bluuebunny/crossref_metadata_2025 huggingface dataset:
The storm‐time access of solar wind ions to the nightside ring current and plasma sheet
Authors: Peroomian Vahé , El‐Alaoui Mostafa
Published: June 2008

We investigated the storm‐time entry of solar wind ions into the magnetosphere by carrying out a large‐scale kinetic particle tracing calculation for the 24–25 September 1998 and the 17 April 2002 geomagnetic storms. For each storm, we simulated the magnetosphere by using a global magnetohydrodynamic (MHD) code that was driven by solar wind and interplanetary magnetic field (IMF) data from spacecraft upstream of Earth. We then launched ions in the solar wind in the global time‐dependent fields obtained from the MHD simulation, beginning prior to storm onset and extending into the main phase. We collected those ions that successfully reached the nightside plasma sheet and ring current, and then determined the mechanisms of entry and transport responsible for the injection of these ions into the magnetotail. We found that, in agreement with quiet time entry results, the IMF By component strongly influenced whether ions entered through the dawn or dusk flanks, and changes in IMF By were immediately reflected on the ion entry pattern. Also, in addition to the usual dayside merging source, ion entry into the magnetosphere was facilitated by dynamic pressure enhancements, during which entry occurred over a wide swath of latitudes and extended from the dayside to locations far downtail. More significantly, because of the warmer storm‐time ion population in the magnetosheath, ions were more readily affected by inhomogeneities and rapid changes in the IMF, which caused solar wind ions to gradient drift onto open field lines and reach the inner magnetosphere.
Variations in the chorus source location deduced from fluctuations of the ambient magnetic field: Comparison of Cluster data and the backward wave oscillator model
Authors: Kozelov B. V. , Demekhov A. G. , Titova E. E. , Trakhtengerts V. Y. , Santolik O. , Macusova E. , Gurnett D. A. , Pickett J. S.
Published: June 2008

We study the motion of the source region of magnetospheric chorus emissions using multipoint measurements of VLF wave emissions and geomagnetic field onboard the Cluster spacecraft. The geomagnetic field data are matched to a parameterized model of the local magnetic field, and the spatiotemporal dynamics of the magnetic field are obtained on this basis. The wave data from the Wide Band Data instrument are used to obtain the power spectral density and number of chorus elements. Comparison of these data shows that the chorus remains related to the magnetic field minimum, while the position of this minimum can vary rather strongly during periods of enhanced geomagnetic activity. These results support the backward wave oscillator (BWO) model of chorus emissions, which attributes chorus generation to an absolute instability of whistler mode waves in the presence of a step‐like velocity distribution of energetic electrons. Such an instability takes place in a small vicinity of the local “magnetic equator” of a magnetic field line. Quantitative agreement between the data and the model is demonstrated by variation of the statistical chorus characteristics with changing of the deduced BWO parameters.
Simulations of coronal type III solar radio bursts: 1. Simulation model
Authors: Li Bo , Cairns Iver H. , Robinson Peter A.
Published: June 2008

A simulation model is developed for type III bursts that originate in the solar corona and are observed at Earth. The model incorporates the three‐dimensional structure of the source region, dynamics in the source of electron beam, Langmuir waves, ion‐sound waves, electromagnetic emissions at the fundamental (fp) and second harmonic (2fp) of the plasma frequency, and propagation of electromagnetic radiation from the corona to interplanetary space, and it predicts the radiation dynamic spectrum measured by a remote observer. During the propagation of the radiation, the effects of refraction and reflection on large‐scale density variations, scattering off small‐scale density fluctuations, and free‐free absorption are taken into account. The scattering of fp emission is modeled numerically on the basis of an analytic approach developed previously. The numerical results confirm approximations made in the approach and generalize it to more realistic solar plasma conditions.
Simulations of coronal type III solar radio bursts: 2. Dynamic spectrum for typical parameters
Authors: Li Bo , Cairns Iver H. , Robinson Peter A.
Published: June 2008

Predictions are presented for the dynamic spectrum of a coronal type III burst observed at Earth, using a newly developed simulation model and employing realistic electron release and coronal parameters. The spectrum is studied in detail in association with the dynamics of beam and waves in the source. The frequency drift rate, radio flux, brightness temperature, and temporal profile of the type III burst agree semiquantitatively with typical observations. The simulation model is thus viable. Because of strong free‐free absorption and scattering‐induced damping, the flux of fp emission is significantly lower than that of 2fp emission and is below the lower thresholds of typical radio instruments. Moreover, the fp emission terminates at frequencies higher than the minimum simulated, and the 2fp emission appears to terminate at higher coronal altitudes that are not simulated because of computational limitations. Further simulations indicate that F‐H pairs may exist under favorable conditions (e.g., generally, lower levels and larger length scales of the density fluctuations).
Detailed nature of the 660 km region of the mantle from global receiver function data
Authors: Andrews J. , Deuss A.
Published: June 2008

We use a global data set of receiver functions to study the range of observations for the region at the base of the mantle transition zone, around the 660 km discontinuity. A variety of signals has already been observed in regional studies; here we characterize the breadth of such observations on a global scale. While the 410 km discontinuity is usually found to be simple in shape, the 660 km discontinuity often shows broad or asymmetric peaks and sometimes multiple signals. Unlike previous studies on the subject, we show that complexity of structure is not limited to subduction zones. Reflectivity synthetics are used to show that the observed signals can be generated by structures with combinations of sharp discontinuities and velocity gradients around 660 km depth. Mineral physics suggests that at 410 km depth only the olivine phase transition is important. In contrast, at 660 km depth both the olivine and nonolivine transitions generate multiple discontinuities and gradients, which could be visible to Pds signals. Seismic observations of a simple 410 km signal and a complex 660 km signal might therefore be expected from the predictions of mineral physics. However, a mantle of uniform composition fails to explain the variety of signals seen in our data set, requiring laterally varying chemical composition at the base of the mantle transition zone.
Fore arc structure and plate boundary earthquake sources along the southwestern Kuril subduction zone
Authors: Okamura Yukinobu , Tsujino Takumi , Arai Kohsaku , Sasaki Tomoyuki , Satake Kenji , Joshima Masato
Published: June 2008

The geologic structure and gravity anomalies of the fore arc wedge along the southwestern Kuril arc were compared with the sources of seismic waves and tsunamis of the 1952, 1973, and 2003 plate boundary earthquakes. The source areas are generally located beneath fore arc basins in the upper slope which has been subsiding, except for the tsunami source of the 1952 earthquake, while the slip amount varies beneath the basins. Large slip of seismic sources of the 1952 and 2003 earthquakes occurred under the low gravity anomaly zone of a fore arc basin and a structural ridge along the N‐S‐oriented collision zone between the Kuril and NE Japan fore arcs, where there is inferred to be a zone of a strong basal erosion of the overriding plate. The tsunami sources are located under the subsiding area to the east of the collision zone. These comparisons indicate that the source areas are primarily restricted to the region under the subsiding area of the upper slope, and the lateral change of slip amount in the source areas is related to the collision tectonics of the fore arc sliver. The 1952 tsunami source extended seaward, which was presumably induced by the slip of the larger seismic source under the upper slope. The lack of large‐scale slope failure or splay faults in the middle to lower slope suggests that the slip along the plate boundary is responsible for tsunami generation. A subducting seamount presumably prevented the seaward propagation of the rupture beneath the middle to lower slope.
Seismic array detection of subducted oceanic crust in the lower mantle
Authors: Rost Sebastian , Garnero Edward J. , Williams Quentin
Published: June 2008

We analyze short‐period precursory energy to PP that can be observed in seismograms in the distance range from ∼95° to 105° to infer the behavior of subducted slabs beneath western Pacific subduction zones. PP is a P wave once reflected at the free surface between the source and receiver. Using high‐resolution seismic array techniques, we analyze the incidence angle, timing, and azimuth of the PP precursors. The precursory energy is resolved to originate from off great circle path azimuths and is consistent with scattering by small‐scale heterogeneities. Assuming single scattering, upper mantle‐ and midmantle‐derived scatterer locations show a strong geographical and depth correlation to high seismic velocities in tomographic studies. Scattering locations beneath the Tonga and Mariana subduction zones outline continuous dipping structures to a depth of at least 1000 km, consistent with scattering associated with subducted former oceanic lithosphere. Scatterer locations uniquely explain the timing, slowness, and back azimuth of the PP precursors at the array. The observed reflections can be explained with the velocity impedance variations expected for high‐pressure basalt juxtaposed with pyrolite or harzburgite and thus may be due to the paleo‐Mohorovičić discontinuity within subducted slabs. These results are consistent with basaltic crust penetrating into the lower mantle. This method provides a means for tracking the location of geochemically enriched former oceanic crust in the lower mantle by using recordings of globally distributed seismic arrays and is complementary to longer‐wavelength constraints on high seismic velocity slabs inferred from tomography.
Dissipation analysis as a guide to mode selection during crustal extension and implications for the styles of sedimentary basins
Authors: Buiter Susanne J. H. , Huismans Ritske S. , Beaumont Christopher
Published: June 2008

We analyze the initial modes of continental extension with the aim of providing an improved understanding of the dynamic development of sedimentary basins. We first examine simple two‐layer crustal‐scale models which consist of a frictional‐plastic upper crust bonded to a linear viscous lower crust of equal thickness. The mode of deformation is predicted by using an analytical analysis of the rate of internal dissipation of energy and the gravitational rate of work. It is assumed that models deform in the mode in which the total rate of work is minimized. For strain‐softening models we predict the following modes of crustal extension: (1) pure shear, (2) multiple conjugate or parallel shear zones, (3) two shear zones, which form either one symmetric basin or two asymmetric basins, and (4) a single shear zone forming an asymmetric basin. The transitions between these modes are shown to depend on the trade off between “gains” that reduce the rate of energy dissipation and “penalties” that increase it. A single asymmetric basin is preferred for a strong brittle layer which has a high amount of strain softening (high plastic gain), a weak viscous layer and slow extension (low viscous penalty). A decrease in the plastic gain and/or an increase in the viscous penalty leads to modes with more shear zones in the upper crust. The pure shear mode is found for low strain softening, a high viscosity, and/or fast extension. Results of finite element calculations of equivalent simple two‐layer models agree with the analytical mode predictions.
Early Jurassic magnetostratigraphy and paleolatitudes from the Hartford continental rift basin (eastern North America): Testing for polarity bias and abrupt polar wander in association with the central Atlantic magmatic province
Authors: Kent Dennis V. , Olsen Paul E.
Published: June 2008

To determine whether the ∼200 Ma central Atlantic magmatic province (CAMP) coincides with a normal polarity bias and a purported abrupt change in polar wander at the J1 cusp, we collected samples for paleomagnetic study from 80 sites distributed over a ∼2500‐m‐thick section of sedimentary units that are interbedded with and overlie CAMP lavas in the Hartford basin, which together represent the initial 2.4 Ma of the Jurassic according to cycle stratigraphic analysis. Characteristic directions carried by hematite were isolated by thermal demagnetization in 71 sites and define a coherent magnetostratigraphy supported by a positive reversal test and an interbasin fold test. Despite a pronounced overall normal polarity bias (only three relatively short reverse polarity intervals could be confirmed in the sampled section), normal polarity Chron H24n that encompasses the CAMP extrusive zone is no more than 1.6 Ma in duration. Elongation/inclination analysis of the 315 characteristic directions, which have a flattened distribution, produces a result in agreement with a published mean direction for the CAMP volcanic units as well as published results similarly corrected for inclination error from the Newark basin. The three data sets (CAMP volcanics, Newark corrected sediments, and Hartford corrected sediments) provide a 201 Ma reference pole for eastern North America at 67.0°N, 93.8°E, A95 = 3.2°. Paleopoles from the Moenave and Wingate formations from the Colorado Plateau that virtually define the J1 cusp can be brought into agreement with the 201 Ma reference pole with corrections for net clockwise rotation of the plateau relative to eastern North America and presumed sedimentary inclination error. The corrected data show that apparent polar wander for North America proceeds directly toward higher latitudes over the Late Triassic and Early Jurassic with no obvious change that can be associated with CAMP.
Variability of the Kuroshio Current south of Sagami Bay as observed using long‐range coastal HF radars
Authors: Ramp Steven R. , Barrick Donald E. , Ito Tomotaka , Cook Michael S.
Published: June 2008

Ocean surface currents between Cape Nojima and Hachijo Island have been mapped since fall 2000 using a pair of SeaSonde long‐range HF radars. During September 2000 through December 2001, the no large meander (NLM) nearshore (n) and offshore (o) modes were observed. The surface current maps allowed new details to be observed in the structure of these modes and the transitions between them. Two noteworthy phenomena include blocking of the surface currents when the Kuroshio was in an extreme nearshore position behind the Zenisu Ridge and the “Kyucho” pattern when the current retroflexed from the NLMo position. In early 2004, a large meander (LM) developed and was well established in its historical position south of Honshu by August 2004. Subsequently, the LM continued propagating downstream, but stopped when it encountered the Izu Ridge. It then moved back to its original position near 137.5°E, and the process repeated itself. This east‐west oscillation resulted in two common positions for the LM south of Sagami Bay: from its more westerly position (LMw, for west) the Kuroshio had a very favorable approach to the deep gap between Miyake Island and the Zenisu Ridge, and the currents were strongly toward the northeast through the region. When the meander moved up against the ridge (LMe, for east), a strong along‐ridge current toward the northwest was evident, which turned sharply northeast when it encountered the shallow Zenisu Ridge. The dominant timescale for this within‐mode variability was about 30 days.
Observations of sea ice thickness, surface roughness and ice motion in Amundsen Gulf
Authors: Peterson I. K. , Prinsenberg S. J. , Holladay J. S.
Published: June 2008

Ice thickness and surface roughness measurements of first‐year (FY) sea ice were collected with a fix‐mounted helicopter‐borne electromagnetic (HEM) ‐laser system in Amundsen Gulf in April to May 2004. The modal ice thickness values are in good qualitative agreement with different ice types identified in synthetic aperture radar (SAR) imagery and shown on ice charts produced by the Canadian Ice Service. Modal ice thickness values which generally represent level ice thicknesses were about 2.0 m over landfast ice. A large range of modal ice thicknesses was observed in the mobile ice region, with values of about 0.2 m (young ice) in leads (where there was high radar backscatter), 0.6 m (thin FY ice) in the polynya (where there was medium to high backscatter), and about 1.1–1.9 m (thick FY ice) elsewhere. High surface roughnesses are strongly associated with high radar backscatter in SAR imagery, and are observed in areas of large shear. The ratio of the standard deviations of ice draft and averaged roughness in an area of landfast ice is in good agreement with the ratio of the standard deviations of ice draft and ice‐equivalent roughness expected from isostasy, with constant level ice and snow thickness. However, the standard deviation of ice‐equivalent roughness may be significantly underestimated, due to differences in snow thickness between level and deformed ice, and limitations of the laser processing method. Modal ice (plus snow) thicknesses measured with the HEM system are within the range of historical values measured at Cape Parry.
Mass transport in the Bay of Biscay from an inverse box model
Authors: Fraile‐Nuez Eugenio , Plaza Francisco , Hernández‐Guerra Alonso , Vargas‐Yáñez Manuel , Lavín Alicia
Published: June 2008

Mass transports in the Bay of Biscay for thermocline, intermediate and deep water masses are estimated from a box inverse model applied to hydrographic data from a quasi‐synoptic survey carried out in August 2005. The model obeys conservation statements for mass in a volume of ocean bounded by 43 full depth CTD stations in the horizontal, and neutral density layers in the vertical. It permits advective exchange between layers and an adjustment of the Ekman transport and the freshwater flux divergences. Bay of Biscay has a thermocline transport of −8.0 ± 0.7 Sv with an anticyclonic recirculation of +6.9 ± 0.6 Sv. An equatorward flow of +0.5 ± 0.4 Sv is attributed to the slope current close to the northwestern Spanish coast. The mean wind stress curl for the region corresponds with a clockwise upper layer flow which produces a downwelling of −0.6 ± 0.4 Sv. The surface circulation pattern agrees with the obtained with the Jason‐1 altimeter. Intermediate waters follow the same surface pattern of the thermocline waters as a subsurface eastern boundary current with an eastward flow of −7.9 ± 1.0 Sv and a southwestward flow of +8.0 ± 1.0 Sv. Finally, our results show that deep waters also flow into the box with a net transport of −3.6 ± 2.0 Sv and flow out of the box with a net transport of 2.3 ± 2.0 Sv.
Airborne Fourier transform spectrometer observations in support of EOS Aura validation
Authors: Coffey M. T. , Hannigan J. W. , Goldman A. , Kinnison D. , Gille J. C. , Barnett J. J. , Froidevaux L. , Lambert A. , Santee M. , Livesey N. , Fisher B. , Kulawik S. S. , Beer R.
Published: June 2008

Nearly coincident observations of HNO3, HCl, N2O, and H2O in the vicinity of the northern polar vortex during the NASA Polar Aura Validation Experiment (PAVE) in January and February 2005 have shown reasonably good agreement between aircraft‐borne infrared spectrometer results and results from High Resolution Dynamics Limb Sounder (HIRDLS), Microwave Limb Sounder (MLS), and Tropospheric Emission Spectrometer (TES) instruments aboard the EOS Aura satellite. Mixing ratio profile and column results show that special attention must be given to retrievals that may be disturbed by the dynamics and chemical processing of the polar vortex. Largest differences occur on days when observations were made in regions of the vortex with large gradients in wind and potential vorticity, and the differences were especially noticeable in results for HNO3 and HCl, whose profiles may be dramatically changed by vortex activity. The mean difference between coincident column observations by MLS and the Fourier transform spectrometer (FTS) is 2.4%, VMR profile amounts generally are in good agreement between the satellite observations where they are available. The average difference between coincident HCl column observations by MLS and the FTS is 4.6%.
Global modeling of multicomponent aerosol species: Aerosol optical parameters
Authors: Ayash T. , Gong S. L. , Jia C. Q. , Huang P. , Zhao T. L. , Lavoue D.
Published: June 2008

Canadian Aerosol Module (CAM) has been developed to simulate the atmospheric cycling of principal aerosol species, with the Third Generation Canadian Climate Center General Circulation Model (CCC GCM III) as its climatological driver. Adding an aerosol optical module to this modeling framework, the optical parameters of aerosols are simulated and compared to Sun photometer (AERONET) and satellite (MODIS) observations, as well as lidar observations of aerosol vertical profiles. The model captures well the global distribution and seasonal variation of aerosol optical parameters, showing seasonal maxima of optical depth and absorption over desert and biomass‐burning regions. For most sites and months, the modeled optical depths are within MODIS and AERONET means and standard deviations, and modeled single‐scattering albedo (SSA) and asymmetry factor are within 10% of AERONET retrievals. Fairly good agreement is found between modeled and observed optical depths over tropical oceans, where most models show significant underestimation. The model's overestimation of observed optical depths over parts of Europe by about 0.1 is most likely due to overestimates by older emission inventories. Modeled optical depths and SSA above observed means and standard deviations over areas and at sites within Central Africa and Central and South America suggest overprediction of organic carbon contribution by the model. Common to other models, however, our simulations underestimate the strength of the tropical biomass burning season. Modeled aerosol vertical profiles show better agreement with lidar observations at European sites than at an East Asian site, and more so at upper than at lower altitudes.
Retrieval of cloud properties from near‐ultraviolet, visible, and near‐infrared satellite‐based Earth reflectivity spectra: A comparative study
Authors: van Deelen R. , Hasekamp O. P. , van Diedenhoven B. , Landgraf J.
Published: June 2008

In this study, we investigate the capability to retrieve cloud parameters from near‐ultraviolet, visible, and near‐infrared satellite‐based reflectivity measurements. These parameters are essential to enable trace gas retrievals for cloud‐contaminated satellite scenes. We compare the retrieval of cloud top pressure, cloud fraction, and cloud optical thickness from simulated reflectivity measurements in three wavelength ranges: (1) 350–400 nm, which includes pronounced Ring effect structures; (2) 460–490 nm; and (3) 755–775 nm, which contain absorption features of O2‐O2 and O2, respectively. Retrieval simulations are performed for both a typical noise level of present‐day space‐borne spectrometers and additional random‐like measurement biases. Furthermore, we investigated the importance of the spectral continuum for the retrieval of cloud properties. It is found that reflectivity measurements in the wavelength ranges 350–400 and 755–775 nm provide complementary information on cloud properties. Both spectral windows provide more information on clouds than the 460–490 nm window. The best results are obtained for the combination of the 350–400 and 755–775 nm windows. In this case all three cloud parameters can be retrieved independently, and a high robustness is obtained with respect to random‐like measurement biases. Here it is not required to resolve the Ring effect structures in the near‐ultraviolet window. For this combination of spectral windows the error on retrieved NO2 columns is reduced considerably.
Impact of variations in solar activity on hydrological decadal patterns in northern Italy
Authors: Zanchettin D. , Rubino A. , Traverso P. , Tomasino M.
Published: June 2008

Using spectral and statistical analyses of discharges and basin average precipitation rates acquired over the Po River since the early 1800s, we investigate the impact of variations in solar activity on hydrological decadal patterns over northern Italy. Wet and dry periods appear to alternate in accordance with polarized sunspot cycles. Intriguingly, a solar signature on Po River discharges is detected to be highly significant since the late 1800s, before the onset of sunspots hyperactivity established by the middle 1900s. In particular, observed hydrological patterns over northern Italy are significantly correlated, under periods of quiet sunspot activity, with parameters characterizing the Sun's orbital motion, specifically with the time derivative of the solar angular momentum (τ) which is thought to modulate the strength of the solar wind and sunspot dynamics under weak sunspot activity. The North Atlantic Oscillation (NAO) is detected as potential link between the Sun and Po River discharges, since it is significantly correlated with both solar activity and the decadal variability in the north Italian climate. In particular, positive (negative) NAO anomalies, which are associated with comparatively lower (higher) Po River discharges, are assessed to alternatively correlate at decadal timescales either with τ or with the Earth's geomagnetic activity (GA), which closely follows sunspot activity. This changing correlation seems to be regulated by the strength of sunspot activity: under periods of quiet sunspot activity, a weakening of the GA‐NAO connection and a reinforcement of the τ‐NAO connection is observed. In this sense, the strength of solar activity apparently modulates the connection between the NAO and Po River discharges.
O2/N2 ratios of occluded air in the GISP2 ice core
Authors: Suwa Makoto , Bender Michael L.
Published: June 2008

We present and discuss the record of O2/N2 ratios in air occluded in the GISP2 ice core retrieved from Summit, Greenland. In this study, we examine results for 601 samples from 331 depths measured by 1994, and 92 samples from 46 depths newly measured in 2006. Poorly replicated samples, samples with no replicates and samples falling more than three standard deviations from the mean of each δO2/N2 data set are excluded from the analysis. The majority of poorly replicated samples are from the depth zone associated with the transition between gas in bubbles and gas present as clathrate hydrates. We found that the O2/N2 ratio of samples is depleted by an average value of 7.3‰ during 11 years of storage at −35°C O2/N2 ratios measured at various times were corrected for depletion during storage and combined to form a single data set. The stacked GISP2 δO2/N2 record shows strong spectral power at the orbital frequencies, and δO2/N2 is in antiphase with local summer insolation. This observation is consistent with the earlier findings for the Vostok and Dome Fuji ice cores from East Antarctica. It validates previous conclusions that fractionation during bubble close‐off depends on ice grain properties set at the surface by solar insolation. In addition, the GISP2 δO2/N2 record shows millennial duration signals that are in phase with the local temperature record of rapid climate change. The exact mechanisms by which local summer insolation induces orbital variability in δO2/N2, and by which temperature (or related properties) induce high frequency signals in δO2/N2, remain to be identified.
Mars Exploration Rover Navigation Camera in‐flight calibration
Authors: Soderblom Jason M. , Bell James F. , Johnson Jeffrey R. , Joseph Jonathan , Wolff Michael J.
Published: June 2008

The Navigation Camera (Navcam) instruments on the Mars Exploration Rover (MER) spacecraft provide support for both tactical operations as well as scientific observations where color information is not necessary: large‐scale morphology, atmospheric monitoring including cloud observations and dust devil movies, and context imaging for both the thermal emission spectrometer and the in situ instruments on the Instrument Deployment Device. The Navcams are a panchromatic stereoscopic imaging system built using identical charge‐coupled device (CCD) detectors and nearly identical electronics boards as the other cameras on the MER spacecraft. Previous calibration efforts were primarily focused on providing a detailed geometric calibration in line with the principal function of the Navcams, to provide data for the MER navigation team. This paper provides a detailed description of a new Navcam calibration pipeline developed to provide an absolute radiometric calibration that we estimate to have an absolute accuracy of 10% and a relative precision of 2.5%. Our calibration pipeline includes steps to model and remove the bias offset, the dark current charge that accumulates in both the active and readout regions of the CCD, and the shutter smear. It also corrects pixel‐to‐pixel responsivity variations using flat‐field images, and converts from raw instrument‐corrected digital number values per second to units of radiance (W m−2 nm−1 sr−1), or to radiance factor (I/F). We also describe here the initial results of two applications where radiance‐calibrated Navcam data provide unique information for surface photometric and atmospheric aerosol studies.
Mars Exploration Program 2007 Phoenix landing site selection and characteristics
Authors: Arvidson R. , Adams D. , Bonfiglio G. , Christensen P. , Cull S. , Golombek M. , Guinn J. , Guinness E. , Heet T. , Kirk R. , Knudson A. , Malin M. , Mellon M. , McEwen A. , Mushkin A. , Parker T. , Seelos F. , Seelos K. , Smith P. , Spencer D. , Stein T. , Tamppari L.
Published: June 2008

To ensure a successful touchdown and subsequent surface operations, the Mars Exploration Program 2007 Phoenix Lander must land within 65° to 72° north latitude, at an elevation less than −3.5 km. The landing site must have relatively low wind velocities and rock and slope distributions similar to or more benign than those found at the Viking Lander 2 site. Also, the site must have a soil cover of at least several centimeters over ice or icy soil to meet science objectives of evaluating the environmental and habitability implications of past and current near‐polar environments. The most challenging aspects of site selection were the extensive rock fields associated with crater rims and ejecta deposits and the centers of polygons associated with patterned ground. An extensive acquisition campaign of Odyssey Thermal Emission Imaging Spectrometer predawn thermal IR images, together with ∼0.31 m/pixel Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment images was implemented to find regions with acceptable rock populations and to support Monte Carlo landing simulations. The chosen site is located at 68.16° north latitude, 233.35° east longitude (areocentric), within a ∼50 km wide (N‐S) by ∼300 km long (E‐W) valley of relatively rock‐free plains. Surfaces within the eastern portion of the valley are differentially eroded ejecta deposits from the relatively recent ∼10‐km‐wide Heimdall crater and have fewer rocks than plains on the western portion of the valley. All surfaces exhibit polygonal ground, which is associated with fracture of icy soils, and are predicted to have only several centimeters of poorly sorted basaltic sand and dust over icy soil deposits.
Hydrothermal origin of halogens at Home Plate, Gusev Crater
Authors: Schmidt Mariek E. , Ruff Steven W. , McCoy Timothy J. , Farrand William H. , Johnson Jeffrey R. , Gellert Ralf , Ming Douglas W. , Morris Richard V. , Cabrol Nathalie , Lewis Kevin W. , Schroeder Christian
Published: June 2008

In the Inner Basin of the Columbia Hills, Gusev Crater is Home Plate, an 80 m platform of layered clastic rocks of the Barnhill class with microscopic and macroscopic textures, including a bomb sag, suggestive of a phreatomagmatic origin. We present data acquired by the Spirit Mars Exploration Rover by Alpha Particle X‐Ray Spectrometer (APXS), Mössbauer Spectrometer, Miniature Thermal Emission Spectrometer (Mini‐TES), and Panoramic Camera (Pancam) for the Barnhill class rocks and nearby vesicular Irvine class basalts. In major element concentrations (e.g., SiO2, Al2O3, MgO, and FeO*), the two rock classes are similar, suggesting that they are derived from a similar magmatic source. The Barnhill class, however, has higher abundances of Cl, Br, Zn, and Ge with comparable SO3 to the Irvine basalts. Nanophase ferric oxide (np ox) and volcanic glass were detected in the Barnhill class rocks by Mössbauer and Mini‐TES, respectively, and imply greater alteration and cooling rates in the Barnhill than in the Irvine class rocks. The high volatile elements in the Barnhill class agree with volcanic textures that imply interaction with a briny groundwater during eruption and (or) by later alteration. Differences in composition between the Barnhill and Irvine classes allow the fingerprinting of a Na‐Mg‐Zn‐Ge‐Cl‐Br (±Fe ± Ca ± CO2) brine with low S. Nearby sulfate salt soils of fumarolic origin may reflect fractionation of an acidic S‐rich vapor during boiling of a hydrothermal brine at depth. Persistent groundwater was likely present during and after the formation of Home Plate.
NASA Mars 2007 Phoenix Lander Robotic Arm and Icy Soil Acquisition Device
Authors: Bonitz Robert G. , Shiraishi Lori , Robinson Matthew , Arvidson Raymond E. , Chu P. C. , Wilson J. J. , Davis K. R. , Paulsen G. , Kusack A. G. , Archer Doug , Smith Peter
Published: June 2008

The primary purpose of the Mars 2007 Phoenix Lander Robotic Arm (RA) and associated Icy Soil Acquisition Device (ISAD) is to acquire samples of Martian dry and icy soil (DIS) by digging, scraping, and rasping, and delivering them to the Thermal Evolved Gas Analyzer and the Microscopy, Electrochemistry, and Conductivity Analyzer. The RA will also position (1) the Thermal and Electrical Conductivity Probe (TECP) in the DIS; (2) the TECP at various heights above the surface for relative humidity measurements, and (3) the Robotic Arm Camera to take images of the surface, trench, DIS samples within the ISAD scoop, magnetic targets, and other objects of scientific interest within its workspace. The RA/ISAD will also be used to generate DIS piles for monitoring; conduct DIS scraping, penetration, rasping, and chopping experiments; perform compaction tests; and conduct trench cave‐in experiments. Data from the soil mechanics experiments will yield information on Martian DIS properties such as angle of repose, cohesion, bearing strength, and grain size distribution.
Root‐mean‐square surface slopes of Phoenix landing sites with 75‐cm bistatic radar received by Mars Odyssey
Authors: Gunnarsdottir H. M. , Linscott I. R. , Callas J. L. , Cousins M. D. , Simpson R. A. , Tyler G. L.
Published: June 2008

Between August and December 2005, we conducted 76 oblique‐incidence scattering experiments using the SRI International 46‐m antenna in the Stanford foothills to illuminate Mars for 20‐min periods with an unmodulated, 75‐cm λ, circularly polarized wave. The direct signal and a Martian surface echo, separated by differential Doppler frequency shifts, were received simultaneously by the one‐bit receiver on board the Mars Odyssey spacecraft. Four of the proposed Phoenix landing regions, denoted A–D, were probed by at least one experiment. The surface echoes are characterized by both fluctuating amplitude and varying spectral width, which are responses to surface reflectivity and roughness variations. Our analysis of the echo data is based on quasi‐specular scattering theory and makes use of high‐resolution Mars Orbiter Laser Altimeter (MOLA) topographic maps to model the scattering surface in three dimensions along the specular track of the echo. We find MOLA topography sufficient to model scattering at 75‐cm λ, indicating that the effective horizontal scales being sensed by the radar are at or larger than the MOLA grid spacing of 150–500 m. We find that the RMS surface slopes for the proposed Phoenix landing regions, as determined using the Hagfors scattering law and applicable to those scales, rarely exceed 1°, except in the presence of large craters and other surface irregularities.
Structure, stratigraphy, and origin of Husband Hill, Columbia Hills, Gusev Crater, Mars
Authors: McCoy T. J. , Sims M. , Schmidt M. E. , Edwards L. , Tornabene L. L. , Crumpler L. S. , Cohen B. A. , Soderblom L. A. , Blaney D. L. , Squyres S. W. , Arvidson R. E. , Rice J. W. , Tréguier E. , d'Uston C. , Grant J. A. , McSween H. Y. , Golombek M. P. , Haldemann A. F. C. , de Souza P. A.
Published: June 2008

The strike and dip of lithologic units imaged in stereo by the Spirit rover in the Columbia Hills using three‐dimensional imaging software shows that measured dips (15–32°) for bedding on the main edifice of the Columbia Hill are steeper than local topography (∼8–10°). Outcrops measured on West Spur are conformable in strike with shallower dips (7–15°) than observed on Husband Hill. Dips are consistent with observed strata draping the Columbia Hills. Initial uplift was likely related either to the formation of the Gusev Crater central peak or ring or through mutual interference of overlapping crater rims. Uplift was followed by subsequent draping by a series of impact and volcaniclastic materials that experienced temporally and spatially variable aqueous infiltration, cementation, and alteration episodically during or after deposition. West Spur likely represents a spatially isolated depositional event. Erosion by a variety of processes, including mass wasting, removed tens of meters of materials and formed the Tennessee Valley primarily after deposition. This was followed by eruption of the Adirondack‐class plains basalt lava flows which embayed the Columbia Hills. Minor erosion, impact, and aeolian processes have subsequently modified the Columbia Hills.
Two‐dimensional beam steering array using planar eight‐element composite right/left‐handed leaky‐wave antennas
Authors: Sanada Atsushi
Published: June 2008

A two‐dimensional beam steering array composed of an eight‐element antenna array using composite right/left‐handed leaky‐wave antennas fed by an 8 × 8 Butler matrix network is designed at X‐band. An eight‐way beam switching in one direction by input port switching and a continuous beam steering in the other direction by frequency sweep are achieved. A wide range beam steering operation covering from −55 to +53 degrees by port switching and from −37 to +27 degrees by frequency sweep is demonstrated with the maximum gain of 9.2 dBi.
Characterizing the response of a catchment to an extreme rainfall event using hydrometric and isotopic data
Authors: Lyon Steve W. , Desilets Sharon L. E. , Troch Peter A.
Published: June 2008

In this study we investigate an event‐scale transit time distribution (TTD) for a catchment located in the Santa Catalina Mountains northeast of downtown Tucson, Arizona, USA, during a series of extreme rainfall events. Traditionally, TTD studies look at the long time response of a catchment to an input variation in tracer concentration. Few studies have determined the TTD at the scale of an event. Isotopic and hydrometric data collected during the event considered in this study provide the unique opportunity to characterize the response of the catchment under extreme conditions using both TTD modeling and hydrograph separation. This revealed similarity in the shapes of the event TTD and event water recession hydrograph. Also, the first moment of the event water recession hydrograph and the mean transit time of the TTD were similar. Because of the extreme nature of this event, it is likely that the catchment reaches and relaxes from the maximum possible storage, making its response a time‐invariant characteristic of the catchment on the basis of hydraulic theory. The similarity between the event water recession and event TTD during this characteristic response of the catchment may, thus, allow for the derivation of a time‐invariant event TTD. This result is especially valuable as it lays a basis for catchment similarity analysis linking a catchment's hydrological response and geomorphic properties.
A reference data set of hillslope rainfall‐runoff response, Panola Mountain Research Watershed, United States
Authors: Tromp‐van Meerveld H. J. , James A. L. , McDonnell J. J. , Peters N. E.
Published: June 2008

Although many hillslope hydrologic investigations have been conducted in different climate, topographic, and geologic settings, subsurface stormflow remains a poorly characterized runoff process. Few, if any, of the existing data sets from these hillslope investigations are available for use by the scientific community for model development and validation or conceptualization of subsurface stormflow. We present a high‐resolution spatial and temporal rainfall‐runoff data set generated from the Panola Mountain Research Watershed trenched experimental hillslope. The data set includes surface and subsurface (bedrock surface) topographic information and time series of lateral subsurface flow at the trench, rainfall, and subsurface moisture content (distributed soil moisture content and groundwater levels) from January to June 2002.
Drying front and water content dynamics during evaporation from sand delineated by neutron radiography
Authors: Shokri N. , Lehmann P. , Vontobel P. , Or D.
Published: June 2008

Evaporative drying of porous media is jointly controlled by external (atmospheric) conditions and by media internal transport properties. Effects of different atmospheric potential evaporative demand on observed drying rates were studied in a series of laboratory experiments using sand‐filled Hele‐Shaw cells. We examined two potential evaporation rates of about 8 and 40 mm per day. The evolution and geometry of the drying front (marking the interface between saturated and partially dry regions) and water content distribution above the drying front were measured every 5 min at 0.1 mm spatial resolution using neutron radiography. Water loss rates decreased with time for both rates, but the decrease was more pronounced for high evaporative demand. External evaporative demand had no effect on drying front geometry or spatial water content distribution for depths below 2 mm. Cycles of roughening and smoothing of drying fronts due to interfacial pinning and unpinning were observed. The water content above the front showed irregular patterns due to formation of isolated liquid clusters with the general profile showing a decrease in mean water content with deepening drying front. Measured water content profiles support the hypothesis that liquid flow supply surface evaporation during stage 1 and water content distribution were not affected by external drying rates. Additionally, observed saturation profiles indicate that the corresponding hydraulic conductivity supports fluxes larger than the highest drying rate measured for sand, suggesting that decreasing drying rate was limited by vapor exchange between progressively drying surface and the viscous boundary layer above.
Impact of flow rate, water content, and capillary forces on in situ colloid mobilization during infiltration in unsaturated sediments
Authors: Shang Jianying , Flury Markus , Chen Gang , Zhuang Jie
Published: June 2008

We studied in situ colloid mobilization under transient flow conditions using columns repacked with Hanford sediments. Rainfall infiltration was experimentally simulated using different flow rates and initial moisture conditions. Five series of column experiments were performed with initial infiltration rates of 0.018, 0.036, 0.072, 0.144, and 0.288 cm/min, and the columns reached water saturations in the range of 53 to 81%. The infiltration of water into the columns provided unfavorable conditions for colloid attachment to the sediments. Colloids were eluted by the infiltrating water with the peak colloid concentrations in the outflow coinciding with the arrival of the infiltration front. A larger flow rate led to a greater amount of colloids released from the column. The cumulative amount of colloids released was proportional to the column water content established after steady state flow rates were achieved. We used the advection‐dispersion equation with a first‐order colloid release reaction to analyze the experimental data. The colloid release rate coefficient increased with the increase of water content. We calculated forces exerted on colloids, and found that electrostatic and van der Waals interactions, calculated based on the DLVO (Derjaguin‐Landau‐Verwey‐Overbeek) theory, and hydrodynamic forces, were all less important than capillary forces in controlling colloid release. In one experiment, the ionic strength of the infiltration solution was increased, such that colloid attachment was favorable. Nonetheless, colloids were mobilized and eluted with the infiltration front, implying that non‐DLVO forces, such as capillary forces, played a prominent role in colloid mobilization.
Imaging Yellowstone plume‐lithosphere interactions from inversion of ballistic and diffusive Rayleigh wave dispersion and crustal thickness data
Authors: Stachnik J. C. , Dueker K. , Schutt D. L. , Yuan H.
Published: June 2008

Diffusive and ballistic Rayleigh wave dispersion data from three PASSCAL seismic deployments are combined with crustal thickness constraints from receiver function analysis to produce a high‐resolution shear velocity image of the Yellowstone hot spot track crust and uppermost mantle. This synoptic image shows the following crustal features: the eastern Snake River Plain (ESRP) high‐velocity midcrustal layer, low‐velocity lower crust beneath the 4.0–6.6 Ma Heise caldera field, high‐velocity lower crust beneath the <2.1 Ma Yellowstone Calderas, and low‐velocity upper crustal volume beneath the <2.1 Ma Yellowstone caldera fields. The low‐velocity lower crust beneath the 4.0–6.6 Ma Heise caldera field is found to extend outward 50–80 km from the ESRP margins, consistent with outflow of the magmatically heated and thickened ESRP lower crust. In addition, the lack of 10 km of crustal thickening of the ESRP crust, associated with the estimated 10 km of magmatic thickening, requires that the ESRP lower crust has flowed outward in a complex fashion governed by preexisting lower crustal strength heterogeneity. Within the northern Wyoming province, the so‐called 7.x km/s lower crustal magmatic layer is found to extend westward to the N‐S oriented pre‐Cambrian rift margin. The high‐velocity, hence high‐density, 7.x layer beneath the <2.1 Ma Yellowstone caldera fields has apparently inhibited heating of the subcaldera lower crust and instead magmatic heat and fluids are exchanged with the country rock above 13 km depth. The narrow 80 km diameter plume imaged by body wave tomograms, after being sheared to horizontal by plate drift, is manifest as a very low velocity (3.9 km/s) layer that is only about 110 km wide. The ESRP mantle lithosphere has been thinned to about 28 km thickness by the plume's transport of heat and magma upward, lateral advection of the lower lithosphere by plume shear, and ongoing lithospheric dilatation.