cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.48577/jpl.nckmnt
title: LOWER SURFACE TEMPERATURE AT BRIGHT EPHEMERAL FEATURE SITE ON TITAN’S NORTH POLE

description: We report a temperature dierence in one of the regions on Titan that is documented asa Bright Ephemeral Feature (BEF). Spectra were recorded by Cassini's Composite InfraredSpectrometer (CIRS). BEFs are 5 μm bright areas that appear, disappear, and shift fromyby to yby at Titan's north pole observed in Visual and Infrared Mapping Spectrometer(VIMS) data. They are inferred to be broad-specular reections caused by a smooth surfaceon Titan or a near surface fog |both of which indicate that the atmosphere interacted withthe surface. We used 24 spectra for `on the BEF' and 51 spectra for `o the BEF' region todetermine the temperature dierence during the T121 yby (July 25 2016). At the 410-560cm􀀀1 window where surface emissions are perceptible we see a decrease in temperature by1.20:2 Kelvin. This decrease in temperature might indicate precipitative cooling after afresh rainfall on Titan's land/sea surface.
DOI: 10.48577/jpl.sz3btg
title: The Role of Seasonal Sediment Transport and Sintering in Shaping Titan’s Landscapes

description: Titan is a sedimentary world, with widespread lakes1, rivers2, fans3, eroded canyonlands4, dissected plateaux5, and sand dunes6. The bulk of sediments on Saturn’s moon are thought to be largely made of mechanically weak7 organic grains8-9, possibly prone to rapid abrasion into dust. Yet, Titan’s equatorial sand dunes are thought to be relatively old (10s–100s kyr)10 and active8,10-11. Sustaining Titan’s sand dunes over geologic timescales thus requires a mechanism that produces sand-sized organic particles at equatorial latitudes7. We explore the hypothesis that a combination of sintering, when sediment grains are at rest, and abrasion, when they are transported by methane rivers or nitrogen winds, could produce sand grains with a consistent, equilibrium size. We find that episodic sintering and abrasion may readily produce sand-sized sediments under Titan’s surface conditions, and supply Titan’s equatorial dunes with well-sorted organic sand at Earth-like transport frequencies. Predictions are consistent with geologic constraints on grain sizes in the dune fields12 as well as the frequency of methane rainstorms13 and sand-transporting winds14-15. Our findings support the hypothesis of a global sedimentary cycle on Titan, driven by seasonal climate forcing, and mediated by episodic sintering and abrasion of organic sand grains by rivers and winds.
DOI: 10.48577/jpl.1o7thh
title: ECOSTRESS estimates gross primary production at different times of day from the International Space Station

description: Accurate estimation of gross primary production (GPP), the amount of carbon absorbed by plants via photosynthesis, is of great importance for understanding ecosystem functions, carbon cycling, and climate-carbon feedbacks. Remote sensing has been widely used to quantify GPP at regional to global scales. However, traditional satellites (e.g., Landsat, Terra, Aqua) lack the capability to examine the diurnal cycles of GPP because they observe the Earth’s surface at the same time of day. The Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS), launched on June 2018, observes the land surface temperature (LST) at different times of day with high spatial resolution (70 m × 70 m) from the International Space Station (ISS). Here, we used ECOSTRESS data to predict instantaneous GPP with high spatial resolution based on a data-driven approach. The predictive GPP model was developed based on ECOSTRESS LST observations, along with the Enhanced Vegetation Index (EVI) from the Moderate Resolution Imaging Spectroradiometer (MODIS), land cover type from the National Land Cover Database (NCLD), and meteorological variables. Our model estimated instantaneous GPP across 56 flux tower sites fairly well (R2 = 0.88, Root Mean Squared Error (RMSE) = 2.42 μmol CO2 m-2 s-1). The predicted GPP driven by the ECOSTRESS LST captured the diurnal variations of tower GPP for different biomes. We then produced multiple ECOSTRESS GPP maps for the Central California Foothills and Coastal Mountains, Central California Valley, Sierra Nevada and Coast Range in California. We found that the ECOSTRESS GPP showed distinct changes at different times of day (e.g. higher in late morning, peak around noon, approaching zero at dusk), and clearly depicted the differences in productivity across landscapes (e.g., savannas, croplands, grasslands, and forests) for different times of day. This study demonstrates the feasibility of using ECOSTRESS data for producing instantaneous GPP for different times of day. The ECOSTRESS GPP can shed light on how plant photosynthesis and water use vary over the course of the diurnal cycle and inform agricultural management and future improvement of terrestrial biosphere/land surface models.
DOI: 10.48577/jpl.dioevw
title: Characterizing spatiotemporal patterns of crop phenology across North America during 2000-2016 using satellite imagery and agricultural survey data

description: Crop phenology represents an integrative indicator of climate change and plays a vital role in terrestrial carbon dynamics and sustainable agricultural development. However, spatiotemporal variations of crop phenology remain unclear at large scales. This knowledge gap has hindered our ability to realistically quantify the biogeochemical dynamics in agroecosystems, predict future climate, and make informed decisions for climate change mitigation and adaptation. In this study, we improved an EVI-curve-based approach and used it to detect spatiotemporal patterns in cropping intensity and five major phenological stages over North America during 2000–2016 using vegetation index in combination with agricultural survey data and other ancillary maps. Our predicted crop phenological stages showed strong linear relationships with the survey-based datasets, with R2, RMSEs, and MAEs in the ranges of 0.35 –0.99, three to ten days, and two to eight days, respectively. During the study period, the planting dates were advanced by 0.60 days/year (p &lt; 0.01), and harvesting dates were delayed by 0.78 days/year (p &lt; 0.01) over North America. A minimum temperature increase by 1 ◦C caused a 4.26-day planting advance (r = − 0.50, p &lt; 0. 01) or a 0.66-day harvest delay (r = 0.10, p &lt; 0.01). While, a higher maximumtemperatureresultedinaplantingadvanceby4.48days/◦C(r=− 0.62,p&lt;0.01)oraharvestadvance by 2.22 days/◦C (r = − 0.40, p &lt; 0.01). Our analysis illustrated evident spatiotemporal variations in crop phenology in response to climate change and management practices. The derived crop phenological datasets and cropping intensity maps can be used in regional climate assessments and in developing adaptation strategies.
DOI: 10.48577/jpl.nky4op
title: Coordinated Science Support for Sea-Level Data and Services in the United States

description: In this commentary, we focus on the basic-science foundation that supports sea-level decision-making. Specifically, we discuss the role that U.S. federal science-producing agencies (NASA and NOAA) can play in supporting ongoing and future sea-level adaptation efforts. We discuss current challenges in the work that NASA and NOAA are doing in this area, highlight how these challenges impact stakeholders, and then detail how improved coordination between NASA and NOAA can ultimately benefit stakeholders. While focused on the U.S., many of the challenges and considerations are relevant for other agencies and countries across the globe.
DOI: 10.48577/jpl.chtgtp
title: Spatial covariation between solar-induced fluorescence and vegetation indices from Arctic-Boreal landscapes

description: The Arctic-Boreal Zone (ABZ) is characterized by spatially heterogeneous vegetation composition and structure, leading to challenges for inferring patterns in vegetation productivity. A mechanistic understanding of the patterns and processes underlying spectral remote sensing observations is necessary to overcome these challenges. Solar-induced chlorophyll fluorescence (SIF), near-infrared reflectance of vegetation (NIRv), and chlorophyll/carotenoid index (CCI) show promise for tracking productivity and disentangling links to the activity and distribution of chlorophyll at coarse spatial scales (e.g., 0.5), but their effectiveness for studying mixed landscapes characteristic of the ABZ remains unclear. Here, we use airborne observations collected during NASA’s Arctic-Boreal Vulnerability Experiment to examine the spatial covariation between SIF, NIRv, and CCI at a scale (30 m) commensurate with the best available landcover products across interior Alaska. Additionally, we compare relationships among SIF and vegetation indices from spaceborne observations (TROPOMI and MODIS) resampled to a 0.01 (~1000 m) scale. While model simulations support the link between NIRv and CCI to chlorophyll content and photosynthetic capacity, we find that the strength of the SIF-NIRv linear relationship degrades when scaled from the spaceborne to the airborne scale (R2 = 0.50 vs. 0.23, respectively) whereas the strength of the SIF-CCI linear relationship is steady at both spaceborne and airborne scales (R2 = 0.30 vs. 0.31). The relationship of SIF with either vegetation index is strongly dependent on landcover class at both airborne and spaceborne scales. We provide context for how further work could leverage SIF with reflectance indices measurable from a variety of platforms to improve mapping of vegetation dynamics in this ecoregion.
DOI: 10.48577/jpl.ckgx7h
title: Vertical compositional variations of liquid hydrocarbons in Titan’s alkanofers

description: Context. According to clues left by the Cassini mission, Titan, one of the two solar system bodies having an hydrologic cycle, may harbor liquid hydrocarbon-based analogs of our terrestrial aquifers, referred to as “alkanofers”. Aims. On the Earth, petroleum and natural gas reservoirs show vertical gradient in chemical composition, established over geological timescales. In this work, we investigate the conditions under which Titan’s processes could lead to similar situations. Methods. We built numerical models including barodiusion and thermodiusion (Soret’s eect) in N2+CH4+C2H6 liquid mixtures, relevant for Titan’s possible alkanofers. Our main assumption is the existence of reservoirs of liquids trapped in a porous matrix with low permeability. Results. Due to the small size of the molecule, nitrogen seems to be more sensitive to gravity than ethane, even if the latter has a mass slightly larger. This behavior noticed for an isothermal crust, is reinforced by the presence of a geothermal gradient. Vertical composition gradients, formed over timescales between a fraction of mega-year to several tens of mega-years, are not influenced by molecular diusion coecients. If the alkanofer liquid is in contact with water-ice, we have checked that N2 does not, in general, impede the clathration of C2H6, except in some layers. Interestingly, we found that noble gases could easily accumulate at the bottom of an alkanofer.
DOI: 10.48577/jpl.6jj1kk
title: Simulated microgravity promotes horizontal gene transfer of antimicrobial resistance genes between bacterial genera in the absence of antibiotic selective pressure

description: Bacteria are able to adapt and survive in harsh and changing environments through many mechanisms, with one of them being horizontal gene transfer (HGT). This process is one of the leading culprits in the spread of antimicrobial resistance within bacterial communities and could pose a significant health threat to astronauts if they fell ill, especially on long duration space missions. In order to better understand the degree of HGT activity that could be occurring in space, biosafety level-2, donor and recipient bacteria, were co-cultured under simulated microgravity (SMG) on Earth with concomitant 1G controls. Two antimicrobial resistance genes, blaOXA500 and ISAba1 from the donor, Acinetobacter pittii, were tracked in four recipient strains of Staphylococcus aureus (which did not harbor those genes) using polymerase chain reaction. All four S. aureus strains that were co-cultured with A. pittii under SMG had significantly higher number of isolates that were now blaOXA500 and ISAba1 positive compared to growth at 1G. The acquisition of these genes by the recipient induced a phenotypic change, as these isolates were now resistant to oxacillin, which they were previously susceptible to. This is a novel study, presenting for the first time, the increased HGT activity under SMG and the impact of the space environment in promoting increased gene dissemination within bacterial communities.
DOI: 10.48577/jpl.crooja
title: Dual frequency comb absorption spectroscopy of CH4 up to 1000 Kelvin from 6770-7630 cm-1

description: As infrared telescopes are finding evidence of methane in hot exoplanet atmospheres, it is becoming increasingly important to have accurate high-temperature methane absorption models. To evaluate and update several spectroscopic databases (HITRAN2016, HITEMP, ExoMol), we collected laboratory spectra of the methane icosad (6770-7570 cm-1) using a 200 MHz (0.0067 cm-1) dual frequency comb spectrometer. The pure methane data span 18 to 300 Torr and 296 to 1000 K. We found good agreement with the HITRAN2016 model spectrum at room temperature, and substantial mismatch between our spectra and all absorption models at elevated temperature. We present several updates to HITRAN2016 to improve agreement with the measured high-temperature spectra. Specifically, we assign 4283 lowerstate energies which had previously been given a default value in HITRAN2016 (E 00 HIT = 999 cm-1), update existing lower-state energies for 92 features, and add 293 new high-temperature features in order to improve HITRAN2016 above 300 K. Additionally, we update the band-wide line positions by ∼0.001 cm-1, the self-widths by +7%, and we estimate band-averaged temperature-dependence exponents for selfwidth (0.85) and self-shift (0.58). These measurements are an important step towards merging empirical and theoretical high-temperature methane databases, with the goal of enabling better understanding of exoplanet atmospheres.
DOI: 10.48577/jpl.vsnuwe
title: Causal Mechanisms of Sea-level and Freshwater Content Change in the Beaufort Sea

description: Sea level across the Beaufort Sea has risen at a rate exceeding 2 cm/yr during the past decade. The rapid sea level rise is dominantly halosteric, reflecting an increase in the region’s freshwater content by as much as 400 km3/yr. Here we study the nature and causal mechanism of this change and the attendant seasonal-to-decadal variation from 1992 to 2017 by quantifying their controlling processes using a coupled ocean circulation and sea ice model constrained by satellite and in situ observations. Surface stress and freshwaterflux associated with the melting and freezing of sea-ice are the primary driving forces of these variations, but their relative contribution varies with time-scale. Seasonal change is dictated by the sea-ice variation and interannual change is mostly wind-driven associated with Ekman transport. The two forcings, however, are equally important for decadalchanges that dominate the overall variation. Strengthening anticyclonic surface stresssurrounding the Beaufort Sea intensify the ocean’s lateral Ekman convergence into theregion near the surface where the water is relatively fresh, resulting in the domain’sincrease of both steric height and freshwater content. The strengthening stress alsoenhances sea-ice convergence into the Beaufort Sea where it draws heat from the oceanand melts, further increasing the region’s rise in sea level and freshwater content. Thedecadal variation amounts to a wind-driven coupled diabatic interaction between the ocean and sea-ice, whereby sea-ice serves as an extra-ocean conduit for freshwater transport.
DOI: 10.48577/jpl.8mfclr
title: Revisiting the Global Patterns of Seasonal Cycle in Sea Surface Salinity

description: Argo profiling floats and L-band passive microwave remote sensing have significantly improved the global sampling of sea surface salinity (SSS) in the past 15 years, allowing the study of the range of SSS seasonal variability using concurrent satellite and in situ platforms. Here harmonic analysis was applied to four 0.25° satellite products and two 1° in situ products between 2016 and 2018 to determine seasonal harmonic patterns. The 0.25° World Ocean Atlas (WOA) version 2018 was referenced to help assess the harmonic patterns from a long-term perspective based on the three-year period. The results show that annual harmonic is the most characteristic signal of the seasonal cycle, and semiannual harmonic is important in regions influenced by monsoon and major rivers. The percentage of the observed variance that can be explained by harmonic modes varies with products, with values ranging between 50 and 72 % for annual harmonic and between 15 and 19% for semiannual harmonic. The large spread in the explained variance by the annual harmonic reflects the large disparity in nonseasonal variance (or noise) in the different products. Satellite products are capable of capturing sharp SSS features on meso- and frontal scales and the patterns agree well with the WOA 2018. These products are, however, subject to the impacts of radiometric noises and are algorithm dependent. The coarser-resolution in situ products may underrepresent the full range of high-frequency small scale SSS variability when data record is short, which may have enlarged the explained SSS variance by the annual harmonic.
DOI: 10.48577/jpl.igee8i
title: The Surface Water and Ocean Topography (SWOT) Mission River Database (SWORD): A global river network for satellite data products

description: The upcoming Surface Water and Ocean Topography (SWOT) satellite mission, planned to launch in 2022, is the first mission to focus on measuring hydrological processes in Earth’s surface water. As such, SWOT will vastly expand observations of global rivers ≥100 m wide. SWOT will provide a variety of data products, including a global vector river product containing water surface elevation (WSE), width, slope, and estimated discharge. Practical application and consistency of the SWOT vector products requires a prior global river network database divided into reaches. Here, we introduce the SWOt River Database (SWORD). SWORD will serve as the framework for the SWOT river vector products consisting of river reaches (~10 km long) and nodes (~200 m spacing). We generate SWORD by combining several global river- and satellite-related datasets into one congruent product. When defining river reaches, we incorporate natural and human-created river obstructions, basin boundaries, tributary junctions, and SWOT orbit track information. SWORD contains a total of 209,749 reaches and 10.7 million nodes. Globally, 79% percent of reach lengths are between 8 and 20 km with a median reach length of 10.5 km. 95% of river reaches ≥10 km will have sufficient SWOT observations to provide discharge estimates at least once per orbit cycle. SWORD also contains many useful hydrologic and morphological attributes, and is designed to be expandable in the future. Even before the launch of SWOT, it can serve as a framework for global hydrologic analyses using models, in situ measurements, and additional satellite observations.
DOI: 10.48577/jpl.qls7mp
title: Longitudinal Variations in the Stratosphere of Uranus from the Spitzer Infrared Spectrometer

description: NASA’s Spitzer Infrared Spectrometer (IRS) acquired mid-infrared (5-37 m) disc-averaged spectra of Uranus very near to its equinox in December 2007. A mean spectrum was constructed from observations of multiple central meridian longitudes, spaced equally around the planet, which has provided the opportunity for the most comprehensive globally-averaged characterization of Uranus’ temperature and composition ever obtained (Orton et al., 2014a,b). In this work we analyse the disc-averaged spectra at four separate central meridian longitudes to reveal significant longitudinal variability in thermal emission occurring in Uranus’ stratosphere during the 2007 equinox. We detect a variability of up to 15% at wavelengths sensitive to stratospheric methane, ethane and acetylene at the 0:1-mbar level. The tropospheric hydrogen-helium continuum and deuterated methane absorption exhibit a negligible variation (less than 2%), constraining the phenomenon to the stratosphere. Building on the forward-modelling analysis of the global average study, we present full optimal estimation inversions (using the NEMESIS retrieval algorithm, Irwin et al., 2008) of the Uranus-2007 spectra at each longitude to distinguish between thermal and compositional variability. We found that the variations can be explained by a temperature change of less than 3 K in the stratosphere. Near infrared observations from Keck II NIRC2 in December 2007 (Sromovsky et al., 2009; de Pater et al., 2011), and mid-infrared observations from VLT/VISIR in 2009 (Roman et al., 2020), help to localise the potential sources to either large scale uplift or stratospheric wave phenomena.
DOI: 10.48577/jpl.mmvwbl
title: Latitudinal variation in the abundance of methane (CH4) above the clouds in Neptune's atmosphere from VLT/MUSE Narrow Field Mode Observations.

description: Observations of Neptune, made in 2018 using the new Narrow Field Adaptive Optics mode of the Multi Unit Spectroscopic Explorer (MUSE) instrument at theVery Large Telescope (VLT) from 0.48 - 0.93 microns, are analysed here to determinethe latitudinal and vertical distribution of cloud opacity and methane abundancein Neptune's observable troposphere (0.1 { ~3 bar). Previous observations atthese wavelengths in 2003 by HST/STIS (Karkoschka and Tomasko 2011, Icarus205, 674{694) found that the mole fraction of methane above the cloud tops (at~2 bar) varied from ~% at equatorial latitudes to ~2% at southern polar latitudes, by comparing the observed reectivity at wavelengths near 825 nm controlled primarily by either methane absorption or H2{H2/H2{He collision-inducedabsorption. We nd a similar variation in cloud-top methane abundance in 2018,which suggests that this depletion of methane towards Neptune's pole is potentiallya long-lived feature, indicative of long-term upwelling at mid-equatoriallatitudes and subsidence near the poles. By analysing these MUSE observationsalong the central meridian with a retrieval model, we demonstrate that a broadboundary between the nominal and depleted methane abundances occurs at between20-40 deg. S. We also find a small depletion of methane near the equator,perhaps indicating subsidence there, and a local enhancement near 60 - 70 deg. S,which we suggest may be associated with South Polar Features (SPFs) seen inNeptune's atmosphere at these latitudes. Finally, by the use of both a reflectivity analysis and a principal component analysis, we demonstrate that this depletionof methane towards the pole is apparent at all locations on Neptune's disc, andnot just along its central meridian.