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A new method of physics-based data assimilation for the quiet and disturbed thermosphere

Wed, 03/14/2018 - 19:55
Abstract

The ability to accurately track and predict satellite locations is of paramount importance to space-faring nations. In the low-Earth orbit satellite environment, atmospheric drag is by far the dominant error associated with orbit propagation. Nowcasts of thermospheric density are routinely accomplished through calibration of semi-empirical models using recent data, yet forward predictions degrade quickly as lead time increases. Physics-based approaches offer a great forecasting potential, but one that has yet to be realized due to a lack of robust data assimilation schemes. In an effort to account for the driver/response characteristics of the thermosphere-ionosphere system, a new data assimilative technique is developed. Abandoning the ensemble Kalman filter framework in favor of a variational technique, iterative model re-initialization is applied self-consistently to estimate a time-history of effective solar and geophysical drivers. The current implementation of this technique, referred to as Iterative Re-Initialization, Driver Estimation and Assimilation (IRIDEA), works by ingesting neutral mass density measurements from low-Earth orbiting accelerometers. A long-term simulation is carried out during 2003, a period consisting of a wide range of solar and geomagnetic activity levels. The new technique is shown to greatly reduce RMS errors of the physics-based model relative to ingested observations from the CHAMP satellite as well as to an independent validation data set from the GRACE-A satellite. This work is the first such demonstration of an accurate and robust physics-based method capable of specifying neutral density during both quiet and disturbed times, and has a promising outlook for improving density forecasting capabilities.

Ionospheric Peak Electron Density and Performance Evaluation of IRI-CCIR Near Magnetic Equator in Africa During Two Extreme Solar Activities

Tue, 03/13/2018 - 14:35
Abstract

The F2 layer peak electron density (NmF2) was investigated over Korhogo (Geomagnetic: 1.26°S, 67.38°E), a station near the magnetic equator in the African sector. Data for 1996 and 2000 were, respectively, categorized into low solar quiet and disturbed and high solar quiet and disturbed. NmF2 prenoon peak was higher than the postnoon peak during high solar activity irrespective of magnetic activity condition, while the postnoon peak was higher for low solar activity. Higher NmF2 peak amplitude characterizes disturbed magnetic activity than quiet magnetic condition for any solar activity. The maximum peaks appeared in equinox. June solstice noontime bite out lagged other seasons by 1–2 h. For any condition of solar and magnetic activities, the daytime NmF2 percentage variability (%VR) measured by the relative standard deviation maximizes/minimizes in June solstice/equinox. Daytime variability increases with increasing magnetic activity. The highest peak in the morning time NmF2 variability occurs in equinox, while the highest evening/nighttime variability appeared in June solstice for all solar/magnetic conditions. The nighttime annual variability amplitude is higher during disturbed than quiet condition regardless of solar activity period. At daytime, variability is similar for all conditions of solar activities. NmF2 at Korhogo is well represented on the International Reference Ionosphere-International Radio Consultative Committee (IRI-CCIR) option. The model/observation relationship performed best between local midnight and postmidnight period (00–08 LT). The noontime trough characteristics is not prominent in the IRI pattern during high solar activity but evident during low solar conditions when compared with Korhogo observations. The Nash-Sutcliffe coefficients revealed better model performance during disturbed activities.

Issue Information

Sat, 03/10/2018 - 12:49

No abstract is available for this article.

Evaluation of the Sq magnetic field variation calculated by GAIA

Sat, 03/10/2018 - 00:15
Abstract

Magnetic variations calculated by the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) are compared with those observed at global magnetic observatory network in geomagnetic calm days in order to evaluate accuracy of the ionospheric current system calculated by GAIA. The calculated Y-component magnetic variations can reproduce more than 50% of the observed variations at more than half observatories treated. In particular, GAIA can reproduce more than 75% of the observed Y-component variations in the equinox. Whereas, there is tendency of low correlation of the waveform between the calculated and observed variations in the winter season. Next, GAIA reproduces so well of the X-component variations at the low-latitude observatories. Low correlation between the calculated and observed X-component variations at middle-latitude observatories seems to be caused by inaccurate determination of the position of the ionospheric Sq current vortex. Last, although the calculated Z-component variations does not so well reproduce the observed ones compared with other component, GAIA can reproduce more than 50% of the observed Z-component variation at about half observatories in general. Calculated amplitude of the horizontal magnetic variations (X- and Y-components) exhibit smaller than the observed one, whereas that of the vertical variation (Z-component) is larger than the observed one. This tendency is roughly explained by the induction effect of the Earth that is not considered in GAIA. Thus, GAIA considerably well reproduces the pure ionospheric current system that is not affected by the solid Earth.

Mid-latitude plasma bubbles over China and adjacent areas during a magnetic storm on 08 September 2017

Sat, 03/10/2018 - 00:15
Abstract

This paper presents observations of post-sunset super plasma bubbles over China and adjacent areas during the second main phase of a storm on 08 Sep 2017. The signatures of the plasma bubbles can be seen or deduced from: 1) deep field-aligned total electron content (TEC) depletions embedded in regional ionospheric maps derived from dense Global Navigation Satellite System (GNSS) networks; 2) significant equatorial and mid-latitudinal plasma bite-outs in electron density measurements onboard Swarm satellites; 3) enhancements of ionosonde virtual height and scintillation in local evening associated with strong southward interplanetary magnetic field (IMF). The bubbles/depletions covered a broad area mainly within 20° -45° N and 80° -110° E with bifurcated structures and persisted for nearly 5 hours (∼13-18 UT). One prominent feature is that the bubbles extended remarkably along the magnetic field lines in the form of depleted flux tubes, reaching up to mid-latitude of around 50° N (MLAT: 45.5° N) that maps to an altitude of 6600 km over the magnetic equator. The maximum upward drift speed of the bubbles over the magnetic equator was about 700 m/s, and gradually decreased with altitude and time. The possible triggering mechanism of the plasma bubbles was estimated to be storm-time eastward prompt penetration electric field (PPEF), while the traveling ionospheric disturbance (TID) could play a role in facilitating the latitudinal extension of the depletions.

Modeling the Lower Part of the Topside Ionospheric Vertical Electron Density Profile over the European Region by means of Swarm Satellites Data and IRI UP Method

Thu, 03/08/2018 - 03:05
Abstract

An empirical method to model the lower part of the ionospheric topside region from the F2-layer peak height to about 500-600 km of altitude over the European region, is proposed. The method is based on electron density values recorded from December 2013 to June 2016 by Swarm satellites, and on foF2 and hmF2 values provided by IRI UP (International Reference Ionosphere UPdate), which is a method developed to update the IRI (International Reference Ionosphere) model relying on the assimilation of foF2 and M(3000)F2 data routinely recorded by a network of European ionosonde stations. Topside effective scale heights are calculated by fitting some definite analytical functions (α-Chapman, β-Chapman, Epstein and Exponential) through the values recorded by Swarm and the ones output by IRI UP, with the assumption that the effective scale height is constant in the altitude range considered. Calculated effective scale heights are then modeled as a function of foF2 and hmF2, in order to be operationally applicable to both ionosonde measurements and ionospheric models, like IRI. The method produces two-dimensional maps of the median effective scale height binned as a function of foF2 and hmF2, for each of the considered topside profiles. A statistical comparison with COSMIC/FORMOSAT-3 collected Radio Occultation profiles is carried out to assess the validity of the proposed method, and to investigate which of the considered topside profiles is the best one. The α-Chapman topside function displays the best performance compared to the others, and also when compared to the NeQuick topside option of IRI.

Forward Modeling of Coronal Mass Ejection Flux Ropes in the Inner Heliosphere with 3DCORE

Wed, 03/07/2018 - 20:55
Abstract

Forecasting the geomagnetic effects of solar storms, known as coronal mass ejections (CMEs), is currently severely limited by our inability to predict the magnetic field configuration in the CME magnetic core and by observational effects of a single spacecraft trajectory through its 3-D structure. CME magnetic flux ropes can lead to continuous forcing of the energy input to the Earth's magnetosphere by strong and steady southward-pointing magnetic fields. Here we demonstrate in a proof-of-concept way a new approach to predict the southward field Bz in a CME flux rope. It combines a novel semiempirical model of CME flux rope magnetic fields (Three-Dimensional Coronal ROpe Ejection) with solar observations and in situ magnetic field data from along the Sun-Earth line. These are provided here by the MESSENGER spacecraft for a CME event on 9–13 July 2013. Three-Dimensional Coronal ROpe Ejection is the first such model that contains the interplanetary propagation and evolution of a 3-D flux rope magnetic field, the observation by a synthetic spacecraft, and the prediction of an index of geomagnetic activity. A counterclockwise rotation of the left-handed erupting CME flux rope in the corona of 30° and a deflection angle of 20° is evident from comparison of solar and coronal observations. The calculated Dst matches reasonably the observed Dst minimum and its time evolution, but the results are highly sensitive to the CME axis orientation. We discuss assumptions and limitations of the method prototype and its potential for real time space weather forecasting and heliospheric data interpretation.

The Critical Role of the Research Community in Space Weather Planning and Execution

Tue, 03/06/2018 - 17:55
Abstract

The explosion of interest in space weather in the last 25 years has been due to a confluence of efforts all over the globe, motivated by the recognition that events on the Sun and the consequent conditions in interplanetary space and Earth's magnetosphere, ionosphere, and thermosphere can have serious impacts on vital technological systems. The fundamental research conducted at universities, government laboratories, and in the private sector has led to tremendous improvements in the ability to forecast space weather events and predict their impacts on human technology and health. The mobilization of the research community that made this progress possible was the result of a series of actions taken by the National Science Foundation (NSF) to build a national program aimed at space weather. The path forward for space weather is to build on those successes through continued involvement of the research community and support for programs aimed at strengthening basic research and education in academia, the private sector, and government laboratories. Investments in space weather are most effective when applied at the intersection of research and applications. Thus, to achieve the goals set forth originally by the National Space Weather Program, the research community must be fully engaged in the planning, implementation, and execution of space weather activities, currently being coordinated by the Space Weather Operations, Research, and Mitigation Subcommittee under the National Science and Technology Council.

The Unknown Hydrogen Exosphere: Space Weather Implications

Fri, 03/02/2018 - 17:05
Abstract

Recent studies suggest that the hydrogen (H) density in the exosphere and geocorona might differ from previously assumed values by factors as large as 2. We use the SAMI3 (Sami3 is Also a Model of the Ionosphere) and Comprehensive Inner Magnetosphere-Ionosphere models to evaluate scenarios where the hydrogen density is reduced or enhanced, by a factor of 2, relative to values given by commonly used empirical models. We show that the rate of plasmasphere refilling following a geomagnetic storm varies nearly linearly with the hydrogen density. We also show that the ring current associated with a geomagnetic storm decays more rapidly when H is increased. With respect to these two space weather effects, increased exosphere hydrogen density is associated with reduced threats to space assets during and following a geomagnetic storm.

Advances in Space Weather Data Interpretation and Simulations

Thu, 03/01/2018 - 20:05
Abstract

This editorial highlights recent data and model results for Space Weather readers.

Onsets of solar proton events in satellite and ground-level observations: a comparison

Thu, 03/01/2018 - 15:51
Abstract

The early detection of solar proton event (SPE) onsets is essential for protecting humans and electronics in space, as well as passengers and crew at aviation altitudes. Two commonly compared methods for observing SPEs that are sufficiently large and energetic to be detected on the ground through the creation of secondary radiation — known as ground level enhancements (GLEs) — are (1) a network of ground-based Neutron Monitors (NMs), and (2) satellite-based particle detectors. Until recently, owing to the different time-resolution of the two data sets, it has not been feasible to compare these two types of observations using the same detection algorithm. This paper presents a comparison between the two observational platforms using newly-processed >100 MeV 1-min count rates and fluxes from NOAA's GOES 8-12 satellites, and 1-min count rates from the Neutron Monitor Database. We applied the same detection algorithm to each dataset (tuned to the different background noise levels of the instrument types). Seventeen SPEs with GLEs were studied: GLEs 55-70 from Solar Cycle 23 and GLE 71 from Solar Cycle 24. The median difference in the event detection times by GOES and NM data is 0 minutes, indicating no innate benefit in time of either system. The 10th, 25th, 75th, and 90th percentiles of the onset time differences (GOES minus NMs) are -7.2 min, -1.5 min, 2.5 min, and 4.2 min, respectively. This is in contrast to previous studies in which NM detections led GOES by 8 to 52 minutes without accounting for different alert protocols.

Space-Based Sentinels for Measurement of Infrared Cooling in the Thermosphere for Space Weather Nowcasting and Forecasting

Thu, 03/01/2018 - 15:51
Abstract

Infrared radiative cooling by nitric oxide (NO) and carbon dioxide (CO2) modulates the thermosphere's density and thermal response to geomagnetic storms. Satellite tracking and collision avoidance planning require accurate density forecasts during these events. Over the past several years, failed density forecasts have been tied to the onset of rapid and significant cooling due to production of nitric oxide and its associated radiative cooling via emission of infrared radiation at 5.3 μm. These results have been diagnosed, after the fact, through analyses of measurements of infrared cooling made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument now in orbit over 16 years on the NASA TIMED satellite. Radiative cooling rates for nitric oxide and carbon dioxide have been further shown to be directly correlated with composition and exospheric temperature changes during geomagnetic storms. These results strongly suggest that a network of smallsats observing the infrared radiative cooling of the thermosphere could serve as space weather sentinels. These sentinels would observe and provide radiative cooling rate data in real time to generate nowcasts of density and aerodynamic drag on space vehicles. Currently, radiative cooling is not directly considered in operational space weather forecast models. In addition, recent research has shown that different geomagnetic storm types generate substantially different infrared radiative response, and hence, substantially different thermospheric density response. The ability to identify these storms, and to measure and predict the Earth's response to them, should enable substantial improvement in thermospheric density forecasts.

Calculation of Voltages in Electric Power Transmission Lines During Historic Geomagnetic Storms: An Investigation Using Realistic Earth Impedances

Mon, 02/26/2018 - 15:36
Abstract

Commonly, one-dimensional (1-D) Earth impedances have been used to calculate the voltages induced across electric power transmission lines during geomagnetic storms under the assumption that much of the three-dimensional structure of the Earth gets smoothed when integrating along power transmission lines. We calculate the voltage across power transmission lines in the mid-Atlantic region with both regional 1-D impedances and 64 empirical 3-D impedances obtained from a magnetotelluric survey. The use of 3-D impedances produces substantially more spatial variance in the calculated voltages, with the voltages being more than an order of magnitude different, both higher and lower, than the voltages calculated utilizing regional 1-D impedances. During the March 1989 geomagnetic storm 62 transmission lines exceed 100 V when utilizing empirical 3-D impedances, whereas 16 transmission lines exceed 100 V when utilizing regional 1-D impedances. This demonstrates the importance of using realistic impedances to understand and quantify the impact that a geomagnetic storm has on power grids.

Update on the worsening particle radiation environment observed by CRaTER and implications for future human deep-space exploration

Fri, 02/23/2018 - 00:25
Abstract

Over the last decade, the solar wind has exhibited low densities and magnetic field strengths, representing anomalous states that have never been observed during the space age. As discussed by Schwadron et al. (2014a), the cycle 23–24 solar activity led to the longest solar minimum in more than 80 years and continued into the “mini” solar maximum of cycle 24. During this weak activity, we observed galactic cosmic ray fluxes that exceeded the levels observed throughout the space age, and we observed small solar energetic particle events. Here, we provide an update to the Schwadron et al (2014a) observations from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO). The Schwadron et al. (2014a) study examined the evolution of the interplanetary magnetic field, and utilized a previously published study by Goelzer et al. (2013) projecting out the interplanetary magnetic field strength based on the evolution of sunspots as a proxy for the rate that the Sun releases coronal mass ejections (CMEs). This led to a projection of dose rates from galactic cosmic rays on the lunar surface, which suggested a ∼20% increase of dose rates from one solar minimum to the next, and indicated that the radiation environment in space may be a worsening factor important for consideration in future planning of human space exploration. We compare the predictions of Schwadron et al. (2014a) with the actual dose rates observed by CRaTER in the last 4 years. The observed dose rates exceed the predictions by ∼10%, showing that the radiation environment is worsening more rapidly than previously estimated. Much of this increase is attributable to relatively low-energy ions, which can be effectively shielded. Despite the continued paucity of solar activity, one of the hardest solar events in almost a decade occurred in Sept 2017 after more than a year of all-clear periods. These particle radiation conditions present important issues that must be carefully studied and accounted for in the planning and design of future missions (to the Moon, Mars, asteroids and beyond).

Space Weather Influence on Electromagnetic Geosynchronous Debris Perturbations Using Statistical Fluxes

Fri, 02/23/2018 - 00:25
Abstract

Spacecraft can charge to negative 10's of kilo-Volts at Geosynchronous Earth Orbit (GEO) due to interactions with the space plasma. This raises spacecraft electronics or solar panel damage concerns. Spacecraft charging leads to perturbations which change the orbits of lightweight uncontrolled debris objects. A charged space object experiences a force from the convection electric field as well as the local magnetic field (i.e. Lorentz force v × B), as well as the associated Lorentz torque. If the object is tumbling the Eddy current torques provide a disturbance torque that reduces a spin rate relative to the magnetic field. Prior work assuming a constant “worst case" voltage shows that Lorentz and eddy torques cause significant orbital changes through the attitude dependent solar radiation pressure force.

This paper investigates the effects of electromagnetic perturbations by using a charging model that uses measured flux distributions to better simulate natural charging and includes the convection electric field. This is done for a calm space weather case of KP=2−, a stormy case where KP= 8, and a worst possible case where the voltage is held at -30 kV the entire time. It is found that neglecting electromagnetic effects on lightweight Mylar debris can lead to 1000 kilometer displacements after only a few hours, and the covariances associated with such objects must be increased during periods of high charging.

Gigantic Circular Shock Acoustic Waves in the Ionosphere Triggered by the Launch of FORMOSAT-5 Satellite

Thu, 02/22/2018 - 04:11
Abstract

The launch of SpaceX Falcon 9 rocket delivered Taiwan's FORMOSAT-5 satellite to orbit from Vandenberg Air Force Base in California at 18:51:00 UT on 24 August 2017. To facilitate the delivery of FORMOSAT-5 to its mission orbit altitude of ~720 km, the Falcon 9 made a steep initial ascent. During the launch, the supersonic rocket induced gigantic circular shock acoustic waves (SAWs) in total electron content (TEC) over the western United States beginning approximately 5 min after the liftoff. The circular SAWs emanated outward with ~20 min duration, horizontal phase velocities of ~629–726 m/s, horizontal wavelengths of ~390–450 km, and period of ~10.28 ± 1 min. This is the largest rocket-induced circular SAWs on record, extending approximately 114–128°W in longitude and 26–39°N in latitude (~1,500 km in diameter), and was due to the unique, nearly vertical attitude of the rocket during orbit insertion. The rocket-exhaust plume subsequently created a large-scale ionospheric plasma hole (~900 km in diameter) with 10–70% TEC depletions in comparison with the reference days. While the circular SAWs, with a relatively small amplitude of TEC fluctuations, likely did not introduce range errors into the Global Navigation Satellite Systems navigation and positioning system, the subsequent ionospheric plasma hole, on the other hand, could have caused spatial gradients in the ionospheric plasma potentially leading to a range error of ~1 m.

Statistical Similarities Between WSA-ENLIL+Cone Model and MAVEN in Situ Observations From November 2014 to March 2016

Thu, 02/22/2018 - 04:06
Abstract

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 that 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, that is, 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.

Cross-Calibration of the GPS Constellation CXD Proton Data with GOES EPS

Tue, 02/20/2018 - 20:20
Abstract

Accurate proton flux measurements of the near Earth environment are essential to the understanding of many phenomena which have a direct impact on our lives. Currently there is only a small set of satellites capable of performing these measurements which makes certain studies and analyses difficult. This paper details the capabilities of the Combined X-ray Dosimeter (CXD), flown on 21 satellites of the Global Positioning System (GPS) constellation, as it relates to proton measurements. We present a cross-calibration of the CXD with the Energetic Particle Sensor (EPS) onboard the Geostationary Operational Environmental Satellite (GOES) operated by the National Oceanic and Atmospheric Administration (NOAA). By utilizing Solar Energetic Particle Events (SEPEs) when both sets of satellites were operational we have orders of magnitude in flux and energy to compare against. Robust statistical analyses show that the CXD and GOES flux calculations are similar and that for proton energies > 30 MeV the CXD fluxes are on average within 20% of EPS. Although the CXD has a response to protons as low as 6 MeV the sensitivity at energies below 20 MeV is reduced and so flux comparisons of these are generally worse. Integral flux values > 10 MeV are typically within 40% of EPS. These calibrated CXD data sets will give researchers capabilities to study solar proton access to the inner magnetosphere down to L ~ 4 near the equatorial plane at high temporal cadence.

Using Extreme Value Theory for Determining the Probability of Carrington-Like Solar Flares

Tue, 02/20/2018 - 20:20
Abstract

By their very nature, extreme space weather events occur rarely and, therefore, statistical methods are required to determine the probability of their occurrence. Space weather events can be characterised by a number of natural phenomena such as X-ray (solar) flares, solar energetic particle (SEP) fluxes, coronal mass ejections and various geophysical indices (Dst, Kp, F10.7). In this paper extreme value theory (EVT) is used to investigate the probability of extreme solar flares. Previous work has assumed that the distribution of solar flares follows a power law. However such an approach can lead to a poor estimation of the return times of such events due to uncertainties in the tails of the probability distribution function. Using EVT and GOES X-ray flux data it is shown that the expected 150-year return level is approximately an X60 flare whilst a Carrington-like flare is a one in a 100-year event. In the worst case the 150-year return level is an X90 flare whist a Carrington flare is a one in 30-year event. It is also shown that the EVT results are consistent with flare data from the Kepler space telescope mission.

New Magnetospheric Substorm Injection Monitor: Image Electron Spectrometer On Board a Chinese Navigation IGSO Satellite

Tue, 02/20/2018 - 05:51
Abstract

Substorm injections are one of the most dynamic processes in Earth's magnetosphere and have global consequences and broad implications for space weather modeling. They can be monitored using energetic electron detectors on geosynchronous satellites. The Imaging Electron Spectrometer (IES) on board a Chinese navigation satellite, launched on 16 October 2015 into an inclined geosynchronous satellite orbit (IGSO), provides the first energetic electron measurement in IGSO orbit to the best of our knowledge. The IES was developed by Peking University and is named hereafter as BD-IES. Using a pin-hole technique, the BD-IES instrument measures 50–600 keV incident electrons in eight energy channels from nine directions covering a range of 180° in polar angle. Data collection by the BD-IES instrument have recently passed the 1 year mark, which reflects a successful milestone for the mission. The innermost and outermost signatures of substorm injection at L ~ 6 and 12 have been observed by the BD-IES with a high L shell spatial coverage, complementary to the existing missions such as the Van Allen Probes that covers the range below L ~ 6. There are another two BD-IES instruments to be installed in the coming Chinese Sun-synchronous and geosynchronous satellites, respectively. Such a configuration will provide a unique opportunity to investigate inward and outward radial propagation of the substorm injection region simultaneously at high and low L shells. It will further elucidate potential mechanisms for the particle energization and transport, two of the most important topics in magnetospheric dynamics.

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