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  • 1
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    Off-great-circle paths in transequatorial propagation 2. Non-magnetic-field-aligned reflections (2016)
    Wiley
    Details
    Publication Date: 2016-09-16
    Description: There is considerable evidence that plasma structure in nighttime equatorial F layer develops from large-scale wave structure (LSWS) in bottomside F layer. However, crucial details of how this process proceeds, from LSWS to equatorial plasma bubbles (EPBs), remain to be sorted out. A major obstacle to success is the paucity of measurements that provide a space-time description of the bottomside F layer over a broad geographical region. The transequatorial propagation (TEP) experiment is one of few methods that can do so. New findings using a TEP experiment, between Shepparton (SHP), Australia, and Oarai (ORI), Japan, are presented in two companion papers. In Paper 1 (P1): (1) off-great-circle (OGC) paths are described in terms of discrete and diffuse types; (2) descriptions of OGC paths are generalized from a single-reflection to a multiple-reflection process; and (3) discrete type is shown to be associated with an unstructured but distorted upwelling, whereas the diffuse type is shown to be associated with EPBs. In Paper 2 (P2), attention is placed on differences in east-west (EW) asymmetry, found between OGC paths from the SHP-ORI experiment and those from another near-identical TEP experiment. Differences are reconciled by allowing three distinct sources for the EW asymmetries: (1) reflection properties within an upwelling (see P1), (2) OGC paths that depend on magnetic declination of geomagnetic field ( B ), and (3) OGC paths supported by non- B -aligned reflectors at latitudes where inclination of B is finite.
    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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    Off-great-circle paths in transequatorial propagation 1. Discrete and diffuse types (2016)
    Wiley
    Details
    Publication Date: 2016-09-17
    Description: There is mounting evidence that plasma structure in nighttime equatorial F layer evolves from large-scale wave structure (LSWS) in the bottomside F layer. This process cannot be ignored because equatorial plasma bubbles (EPBs), arise from large-amplitude LSWS; and, because intense radiowave scintillations are associated with EPBs, understanding the LSWS-to-EPB process is a crucial step toward reliable space-weather forecasting. In this regard, the transequatorial propagation (TEP) experiment appears to be most useful among available research instruments. After a lapse of 30 years, the TEP experiment has been resurrected [e.g., Maruyama and Kawamura , 2006]; a goal of this research is to understand TEP measurements well enough so that they can be used to diagnose the LSWS-to-EPB process. Toward this end, new results are presented in two companion papers. Herein (P1), off-great-circle (OGC) propagation paths are shown to consist of two types, discrete and diffuse. The new findings include: (1) a generalized multi-reflection model that can explain most of the observed properties; (2) the discrete type is supported by multi-reflections from an unstructured upwelling, (3) the diffuse type is supported by reflections from plasma structure in EPBs; and (4) the observed east-west (EW) asymmetry can be explained in terms of a distorted upwelling or plasma structure along the west wall of an upwelling. In Paper 2 (P2), a second form of observed EW asymmetry is explained in terms of plasma structure, which is not aligned with the geomagnetic field. The findings strongly confirm a close relationship between upwellings, ESF patches, and OGC paths.
    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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    A simple model to relate ionogram signatures to large-scale wave structure (2012)
    Wiley
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    Publication Date: 2012-09-27
    Description: The development of plasma structure in the nighttime equatorial F region, known as equatorial spread F (ESF), appears to be controlled by the preceding presence of large-scale wave structure (LSWS). To understand this process, knowledge of the properties of LSWS is crucial. Information about LSWS appears to reside in two ionogram signatures, multi-reflected echoes (MREs) and the so-called “satellite” traces (STs). However, how LSWS is related to MREs and STs is not yet clear. To gain insight, a tilted, linear reflector, modulated by LSWS, is described and shown to be capable of explaining even the most puzzling forms of MREs and STs. With this kind of model, ionogram signatures can be used to infer the nature of LSWS.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Ionogram signatures of large-scale wave structure and their relation to equatorial spread F (2012)
    Wiley
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    Publication Date: 2012-08-16
    Description: Observations of signatures of the large-scale wave structure (LSWS) and subsequent development of equatorial spread F (ESF) by using data from a newly installed digital ionosonde at Trivandrum (8.5°N; 77°E; 0.5°N magnetic dip latitude) are presented. The LSWS signatures are observed using the ionograms with echo directions. The ‘satellite’ traces are shown as echoes from oblique directions, when an upwelling (associated with LSWS) is not directly over the ionosonde location. When an upwelling is centered overhead, and the radius of curvature of the isodensity contours matches the height of reflection, signals from various directions can add in phase to enhance the ionospheric reflection coefficient, and produce another ionogram signature, referred to as multireflected echoes (MREs). It is also shown that the generation of ESF is related to the presence of LSWS. The skymaps also show the presence of small-scale wave structures in the bottomside F region. The investigation also indicates that the range spread F (RSF) occurs because of the reflections from the embedded smaller-scale structures within the large-scale upwelling.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    On seeding, large-scale wave structure, equatorial spread F, and scintillations over Vietnam (2011)
    Wiley
    Details
    Publication Date: 2011-10-18
    Description: Understanding the day-to-day variability in occurrence of equatorial spread F (ESF) remains as a high-priority objective in space weather research. A major difficulty has been an inability to resolve the roles being played by large-scale wave structure (LSWS) and the post-sunset rise (PSSR) of the equatorial F layer, in the production of ESF. In this paper, we show conclusively that total electron content (TEC), measured as a function of latitude and longitude, provides clear, routine descriptions of LSWS. Then, together with ionosonde data, we show, for the first time, that while a seed for LSWS can occur in the late afternoon, its amplification takes place mostly during the PSSR. Implications of these findings are discussed in light of existing theories.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    On the application of differential phase measurements to study the zonal large scale wave structure (LSWS) in the ionospheric electron content (2012)
    Wiley
    Details
    Publication Date: 2012-03-06
    Description: The GNU Radio Beacon Receiver (GRBR) Network has been recently established to provide coverage of Southeast Asia and Pacific low-latitude regions, with planned extensions into the Indian and African longitude sectors. With the availability of CERTO (Coherent Electromagnetic Radio Tomography) beacon transmissions from Communication/Navigation Outage Forecasting System (C/NOFS) satellite, which is in a unique low-inclination (13°) orbit, it is now possible to study zonal large scale wave structure (LSWS) in ionospheric total electron content (TEC) with fine spatial resolution over a wide longitudinal region. An automated procedure to determine absolute TEC from relative TEC measurements for low inclination CNOFS orbits has been implemented through a simple single station procedure for initial offset estimation, which is shown to be consistent with the better established two station method and with observations from a Digisonde. The LSWS is extracted by subtracting the background variation from longitudinal variation of TEC. The upwellings of LSWS manifest as depletions in the residual TEC variations. Further, these zonal structures have been found, in general, to be aligned with geomagnetic field lines, and the scintillation patches have been found to align with the west walls of TEC depletions. This spatial alignment recapitulates the premise that the observed zonal wave-like structures in TEC are the manifestations of bottom side LSWS. Hence, the methodology presented in this paper, would prove useful in future, to study the characteristics of LSWS on a regular basis.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Climatology of plasma density depletions observed by DMSP in the dawn sector (2011)
    Wiley
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    Publication Date: 2011-03-19
    Description: Prior to the launch of the Communication/Navigation Outage Forecasting System (C/NOFS) satellite, equatorial plasma bubbles (EPBs) were regarded as postsunset phenomena. However, during this recent solar minimum the planar Langmuir probe (PLP) on the C/NOFS satellite has detected very few EPBs after sunset; most plasma density depletions have been observed between local midnight and dawn. We take advantage of the long history of plasma density measurements by a similar sensor on Defense Meteorological Satellite Program (DMSP) spacecraft to determine whether this change is typical of solar minima in general or unique to the present extended quiet time. In 2008 and 2009 the DMSP occurrence rates of topside plasma depletions in the dawn sector were unexpectedly high around the June and December solstices and extremely low near the March and September equinoxes. Dawn sector measurements from solar minimum years 1996–1997 exhibit similar seasonal and longitudinal distributions, but occurrence rates are significantly lower. While our analysis suggests that prevailing low levels of solar EUV flux and driving electric fields establish conditions favorable for the growth of postmidnight depletions, the primary causes of observed seasonal-longitudinal distributions remain unresolved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 8
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    Characteristics of Large Scale Wave Structure (LSWS) observed from African and Southeast Asian longitudinal sectors (2014)
    Wiley
    Details
    Publication Date: 2014-02-24
    Description: [1]  The so-called large scale wave structure (LSWS) at the base of F-layer is the earliest manifestation of seed perturbation for the Rayleigh-Taylor (R-T) instability. It has been found to play a deterministic role in the development of equatorial plasma bubbles (EPBs). Except for a few case studies, a comprehensive investigation has not been conducted to determine the characteristics of LSWS. One reason is that it is not straightforward with existing sensors to detect LSWS, particularly, in the spatial domain. In this scenario, a comprehensive study was carried out, for the first time, on the spatial and temporal characteristics of LSWS. Observations were made over the African and Southeast Asian sectors during the year 2011. The observations confirm the findings from case studies, that these wave structures can occur a few degrees west of E-region sunset terminator, and can grow significantly in amplitude at longitudes east of sunset terminator. With the use of additional stations that are located on either side of dip equator, the phase fronts of these spatial structures are shown to be aligned with geomagnetic field ( ) lines over a wide latitudinal belt of 5-6 o (~500 – 600 km) centered on dip equator. The zonal wavelengths of these structures are found to vary from 100 to 700 km which is consistent with the earlier reports. A new statistical finding is that EPBs were consistently observed when the amplitudes of LSWS were grown to sufficient strengths. These results provide better insights on the underlying physical processes involved in excitation of LSWS in terms of important roles being played by the E-region electrical loading and the polarization electric fields that are induced via spatially varying dynamo current due to neutral wind perturbations associated with Atmospheric Gravity Waves (AGWs).
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 9
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    Effects of tidal forcing, conductivity gradient, and active seeding, on the climatology of equatorial spread F over Kwajalein (2014)
    Wiley
    Details
    Publication Date: 2014-12-07
    Description: Plasma structure in nighttime equatorial F layer, referred to as equatorial spread F (ESF), displays climatology whose seasonal variation depends on longitude. At longitudes where ESF favors equinoxes, times when maxima occur, can be predicted in terms of the day of year, when E -region sunset is simultaneous in conjugate hemispheres [ Tsunoda , 1985] (i.e., ‘sunset nodes’). Aside from occurrences around equinoxes, there are only three longitudes, where ESF also occurs during a solstice; one is the central Pacific region. Here, ESF activity is strong during June solstice, when solar activity is high. To understand this puzzling behavior, ESF climatology over the Kwajalein Atoll, was compared with properties of the post-sunset rise (PSSR) of F layer and seeding activity in troposphere. Key findings are as follows. (1) Maxima in PSSR velocity ( V PSSR ) is better aligned with equinoxes, than with sunset nodes; hence, seasonal pattern of V PSSR , not only sunset nodes, should be included in interpretation of ESF climatology. (2) Source of V PSSR during solstice appears to differ from that during equinoxes. (3) Equinoctial maxima in V PSSR could be related to a semiannual variation in equatorial electrojet strength and its contribution to polarization of the F -region dynamo current. (4) Enhanced V PSSR during June solstice is interpreted in terms of tidal forcing with a wave number of two. (5) Displacements of maxima in ESF climatology from maxima in V PSSR are shown to be consistent with deep convective activity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    Prepublication data sharing (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-09-11
    Description: Rapid release of prepublication data has served the field of genomics well. Attendees at a workshop in Toronto recommend extending the practice to other biological data sets.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3073843/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3073843/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Toronto International Data Release Workshop Authors -- Birney, Ewan -- Hudson, Thomas J -- Green, Eric D -- Gunter, Chris -- Eddy, Sean -- Rogers, Jane -- Harris, Jennifer R -- Ehrlich, S Dusko -- Apweiler, Rolf -- Austin, Christopher P -- Berglund, Lisa -- Bobrow, Martin -- Bountra, Chas -- Brookes, Anthony J -- Cambon-Thomsen, Anne -- Carter, Nigel P -- Chisholm, Rex L -- Contreras, Jorge L -- Cooke, Robert M -- Crosby, William L -- Dewar, Ken -- Durbin, Richard -- Dyke, Stephanie O M -- Ecker, Joseph R -- El Emam, Khaled -- Feuk, Lars -- Gabriel, Stacey B -- Gallacher, John -- Gelbart, William M -- Granell, Antoni -- Guarner, Francisco -- Hubbard, Tim -- Jackson, Scott A -- Jennings, Jennifer L -- Joly, Yann -- Jones, Steven M -- Kaye, Jane -- Kennedy, Karen L -- Knoppers, Bartha Maria -- Kyrpides, Nikos C -- Lowrance, William W -- Luo, Jingchu -- MacKay, John J -- Martin-Rivera, Luis -- McCombie, W Richard -- McPherson, John D -- Miller, Linda -- Miller, Webb -- Moerman, Don -- Mooser, Vincent -- Morton, Cynthia C -- Ostell, James M -- Ouellette, B F Francis -- Parkhill, Julian -- Raina, Parminder S -- Rawlings, Christopher -- Scherer, Steven E -- Scherer, Stephen W -- Schofield, Paul N -- Sensen, Christoph W -- Stodden, Victoria C -- Sussman, Michael R -- Tanaka, Toshihiro -- Thornton, Janet -- Tsunoda, Tatsuhiko -- Valle, David -- Vuorio, Eero I -- Walker, Neil M -- Wallace, Susan -- Weinstock, George -- Whitman, William B -- Worley, Kim C -- Wu, Cathy -- Wu, Jiayan -- Yu, Jun -- 062023/Wellcome Trust/United Kingdom -- 077198/Wellcome Trust/United Kingdom -- U54 HG003273/HG/NHGRI NIH HHS/ -- U54 HG003273-04/HG/NHGRI NIH HHS/ -- U54 HG003273-04S1/HG/NHGRI NIH HHS/ -- U54 HG003273-05/HG/NHGRI NIH HHS/ -- U54 HG003273-05S1/HG/NHGRI NIH HHS/ -- U54 HG003273-05S2/HG/NHGRI NIH HHS/ -- U54 HG003273-06/HG/NHGRI NIH HHS/ -- U54 HG003273-06S1/HG/NHGRI NIH HHS/ -- U54 HG003273-06S2/HG/NHGRI NIH HHS/ -- U54 HG003273-07/HG/NHGRI NIH HHS/ -- U54 HG003273-08/HG/NHGRI NIH HHS/ -- Biotechnology and Biological Sciences Research Council/United Kingdom -- Wellcome Trust/United Kingdom -- England -- Nature. 2009 Sep 10;461(7261):168-70. doi: 10.1038/461168a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19741685" target="_blank"〉PubMed〈/a〉
    Keywords: *Access to Information ; Cooperative Behavior ; *Guidelines as Topic ; Human Genome Project ; Humans ; Ontario ; *Publishing/ethics/standards ; *Research/standards ; Research Personnel/ethics/standards
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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