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  • 1
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    Top-down estimate of anthropogenic emission inventories and their interannual variability in Houston using a mesoscale inverse modeling technique (2011)
    Wiley
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    Publication Date: 2011-10-19
    Description: Texas Air Quality Study field campaigns took place in eastern Texas in August–October of 2000 and 2006. Several flights of NOAA and NCAR research aircraft were dedicated to characterizing anthropogenic emissions over Houston. We present results from an inverse modeling technique that uses three atmospheric transport models and these aircraft observations to assess and improve existing emission inventories. We used inverse modeling techniques to improve the spatial and temporal emissions' distribution of CO, NOy, and SO2 predicted by the 4 km resolution U.S. Environmental Protection Agency (EPA) National Emission Inventory (NEI) for 2005. Differences between the prior and posterior inventories are discussed in detail. In September 2006, we found that the prior daytime CO emissions in the Houston urban area have to be reduced by 41% ± 8%. Over the Houston Ship Channel, where industrial emissions are predominant, the prior emissions have to be decreased by 43% ± 5% for CO and 51% ± 5% for NOy. Prior NOy emissions from other major ports around Houston also have to be reduced, probably owing to uncertain nearshore ship emissions in the EPA NEI inventory. Using the measurements from the two field campaigns, we assessed the emissions' variability between August 2000 and September 2006. Daytime CO emissions from the Houston urban area have decreased by 8% ± 3%, while the NOy emissions have increased by 20% ± 6%. In the Houston Ship Channel, daytime NOy emissions have increased by 13% ± 7%. Our results show qualitative consistencies with known changes in Houston emissions' sources.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    A new inversion method to calculate emission inventories without a prior at mesoscale: Application to the anthropogenic CO2 emission from Houston, Texas (2012)
    Wiley
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    Publication Date: 2012-03-10
    Description: We developed a new inversion method to calculate an emission inventory for an anthropogenic pollutant without a prior emission estimate at mesoscale. This method employs slopes between mixing ratio enhancements of a given pollutant (CO2, for instance) with other co-emitted tracers in conjunction with the emission inventories of those tracers (CO, NOy, and SO2 are used in this example). The current application of this method employed in situ measurements onboard the NOAA WP-3 research aircraft during the 2006 Texas Air Quality Study (TexAQS 2006). We used 3 different transport models to estimate the uncertainties introduced by the transport models in the inversion. We demonstrated the validity of the new inversion method by calculating a 4 × 4 km2 emission inventory of anthropogenic CO2 in the Houston area in Texas, and comparing it to the 10 × 10 km2 Vulcan emission inventory for the same region. The calculated anthropogenic CO2 inventory for the Houston Ship Channel, home to numerous major industrial and port emission sources, showed excellent agreement with Vulcan. The daytime CO2 average flux from the Ship Channel is the largest urban CO2 flux reported in the literature. Compared to Vulcan, the daytime urban area CO2 emissions were higher by 37% ± 6%. Those differences can be explained by uncertainties in emission factors in Vulcan and by increased emissions from point sources and on-road emitters between 2002, the reference year in Vulcan, and 2006, the year that the TexAQS observations were made.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Inverse Energy Dispersion of Energetic Ions Observed in the Magnetosheath (2016)
    Wiley
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    Publication Date: 2016-07-09
    Description: We present a case study of energetic ions observed by the Energetic Particle Detector (EPD) on the Magnetospheric Multiscale (MMS) spacecraft in the magnetosheath just outside the subsolar magnetopause that occurred at 1000 UT on December 8, 2015. As the magnetopause receded inward, the EPD observed a burst of energetic (50−5000 keV) proton, helium, and oxygen ions that exhibited an inverse dispersion, with the lowest energy ions appearing first. The prolonged interval of fast antisunward flow observed in the magnetosheath and transient increases in the H components of global ground magnetograms demonstrate that the burst appeared at a time when the magnetosphere was rapidly compressed. We attribute the inverse energy dispersion to the leakage along reconnected magnetic field lines of betatron-accelerated energetic ions in the magnetosheath and a burst of reconnection has an extent of about 1.5 R E using combined Super Dual Auroral Radar Network (SuperDARN) radar and EPD observations.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 4
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    Abrupt Stratospheric Vortex Weakening Associated With North Atlantic Anticyclonic Wave Breaking (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The sudden stratospheric warming (SSW) of 12 February 2018 was not forecast by any extended‐range model beyond 12 days. From early February, all forecast models that comprise the subseasonal‐to‐seasonal (S2S) database abruptly transitioned from indicating a strong stratospheric polar vortex (SPV) to a high likelihood of a major SSW. We demonstrate that this forecast evolution was associated with the track and intensity of a cyclone in the northeast Atlantic, with an associated anticyclonic Rossby wave break, which was not well forecast. The wave break played a pivotal role in building the Ural high, which existing literature has shown was a precursor of the 2018 SSW. The track of the cyclone built an anomalously strong sea level pressure dipole between Scandinavia and Greenland (termed the S‐G dipole), which we use as a diagnostic of the wave break. Forecasts that did not capture the magnitude of this event had the largest errors in the SPV strength and did not show enhanced vertical wave activity. A composite of 49 similarly strong wintertime (November–March) S‐G dipoles in reanalysis shows associated anticyclonic wave breaking leading to significantly enhanced vertical wave activity and a weakened SPV in the following days, which occurred in 35% of the 15‐day periods preceding observed major SSWs. Our results indicate a particular transient trigger for weakening the SPV, complementing existing results on the importance of tropospheric blocking for disruptions to the Northern Hemisphere extratropical stratospheric circulation.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
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  • 5
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    Asymmetric Ionospheric Outflow Observed at the Dayside Magnetopause (2015)
    Wiley
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    Publication Date: 2015-04-17
    Description: An important source of the terrestrial magnetospheric plasma is the Earth's ionospheric outflows from the high latitude regions of both hemispheres. The ionospheric ion outflows have rarely been observed at the dayside magnetopause. We report Cluster observations of the ionospheric ion outflows observed at the dayside magnetopause. The low-energy (up to 1.5 keV) electrons are detected with bi-directional pitch angle distributions indicating that the magnetic field lines are closed. The unidirectional cold ions (〈200 eV) are observed in the magnetosphere by both C1 and C3. The pitch angle distributions (0°– –75°) of the cold ions (〈1 keV) at the dayside magnetopause indicate that these cold ions are the ionospheric outflows comingonly from the southern hemisphere. The cold ions (〈200 eV) fluxes are modulated by the ULF wave electric field. Two different species (possibly H + and He + ) are observed in the magnetosphere. Our results suggest that the ionospheric outflows can directly reach the dayside magnetopause region and may participate in the reconnection process.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 6
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    Observations of the Antarctic Circumpolar Current over the Udintsev Fracture Zone, the narrowest choke point in the Southern Ocean (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract An up‐to‐date map of the Antarctic Circumpolar Current (ACC) fronts is constructed from the latest version of mean dynamic topography from satellite altimetry, and reveals the narrowest ACC width in the Udintsev Fracture Zone (UFZ), with the strongest concentration of the three major ACC fronts within a limited distance as short as 170 km, about 40% narrower than that at Drake Passage. At 144°W, at the entrance of the UFZ, which lies between the Pacific‐Antarctic Ridge (PAR) and its eastwardly‐offset segment (offset PAR segment), there is a triple confluence of the Subantarctic Front (SAF), Polar Front (PF), and Southern ACC Front. Downstream of this longitude, the SAF progressively meanders northward over the relatively shallow offset PAR segment before channeling through the Eltanin Fracture Zone, thus diverging from the PF which proceeds through the UFZ. In‐situ observations from two recent cruises at 144°W confirm the satellite altimetry‐derived frontal circulation in the UFZ region, and yield a baroclinic transport relative to the bottom of 113 x 106 m3 s‐1, comparable to that through Drake Passage. The hydrographic sections show no Antarctic bottom water colder than 0.2°C. Characteristics of major water masses are described and the implications for their potential downstream modifications at Drake Passage are discussed in terms of the meridional overturning circulation across the ACC. Mesoscale eddy activity with periods shorter than 90 days is predominantly concentrated in the immediate downstream area of the offset PAR segment, suggesting a substantial poleward eddy heat flux there.
    Print ISSN: 2169-9275
    Electronic ISSN: 2169-9291
    Topics: Geosciences , Physics
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  • 7
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    Plasma and Energetic Particle Behaviors during Asymmetric Magnetic Reconnection at the Magnetopause (2014)
    Wiley
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    Publication Date: 2014-02-15
    Description: [1]  The factors controlling asymmetric reconnection and the role of the cold plasma population in the reconnection process are two outstanding questions. We present a case study of multipoint Cluster observations demonstrating that the separatrix and flow boundary angles are greater on the magnetosheath than the magnetospheric side of the magnetopause, probably due to the stronger density than magnetic field asymmetry at this boundary. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection in the diffusion region near the subsolar magnetopause, the colder ions are simply entrained by E × B drifts at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play only a very limited role in asymmetric reconnection, in contrast to previous simulation studies. Three cold ion populations (probably H + , He + , and O + ) appear in the energy spectrum, consistent with ion acceleration to a common velocity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 8
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    Warm Circumpolar Deep Water at the Western Getz Ice Shelf Front, Antarctica (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The Getz Ice Shelf is one of the largest sources of fresh water from ice shelf basal melt in Antarctica. We present new observations from three moorings west of Siple Island 2016–2018. All moorings show a persistent flow of modified Circumpolar Deep Water toward the western Getz Ice Shelf. Unmodified Circumpolar Deep Water with temperatures up to 1.5 °C reaches the ice shelf front in frequent episodes. These represent the warmest water observed at any ice shelf front in the Amundsen Sea. Mean currents within the warm bottom layer of 18–20 cm/s imply an advection time scale of 7 days from shelf break to ice shelf front. Zonal wind stress at the shelf break affects heat content at the ice shelf front on weekly to monthly time scales. Our 2‐year mooring records also evince that upwelling over the shelf break controls thermocline depth on subannual to annual time scales.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 9
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    MMS Observation of Inverse Energy Dispersion in Shock Drift Accelerated Ions (2017)
    Wiley
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    Publication Date: 2017-03-10
    Description: The four Magnetospheric Multiscale (MMS) spacecraft observed a ∼1 min burst of energetic ions (50−1000 keV) in the region upstream from the subsolar quasi-perpendicular bow shock on December 6, 2015. The composition, flux levels, and spectral indices of these energetic protons, helium, and oxygen ions greatly resemble those seen in the outer magnetosphere earlier while MMS crossed the magnetopause and differ significantly from those simultaneously observed far upstream by ACE. However, the event cannot be explained solely in terms of leakage from the magnetosphere. The strongly southward orientation of the interplanetary magnetic field (IMF) lines at the time of the event precludes any connection to the magnetosphere. This point is confirmed by the presence of energetic electrons, known to occur on magnetic field lines that graze the bow shock rather than connect to the magnetosphere. We suggest that the ions gradient drifted out of the nearby quasi-parallel foreshock and into the quasi-perpendicular bow shock. Each of the ion species exhibited an inverse energy dispersion. As predicted by models for shock drift acceleration, the energies of the ions increased as θ B n , the angle between the IMF and the shock normal, increased. Finally, we note that a similar event was observed a few minutes later in the subsolar magnetosheath, indicating that such events can be swept downstream of the bow shock.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    A Statistical Study of Plasmaspheric Plumes and Ionospheric Outflows Observed at the Dayside Magnetopause (2016)
    Wiley
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    Publication Date: 2016-01-12
    Description: We present a statistical study of plasmaspheric plumes and ionospheric outflows observed by the Cluster spacecraft near the dayside magnetopause. Plasmaspheric plumes are identified when the low-energy ions (〈 1 keV) with ∼90° pitch angle distributions are observed by the CIS/HIA instrument. The ionospheric outflows are characterized by unidirectional or bidirectional field-aligned pitch angle distributions of low-energy ions observed in the dayside magnetosphere. 43 (10%) plasmaspheric plume events and 32 (7%) ionospheric outflow events were detected out of the 442 times that C3 crossed the dayside magnetopause between 2007 and 2009. The occurrence rate of plumes at duskside is significantly higher than that at dawnside. The occurrence rate of outflows shows a weak dawn-dusk asymmetry. We investigate the dependence of the occurrence rates of plumes and ionospheric outflows on geomagnetic activity and on solar wind/IMF conditions. The plume events tend to occur during southward IMF (duskward solar wind electric field) and moderate geomagnetic activity ( K p = 3, -30 ≤ D s t 〈-10 nT). However, the ionospheric outflow events tend to occur during northward IMF (dawnward solar wind electric field). The ionospheric outflows do not occur when K p = 0, and the occurrence rate of the ionospheric outflows does not have a clear D s t dependence. 75% (46%) of the outflows are observed in the duskside for negative (positive) IMF B y . Conversely, 54% (25%) of the outflows are observed in the dawnside for positive (negative) IMF B y . Finally, the occurrence rates of both plumes and outflows increase with solar wind dynamic pressure.
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    Topics: Geosciences , Physics
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