Antarctic Analog for Dilational Bands on Europa

Europa's surface shows signs of extension, which is revealed as lithospheric dilation expressed along ridges, dilational bands and ridged bands. Ridges, the most common tectonic feature on Europa, comprise a central crack flanked by two raised banks a few hundred meters high on each side. Together these three classes may represent a continuum of formation. In Tufts' Dilational Model ridge formation is dominated by daily tidal cycling of a crack, which can be superimposed with regional secular dilation. The two sources of dilation can combine to form the various band morphologies observed. New GPS data along a rift on the Ross Ice Shelf, Antarctica is a suitable Earth analog to test the framework of Tufts' Dilational Model. As predicted by Tufts' Dilational Model, tensile failures in the Ross Ice Shelf exhibit secular dilation, upon which a tidal signal can be seen. From this analog we conclude that Tufts' Dilational Model for Europan ridges and bands may be credible and that the secular dilation is most likely from a regional source and not tidally driven

Assessment of ICESat-2 Ice Sheet Surface Heights, Based on Comparisons over the Interior of the Antarctic Ice Sheet

We collected kinematic Global Navigation Satellite Systems (GNSS) surface height data, on a 750km groundbased traverse of the flat interior of the Antarctic ice sheet, for comparison with Ice, Cloud, and Land Elevation Satellite2 (ICESat2) surface heights. Vertical errors in the GNSS data are estimated to be 5.6 cm, comparable to results from a previous traverse and with yeartoyear comparisons. Comparisons of the GNSS heights and 6 months of ICESat2 ATL03 photonbased heights and ATL06 segmentbased heights indicate that the accuracy and precision of ICESat2 data are comparable to that of results from the ICESat mission: ATL03 is currently accurate to better than 5 cm with better than 13 cm of surface measurement precision, while ATL06 is currently accurate to better than 3 cm with better than 9 cm of surface measurement precision

Assessment of altimetry using ground-based GPS data from the 88S Traverse, Antarctica, in support of ICESat-2

We conducted a 750&thinsp;km kinematic GPS survey, referred to as the 88S Traverse, based out of South Pole Station, Antarctica, between December 2017 and January 2018. This ground-based survey was designed to validate spaceborne altimetry and airborne altimetry developed at NASA. The 88S Traverse intersects 20&thinsp;% of the ICESat-2 satellite orbits on a route that has been flown by two different Operation IceBridge airborne laser altimeters: the Airborne Topographic Mapper (ATM; 26 October 2014) and the University of Alaska Fairbanks (UAF) Lidar (30 November and 3 December 2017). Here we present an overview of the ground-based GPS data quality and a quantitative assessment of the airborne laser altimetry over a flat section of the ice sheet interior. Results indicate that the GPS data are internally consistent (1.1±4.1&thinsp;cm). Relative to the ground-based 88S Traverse data, the elevation biases for ATM and the UAF lidar range from −9.5 to 3.6&thinsp;cm, while surface measurement precisions are equal to or better than 14.1&thinsp;cm. These results suggest that the ground-based GPS data and airborne altimetry data are appropriate for the validation of ICESat-2 surface elevation data.</p

The Supernova Remnant CTB104A : Magnetic Field Structure and Interaction with the Environment

We present new, high resolution 1420 and 408 MHz continuum images and HI and 12CO (J=1-0) spectral line maps of the diffuse supernova remnant CTB104A (G93.7-0.3). Analysis of the complex continuum emission reveals no significant spectral index variations across the remnant. Three prominences around CTB104A are found to be related to the SNR, while one extension to the east is identified as an HII region associated with a background molecular shell. Small scale polarization and rotation measure (RM) structures are turbulent in nature, but we find a well-ordered RM gradient across the remnant, extending from southeast to northwest. This gradient does not agree with the direction of the global Galactic magnetic field, but does agree with a large-scale RM anomaly inferred from rotation measure data by Cleg et al. (1992). We show that the observed morphology of CTB104A is consistent with expansion in a uniform magnetic field, and this is supported by the observed RM distribution. By modeling the RM gradient with a simple compression model we have determined the magnetic field strength within the remnant as Bo ~ 2.3 micro G. We have identified signatures of the interaction of CTB104A with the surrounding neutral material, and determined its distance, from the kinematics of the HI structure encompassing the radio emission, as 1.5 kpc. We also observed clear breaks in the HI shell that correspond well to the positions of two of the prominences, indicating regions where hot gas is escaping from the interior of the SNR.Comment: 7 pages, Latex with aastex and emulateapj5, 12 figures, ApJ accepte

The Molecular Environment of the Gamma-ray Source TeV J2032+4130

The mysterious very high energy gamma-ray source, TeV J2032+4130, is coincident with the powerful Cygnus OB2 stellar association, though a physical association between the two remains uncertain. It is possible that the detected very high energy photons are produced via an overdensity of locally accelerated cosmic rays impinging on molecular clouds in the source region. In order to test this hypothesis, we used the Kitt Peak 12m, the Heinrich-Hertz Submillimeter Telescope (HH-SMT), and the Five College Radio Astronomy Observatory (FCRAO), to obtain observations in the J=1-->0 and J=2-->1 lines of both 12CO and 13CO. We report here on the detection of significant molecular material toward the TeV source region which could be acting as the target of locally accelerated CRs. We also find evidence of compact molecular clumps, showing large line widths in the CO spectra, possibly indicative of energetic processes in this region of Cygnus OB2.Comment: Accepted for publication in ApJ

ICESat-2 Simulated Data from Airborne Altimetery

Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) is scheduled to launch in 2015 and will carry onboard the Advanced Topographic Laser Altimeter System (ATLAS), which represents a new approach to spaceborne determination of surface elevations. Specifically, the current ATLAS design is for a micropulse, multibeam, photon-counting laser altimeter with lower energy, a shorter pulse width, and a higher repetition rate relative to the Geoscience Laser Altimeter (GLAS), the instrument that was onboard ICESat. Given the new and untested technology associated with ATLAS, airborne altimetry data is necessary (1) to test the proposed ATLAS instrument geometry, (2) to validate instrument models, and (3) to assess the atmospheric effects on multibeam altimeters. We present an overview of the airborne instruments and datasets intended to address the ATLAS instrument concept, including data collected over Greenland (July 2009) using an airborne SBIR prototype 100 channel, photon-counting, terrain mapping altimeter, which addresses the first of these 3 scientific concerns. Additionally, we present the plan for further simulator data collection over vegetated and ice covered regions using Multiple Altimeter Beam Experimental Lidar (MABEL), intended to address the latter two scientific concerns. As the ICESAT-2 project is in the design phase, the particular configuration of the ATLAS instrument may change. However, we expect this work to be relevant as long as ATLAS pursues a photon-counting approach

Interstellar Turbulence: II. Energy Spectra of Molecular Regions in the Outer Galaxy

The multivariate tool of Principal Component Analysis (PCA) is applied to 23 fields in the FCRAO CO Survey of the Outer Galaxy. PCA enables the identification of line profile differences which are assumed to be generated from fluctuations within a turbulent velocity field. The variation of these velocity differences with spatial scale within a molecular region is described by a singular power law, delta v= c L^alpha which can be used as a powerful diagnostic to turbulent motions. For the ensemble of 23 fields, we find a mean value alpha = 0.62 +- 0.11. From a recent calibration of this method using fractal Brownian motion simulations (Brunt & Heyer 2001), the measured velocity difference-size relationship corresponds to an energy spectrum, E(k), which varies as k^-beta, where beta = 2.17 +- 0.31. We compare our results to both decaying and forced hydrodynamic simulations of turbulence. We conclude that energy must be continually injected into the regions to replenish that lost by dissipative processes such as shocks. The absence of large, widely distributed shocks within the targeted fields suggests that the energy is injected at spatial scales less than several pc.Comment: 24 pages, 10 figures, accepted by Ap

Ice-Shelf Flexure and Tidal Forcing of Bindschadler Ice Stream, West Antarctica

Viscoelastic models of ice-shelf flexure and ice-stream velocity perturbations are combined into a single efficient flowline model to study tidal forcing of grounded ice. The magnitude and timing of icestream response to tidally driven changes in hydrostatic pressure and/or basal drag are found to depend significantly on bed rheology, with only a perfectly plastic bed allowing instantaneous velocity response at the grounding line. The model can reasonably reproduce GPS observations near the grounding zone of Bindschadler Ice Stream (formerly Ice Stream D) on semidiurnal time scales; however, other forcings such as tidally driven ice-shelf slope transverse to the flowline and flexurally driven till deformation must also be considered if diurnal motion is to be matche

Online test purchased new psychoactive substances in 5 different European countries; a snapshot study of chemical composition and price

Background: New psychoactive substances (NPS) are on offer worldwide online, in order to shed light on the purity and price of these substances in the European Union, a research collaboration was set up involving France, United Kingdom (UK), the Netherlands, Czech Republic and Poland. Methods: Per country, around 10 different NPS were test purchased from different webshops. Then, chemical analysis of NPS was done with according reference standards to identify and quantify the contents. Results: In contrast to what is generally advertised on the webshops (>99%), purity varied considerably per test purchased NPS. Several NPS were mislabelled, some containing chemical analogues (e.g. 25B/C-NBOMe instead of 25I-NBOMe, pentedrone instead of 3,4- DMMC). But in some cases NPS differed substantially from what was advertised (e.g. pentedrone instead of AMT or 3-FMC instead of 5-MeO-DALT). Per gram, purity-adjusted prices of cathinones differed substantially between three countries of test purchase, with Poland being the least expensive. Synthetic cannabinoids were relatively the most expensive in the Czech Republic and least expensive in the UK. Conclusions: The current findings provides a snapshot of the price and chemical contents of NPS products purchased by different countries and in different webshops. There is a potential danger of mislabelling of NPS. The great variety in price and purity of the delivered products might be the result of the market dynamics of supply and demand and the role of law enforcement in different European countries