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  • 1
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    An empirical model of the drift velocity of equatorial plasma depletions (2012)
    Wiley
    Details
    Publication Date: 2012-12-12
    Description: The Far-Ultraviolet Imager on the IMAGE spacecraft (IMAGE-FUV) has been used to observe O+ plasma depletions in the post-sunset equatorial ionosphere. Small-scale density irregularities associated with such depletions are believed to adversely affect trans-ionospheric radio signals such as GPS. Prediction of the motion of these plasma depletions is a necessary component of the ability to forecast the occurrence of such radio signal interference. An automated method has recently been developed to identify and track the position and zonal drift velocity of these depletions. Here we use this method to create a large database of the zonal drift velocities of these depletions. We present an empirical model based on these observations that describes the observed drift velocities as a function of both local time and magnetic latitude, which is essential to represent their behavior. A comparison of the observed drift velocities with zonal winds from both an empirical model (Horizontal Wind Model; HWM07) and a first-principles model (the TIEGCM) reveals that the plasma depletions' drift velocities have a latitudinal gradient that cannot be explained solely by the F-region dynamo in the post-sunset period, at least by these climatological models. This suggests that these plasma depletions may not simply drift with the background F-region plasma. It has previously been suggested that vertical polarization electric fields associated with the plasma depletions are responsible for their zonal drifts exceeding the background flow, which may explain the previously-observed discrepancy in the drift velocities and the discrepancy in their gradients reported here.
    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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    On the signature of the quasi-3-day wave in the thermosphere during the January 2010 URSI World Day Campaign (2012)
    Wiley
    Details
    Publication Date: 2012-06-05
    Description: Ultra-fast Kelvin waves with periods of 3–5 days are important in the coupling of the lower atmosphere to the thermosphere and ionosphere. Here we focus on the observations and effects of a 3-day wave during January 2010. As this time period coincides with a stratospheric warming event, a coordinated set of observations with incoherent scatter radars are available. While there is no evidence that the occurrence of this 3-day wave is connected with this event, these observations offer an unprecedented glimpse of the thermospheric conditions during this period, including the first-ever detection of a 3-day wave with an incoherent scatter radar. Using a combination of ground- and space-based observations, we identify an eastward moving zonal wave number-one 3-day equatorial wave that is comprised of a Kelvin wave at the lowest latitudes and a Rossby-gravity wave at higher latitudes. In the equatorial region, the vertical wavelength is ∼40 km and the wave peaks in amplitude around 95–100 km altitude. The wave observed here is only seen to propagate to around 105 km altitude. Evidence of an interaction between this wave and the diurnal tide is seen between 82–88 km. The resultant 3-day periodicity in the diurnal tide is seen to propagate up to altitudes of ∼150 km. This could have a significant impact on the ionosphere via modulation of the E-region dynamo, thus carrying the 3-day periodicity to higher altitudes.
    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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    Signatures of the 3-day wave in the low-latitude and midlatitude ionosphere during the January 2010 URSI World Day campaign (2012)
    Wiley
    Details
    Publication Date: 2012-06-06
    Description: Recent studies of the equatorial ionosphere have found evidence of forcing by atmospheric Ultra Fast Kelvin (UFK) waves. This study investigates the quasi-3-day UFK wave and its effects on the variations of the ionosphere at low latitudes and midlatitudes using coordinated observations of both the atmosphere and ionosphere during the January 2010 URSI World Day campaign. The global maps of TEC from the IGS ground-based GPS product demonstrate a 3-day periodic variation during January 15–25. This variation has the largest amplitude at 15° magnetic latitude and extends into lower latitudes. Simultaneously, a 3-day wave is observed in the mesosphere in the zonal wind measurements by a meteor radar at the magnetic equator. The latitudinal range of the TEC variation (20°S–20°N) is also consistent with that of the 3-day wave. The Incoherent Scatter Radar (ISR) observations show a 3-day signature in vertical ion drifts over Jicamarca (11.9°S, 76°W) and in the electron densities in the top side of ionosphere measured from Millstone Hill (42.6°N, 71.5°W). This signature is consistent with the fountain effect in the equatorial region, and shows the impact on the topside ionosphere at midlatitudes. The UFK wave is trapped within ±30° geographic latitude, but this study shows that the effects of the wave could reach the ionosphere at the higher latitude even as high as 40°N (50°N magnetic latitude).
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    Topics: Geosciences , Physics
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  • 4
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    Rapid decay of storm time ring current due to pitch angle scattering in curved field line (2011)
    Wiley
    Details
    Publication Date: 2011-03-23
    Description: The storm time ring current sometimes exhibits rapid decay, as suggested from the Dst index, but the underlying mechanism is unknown. By means of a simulation with pitch angle scattering due to the field line curvature (FLC), together with the charge exchange and adiabatic loss cone loss, we investigated rapid decay of the storm time ring current for the large magnetic storm that occurred on 12 August 2000. When all three loss processes were included, the Dst (SYM-H) index showed rapid recovery with an e-folding time of ∼6 h. However, without FLC scattering, the simulated Dst (SYM-H) index showed a slower recovery with an e-folding time of ∼12 h. Overall flux of energetic neutral hydrogen with energy ≥ 39 keV was significantly reduced by the FLC scattering and is consistent with data from the high energy neutral analyzer (HENA) on board the IMAGE satellite. Power of precipitating protons showed a fairly good agreement with data from the far ultraviolet (FUV) imager on board IMAGE. These fairly good agreements with observations lead to the possible conclusion that the FLC scattering is a significant loss mechanism for the ring current ions, and the main oval of the proton aurora is likely a manifestation of the precipitating loss of the protons for this particular storm.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 5
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    Metazoan calcium carbonate biomineralizations: macroevolutionary trends - challenges for the coming decade (2014)
    Societe Geologique de France (SGF)
    Details
    Publication Date: 2014-07-18
    Description: Calcium carbonate-based biominerals, also referred as biocalcifications, are the most abundant biogenic mineralized products at the surface of the Earth. In this paper, we summarize general concepts on biocalcifications and we sketch macro-evolutionary trends throughout the history of the Earth, from Archean to Phanerozoic times. Then, we expose five fundamental issues that represent key-challenges in biocalcification researches for the coming decade: the first one concerns the comprehension of the micro- and nano-structure of calcium carbonate biominerals from a mineral viewpoint, while the second one deals with the understanding of the dynamic process of their fabrication. The third one treats the subtle interplay between organics and the mineral phase. The fourth issue focuses on an environmental challenge related to ocean acidification (OA); at last, the diagenetic processes that affect biogenic calcium carbonate mineral constitute the fifth issue.
    Print ISSN: 0037-9409
    Electronic ISSN: 0037-9409
    Topics: Geosciences
    Published by Societe Geologique de France (SGF)
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  • 6
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    Root cause analysis for young engineers (2013)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2013-04-30
    Description: Root Cause Analysis, an IBI prize-winning module, requires students to use a systematic approach to analyze complex problems.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Immel, Joe -- New York, N.Y. -- Science. 2013 Apr 26;340(6131):444-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Science and Engineering, Technology High School, Rohnert Park, CA 94928, USA. immel@immel.com〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23626998" target="_blank"〉PubMed〈/a〉
    Keywords: Engineering/*education ; Humans ; Information Dissemination ; *Problem Solving ; Research/*education ; *Root Cause Analysis
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Impacts of atmospheric Ultra Fast Kelvin waves on radio scintillations in the equatorial ionosphere (2013)
    Wiley
    Details
    Publication Date: 2013-01-27
    Description: [1]  We present a statistical analysis of the amplitudes of GPS scintillations (S4 index) observed throughout 2008–2010 using the satellite radio occultation measurements of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). Here, for the first time, periodic variability in the occurrence of S4 is investigated using these data. Significant variations of S4 with periods of 2.5–4 days (quasi-3 days) are identified from the observations during post-sunset hours (19–24 hours local time) between 15°S–15°N magnetic latitude during this three year interval. Coherence analyses of these variations with the geomagnetic Ap index, solar EUV irradiance, and atmospheric wind measurements from an equatorial mesosphere meteor radar at Thumba, India (8.5°N, 77°E) are performed, providing a measure of the relationship between variations in the scintillations and potential drivers. The quasi-3 day variations in S4 are found to co-vary with the variations of the three drivers examined. In particular, the S4 signatures are found to be coherent with the atmospheric Ultra Fast Kelvin (UFK) planetary waves characterized by the zonal wind measurements of the radar. This study shows that these UFK waves are as important as the solar and geomagnetic drivers in forcing the day-to-day variations of the occurrence of equatorial spread-F.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 8
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    An empirical model of the drift velocity of equatorial plasma depletions (2013)
    Wiley
    Details
    Publication Date: 2013-01-05
    Description: [1]  The Far-Ultraviolet Imager on the IMAGE spacecraft (IMAGE-FUV) has been used to observe O + plasma depletions in the post-sunset equatorial ionosphere. Small-scale density irregularities associated with such depletions are believed to adversely affect trans-ionospheric radio signals such as GPS. Prediction of the motion of these plasma depletions is a necessary component of the ability to forecast the occurrence of such radio signal interference. An automated method has recently been developed to identify and track the position and zonal drift velocity of these depletions. Here we use this method to create a large database of the zonal drift velocities of these depletions. We present an empirical model based on these observations that describes the observed drift velocities as a function of both local time and magnetic latitude, which is essential to represent their behavior. A comparison of the observed drift velocities with zonal winds from both an empirical model (Horizontal Wind Model; HWM07) and a first-principles model (the TIEGCM) reveals that the plasma depletions' drift velocities have a latitudinal gradient that cannot be explained solely by the F-region dynamo in the post-sunset period, at least by these climatological models. This suggests that these plasma depletions may not simply drift with the background F-region plasma. It has previously been suggested that vertical polarization electric fields associated with the plasma depletions are responsible for their zonal drifts exceeding the background flow, which may explain the previously-observed discrepancy in the drift velocities and the discrepancy in their gradients reported here.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Gravity Wave Variations during Elevated Stratopause Events using SABER Observations (2013)
    Wiley
    Details
    Publication Date: 2013-05-11
    Description: [1]  Elevated stratopauses formed at ~80–90 km altitude during the recovery phase of stratospheric sudden warmings in February 2006 and 2009. These likely occurred in response to changes in the downward circulation due to gravity waves (GWs) and/or planetary waves in the mesosphere and the lower thermosphere (MLT). However, the physical mechanisms are not fully understood, due in part to the lack of global GW observations in the MLT. This study presents global-scale GW observations in the MLT during elevated stratopause events using TIMED-SABER temperature observation, which provide a better insight into the formation of an elevated stratopause. During the downward movement of elevated stratopause events in 2006 and 2009, GWs were suppressed below ~60 km and enhanced above ~60 km at high latitudes compared to non-elevated stratopause years (2005 and 2007). Global SABER GW observations indicate that the regions of GW enhancement propagate from low-mid latitudes to high latitudes in association with the equatorward shift of the polar night jet during elevated stratopause events. Ray-tracing simulations show enhancements of the poleward propagation of GWs during elevated stratopause events as well as continuous propagation of non-orographic GWs within high latitudes. Therefore, our results suggest that meridional propagation of GWs from lower to higher latitudes, which is typically not included in global-scale models, plays an important role in determining GW variations and thus the downward movement of an elevated stratopause, in addition to non-orographic GWs originating at high latitudes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    Ionospheric Redistribution during Geomagnetic Storms (2013)
    Wiley
    Details
    Publication Date: 2013-11-09
    Description: ABSTRACT [1]  The abundance of plasma in the daytime ionosphere is often seen to grow greatly during geomagnetic storms. Recent reports suggest the magnitude of the plasma density enhancement depends on the UT of storm onset. This possibility is investigated over a 7-year period using global maps of ionospheric total electron content (TEC) produced at the Jet Propulsion Laboratory. The analysis confirms that the American sector exhibits, on average, larger storm-time enhancement in ionospheric plasma content, up to50% in the afternoon middle-latitude region and 30% in the vicinity of the high-latitude auroral cusp, with largest effect in the Southern Hemisphere. We investigate whether this effect is related to the magnitude of the causative magnetic storms. Using the same advanced Dst index employed to sort the TEC maps into quiet and active (Dst 〈 -100 nT) sets, we find variation in storm strength that corresponds closely to the TEC variation, but follows it by 3-6 hours. For this and other reasons detailed in this report, we conclude that the UT-dependent peak in stormtime TEC is likely not related to the magnitude of external stormtime forcing, but more likely attributable to phenomena such as the low magnetic field in the South American region. The large Dst variation suggests a possible system-level effect of the observed variation in ionospheric storm response on the measured strength of the terrestrial ring current, possibly connected through UT-dependent modulation of ion outflow.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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