, Gamma approx. 2.8 is determined by soft-photon upscattering and photon trapping in converging flow into BH. In the TL model for corona the QPO frequency vnu(sub high) is related to the gravitational (close to Keplerian) frequency nu(sub K) at the outer (adjustment) radius and nu(sub low) is related to the TL s normal mode (magnetoacoustic) oscillation frequency nu(sub MA). The observed correlations between index and low and high QPO frequencies are readily explained in terms of this model. We also suggest a new method for evaluation of the BH mass using the index-frequency correlation.

Beschreibung: Ancient geologic and hydrologic phenomena on Mars observed through the magnetic data provide windows to the ancient past through the younger Argyre and Hellas impacts, the northern plains basement and the rock materials that mantle the basement, and the Tharsis and Elysium magmatic complexes (recently referred to as superplumes). These signatures, coupled with highly degraded macrostructures (tectonic features that energetic planet during its embryonic development (0.5 Ga or so of activity) with an active dynamo and magnetosphere. One such window into the ancient past occurs northwest of the Hellas impact basin in Arabia Tern. Arabia Terra is one of the few water-rich equatorial regions of Mars, as indicated I through impact crater and elemental information. This region records many unique characteristics, including predominately Noachian materials, a highland-lowland boundary region that is distinct from other boundary regions, the presence of very few macrostructures when compared to the rest of the cratered highlands, the largest region of fretted terrain on Mars, outflow channels such as Mamers Valles that do not have obvious origins, and distinct albedo, thermal inertia, gravity, magnetic, and elemental signatures.

Beschreibung: Pavillion Lake is 5.7km long and an average of 0.8 km in width, and is located in Marble Canyon in the interior of British Columbia, Canada. It is a slightly alkaline, freshwater lake with a maximum-recorded depth of 65m. The basin walls of Pavilion Lake are lined with microbialite structures that are oriented perpendicularly to the shoreline, and which are found from depths of 5 meters to the bottom of the photic zone (light levels 1% of ambient; approximately 30m depth). These structures are speculated to have begun formation nearly 11,000 years ago, after the glacial retreat of the Cordilleran Ice Sheet. They are likely a distinctive assemblage of freshwater calcite microbialites, which display micromorphologies possibly related to the ancient Epiphyton and Girvanella classes of calcareous organosedimentary structures.

Beschreibung: The east rim of the Hellas basin and the surrounding highlands comprise a geologically significant region for evaluating volatile abundance, volatile distribution and cycling, and potential changes in Martian environmental conditions. This region of the Martian surface exhibits landforms shaped by a diversity of geologic processes and has a well-preserved geologic record, with exposures of Noachian, Hesperian, and Amazonian units, as well as spans a wide range in both latitude and elevation due to the magnitude of Hellas basin. In addition, geologically contemporaneous volcanism and volatile-driven activity in the circum-Hellas highlands provide important ingredients for creating habitats for potential Martian life.

Beschreibung: Power spectrum estimation and evaluation of associated errors in the presence of incomplete sky coverage; nonhomogeneous, correlated instrumental noise; and foreground emission are problems of central importance for the extraction of cosmological information from the cosmic microwave background (CMB).

Beschreibung: Observations show that solar activity is distributed nonaxisymmetrically, concentrating at preferred longitudes.

Beschreibung: A preliminary study of the impact of the north-central Pacific circulation in the subtropical stratosphere on ozone variability locally observed by lidar is presented.

Beschreibung: Tvashtar Catena (63 N, 120 W) is one of the most interesting features on Io. This chain of large paterae (caldera-like depressions) has exhibited highly variable volcanic activity in a series of observations. Tvashtar is the type example of a style of volcanism seen only at high latitudes, with short-lived Pele-type plumes and short-lived by intense thermal events. Evidence for a hot spot at Tvashtar was first detected in an eclipse observation in April 1997 (orbit G7) by the Solid State Imager (SSI) on the Galileo Spacecraft. Tvashtar was originally targeted for observation at higher resolution in the close flyby in November 1999 (I25) because of its interesting large-scale topography. There are relatively few but generally larger paterae at high latitudes on Io. I25 images revealed a 25 km long, 1-2 km high lava curtain via a pattern of saturation and bleeding in the CCD image, which requires very high temperatures.

Beschreibung: Hot spots are manifestations of Io s mechanism of internal heating and heat transfer. Therefore, the global distribution of hot spots and their power output has important implications for how Io is losing heat. The end of the Galileo mission is an opportune time to revisit studies of the distribution of hot spots on Io, and to investigate the distribution of their power output.

Beschreibung: Ionian paterae are a class of volcanic feature that are characterized by irregular craters with steep walls, flat floors, and arcuate margins that may or may not exhibit nesting. Loki (310 W, 12 N) is Io's largest patera at approx.200 km in diameter (Figure 1), and may account for 15% of Io's total heat flow. Earth-based infrared data, as well as information collected using the Galileo Near-Infrared Mapping Spectrometer (NIMS) and the Photopolarimeter Radiometer (PPR) have been used to interpret Loki s eruption style. Debate continues over whether Loki s occasional (periodic or not) temperature increases are due to an overturning lava lake within the patera, or to an eruption of surface flows on the patera floor. Interpretation of model results and comparisons with active terrestrial lava lakes suggest that Loki behaves quite differently from active lava lakes on Earth, and that surface flows (rather than an overturning lava lake) are a more likely explanation of Loki's thermal brightening.

Beschreibung: Now that the Galileo spacecraft s tour of the Jupiter system is over, we seek to integrate all available datasets in the hopes of understanding Io as completely as possible. We have compiled information about the morphologies and locations of paterae (volcano-tectonic depressions), mountains, and hotspots on Io in a single database. It is our hope that an analysis of the spatial and temporal relationships between these features will provide more indications of the nature of the crust of Io and the mechanisms leading to these features formation. Since Io s tidal heat escapes through its crust, more knowledge about the crust will lead to an understanding of internal processes, such as magma generation and delivery to the surface, and magnitude and orientation of internal stresses.

Beschreibung: On 25 August 1992, the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite observed a significant enhancement in the abundance of lower stratospheric methyl cyanide (CH3CN) at 100??hPa (~16??km altitude) in a small region off the east coast of Florida.

Beschreibung: We summarize 24 years (1978??2) of ice export estimates and examine, over a 9-year record, the associated variability in the time-varying upward-looking sonar (ULS) thickness distributions of the Fram Strait.

Beschreibung: A three-dimensional (3-D) Global Assimilative Ionospheric Model (GAIM) is currently being developed by a joint University of Southern California and Jet Propulsion Laboratory (JPL) team. To estimate the electron density on a global grid, GAIM uses a first-principles ionospheric physics model and the Kalman filter as one of its possible estimation techniques.

Beschreibung: A variance analysis technique is developed here to extract gravity wave (GW) induced temperature fluctuations from NOAA AMSU-A (Advanced Microwave Sounding Unit-A) radiance measurements. By carefully removing the instrument/measurement noise, the algorithm can produce reliable GW variances with the minimum detectable value as small as 0.1 K2. Preliminary analyses with AMSU-A data show GW variance maps in the stratosphere have very similar distributions to those found with the UARS MLS (Upper Atmosphere Research Satellite Microwave Limb Sounder). However, the AMSU-A offers better horizontal and temporal resolution for observing regional GW variability, such as activity over sub-Antarctic islands.

Beschreibung: The interplanetary shock/electric field event of 5-6 November 2001 is analyzed using ACE interplanetary data. The consequential ionospheric effects are studied using GPS receiver data from the CHAMP and SAC-C satellites and altimeter data from the TOPEX/ Poseidon satellite. Data from ~100 ground-based GPS receivers as well as Brazilian Digisonde and Pacific sector magnetometer data are also used. The dawn-to-dusk interplanetary electric field was initially ~33 mV/m just after the forward shock (IMF BZ = -48 nT) and later reached a peak value of ~54 mV/m 1 hour and 40 min later (BZ = -78 nT). The electric field was ~45 mV/m (BZ = -65 nT) 2 hours after the shock. This electric field generated a magnetic storm of intensity DST = -275 nT. The dayside satellite GPS receiver data plus ground-based GPS data indicate that the entire equatorial and midlatitude (up to +/-50(deg) magnetic latitude (MLAT)) dayside ionosphere was uplifted, significantly increasing the electron content (and densities) at altitudes greater than 430 km (CHAMP orbital altitude). This uplift peaked ~2 1/2 hours after the shock passage. The effect of the uplift on the ionospheric total electron content (TEC) lasted for 4 to 5 hours. Our hypothesis is that the interplanetary electric field ''promptly penetrated'' to the ionosphere, and the dayside plasma was convected (by E x B) to higher altitudes. Plasma upward transport/convergence led to a ~55-60% increase in equatorial ionospheric TEC to values above ~430 km (at 1930 LT). This transport/convergence plus photoionization of atmospheric neutrals at lower altitudes caused a 21% TEC increase in equatorial ionospheric TEC at ~1400 LT (from ground-based measurements). During the intense electric field interval, there was a sharp plasma ''shoulder'' detected at midlatitudes by the GPS receiver and altimeter satellites. This shoulder moves equatorward from -54(deg) to -37(deg) MLAT during the development of the main phase of the magnetic storm. We presume this to be an ionospheric signature of the plasmapause and its motion. The total TEC increase of this shoulder is ~80%. Part of this increase may be due to a "superfountain effect." The dayside ionospheric TEC above ~430 km decreased to values ~45% lower than quiet day values 7 to 9 hours after the beginning of the electric field event. The total equatorial ionospheric TEC decrease was ~16%. This decrease occurred both at midlatitudes and at the equator. We presume that thermospheric winds and neutral composition changes produced by the storm-time Joule heating, disturbance dynamo electric fields, and electric fields at auroral and subauroral latitudes are responsible for these decreases.

Beschreibung: The Palomar Integral Field Spectrograph was used to probe a variety of environments in nine nearby galaxies that span a range of morphological types, luminosities, metallicities, and infrared-to-blue ratios.

Beschreibung: Studies of Martian surface geomorphology and detection of near-surface water ice by the Mars Odyssey gamma ray spectrometer suggest that Mars may have had a water-rich past. While 2 to 5 wt.% of carbonate has been detected in the Martian dust [1,2], no spectral evidence for significant deposits of carbonates or sulfates has been found to date. Most investigations into Mars aqueous mineralogy have been global in scope with only a few regional studies (e.g., [3]). We are searching for localized deposits in putative lacustrine basins utilizing a basin flow model to identify basins with large drainage areas. Such basins are more likely to accumulate high concentrations of aqueous minerals than deep basins which drain only small regions.

Beschreibung: Sulfates are likely to be present on Mars as indicated by the sulfur abundances measured at the Viking and Pathfinder landing sites (approx. 5-10% by weight SO3) [1-3] and because of Mars strongly oxidizing environment. Telescopic observations of Mars tentatively identified weak sulfate bands in near infrared [4] and thermal infrared [5] data. The currently orbiting midinfrared instruments (TES, THEMIS) and the Mini-TES on the Mars Exploration Rover landers may enable a positive identification [6] and determination of the chemistry of the sulfates. Critically important to the identification of these minerals is the presence of their spectra in a spectral library. There exist approximately 370 sulfate-mineral species [7]. Sulfate minerals occur in volcanic, hydrothermal, evaporitic, and chemical-weathering environments.

Beschreibung: The global dichotomy divides the northern lowlands from the southern highlands, except where interrupted by relatively young volcanic provinces and impact basins. An elevation change of 2-4 km is typical across the dichotomy, and more than 6 km locally, over distances of several 100s km to as much as 1300 km [1,2]. A variety of exogenic and endogenic formation models have been proposed. Distinguishing between these models would help constrain the overall thermal evolution of the planet, possibly timing of core formation, and the associated mantle heat flux over time. A first step is to determine whether or not gravitational relaxation plays a role in modifying the boundary. Nimmo and Stevenson [3] examined 10 profiles across the dichotomy and used models of gravitational relaxation to conclude the relaxation has not occurred. In this study we begin by considering the geologic history in detail as inputs for modeling [4].

Beschreibung: The origin of the Martian crustal dichotomy remains a puzzle that when solved can provide an insight to the geological and geophysical evolution of Mars. In this study we model crustal relaxation in order to better constrain the original topographic shape, rheology, and temperature of the Martian crust. Our approach is to model the detailed geologic history of the Ismenius region of Mars, including slope, strain, and timing of faulting [1]. This region may contain the best preserved section of the dichotomy boundary as it is relatively unaffected by large impacts and erosion. So far the only study Martian crustal relaxation [2] suggests that the original topographic shape of the dichotomy is preserved. However, in this area strain from faulting implies at least some relaxation [1].

Beschreibung: We observe two near-limb solar filament eruptions, one of 2000 February 26 and the other of 2002 January 4. For both we use 195 Angstroms, Fe XII images from the Extreme-Ultraviolet Imaging Telescope (EIT) and magnetograms from the Michelson Doppler Imager (MDI), both of which are on the Solar arid Heliospheric Observatory (SOHO). For the earlier event we also use soft X-ray telescope (SXT), hard X-ray telescope (HXT), and Bragg Crystal Spectrometer (BCS) data from the Yohkoh satellite, and hard X-ray data from the BATSE experiment on the Compton Gamma Ray Observation, (CGRO). Both events occur in quadrupolar magnetic regions, and both have coronal features that we infer belong to the same magnetic cavity structures as the filaments. In both cases, the cavity and filament first rise slowly at approximately 10 kilometers per second prior to eruption and then accelerate to approximately 100 kilometers per second during the eruption, although the slow-rise movement for the higher altitude cavity elements is clearer in the later event. We estimate that both filaments and both cavities contain masses of approximately 10(exp 14)-10(exp 15) and approximately 10(exp 15)-10(exp 16)g, respectively. We consider whether two specific magnetic reconnection-based models for eruption onset, the tether cutting and the breakout models, are consistent with our observations. In the earlier event, soft X-rays from SXT show an intensity increase during the 12 minute interval over which fast eruption begins, which is consistent with tether-cutting-model predictions. Substantial hard X-rays, however, do not occur until after fast eruption is underway, and so this is a constraint the tether-cutting model must satisfy. During the same 12 minute interval over which fast eruption begins, there are brightenings and topological changes in the corona indicative of high-altitude reconnection early in the eruption, and this is consistent with breakout predictions. In both eruptions, the state of the overlying loops at the time of onset of the fast-rise phase of the corresponding filament can be compared with expectations from the breakout model, thereby setting constraints that the breakout model must meet. Our findings are consistent with both runaway tether-cutting-type reconnection and fast breakout-type reconnection, occurring early in the fast phase of the February eruption and with both types of reconnection being important in unleashing the explosion, but we are not able to say which, if either, type of reconnection actually triggered the fast phase. In any case, we have found specific constraints that either model, or any other model, must satisfy if correct.

Beschreibung: Numerous studies have documented the effect of El Nino-Southern Oscillation (ENSO) on rainfall in many regions of the globe. The question of whether ENSO is the single most important factor in interannual rainfall variability has received less attention, mostly because the kind of data that would be required to make such an assessment were simply not available. Until 1979 the evidence linking El Nino with changes in rainfall around the world came from rain gauges measuring precipitation over land masses and a handful of islands. From 1980 until the launch of the Tropical Rainfall Measuring Mission (TRMM) in November 1997 the remote sensing evidence was confined to ocean rainfall because of the very poor sensitivity of the instruments over land. In this paper we summarize the results of a principal component analysis of TRMM's 60-month (January 1998 to December 2002) global land and ocean remote-sensing record of monthly rainfall accumulations. Contrary to the first principal component of the rainfall itself, the first three indices of the anomaly are most sensitive to precipitation over the ocean rather than over the land. With the help of archived surface station data the first TRMM rain anomaly index is extended back several decades. Comparison of the extended index with the Southern Oscillation Index confirms that the first principal component of the rainfall anomaly is strongly correlated with the ENSO indices.

Beschreibung: A back-and-forth orbit integration technique, developed for our previous investigation of the splitting of the parent of the sungrazers C/1882 R1 and C/1965 S1, is now applied in an effort to understand the history and orbital evolution of the Kreutz sungrazer system, starting with the birth of two subgroups, which show prominently among the bright members and whose inception dates back to the progenitor's breakup into two superfragments. The integration technique is used to reproduce the motion of comet C/1843 D1 - the second brightest sungrazer known and presumably the most massive surviving piece of superfragment I - from the motion of C/1882 R1 - the brightest sungrazer on record and arguably the most massive surviving piece of superfragment II. Running the orbit of C/1882 R1 back to A.D. 326, the progenitor comet is found to have split at a heliocentric distance of 50 AU and nearly 30 yr before perihelion. The superfragments acquired separation velocities of similar to8 m s(-1) in opposite directions. Using the same technique, we show next that (1) the motions of two additional sungrazers, C/1880 C1 and C/1887 B1, are matched extremely well if these objects shared a common parent with C/1843 D1, and (2) C/1963 R1 (Pereyra), the second brightest subgroup I member on record, is more closely related to subgroup II objects (such as C/1882 R1 and C/1965 S1) than to C/1843 D1. This finding raises serious doubts about the major role of the subgroups in the system's orbital history and offers an incentive for considering an alternative dynamical scenario. The fragmentation models for C/1963 R1 and two additional bright sungrazers, C/1945 X1 and C/1970 K1, suggest that (1) these comets may have been the most massive pieces of the fragment populations formed from their respective disintegrating parents, and (2) the course of evolution of the Kreutz system at the upper end of the mass spectrum may be better ascertained from the distribution of the sungrazers' arrival times than from the sources of subgroups. If so, the fragment hierarchy should be determined primarily by the cascading nature of the fragmentation process, which was recently shown by Sekanina to control the evolution of minor fragments as well. The sungrazer system's estimated age is in any case very short, less than 1700 yr.

Beschreibung: We report detections of X-rays from HH 80 and HH 81 with the ACIS instrument on the Chandra X-Ray Observatory.

Beschreibung: The processes and mechanisms involved in the rotation and alignment of interstellar dust grains have been of great interest in astrophysics ever since the surprising discovery of the polarization of starlight more than half a century ago. Numerous theories, detailed mathematical models, and numerical studies of grain rotation and alignment with respect to the Galactic magnetic field have been presented in the literature. In particular, the subject of grain rotation and alignment by radiative torques has been shown to be of particular interest in recent years. However, despite many investigations, a satisfactory theoretical understanding of the processes involved in subject, we have carried out some unique experiments to illuminate the processes involved in the rotation of dust grains in the interstellar medium. In this paper we present the results of some preliminary laboratory experiments on the rotation of individual micron/submicron-sized, nonspherical dust grains levitated in an electrodynamic balance evacuated to pressures of approximately 10(exp -3) to 10(exp -5) torr. The particles are illuminated by laser light at 5320 A, and the grain rotation rates are obtained by analyzing the low-frequency (approximately 0 - 100 kHz) signal of the scattered light detected by a photodiode detector. The rotation rates are compared with simple theoretical models to retrieve some basic rotational parameters. The results are examined in light of the current theories of alignment.

Beschreibung: Recent studies have shown that strong correlations are observed between the low frequencies (1-10 Hz) of quasi-periodic oscillations (QPOs) and the spectral power law index of several black hole (BH) candidate sources, in low (hard) states, steep power law (soft) states, and transitions between these states. The observations indicate that the X-ray spectra of such state (phases) show the presence of a power-law component and are sometimes related to simultaneous radio emission, indicating the probable presence of a jet. Strong QPOs (〉20% rms) are present in the power density spectrum in the spectral range where the power-law component is dominant (i.e., 60%90%). This evidence contradicts the dominant, long-standing interpretation of QPOs as a signature of the thermal accretion disk. We present the data from the literature and our own data to illustrate the dominance of power-law index-QPO frequency correlations. We provide a model that identifies and explains the origin of the QPOs and how they are imprinted on the properties of the power-law flux component. We argue for the existence of a bounded compact coronal region that is a natural consequence of the adjustment of the Keplerian disk flow to the innermost sub-Keplerian boundary conditions near the central object and that ultimately leads to the formation of a transition layer (TL) between the adjustment radius and the innermost boundary. The model predicts two phases or states dictated by the photon upscattering produced in the TL: (1) a hard state, in which the TL is optically thin and very hot (kT approximately greater than 50 keV), producing photon upscattering via thermal Comptonization (the photon spectrum index Gamma approximates 1.7 for this state is dictated by gravitational energy release and Compton cooling in an optically thin shock near the adjustment radius), and (2) a soft state that is optically thick and relatively cold (kT approximately less than 5 keV the index for this state, Gamma approximates 2.8, is determined by soft-photon upscattering and photon trapping in a converging flow into the BH). In the TL model for the corona, the QPO frequency V(sub high) is related to the gravitational (close to Keplerian) frequency V(sub K) at the outer (adjustment) radius and v(sub low) is related to the TL's normal mode (magnetoacoustic) oscillation frequency v(sub MA) . The observed correlations between index and low and high QPO frequencies are readily explained in terms of this model. We also suggest a new method for evaluation of the BH mass using the index-frequency correlation.

Beschreibung: The Constellation-X mission will address the questions: "What happens to matter close to a black hole?" and "What is Dark Energy?" These questions are central to the NASA Beyond Einstein Program, where Constellation-X plays a central role. The mission will address these questions by using high throughput X-ray spectroscopy to observe the effects of strong gravity close to the event horizon of black holes, and to observe the formation and evolution of clusters of galaxies in order to precisely determine Cosmological parameters. To achieve these primary science goals requires a factor of 25-100 increase in sensitivity for high resolution spectroscopy. The mission will also perform routine high- resolution X-ray spectroscopy of faint and extended X-ray source populations. This will provide diagnostic information such as density, elemental abundances, velocity, and ionization state for a wide range of astrophysical problems. This has enormous potential for the discovery of new unexpected phenomena. The Constellation-X mission is a high priority in the National Academy of Sciences McKee-Taylor Astronomy and Astrophysics Survey of new Astrophysics Facilities for the first decade of the 21st century.

Beschreibung: Previous observations of the luminous Seyfert 1 galaxy 1H 0419-577 have found its X-ray spectrum to range from that of a typical Seyfert 1 with 2-10 keV power law index Gamma approx. 1.9 to a much flatter power law of Gamma approx. 1.5 or less. We report here a new XMM-Newton observation which allows the low state spectrum to be studied in much greater detail than hitherto. We find a very hard spectrum (Gamma approx. 1.0), which exhibits broad features that can be modelled myth the addition of an extreme relativistic Fe K emission line or with partial covering of the underlying continuum by a substantial column density of near-neutral gas. Both the EPIC and RGS data show evidence for strong line emission of OVII and OVIII requiring an extended region of low density photoionised gas in 1H 0419-577. Comparison with an earlier XMM-Newton observation when 1H 0419-577 was 'X-ray bright' indicates the dominant spectral variability occurs via a steep power law component.

Beschreibung: We present new XMM-Newton results on the field around the NGC346 star cluster in the SMC. This continues and extends previously published work on Chandra observations of the same field. The two XMM-Newton observations were obtained, respectively, six months before and six months after the previously published Chandra data. Of the 51 X-ray sources detected with XMM-Newton, 29 were already detected with Chandru. Comparing the properties of these X-ray sources in each of our three datasets has enabled us to investigate their variability on times scales of a year. Changes in the flux levels and/or spectral properties were observed for 21 of these sources. In addition, we discovered long-term variations in the X-ray properties of the peculiar system HD5980, a luminous blue variable star, that is likely to be a colliding wind binary system, which displays the largest luminosity during the first XMM-Newton observation.

Beschreibung: We apply the GSFC trajectory model with a series of ozonesondes to derive ozone loss rates in the lower stratosphere for the AASE-2/EASOE mission (January - March 1992) and for the SOLVE/THESEO 2000 mission (January - March 2000) in an approach similar to Match. Ozone loss rates are computed by comparing the ozone concentrations provided by ozonesondes launched at the beginning and end of the trajectories connecting the launches. We investigate the sensitivity of the Match results on the various parameters used to reject potential matches in the original Match technique and conclude that only a filter based on potential vorticity changes along the calculated back trajectory seems necessary. Our study also demonstrates that calculated ozone loss rates can vary by up to a factor of two depending upon the precise trajectory paths calculated for each trajectory. As a result an additional systematic error might need to be added to the statistical uncertainties published with previous Match results. The sensitivity to the trajectory path is particularly pronounced in the month of January, the month during which the largest ozone loss rate discrepancies between photochemical models and Match are found. For most of the two study periods, our ozone loss rates agree with those previously published. Notable exceptions are found for January 1992 at 475 K and late February/early March 2000 at 450 K, both periods during which we find less loss than the previous studies. Integrated ozone loss rates in both years compare well with those found in numerous other studies and in a potential vorticity/potential temperature approach shown previously and in this paper. Finally, we suggest an alternate approach to Match using trajectory mapping that appears to more accurately reflect the true uncertainties associated with Match and reduces the dependence upon filters that may bias the results of Match through the rejection of greater than or equal to 80% of the matched sonde pairs and 〉99% of matched observations.

Beschreibung: We present new interstellar dust models which have been derived by simultaneously fitting the far ultraviolet to near infrared extinction, the diffuse infrared emission, and, unlike previous models, the elemental abundances in dust for the diffuse interstellar medium. We found that dust models consisting of a mixture of spherical graphite and silicate grains, polycyclic aromatic hydrocarbon (PAH) molecules, in addition to porous composite particles containing silicate, organic refractory, and water ice, provide an improved .t to the UV-to-infrared extinction and infrared emission measurements, while consuming the amounts of elements well within the uncertainties of adopted interstellar abundances, including B star abundances. These models are a signi.cant improvement over the recent Li & Draine (2001, ApJ, 554, 778) model which requires an excessive amount of silicon to be locked up in dust: 48 ppm (atoms per million of H atoms), considerably more than the solar abundance of 34 ppm or the B star abundance of 19 ppm.

Beschreibung: The X-ray and gamma-ray spectrum of rotation-powered millisecond pulsars is investigated in a model for acceleration and pair cascades on open field lines above the polar caps. Although these pulsars have low surface magnetic fields, their short periods allow them to have large magnetospheric potential drops, but the majority do not produce sufficient pairs to completely screen the accelerating electric field. In these sources, the primary and secondary electrons continue to accelerate to high altitude and their Lorentz factors are limited by curvature and synchrotron radiation reaction. The accelerating particles maintain high Lorentz factors and undergo cyclotron resonant absorption of radio emission, that produces and maintains a large pitch angle, resulting in a strong synchrotron component. The resulting spectra consist of several distinct components: curvature radiation from primary electrons dominating from 1 - 100 GeV, synchrotron radiation from primary and secondary electrons dominating up to about 100 MeV, and much weaker inverse-Compton radiation from primary electrons a t 0.1 - 1 TeV. We find that the relative size of these components depends on pulsar period, period derivative, and neutron star mass and radius with the level of the synchrotron component also depending sensitively on the radio emission properties. This model is successful in describing the observed X-ray and gamma-ray spectrum of PSR J0218+4232 as synchrotron radiation, peaking around 100 MeV and extending up to a turnover around several GeV. The predicted curvature radiation components from a number of millisecond pulsars, as well as the collective emission from the millisecond pulsars in globular clusters, should be detectable with AGILE and GLAST. We also discuss a hidden population of X-ray-quiet and radio-quiet millisecond pulsars which have evolved below the pair death line, some of which may be detectable by telescopes sensitive above 1 GeV. Subject headings: pulsars: general - radiation mechanisms: nonthermal - stars: neutron - gamma rays: theory

Beschreibung: Since the ICRF was generated in 1995, VLBI modeling and estimation, data quality: source position stability analysis, and supporting observational programs have improved markedly. There are developing and potential applications in the areas of space navigation Earth orientation monitoring and optical astrometry from space that would benefit from a refined ICRF with enhanced accuracy, stability and spatial distribution. The convergence of analysis, focused observations, and astrometric needs should drive the production of a new realization in the next few years.

Beschreibung: The Observing Strategies Sub-group of IVS's Working Group 3 has been tasked with producing a vision for the following aspects of geodetic VLBI: antenna-network structure and observing strategies; source strength/structure/distribution; frequency bands, RFI; and field system and scheduling. These are high level considerations that have far reaching impact since they significantly influence performance potential and also constrain requirements for a number of other \VG3 sub-groups. The paper will present the status of the sub-group's work on these topics.

Beschreibung: We report the results of a search for burst oscillations during thermonuclear X-ray bursts from the low mass X-ray binary (LMXB) EXO 0748-676. With the proportional counter array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) we have detected a 45 Hz oscillation in the average power spectrum of 38 thermonuclear X-ray bursts from this source. We computed power spectra with 1 Hz frequency resolution for both the rising and decaying portions of 38 X-ray bursts from the public RXTE archive. We averaged the 1 Hz power spectra and detected a significant signal at 45 Hz in the decaying phases of the bursts. The signal is detected at a significance level of 4 x 10 (exp -8) similar signal was detected in the rising intervals. The oscillation peak is unresolved at 1 Hz frequency resolution, indicating an oscillation quality factor, Q = nu (sub 0)/Delta nu (sub fwhm) greater than 45, and the average signal amplitude is approximately equal to 3% (rms) The detection of 45 Hz burst oscillations from EXO 0748-676 provides compelling evidence that this is the neutron star spin frequency in this system. We use the inferred spin frequency to model the widths of absorption lines from the neutron star surface and show that the widths of the absorption lines from EXO 0748-676 recently reported by Cottam et al. are consistent with a 45 Hz spin frequency as long as the neutron star radius is in the range from about 9.5 - 15 km. With a known spin frequency, precise modelling of the line profiles from EXO 0748-676 holds great promise for constraining the dense matter equation of state.

Beschreibung: The goal of the Orbiting Wide-field Light-collectors (0WL) mission is to study the origin and physics of the highest energy particles known in nature, the ultra- high energy cosmic rays (UHECRs). The OWL mission consists of telescopes with UV sensitive cameras on two satellites operating in tandem to view in stereo the development of the giant particle showers induced in the Earth s atmosphere by UHECRs. This paper discusses the characteristics of the 0WL mission.

Beschreibung: We present RHESSI observF5oss of three homologous flares, which occurred between April 14 and 16, 2002. We find that the RHESSI images of all three flares at energies between 6 and 25 keV had some common features: (1) A. separate coronal source up to approx. 30 deg. above the flare loop appeared in the early impulsive phase and stayed stationary for several minutes. (2) Before the flare loop moved upward; previously reported by others, the flare loop-top centroid moved downward for 2-4 minutes during the early impulsive phase of the Ears: falling by 13 - 30% of its initial height with a speed between 8 and 23 km/s. We conclude that these features are associated with the formation and development of a current sheet between the loop-top and the coronal source. In the April 14-15 flare, we find that the hard X-ray flux (greater than 25 keV) is correlated with the rate at which the flare loop moves upward, indicating that the faster the loop grows, the faster the reconnection rate, and therefore, the greater the flux of accelerated electrons. Subject headings: Sun: L'iaies-Sun: X-1-ay-s -

Beschreibung: Climate models often rely on standard atmospheres to represent various regions; these broadly capture the important physical and radiative characteristics of regional atmospheres, and become benchmarks for simulations by researchers. The high Antarctic plateau is a significant region of the earth for which such standard atmospheres are as yet unavailable. Moreover, representative profiles from atmospheres over other regions of the planet, including &om the northern high latitudes, are not comparable to the atmosphere over the Antarctic plateau, and are therefore only of limited value as substitutes in climate models. Using data from radiosondes, ozonesondes and satellites along with other observations from South Pole station, typical seasonal atmospheric profiles for the high plateau are compiled. Proper representations of rapidly changing ozone concentrations (during the ozone hole) and the effect of surface elevation on tropospheric temperatures are discussed. The differences between standard profiles developed here and the most similar standard atmosphere that already exists - namely, the Arctic Winter profile - suggest that these new profiles will be extremely useful to make accurate representations of the atmosphere over the high plateau.

Beschreibung: We report on Chandra ACE observations of the ultracompact AM CVn binary ES Cet. This object has a 10.3 minute binary period and is the most compact of the confirmed AM CVn systems. We have, for the first time, unambiguously detected the X-ray counterpart to ES Cet. In a 20 ksec ACIS-S image a point-like X-ray source is found within 1 sec. of the catalogued optical position. The mean countrate in ACIS-S is 0.013/s, and there is no strong evidence for variability. We folded the X-ray data using the optical ephemeris of Warner & Woudt, but did not detect any significant modulation. If an approx. = 100% modulation similar to those seen in the ultracompact candidates V407 Vu1 and Rx J0806.3+1527 were present then we would have detected it. The upper limit (3(sigma)) to any modulation at the putative orbital period is approx. 40% (rms). We extract the first X-ray spectrum from ES Cet, and find that it is not well described by simple continuum models. We find suggestive evidence for discrete spectral components at approx. 470 and 890 eV, that can be modelled as gaussian emission lines. In comparison with recent X-ray detections of nitrogen and neon in another AM CVn system (GP Com), it appears possible that these features may represent emission lines from these same elements; however, deeper spectroscopy will be required to confirm this. Our best spectral model includes a black body continuum with kT = 0.8 keV along with the gaussian lines. The 0.2 - 5 keV X-ray flux was approx. 7 x 10(exp -14) ergs/sq cm s. The luminosity implied by this flux for any reasonable distance is much smaller than that expected for a mass accretion rate as high as m = 10(exp -8) solar mass/yr, suggesting that the bulk of the accretion luminosity is below 100 eV and not seen with Chandra. We discuss the implications of our results for the nature of ES Cet.

Beschreibung: Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating into an ambient plasma. We find that the growth times depend on the Lorenz factors of jets. The jets with larger Lorenz factors grow slower. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The small scale magnetic field structure generated by the Weibel instability is appropriate to the generation of "jitter" radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation resulting from small scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

Beschreibung: We present observations and an interpretation of a unique multiple-turn spiral flux tube eruption from active region 10030 on 2002 July 15. The TRACE C IV observations clearly show a flux tube that is helical and erupting from within a sheared magnetic field. These observations are interpreted in the context of the breakout model for magnetic field explosions. The initiation of the helix eruption. as determined by a linear backward extrapolation, starts 25 s after the peak of the flare's strongest impulsive spike of microwave gyrosynchrotron radiation early in the flare s explosive phase, implying that the sheared core field is not the site of the initial reconnection. Within the quadrupolar configuration of the active region, the external and internal reconnection sites are identified in each of two consecutive eruptive flares that produce a double coronal mass ejection (CME). The first external breakout reconnection apparently releases an underlying sheared core field and allows it to erupt, leading to internal reconnection in the wake of the erupting helix. This internal reconnection releases the helix and heats the two-ribbon flare. These events lead to the first CME and are followed by a second breakout that initiates a second and larger halo CME. The strong magnetic shear in the region is compatible with the observed rapid proper motion and evolution of the active region. The multiple-turn helix originates from above a sheared-field magnetic inversion line within a filament channel. and starts to erupt only after fast breakout reconnection has started. These observations are counter to the standard flare model and support the breakout model for eruptive flare initiation.

Beschreibung: Measurements by Ulysses in the high-speed polar solar wind have shown the wind to carry some fine-scale structures in which the magnetic field reverses direction by having a switchback fold in it. The lateral span of these magnetic switchbacks, translated back to the Sun, is of the scale of the lanes and cells of the magnetic network in which the open magnetic field of the polar coronal hole and polar solar wind are rooted. This suggests that the magnetic switchbacks might be formed from network-scale magnetic loops that erupt into the corona and then undergo reconnection with the open field. This possibility motivated us to undertake the study reported here of the structure of Ha macrospicules observed at the limb in polar coronal holes, to determine whether a significant fraction of these eruptions appear to be erupting loops. From a search of the polar coronal holes in 6 days of image- processed full-disk Ha movies from Big Bear Solar Observatory, we found a total of 35 macrospicules. Nearly all of these (32) were of one or the other of two different forms: 15 were in the form of an erupting loop, and 17 were in the form of a single column spiked jet. The erupting-loop macrospicules are appropriate for producing the magnetic switchbacks in the polar wind. The spiked-jet macrospicules show the appropriate structure and evolution to be driven by reconnection between network-scale closed field (a network bipole) and the open field rooted against the closed field. This evidence for reconnection in a large fraction of our macrospicules (1) suggests that many spicules may be generated by similar but smaller reconnection events and (2) supports the view that coronal heating and solar wind acceleration in coronal holes and in quiet regions are driven by explosive reconnection events in the magnetic network.

Beschreibung: The VLBI antenna (GILCREEK) at Fairbanks, Alaska observes in networks routinely twice a week with operational networks and on additional days with other networks on a more uneven basis. The Fairbanks antenna position is about 150 km north of the Denali fault and from the earthquake epicenter. We examine the transient behavior of the estimated VLBI position during the year following the earthquake to determine how the rate of change of postseismic deformation has changed. This is compared with what is seen in the GPS site position series.

Beschreibung: RX 51914.4+2456 is a candidate double-degenerate binary with a putative 1.756 mHz orbital frequency. In a previous timing study using archival ROSAT and ASCA data we reported evidence for an increase of the putative orbital frequency at a rate consistent with expectations for gravitational radiation from the system. Here we report the results of new Chandra timing observations which confirm the previous indications of spin-up of the X-ray frequency, and provide much tighter constraints on the frequency derivative, u. We obtained with Chandra a total of 75 ksec of exposure in two epochs separated in time by 10.3 months. The total time span of the archival ROSAT, ASCA and new Chandra data is now 10.2 years. This more than doubles the interval spanned by the ROSAT and ASCA data alone, providing much greater sensitivity to a frequency derivative. With the addition of the Chandra data an increasing frequency is unavoidable, and the mean i/ is 5.9f0.9 x 10-l' Hz s-'. Interestingly, power spectra of the longest Chandra pointing show evidence for a sideband structure to the 1.756 mHz frequency. The fundamental and first harmonic show evidence for upper sidebands with a frequency separation of E 0.5 mHz from their parent peaks. Additionally, the first and second harmonics show evidence for lower sidebands with approximately half the frequency separation of the upper sidebands. Similar sideband structure is a common feature of Intermediate Polars (Ips)-although it is usually observed in the optical-and suggests the presence of a longer period in the system, perhaps the previously unseen orbital period. If this is correct the sideband structure indicates an orbital period close to 1 hr, and the observed u likely represents the accretion-induced spin-up of a white dwarf. We discuss the implications of these findings for the nature of RX J1914.4+2456.

Beschreibung: Whereas the surface units of the northern plain of Mars generally exhibit ages ranging from late Hesperian to Amazonian, interpretation of precise topographic measurements indicate that the age of the underlying "basement" is early Noachian, or almost as old as the southern highlands. This suggests that widespread but relatively superficial resurfacing has occurred throughout the northern plains since the end of early heavy bombardment. In this abstract I examine some of the possible implications of the subsurface structure inferred for the Utopia basin from gravity data on the nature of this resurfacing. The large, shallow, circular depression in Utopia Planitia has been identified as a huge impact basin, based on both geological evidence and detailed analysis of MOLA topography. Its diameter (approx. 3000 km) is equivalent to that of the Hellas basin, as is its inferred age (early Noachian). However, whereas Hellas is extremely deep with rough terrain and large slopes, the Utopia basin is a smooth, shallow, almost imperceptible bowl. Conversely, Utopia displays one of the largest (non-Tharsis-related) positive geoid anomalies on Mars, in contrast to a much more subdued negative anomaly over Hellas.

Beschreibung: The ubiquity of accretion disks around pre-main sequence and young main sequence stars having the potential to form planetary systems is now well established. However, unknown is an accurate estimate of the fraction of single stars with disks that have produced planetary systems. Theoretical models of particle aggregation show that if particles can grow from submicron to mm to cm in size, then the formation of planetesimals is possible in the time before the disk dissipates. The problem remains to understand how grains condense from nebular gases, and how relic interstellar grains survive and are modified by their transport in the disk. If grains are lofted above the disk photosphere by processes such as winds, turbulent convection, or changes in vertical structure, the evolution of dust can be investigated by observing the properties of the small (less than or = 1 micron) grains in the optically thin disk surface layer or atmosphere.

Beschreibung: For the years 1999-2003, we estimate the time-varying perennial ice zone (PIZ) coverage and construct the annual cycles of multiyear (MY, including second year) ice coverage of the Arctic Ocean using QuikSCAT backscatter, MY fractions from RADARSAT, and the record of ice export from satellite passive microwave observations. An area balance approach extends the winter MY coverage from QuikSCAT to the remainder of the year. From these estimates, the coverage of MY ice at the beginning of each year is 3774 x 10(exp 3) sq km (2000), 3896 x 10(exp 3) sq km (2001), 4475 x 10(exp 3) sq km (2002), and 4122 x 10(exp 3) sq km (2003). Uncertainties in coverage are approx.150 x 10(exp 3) sq km. In the mean, on 1 January, MY ice covers approx.60% of the Arctic Ocean. Ice export reduces this coverage to approx.55% by 1 May. From the multiple annual cycles, the area of first-year (FY) ice that survives the intervening summers are 1192 x 10(exp 3) sq km (2000), 1509 x 10(exp 3) sq km (2001), and 582 x 10(exp 3) sq km (2002). In order for the MY coverage to remain constant from year to year, these replenishment areas must balance the overall area export and melt during the summer. The effect of the record minimum in Arctic sea ice area during the summer of 2002 is seen in the lowest area of surviving FY ice of the three summers. In addition to the spatial coverage, the location of the PIZ is important. One consequence of the unusual location of the PIZ at the end of the summer of 2002 is the preconditioning for enhanced export of MY ice into the Barents and Kara seas. Differences between the minimums in summer sea ice coverage from our estimates and passive microwave observations are discussed.

Beschreibung: Fully relativistic and causal equations for the flow of charge in curved spacetime are derived. It is believed that this is the first set of equations to be published that correctly describes the flow of charge, as well as the evolution of the electromagnetic field, in highly dynamical relativistic environments on timescales much shorter than the collapse time (GM/c3).

Beschreibung: Bi-directional reflectances of marine liquid water clouds, as measured by the Multiangle Imaging SpectroRadiometer (MISR), are compared with plane-parallel radiative transfer model calculations.

Beschreibung: We present the results of stellar photometry of polar ring galaxies NGC 2685 and NGC 4650A, using the archival data obtained with the Hubble Space Telescope's Wide Field Planetary Camera 2.

Beschreibung: The metal-poor stars in the halo of the Milky Way galaxy were among the first objects formed in our Galaxy. These Population II stars are the oldest objects in the universe whose ages can be accurately determined. Age determinations for these stars allow us to set a firm lower limit, to the age of the universe and to probe the early formation history of the Milky Way. The age of the universe determined from studies of Population II stars may be compared to the expansion age of the universe and used to constrain cosmological models. The largest uncertainty in estimates for the ages of stars in our halo is due to the uncertainty in the distance scale to Population II objects. We propose to obtain accurate parallaxes to a number of Population II objects (globular clusters and field stars in the halo) resulting in a significant improvement in the Population II distance scale and greatly reducing the uncertainty in the estimated ages of the oldest stars in our galaxy. At the present time, the oldest stars are estimated to be 12.8 Gyr old, with an uncertainty of approx. 15%. The SIM observations obtained by this key project, combined with the supporting theoretical research and ground based observations outlined in this proposal will reduce the estimated uncertainty in the age estimates to 5%).

Beschreibung: The Crustal Dynamics Data Information System (CDDIS) has supported the International GPS Service (IGS) as a global data center since 1992. The CDDIS activities within the IGS during 2001 are summarized below; this report also includes any changes or enhancements made to the CDDIS during the past year. General CDDIS background and system information can be found in the CDDIS data center summary included in the IGS 1994 Annual Report (Noll, 1995) as well as the subsequent updates (Noll, 1996, Noll, 1997, Noll, 1998, Noll, 1999, and Noll, 2001).

Beschreibung: The Space Interferometer Mission (SIM) will provide a census of planetary systems by con- ducting a broad survey of 2,000 stars that will be sensitive to the presence of planets with masses as small as approx. 15 Earth masses (1 Uranus mass) and a deep survey of approx. 250 of the nearest, stars with a mass limit of approx.3 Earth masses. The broad survey will include stars spanning a wide range of ages, spectral types, metallicity, and other important parameters. Within this larger context, the Young Stars and Planets Key Project will study approx. 200 stars with ages from 1 Myr to 100 Myr to understand the formation and dynamical evolution of gas giant planets. The SIM Young Stars and Planets Project will investigate both the frequency of giant planet formation and the early dynamical history of planetary systems. We will gain insight into how common the basic architecture of our solar system is compared with recently discovered systems with close-in giant planets by examining 200 of the nearest (less than 150 pc) and youngest (1-100 Myr) solar-type stars for planets. The sensitivity of the survey for stars located 140 pc away is shown in the planet mass-separation plane. We expect to find anywhere from 10 (assuming that only the presently known fraction of stars. 5-7%, has planets) to 200 (all young stars have planets) planetary systems. W-e have set our sensitivity threshold to ensure the detection of Jupiter-mass planets in the critical orbital range of 1 to 5 AU. These observations, when combined with the results of planetary searches of mature stars, will allow us to test theories of planetary formation and early solar system evolution. By searching for planets around pre-main sequence stars carefully selected to span an age range from 1 to 100 Myr, we will learn a t what epoch and with what frequency giant planets are found at the water-ice snowline where they are expected to form. This will provide insight into the physical mechanisms by which planets form and migrate from their place of birth, and about their survival rate. With these data in hand, we will provide data, for the first time, on such important questions as: What processes affect the formation and dynamical evolution of planets? When and where do planets form? What is initial mass distribution of planetary systems around young stars? How might planets be destroyed? What is the origin of the eccentricity of planetary orbits? What is the origin of the apparent dearth of companion objects between planets and brown dwarfs seen in mature stars? The observational strategy is a compromise between the desire to extend the planetary mass function as low as possible and the essential need to build up sufficient statistics on planetary occurrence. About half of the sample will be used to address the "where" and "when" of planet formation. We will study classical T Tauri stars (cTTs) which have massive accretion disks and post- accretion, weak-lined T Tauri stars (wTTs). Preliminary estimates suggest the sample will consist of approx. 30% cTTs and approx. 70% wTTs, driven in part by the difficulty of making accurate astrometric measurements toward objects with strong variability or prominent disks.

Beschreibung: We present small-aperature(15) photometry and new high-resolution images at 10 mu (N band) for 87 Seyfert galaxies from the Extended 12 mu Sample drawn from the IRASX database.

Beschreibung: We present deep submillimeter observations of 17 galaxies at z = 0.5 that are hosts of a Type Ia supernova.

Beschreibung: Temperature-Salinity (T-S) relationship variability in the pycnocline of the eastern equatorial Pacific Ocean (NINO3 region, 5 degrees S ??degrees N, 150 degrees W ?? degrees W) over the last two decades is investigated using observational data and model simulation.

Beschreibung: The radiative lifetime of the 1S0 level was found to be 540 +/- 27 ms. This is in good agreement with a previous measurement and with a number of theoretical calculations. Metastable lifetimes, when combined with collisional excitation rates, can provide a diagnostic for electron density Ne in a stellar or solar plasma.

Beschreibung: We have obtained Far Ultraviolet Spectroscopic Explorer and Hubble Space Telescope STIS spectra of HR 4796A, a nearby 8 Myr old main-sequence star that possesses a dusty circumstellar disk whose inclination has been constrained from high-resolution near-infrared observations to be 17 degrees from edge-on.

Beschreibung: Fischer-Tropsch catalysis has been suggested as a means of driving hydrocarbon chemistry in oxygen rich regions such as the protosolar nebula. In addition to producing hydrocarbons, Fischer-Tropsch catalysis also produces water, and it is therefore possible that such processes could account for the recent observations of water in the circumstellar envelope of asymptotic giant branch star IRC +10216.

Beschreibung: We show that the reconstructed sensitivity of the sea level temperature to long term solar forcing in the Northern Hemisphere is in very good agreement with the empirical temperature pattern corresponding to changes of the North Annular Mode (NAM).

Beschreibung: A fluid, mobile atmosphere and oceans surrounds the solid Earth and upon its land surface lays a continually changing distribution of ice, snow, and ground water.

Beschreibung: A number of recent lines of evidence point towards the presence of hot, outflowing plasma from the central regions of compact Galactic and extragalactic X-ray sources. Additionally, it has long been noted that many of these sources exhibit an "excess" continuum component, above approx. 10 keV, usually attributed to Compton Reflection from a static medium. Motivated by these facts, as well as by recent observational constraints on the Compton reflection models - specifically apparently discrepant variability timescales for line and continuum components in some cases - we consider possible of effects of out-flowing plasma on the high-energy continuum spectra of accretion powered compact objects. We present a general formulation for photon downscattering diffusion which includes recoil and Comptonization effects due to divergence of the flow. We then develop an analytical theory for the spectral formation in such systems that allows us to derive formulae for the emergent spectrum. Finally we perform the analytical model fitting on several Galactic X-ray binaries. Objects which have been modeled with high-covering-fraction Compton reflectors, such as GS1353-64 are included in our analysis. In addition, Cyg X-3, is which is widely believed to be characterized by dense circumstellar winds with temperature of order 10(exp 6) K, provides an interesting test case. Data from INTEGRAL and RXTE covering the approx. 3 - 300 keV range are used in our analysis. We further consider the possibility that the widely noted distortion of the power-law continuum above 10 keV may in some cases be explained by these spectral softening effects.

Beschreibung: The well known black-hole X-ray binary transient XTE J1550-564 underwent an outburst during the spring of 2003 which was substantially underluminous in comparison to previous periods of peak activity in that source. In addition, our analysis shows that it apparently remained in the hard spectral state over the duration of that outburst. This is again in sharp contrast to major out-bursts of that source in 1998/1999 during which it exhibited an irregular light curve, multiple state changes and collimated outflows. This leads us to classify it as a failed outburst. We present the results of our study of the spring 2003 event including light curves based on observations from both INTEGRAL and RXTE. In addition, we studied the evolution of the high-energy 3-300 keV continuum spectrum using data obtained with three main instruments on INTEGRAL. These spectra are consistent with typical low-hard-state thermal Comptonization emission. We also consider the 2003 event in the context of a multi-source, multi-event period-peak luminosity diagram in which it is a clear outlyer. We then consider the possibility that the 2003 event was due to a discrete accretion event rather than a limit-cycle instability. In that context, apply model fitting to derive the timescale for viscous propagation in the disk, and infer some physical characteristics.

Beschreibung: The current cache of S/X-band geodetic/astrometric VLBI data accumulated since 1979 is approx. 5 million observations and is increasing by approx. 300,000 observations per year. The long time interval and access to all such VLBI data for re-analysis have contributed to their usefulness for the terrestrial and celestial reference frames, Earth orientation parameters, tidal and non-tidal loading, and troposphere. While data access and integrity have been maintained through the Mark III data base system as storage devices and media have evolved, past transitions have been major projects. A new format and retention concept to ensure eternal archiving and access should make use of self-documentation, generalized media, network connectivity and multiple redundancy. Similarly permanent organizations or sequences of organizations are also necessary.

Beschreibung: Solar proton events (SPEs) are known to have caused changes in constituents in the Earth's polar neutral middle atmosphere. The past four years, 2000-2003, have been replete with SPEs and huge fluxes of high energy protons occurred in July and November 2000, September and November 2001, and October 2003. The highly energetic protons produce ionizations, excitations, dissociations, and dissociative ionizations of the background constituents, which lead to the production of HOx (H, OH, HO2) and NOy (N, NO, NO2, NO3, N2O5, HNO3, HO2NO2, ClONO2, BrONO2). The HOx increases lead to short-lived ozone decreases in the polar mesosphere and upper stratosphere due to the short lifetimes of the HOx constituents. Large mesospheric ozone depletions (〉70%) due to the HOx enhancements were observed and modeled as a result of the very large July 2000 SPE. The NOy increases lead to long-lived stratospheric ozone changes because of the long lifetime of the NOy family in this region. Polar total ozone depletions 〉1% were simulated in both hemispheres for extended periods of time (several months) as a result of the NOy enhancements due to the very large SPEs.

Beschreibung: We calculate the efficiency of iron K line emission and iron K absorption in photoionized models using a new set of atomic data. These data are more comprehensive than those previously applied to the modeling of iron K lines from photoionized gases, and allow us to systematically examine the behavior of the properties of line emission and absorption as a function of the ionization parameter, density and column density of model constant density clouds. We show that, for example, the net fluorescence yield for the highly charged ions is sensitive to the level population distribution produced by photoionization, and these yields are generally smaller than those predicted assuming the population is according to statistical weight. We demonstrate that the effects of the many strongly damped resonances below the K ionization thresholds conspire to smear the edge, thereby potentially affecting the astrophysical interpretation of absorption features in the 7-9 keV energy band. We show that the centroid of the ensemble of K(alpha) lines, the K(beta) energy, and the ratio of the K(alpha(sub 1)) to K(alpha(sub 2)) components are all diagnostics of the ionization parameter of our model slabs.

Beschreibung: We report on a short, XMM-Newton observation of the radio-quiet Narrow Line Seyfert 1 PG 1402+261. The EPIC X-ray spectrum of PG 1402+261 shows a strong excess of counts between 6 - 9 keV in the rest frame. This feature can be modeled by an unusually strong (equivalent width 2 keV) and very broad energy at 7.3 keV appears blue-shifted with respect to the iron Kalpha emission band between 6.4 - 6.97 keV, whilst the blue-wing of the line extends to 9 keV in the quasar rest frame. The line profile can be fitted by reflection from the inner accretion disk, but an inclination angle of greater than 60 degrees is required to model the extreme blue-wing of the line. Furthermore the extreme strength of the line requires a geometry whereby the hard X-ray emission from PG1402+261 above 2 keV is dominated by the pure-reflection component from the disk, whilst little or none of the direct hard power-law is observed. Alternatively the spectrum above 2 keV may instead be explained by an ionized absorber, if the column density is sufficiently high (NH greater than 3 x 10(exp 23) per square centimeter) and if the matter is ionized enough to produce a deep (tau approximately equal to 1) iron K-shell absorption edge at 9 keV. This absorber could originate in a large column density, high velocity outflow, perhaps similar to those which appear to be observed in several other high accretion rate AGN. Further observations, especially at higher spectral resolution, are required to distinguish between the accretion disk reflection or outflow scenarios.

Beschreibung: Accretion from a disk onto a collapsed, relativistic star - a neutron star or black hole - is the mechanism widely believed to be responsible for the emission from compact X-ray binaries. Because of the extreme spatial resolution required, it is not yet possible to directly observe the evolution or dynamics of the inner parts of the accretion disk where general relativistic effects are dominant. Here, we use the bright X-ray emission from a superburst on the surface of the neutron star 4U 1820-30 as a spotlight to illuminate the disk surface. The X-rays cause iron atoms in the disk t o fluoresce, allowing a determination of the ionization state, covering factor and inner radius of the disk over the course of the burst. The time-resolved spectral fitting shows that the inner region of the disk is disrupted by the burst, possibly being heated into a thicker, more tenuous flow, before recovering its previous form in approximately 1000 s. This marks the first instance that the evolution of the inner regions of an accretion disk has been observed in real-time.

Beschreibung: I have done detailed petrologic study of Ibitira, nominally classified as a basaltic eucrite. The Fe/Mn ratio of Ibitira pyroxenes with 〈10 mole % wollastonite component is 36.4 0.4, and is well-resolved from those of five basaltic eucrites studied for comparison; 31.2-32.2. Data for the latter completely overlap. Ibitira pyroxenes have lower Fe/Mg than the basaltic eucrite pyroxenes. Thus, the higher Fe/Mn ratio does not reflect a simple difference in oxidation state. Ibitira also has an oxygen isotopic composition, alkali element contents and a Ti/Hf ratio that distinguish it from basaltic eucrites. These differences support derivation from a distinct parent asteroid. Ibitira is the first recognized representative of the fifth known asteroidal basaltic crust.

Beschreibung: The Shock Compression Laboratory in the Department of Earth and Planetary Sciences at Harvard is a new facility for the study of impact and collisional phenomena. The following describes the experimental capabilities of the laboratory.

Beschreibung: Various killing mechanisms have been suggested to contribute to the mass extinctions at the KT boundary, including severe, global deterioration of the atmosphere and hydrosphere due to SO(x) released from heavily shocked, sulfate-bearing target rocks. The devolatilization of anhydrite is predominantly inferred from thermodynamic considerations and lacks experimental confirmation. To date, the experimentally determined shock behavior of anhydrite is limited to solid-state effects employing X-ray diffraction methods. The present report employs additional methods to characterize experimentally shocked anhydrite.

Beschreibung: Osmium isotope data had shown that Ivory Coast tektites contain an extraterrestrial component, but do not allow distinction between chondritic and iron meteorite contamination. PGE abundances of Ivory Coast tektites and impactites and target rocks from the Bosumtwi crater, the source crater of the Ivory Coast tektites, were all relatively high and did not allow to resolve the presence, or identify the nature, of the meteoritic component. However, Cr isotope analyses of an Ivory Coast tektite yielded a distinct 53Cr excess of 0.30+/-0.06, which indicates that the Bosumtwi impactor was an ordinary chondrite.

Beschreibung: The Miniature Thermal Emission Spectrometer (Mini-TES) has provided remote measurements of the mineralogy and thermophysical properties of the scene surrounding the Mars Exploration Rovers. The specific scientific objectives of this investigation are to: (1) determine the mineralogy of rocks and soils; (2) determine the thermophysical properties of surface materials; and (3) determine the temperature profile, dust and water-ice opacity, and water vapor abundance in the lower atmospheric boundary layer.

Beschreibung: The second MER rover (Opportunity) landed on Meridiani Planum on January 24, 2004 inside a shallow crater. The science rational for the selection of the landing site centered on detection of the mineral hematite from martian orbit by the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) [1,2]. Other smaller occurrences of hematite are in Aram Chaos and several isolated spots in Valles Marineris. Proposed formation pathways for martian hematite include both aqueous (e.g., low temperature precipitation of Fe oxides/oxyhydroxides in a lacustrine environment, laterite-style weathering, and precipitation from fluids having a hydrothermal origin) and dry (e.g., oxidation of magnetite rich ash) processes [e.g., 1,2,3]. The crystallographic c-face of martian hematite must be exaggerated to account for the thermal emissions spectra and it must be gray in color so as to account for the absence of the characteristic spectral signature of red hematite at visible wavelengths

Beschreibung: Though plausible explanations for the high latitude subsurface hydrogen features on Mars have been put forth, there still lacks a consensus on the nature of the low-latitude hydrogen features found in Arabia Terra and Daedalia Planum. While equivalent water mass fractions in these regions are low enough to potentially be explained by the presence of hydrated minerals, it still remains possible that such features are the remnants of ice deposits left from a previous period of high obliquity and which is now thermally unstable and subliming. In order to explore the thermal stability of putative ice deposits at low latitudes, we use the Geophysical Fluid Dynamics Laboratory (GFDL) Mars GCM with a newly integrated subsurface scheme to trace the deposition and sublimation rates of water ice, adsorbate and vapor across the planet at varying obliquities. In addition, these results help resolve the question of the dominant means of ice emplacement in the near surface, whether such ice is the result of buried surface deposits, or in situ emplaced ice due to vapor diffusion.

Beschreibung: The Flynn Creek impact structure is located in Tennessee, USA (36 deg.17 min.N, 85 deg.40 min.W). The structure was first mapped as a crypto-volcanic by Wilson and Born in 1936 [1]. Although they did not properly identify the stratigraphy within the crater or the causal mechanism, they did correctly define the horizontal extent of the crater. More detailed surface and subsurface research by Roddy (1979) accurately described the crater as being an impact structure with a diameter of 3.8 km. It formed around 360 Ma, which corresponds to the interval between the deposition of the Nashville Group and the Chattanooga Shale. Although there is limited rock outcrop in the area, there are exposed surface faults, folds, and large outcrops of impact breccia within the crater.

Beschreibung: Angrites constitute a small, but important group of basaltic achondrites showing unusual mineralogy and old crystallization ages. The currently known angrites are divided into two subgroups. Angra dos Reis (ADOR) and LEW86010 show slow cooling histories ("slowly-cooled" angrites) and differ from the later found angrites (LEW87051, Asuka 881371, Sahara 99555, D Orbigny, NWA1670, NWA1298). This second group has textures that suggest rapid cooling histories ("quenched" angrites). The petrogenesis of angrites has been controversial, partly due to the small number of available samples. In this abstract, we suggest a possible parent melt composition for the quenched angrites and its relationship to the partial melts of carbonaceous chondrites.

Beschreibung: Ureilites are ultramafic achondrites composed primarily of olivine and pyroxene with intergranular fine-grained metal, sulfides, and silicates. Ureilites contain significant amounts of carbon (up to about 6.5 wt%) as graphite, lonsdaleite, and/or diamond. It has been shown that carbon-silicate redox (i.e. "smelting") reactions are responsible for the negative FeO-MnO (or positive Fe/Mn-Fe/Mg with constant Mn/Mg) trend seen in the mineral and bulk compositions of ureilites and for the positive correlation between modal percent pigeonite and mg#. Carbon redox reactions are strongly exothermic and pressure dependent; so ureilites with the largest mg# are the most reduced, experienced the highest temperatures, and formed at the lowest pressures, i.e. near the surface of the ureilite parent body. Ureilites with the largest mg# have the smallest the delta(sup 18)O and the largest Delta(sup 17)O. To explain this, Singletary and Grove proposed that heterogeneous accretion took place on the ureilite parent body, which lead to a radial distribution of the oxygen isotopes. To further investigate possible relationships, we performed carbon isotope and electron probe measurements on a suite of 27 ureilites in order to see the type of correlation that exists between mg#, oxygen isotopes, and carbon.

Beschreibung: When a meteorite enters into the earth's atmosphere, it is immediately subjected to various chemical reactions between its minerals and the elements in our thick atmosphere. These reactions alter the mineralogy of the meteorites. Some examples of the altered minerals in some meteorites are summarized. If meteorites can be linked to their corresponding parent body asteroid in space, we can improve our understanding of the solar system. Spectroscopy has been used in determining the links between asteroids and meteorites. However, meteorite weathering in the Earth s atmosphere also has an effect on meteorite spectra, and altered spectra can easily confuse asteroid connections. The goal of this project is to study the mineral and spectral changes due to Earth's environment and to design a computer simulation to correct meteorite spectra for the effects of terrestrial weathering.

Beschreibung: Despite evidence from ground-based data that flow over mountains is a dominant source of gravity waves (GWs) for the Northern Hemisphere winter middle atmosphere, GW-related signals in global limb radiances from the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) have shown little direct evidence of mountain waves.

Beschreibung: Absorbing the electromagnetic radiation in several regions of the solar spectrum, CO2 plays an important role in the Earth radiation budget since it produces the greenhouse effect. Many natural processes in the Earth s system add and remove carbon dioxide. Overall, measurements of atmospheric carbon dioxide at different sites around the world show an increased carbon dioxide concentration in the atmosphere. At Mauna Loa Observatory (Hawaii) the measured carbon dioxide increased from 315 to 365 ppm, in the period 1958 2000 [Keeling et al., 2001]. While at the large scale, the relationship between CO2 increase and global warming is established [IPCC, 1996], at the local scale, many studies are still needed to understand regional and local sources of carbon dioxide, such as volcanoes. The volcanic areas are particularly rich in carbon dioxide; this is due to magma degassing in the summit craters region of active volcanoes, and to the presence of fractures and active faults [Giammanco et al., 1998]. Several studies estimate a global flux of volcanic CO2 (34+/-24)10(exp 6) tons/day from effusive volcanic emissions, such as the tropospheric volcanic plume (Table 1) [McClelland et al., 1989]. Plumes are a turbulent mixture of gases, solid particles and liquid droplets, emitted continuously at high temperature from summit craters, fumarolic fields or during eruptive episodes. Inside the plume, water vapour represents 70 90% of the volcanic gases. The main gaseous components are CO2, SO2, HCl, H2, H2S, HF, CO, N2 and CH4. Other plume components are volcanic ash, aqueous and acid droplets and solid sulphur-derived particles [Sparks et al., 1997]. Volcanic gases and aerosols are evidences of volcanic activity [Spinetti et al., 2003] and they have important climatic and environmental effects [Fiocco et al., 1994]. For example, Etna volcano is one of the world s major volcanic gas sources [Allard et al., 1991]. New studies on volcanic gaseous emissions have pointed out that a variation of the gas ratio CO2/SO2 is related to eruptive episodes [Caltabiano et al., 1994]. However, measurements and monitoring of volcanic carbon dioxide are difficult and often hazardous, due to the high background presence of atmospheric CO2 and the inaccessibility of volcanic sites. Hyperspectral remote sensing is a suitable technique to overcome the difficulties of ground measurement. It permits a rapid, comprehensive view of volcanic plumes and their evolution over time, detection of all gases with absorption molecular lines within the sensor s multispectral range and, in general, measurement of all the volatile components evolving from craters. The molecular and particle plume components scatter and absorb incident solar radiation. The integral of the radiation difference composes the signal measured by the remote spectrometer. The inversion technique consists of retrieving the plume component concentrations, hence decomposing the signal into the different contributions. The accuracy of remote sensing techniques depends primarily on the sensor capability and sensitivity.

Beschreibung: We present rotational light-curve data for Saturn's satellite Phoebe taken over the observing period prior to the Cassini mission's encounter with that moon.

Beschreibung: The high resolution UV capabilities (lamda/delta lambda = 10(sup 5)) of the Hubble Space Telscope (HST) equipped with the Space Telescope Imaging Spectrograph (STIS) reflects a need for high resolution laboratory UV spectral data base for comparison with observation.

Beschreibung: A remarkably linear, bipolar, knotty jet was recently discovered in Hen 2-90, an object classified as a young planetary nebula. Using two-dimensional, magnetohydrodynamic simulations, we investigate periodic variations in jet density and velocity as the mechanism for producing the jet and its knotty structures.

Beschreibung: The new MLS data are consistent with convective input of H(sub 2)O into the bottom of the TTL followed by slow ascent with a maximum relative amplitude in the seasonal cycle occurring near the tropopause nearly in phase with the tropopause temperature seasonal cycle.

Beschreibung: The Astrophysics of Reference Frame Tie Objects Key Science program will investigate the underlying physics of SIM grid objects. Extragalactic objects in the SIM grid will be used to tie the SIM reference frame to the quasi-inertial reference frame defined by extragalactic objects and to remove any residual frame rotation with respect to the extragalactic frame. The current realization of the extragalactic frame is the International Celestial Reference Frame (ICRF). The ICRF is defined by the radio positions of 212 extragalactic objects and is the IAU sanctioned fundamental astronomical reference frame. This key project will advance our knowledge of the physics of the objects which will make up the SIM grid, such as quasars and chromospherically active stars, and relates directly to the stability of the SIM reference frame. The following questions concerning the physics of reference frame tie objects will be investigated.

Beschreibung: The Hydrosphere State (HYDROS) Mission has been selected for the National Aeronautics and Space Administration (NASA) Earth System Science Pathfinder (ESSP) program. The objectives of HYDROS are to provide frequent, global measurements of surface soil moisture and surface freeze/thaw state. In order to adequately measure these geophysical parameters, a system capable of simultaneously measuring L-Band radiometer brightness temperatures at 40 km resolution and L-Band radar backscatter at 3 km resolution over a very wide swath is required. In addition, these science requirements must be satisfied under the stringent cost-cap imposed on all ESSP missions. As a solution to this challenging set of requirements, a relatively large, six meter, conically-scanning reflector antenna architecture was selected for the mission design. The HYDROS instrument will fly on a General Dynamics SA-200HP spacecraft bus. Although large deployable mesh antennas have been used in communication applications, this will mark the first time such technology is applied in a rotating configuration for high-resolution remote sensing.

Beschreibung: Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39-Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50-4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4561.9+/-0.1 Myr and 4560- 4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later Ar-40 diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the post-assembly metamorphism may have been as late as approx.4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx.4560 to approx.4576 Myr. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and s,uggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni concentration profiles in IAB metal (Herpfer et al., 1994). An explanation for the difference in radiometric ages of IABs may reside in combinations of the following: a) I-Xe ages have very high closure temperatures and were not reset during metamorphism; b) a bias exists in the K-40 decay constants; c) the reported Sm-Nd and Rb-Sr ages for Caddo are in error by amounts equal to or exceeding their reported 2-sigma uncertainties; and 4) the IAB parent body may have experienced a mild metamorphism approx.30 Myr after the initial heating that produced differentiation of Caddo silicate and mixing of silicate and metal.

Beschreibung: Ice I exhibits a complex rheology at temperature and pressure conditions appropriate for the interiors of the ice I shells of Europa, Ganymede, and Callisto. We use numerical methods and existing parameterizations of the critical Rayleigh number to determine the conditions required to trigger convection in an ice I shell with the stress-, temperature- and grain size- dependent rheology measured in laboratory experiments by Goldsby and Kohlstedt [2001]. The critical Rayleigh number depends on the ice grain size and the amplitude and wavelength of temperature perturbation issued to an initially conductive ice I shell. If the shells have an assumed uniform grain size less than 0.4 mm, deformation during initial plume growth is accommodated by Newtonian volume diffusion. If the ice grain size is between 0.4 mm and 3 cm, deformation during plume growth is accommodated by weakly non-Newtonian grain boundary sliding, where the critical ice shell thickness for convection depends on the amplitude of temperature perturbation to the _0.5 power. If the ice grain size exceeds 2 cm, convection can not occur in the ice I shells of the Galilean satellites regardless of the amplitude or wavelength of temperature perturbation. If the grain size in a convecting ice I shell evolves to effective values greater than 2 cm, convection will cease. If the ice shell has a grain size large enough to permit flow by dislocation creep, the ice is too stiff to permit convection, even in the thickest possible ice I shell. Consideration of the composite rheology implies that estimates of the grain size in the satellites and knowledge of their initial thermal states are required when judging the convective instability of their ice I shells.

Beschreibung: The Gravity Recovery and Climate Experiment (GRACE), launched on March 17, 2002, represents the state-of-the-art in geodetic observations of the static and time varying components of the Earth's geopotential field. The fundamental measurement used to observe gravity is the inter-satellite range and range rate between two coplanar, low altitude satellites obtained from a K-band ranging (KBR) system. In addition to the K-band ranging system, each satellite possess a Super-STAR Accelerometer, a GPS receiver/antenna package, Star Cameras and a Laser Retro Reflector (LRR) to complete the compliment of science instruments. The GRACE project has now released two years of Level 1B data derived from the science instruments and sensors. An integral component of our time variable gravity research is the reduction, calibration and analyses of these Level 1B data. In particular we have analyzed several months of K-band ranging (KBR1B), accelerometry (ACC1B) and GPS navigation (GNAV1B) data. Accelerometer calibration and KBR data reduction methodology and results will be presented. We discuss the impact of these analyses on the recovery of time variable gravity.

Beschreibung: The salar de Uyuni is a massive dry salt lake that lies at the lowest point of an internal/drainage basin in the Bolivian Altiplano. Its topography is remarkable for its extraordinary flatness over almost a full degree of latitude and longitude. We surveyed a 54 x 45 km region of the salar with kinematic GPS in September, 2002 and found a topographic range of only 80 cm over the entire surveyed area. Furthermore, the survey revealed distinct surface features with several dominant wavelengths and orientations. Some of these appear to be aligned with orographic features that intersect the salar, leading us to conjecture that they are the surface expression of high-density mountains that have been buried by low-density basin sediments. Over the oceans, a similar correspondence between basin bathymetry and surface topography is exploited to map the seafloor using sea-surface satellite altimetry measurements, with the sea surface following geoid undulations due to the underwater mass distribution. On the salar, annual flooding creates a shallow lake whose surface also lies on a equipotential surface shaped by the distribution of underlying mass. The link to the actual salar surface is via the dissolution and redeposition of salt by the lake waters, which appears to push the system to an equilibrium of constant water depth and the coincidence of the shapes of the lake surface and bottom. To test our hypothesis about the origin of the surface features on the salar, we compare our GPS survey elevations with the equipotential surface generated from local gravity measurements in conjunction with gravity and potential values from the EGM96 global geopotential model. 50% of the variance of the GPS elevations can be explained by equipotential surface undulations from the EGM96 model alone, and an additional 40% is explained by the shorter-wavelength equipotential surface derived from local gravity. We examine the unexplained 10% of elevation variance from the standpoint of errors in the equipotential surface calculation and possible unmodelled surface processes.

Beschreibung: NASA's Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat) is Earth's first polar-orbiting satellite laser altimeter. Its primary purpose is to measure ice sheet elevation change, with a scientific requirement of detecting changes as low as 1.5 centimeters per year. This goal requires precise calibration and validation of the instrument. One approach for validating the GLAS range measurement involves comparison with a land reference target. Dry salt lakes are ideal for this purpose since they are large, stable, easily surveyed using kinematic GPS, and have albedos similar to that of ice. We selected the largest dry salt lake in the world, the salar de Uyuni in Bolivia, as a reference target for GLAS. In September 2002 we surveyed a 54 x 45 kilometer area of the salar with car-mounted kinematic GPS, using the data to construct a DEM of the surface. To date there have been six ICESat passes across our survey area, along two intersecting tracks. The first two passes occurred during "Laser 2A" operation (September to November 2003), the second two during "Laser 2B" operation (February to March 2004), and the final two during "Laser 2C" (June to July 2004). We compare GLAS elevations from all six passes with the salar de Uyuni DEM, showing how differing conditions between passes affected the performance of the GLAS instrument and providing an estimate of the relative and absolute accuracy of the range measurement. To check our results, we also compare the GLAS elevations along the same tracks with the mean sea-surface derived from TOPEX over the ocean on either side of South America.

Beschreibung: Salt flats are aptly named: they are composed largely of salt, and are maintained as nearly equipotential surfaces via frequent flooding. The salar de Uyuni, on the Altiplano in southwestern Bolivia, is the largest salt flat on Earth, with an area of 9,800 sq km. Except for a few bedrock islands, it has less than 40 cm of relief. The upper-most salt unit averages 5 m thick and contains 50 cu km of nearly pure halite. It includes most of the salt that was in solution in paleolake Minchin, which attained a maximum area of 60,000 sq km and a maximum depth of 150 m, roughly 15 kyr ago. Despite approx. 10 m of differential isostatic rebound since deposition, the salar surface has been actively maintained as an extraordinarily flat and smooth surface by annual flooding during the rainy season. We have used the strong optical absorption properties of water in the visible band to map spatial variations in water depth during a time when the salar was flooded. As water depth increases, the initially pure white surface appears both darker and bluer. We utilized MISR images taken during the interval from April to November 2001. The red and infra-red bands (672 and 867 nm wavelength) were most useful since the water depth is small and the absorption at those wavelengths is quite strong. Nadir pointed MISR images have 275 m spatial resolution. To aid in our evaluation of water depth variations over the saiar surface, we utilized two sources of direct topographic measurements: several ICESAT altimetry tracks cross the area, and a 40x50 km GPS grid was surveyed to calibrate ICESAT. A difficulty in using these data types is that both give salt surface elevations relative to the ellipsoid, whereas the water surface will, in the absence of wind or tidal disturbances, follow an equipotential surface. Geoid height is not known to the required accuracy of a few cm in the central Andes. As a result, before comparing optical absorption from MISR to salt surface topography from GPS or ICESAT, we removed the longest wavelengths from both.

Beschreibung: We have analyzed GRACE Level 1-B data in 2003 and assessed a new approach for extracting time variable gravity that isolates the gravity signal in both time and space. The Level-1B satellite-to-satellite range rate (KBRR) data and accelerometry are processed in daily arcs using the precise orbit products produced by the GRACE team from GPS to calibrate both the accelerometer and KBRR data. We then adjusted select components of the intersatellite baseline vector for each data segment isolated to the region of interest. Herein, we solved for mass anomalies in 45 deg x 45 deg blocks over the Amazon and the nearby Atlantic Ocean and estimate mass flux in units of cm of water over each block. We show with this approach that we can recover mass anomalies on a submonthly basis with 10 to 15 day temporal resolution. We discuss the important issues related to this solution, including the size of the mascon blocks, the weight given to the temporal and spatial constraint used to stabalize the solutions, as well as the optimal correlation in time and distance. We compare the the mascon results with solutions obtained from the more standard approach using spherical harmonics and with independent hydrology models and lake data. This technique demonstrates that sub-monthly medium wavelength mass flux phenomena are well sensed by the hyper-precise line of sight velocity data produced from GRACE.

Beschreibung: The purpose of this project was to provide the community access to magnetosheath data near Earth. We provided 27 years of IMP 8 magnetosheath proton velocities, densities, and temperatures with our best (usually 1-min.) time resolution. IMP 8 crosses the magnetosheath twice each 125 day orbit, and we provided magnetosheath data for the roughly 27 years of data for which magnetometer data are also available (which are needed to reliably pick boundaries). We provided this 27 years of IMP 8 magnetosheath data to the NSSDC; this data is now integrated with the IMP 8 solar wind data with flags indicating whether each data point is in the solar wind, magnetosheath, or at the boundary between the two regions. The plasma speed, density, and temperature are provided for each magnetosheath point. These data are also available on the MIT web site ftp://space .mit.edu/pub/plasma/imp/www/imp.html. We provide ASCII time-ordered rows of data giving the observation time, the spacecraft position in GSE, the velocity is GSE, the density and temperature for protons. We also have analyzed and archived on our web site the Wind magnetosheath plasma parameters. These consist of ascii files of the proton and alpha densities, speeds, and thermal speeds. These data are available at ftp://space.mit.edu/pub/plasma/wind/sheath These are the two products promised in the work statement and they have been completed in full.

Beschreibung: The first findings from a year of WMAP satellite operations provide a detailed full sky map of the cosmic microwave background radiation. The observed temperature anisotropy, combined with the associated polarization information, encodes a wealth of cosmological information. The results have implications for the history, content, and evolution of the universe, and its large scale properties. These and other aspects of the mission will be discussed.

Beschreibung: We present latest result in understanding the potential relationship between tectonic stress, electro-chemical and thermodynamic processes in the Earths crust and atmosphere with an increase in IR flux as a potential signature of electromagnetic (EM) phenomena that are related to earthquake activity, either pre-, co- or post seismic. Thermal infra-red (TIR) surveys performed by the polar orbiting (NOAA/AVHRR MODIS) and geosynchronous weather satellites (GOES, METEOSAT) gave an indication of the appearance (from days to weeks before the event) of "anomalous" space-time TIR transients that are associated with the location (epicenter and local tectonic structures) and time of a number of major earthquakes with M〉5 and focal depths less than 50km. We analyzed broad category of associated pre-earthquake events, which provided evidence for changes in surface temperature, surface latent heat flux, chlorophyll concentrations, soil moisture, brightness temperature, emissivity of surface, water vapour in the atmosphere prior to the earthquakes occurred in Algeria, India, Iran, Italy, Mexico and Japan. The cause of such anomalies has been mainly related to the change of near-surface thermal properties due to complex lithosphere-hydrosphere-atmospheric interactions. As final results we present examples from the most recent (2000-2004) worldwide strong earthquakes and the techniques used to capture the tracks of EM emission mid-IR anomalies and a methodology for practical future use of such phenomena in the early warning systems.