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  • Articles  (9)
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  • Wiley  (9)
  • American Chemical Society
  • American Institute of Physics (AIP)
  • American Physical Society
  • National Academy of Sciences
  • Springer Nature
  • 2015-2019  (9)
  • 1985-1989
  • Space Weather  (9)
  • 39520
  • 1
    Publication Date: 2019
    Description: Abstract The Sun was remarkably active during the first week of September 2017 producing numerous solar flares, solar radiation storms and coronal mass ejections (CME). This activity caused disruption to terrestrial high frequency (HF, 3‐30 MHz) radio communication channels including observations with the SuperDARN HF radars. In this paper, we analyze the response of SuperDARN ground‐scatter observations and decreases in background sky noise level in response to multiple solar flares occurring in quick succession and co‐occurring with solar energetic protons and auroral activity. We estimate the attenuation in HF signal strength using an approach similar to riometry and find that the radars exhibit a nonlinear response to compound solar flare events. Additionally, we find the three different space weather drivers have varying degrees of influence on the HF signal properties at different latitudes. Our study demonstrates that in addition to monitoring high latitude convection, SuperDARN observations can be used to study the spatiotemporal evolution of disruption to HF communication during extreme space weather conditions.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2016-08-20
    Description: Key Points Resource Letter for space weather Reference to article with extensive referecnes
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2016-01-27
    Description: Energetic electron observations in Earth's radiation belts are typically sparse and multi-point studies often rely on serendipitous conjunctions. This paper establishes the scientific utility of the Combined X-ray Dosimeter (CXD), currently flown on 19 satellites in the Global Positioning System (GPS) constellation, by cross-calibrating energetic electron measurements against data from the Van Allen Probes. By breaking our cross-calibration into two parts – one that removes any spectral assumptions from the CXD flux calculation, and one that compares the energy spectra – we first validate the modeled instrument response functions, then the calculated electron fluxes. Unlike previous forward modeling of energetic electron spectra we use a combination of four distributions that, together, capture a wide range of observed spectral shapes. Our two-step approach allowed us to identify, and correct for, small systematic offsets between block IIR and IIF satellites. Using the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron-Proton Telescope (REPT) on Van Allen Probes as a “gold standard” we demonstrate that the CXD instruments are well-understood. A robust statistical analysis shows that CXD and Van Allen Probes fluxes are similar and the measured fluxes from CXD are typically within a factor of 2 of Van Allen Probes at energies ≲4 MeV. We present data from 17 CXD-equipped GPS satellites covering the 2015 “St. Patrick's Day” geomagnetic storm to illustrate the scientific applications of such a high data density satellite constellation, and therefore demonstrate that the GPS constellation is positioned to enable new insights in inner magnetospheric physics and space weather forecasting.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2016-03-12
    Description: Analysis of particle pitch angle distributions (PADs) has been used as a mean to comprehend a multitude of different physical mechanisms that lead to flux variations in the Van Allen belts and also to particle precipitation into the upper atmosphere. In this work we developed a neural network-based data clustering methodology that automatically identifies distinct PAD types in an unsupervised way using particle flux data. One can promptly identify and locate three well-known PAD types in both time and radial distance, namely 90°-peaked, butterfly, and flattop distributions. In order to illustrate the applicability of our methodology we used relativistic electron flux data from the whole month of November, 2014, acquired from the Relativistic Electron-Proton Telescope (REPT) instrument onboard the Van Allen Probes, but it is emphasized that our approach can also be used with multi-platform spacecraft data. Our PAD classification results are in reasonably good agreement with those obtained by standard statistical fitting algorithms. The proposed methodology has a potential use for Van Allen belt's monitoring.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2016-11-22
    Description: It is observed that charged particle intensities are very high near the South Atlantic Anomaly (SAA) and are a potential hazard to spacecraft passing through the region. In this study, we examine the secular drift of the SAA location at ∼400-600 kilometers altitude over nearly two solar cycles, using particle count rates to trace the geomagnetic field lines in the region near the SAA. We use data from the Low-Energy Ion Composition Analyzer (LICA) sensor onboard the SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer) spacecraft to measure both the longitudinal and latitudinal drift of the SAA. We find that the longitudinal drift rate is 0.20 ± 0.04 ∘ west/yr, and that the latitudinal drift rate is 0.11 ± 0.01 ∘ south/yr. These measurements are compared with the IGRF12 model calculations based on an analysis of magnetic field minima in the region of the SAA. Our results, which are in good agreement with model results and prior measurements when declining spacecraft altitude is taken into account, have important space weather implications.
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    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
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  • 6
    Publication Date: 2017-12-27
    Description: Normal solar wind flows and intense solar transient events interact directly with the upper Martian atmosphere due to the absence of an intrinsic global planetary magnetic field. Since the launch of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, there are now new means to directly observe solar wind parameters at the planet's orbital location for limited time spans. Due to MAVEN's highly elliptical orbit, in situ measurements cannot be taken while MAVEN is inside Mars' magnetosheath. To model solar wind conditions during these atmospheric and magnetospheric passages, this research project utilized the solar wind forecasting capabilities of the WSA-ENLIL+Cone model. The model was used to simulate solar wind parameters which included magnetic field magnitude, plasma particle density, dynamic pressure, proton temperature, and velocity during a four Carrington rotation-long segment. An additional simulation that lasted 18 Carrington rotations was then conducted. The precision of each simulation was examined for intervals when MAVEN was in the upstream solar wind, i.e., with no exospheric or magnetospheric phenomena altering in situ measurements. It was determined that generalized, extensive simulations have comparable prediction capabilities as shorter, more comprehensive simulations. Generally, this study aimed to quantify the loss of detail in long-term simulations and to determine if extended simulations can provide accurate, continuous upstream solar wind conditions when there is a lack of in situ measurements.
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    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
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  • 7
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    Wiley
    Publication Date: 2016-10-25
    Description: This manuscript comments on the new Presidential Executive Order relating to Space Weather
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
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  • 8
    Publication Date: 2017-05-27
    Description: Fundamental research on Earth's space radiation environment is essential for the design and the operations of modern technologies – for communications, weather, navigation, national security – that fly in the hostile space weather conditions above Earth's atmosphere. As the technologies become ever more advanced, more sophisticated understanding – and even predictability – of the environment is required for mission success
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    Topics: Geosciences , Physics
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  • 9
    Publication Date: 2019
    Description: Abstract The auroral substorm has been extensively studied over the last six decades. However, our understanding of its driving mechanisms is still limited and so is our ability to accurately forecast its onset. In this study, we present the first deep learning‐based approach to predict the onset of a magnetic substorm, defined as the signature of the auroral electrojets in ground magnetometer measurements. Specifically, we use a time history of solar wind speed (Vx), proton number density, and IMF components as inputs to forecast the occurrence probability of an onset over the next one hour. The model has been trained and tested on a dataset derived from the SuperMAG list of magnetic substorm onsets and can correctly identify substorms ∼75% of the time. In contrast, an earlier prediction algorithm correctly identifies ∼21% of the substorms in the same dataset. Our model's ability to forecast substorm onsets based on solar wind and IMF inputs prior to the actual onset time, and the trend observed in IMF Bz prior to onset together suggest a majority of the substorms may not be externally triggered by northward turnings of IMF. Furthermore, we find that IMF Bz and Vx have the most significant influence on model performance. Finally, principal component analysis shows a significant degree of overlap in the solar wind and IMF parameters prior to both substorm and non‐substorm intervals, suggesting that solar wind and IMF alone may not be sufficient to forecast all substorms, and preconditioning of the magnetotail may be an important factor.
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    Topics: Geosciences , Physics
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