CSS Research

Permanent URI for this collectionhttps://hdl.handle.net/10735.1/3868


Recent Submissions

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    Temporal Characteristic of the Mesoscale Plasma Flow Perturbations in the High-Latitude Ionosphere
    (Amer Geophysical Union, 2019-01-03) Chen, Yun-Ju; Heelis, Roderick A.; 0000-0003-0900-3999 (Chen, Y-J; 0000-0002-5543-5357 (Heelis, RA; Chen, Yun-Ju; Heelis, Roderick A.
    Spatial and temporal characteristics of flow perturbations in the high-latitude ionosphere are important considerations for energy deposition from the magnetosphere. In this study, we examine the temporal characteristics of plasma flow perturbations with spatial scales between 100 and 400 km from two consecutive Defense Meteorological Satellite Program (DMSP) passes that have about the same orbital plane and sample time spacing between a few seconds and 20 min during local summer seasons in 2007-2015. The temporal characteristics of mesoscale flow perturbations are described by rise and saturation times for growth and decay derived from the changes in magnitude of perturbations and the time separation between consecutive samples. Observations suggest that the rise times for both growth and decay are shorter for small spatial scales (1-2 min, 100-200 km) and longer for large spatial scales (3-5 min, 200-400 km). The saturation time for decay is similar to 10 min for small scales and similar to 20 min for large scales. The growth saturation time is about 5-10 min for both scale sizes. These characteristic times for growth are always shorter than the decay times. If the difference in these characteristic times between growth and decay is produced by motion of a perturbation with the background flow through the observed volume, then a longitudinal scale size of 750 km or 1.5 hr of local time is implied.
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    Event Studies of O⁺ Density Variability Within Quiet-Time Plasma Sheet
    (Blackwell Publishing Ltd, 2019-06-18) Wang, C. -P; Fuselier, S. A.; Hairston, Marc; Zhang, X. -J; Zou, S.; Avanov, L. A.; Strangeway, R. J.; Ahmadi, N.; Bortnik, J.; 0000-0003-4524-4837 (Hairston, MR); Hairston, Marc
    To understand the variations of the O⁺ ions in the quiet-time plasma sheet between the regions of cold-dense plasma sheet (CDPS) and hot plasma sheet (HPS), we conduct three event studies. These studies investigate the O⁺ densities in the two regions and how they are correlated with the strength of two magnetospheric sources important to ion outflows: the soft electron flux and Poynting flux toward the ionosphere. The CDPS is characterized by two-component ions (one hot component mixed with one cold component), while the HPS ions consist of only one single hot component. Comparing the O⁺ density between the CDPS and HPS of the same event, the average CDPS O⁺ density was higher by a factor of ~2–5. Compared to the HPS, the soft electron flux source within the CDPS was higher, consistent with the fact that the soft electron precipitation and O⁺ upward number fluxes observed in the ionosphere were also higher within the CDPS. In the plasma sheet, broadband ultralow-frequency electric and magnetic field waves with the characteristics of kinetic Alfvén waves were often more intense within the CDPS, providing a stronger Poynting flux source. In addition, electron resonant interaction with kinetic Alfvén waves results in acceleration along the magnetic fields and, thus, may drive the observed soft electron precipitation. These correlations suggest that the higher soft electron precipitation and Poynting flux coming from the magnetospheric CDPS likely produce larger ionospheric O⁺ outflows back to the magnetosphere, thus resulting in the higher O⁺ density within the CDPS. ©2019. American Geophysical Union. All Rights Reserved.
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    Modeling Energetic Electron Nonlinear Wave-Particle Interactions with Electromagnetic Ion Cyclotron Waves
    (Blackwell Publishing Ltd, 2019-04-15) Zheng, Liheng; Chen, Lunjin; Zhu, Hui; 0000-0003-2489-3571 (Chen, L); 0000-0001-9068-4431 (Zheng, L); 0000-0003-3556-8096 (Zhu, H); Zheng, Liheng; Chen, Lunjin; Zhu, Hui
    Electromagnetic ion cyclotron (EMIC) waves in duskside plasmasphere and plasmaspheric plume scatter megaelectron volt electrons into the loss cone and are considered a major loss mechanism for the outer radiation belt. Wave-particle interaction between energetic electrons and EMIC waves has been studied extensively by the quasi-linear diffusion theory. However, EMIC waves are typically strong enough to trigger nonlinear wave-particle interaction effects and transport electrons in very different ways from quasi-linear diffusion. New mathematical method is therefore in demand to study the evolution of energetic electron distribution in response to nonlinear wave-particle interaction. In this work, we present a Markov chain description of the wave-particle interaction process, in which the electron distribution is represented by a state vector and is evolved by the Markov matrix. The Markov matrix is a matrix form of the electron response Green's function and could be determined from test particle simulations. Our modeling results suggest that electron loss rate is not significantly affected by phase bunching and phase trapping, but for strong EMIC waves, electron distribution is more saturated near loss cone than quasi-linear theory prediction, and negative electron phase space density slope develops inside loss cone. ©2019. American Geophysical Union. All Rights Reserved.
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    Estimating the Daily Pollen Concentration in the Atmosphere Using Machine Learning and NEXRAD Weather Radar Data
    (Springer International Publishing, 2019-06-07) Zewdie, Gebreab K.; Lary, David J.; Liu, Xun; Wu, Daji; Levetin, E.; Zewdie, Gebreab K.; Lary, David J.; Liu, Xun; Wu, Daji
    Millions of people have an allergic reaction to pollen. The impact of pollen allergies is on the rise due to increased pollen levels caused by global warming and the spread of highly invasive weeds. The production, release, and dispersal of pollen depend on the ambient weather conditions. The temperature, rainfall, humidity, cloud cover, and wind are known to affect the amount of pollen in the atmosphere. In the past, various regression techniques have been applied to estimate and forecast the daily pollen concentration in the atmosphere based on the weather conditions. In this research, machine learning methods were applied to the Next Generation Weather Radar (NEXRAD) data to estimate the daily Ambrosia pollen over a 300 km × 300 km region centered on a NEXRAD weather radar. The Neural Network and Random Forest machine learning methods have been employed to develop separate models to estimate Ambrosia pollen over the region. A feasible way of estimating the daily pollen concentration using only the NEXRAD radar data and machine learning methods would lay the foundation to forecast daily pollen at a fine spatial resolution nationally. © 2019, Springer Nature Switzerland AG.
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    Applying Deep Neural Networks and Ensemble Machine Learning Methods To Forecast Airborne Ambrosia Pollen
    (MDPI AG, 2019-06-04) Zewdie, Gebreab K.; Lary, David J.; Levetin, E.; Garuma, G. F.; Zewdie, Gebreab K.; Lary, David J.
    Allergies to airborne pollen are a significant issue affecting millions of Americans. Consequently, accurately predicting the daily concentration of airborne pollen is of significant public benefit in providing timely alerts. This study presents a method for the robust estimation of the concentration of airborne Ambrosia pollen using a suite of machine learning approaches including deep learning and ensemble learners. Each of these machine learning approaches utilize data from the European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric weather and land surface reanalysis. The machine learning approaches used for developing a suite of empirical models are deep neural networks, extreme gradient boosting, random forests and Bayesian ridge regression methods for developing our predictive model. The training data included twenty-four years of daily pollen concentration measurements together with ECMWF weather and land surface reanalysis data from 1987 to 2011 is used to develop the machine learning predictive models. The last six years of the dataset from 2012 to 2017 is used to independently test the performance of the machine learning models. The correlation coefficients between the estimated and actual pollen abundance for the independent validation datasets for the deep neural networks, random forest, extreme gradient boosting and Bayesian ridge were 0.82, 0.81, 0.81 and 0.75 respectively, showing that machine learning can be used to effectively forecast the concentrations of airborne pollen.
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    Seasonal and Temporal Variations of Field-Aligned Currents and Ground Magnetic Deflections During Substorms
    (Amer Geophysical Union) Forsyth, C.; Shortt, M.; Coxon, J. C.; Rae, I. J.; Freeman, M. P.; Kalmoni, N. M. E.; Jackman, C. M.; Anderson, B. J.; Milan, S. E.; Burrell, Angeline G.; Burrell, Angeline G.
    Field-aligned currents (FACs), also known as Birkeland currents, are the agents by which energy and momentum are transferred to the ionosphere from the magnetosphere and solar wind. This coupling is enhanced at substorm onset through the formation of the substorm current wedge. Using FAC data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment and substorm expansion phase onsets identified using the Substorm Onsets and Phases from Indices of the Electrojet technique, we examine the Northern Hemisphere FACs in all local time sectors with respect to substorm onset and subdivided by season. Our results show that while there is a strong seasonal dependence on the underlying FACs, the increase in FACs following substorm onset only varies by 10% with season, with substorms increasing the hemispheric FACs by 420kA on average. Over an hour prior to substorm onset, the dayside currents in the postnoon quadrant increase linearly, whereas the nightside currents show a linear increase starting 20- 30min before onset. After onset, the nightside Region 1, Region 2, and nonlocally closed currents and the SuperMAG AL (SML) index follow the Weimer (1994, https://doi.org/10.1029/93JA02721) model with the same time constants in each season. These results contrast earlier contradictory studies that indicate that substorms are either longer in the summer or decay faster in the summer. Our results imply that, on average, substorm FACs do not change with season but that their relative impact on the coupled magnetosphere-ionosphere system does due to the changes in the underlying currents. Plain Language Summary Earth is surrounded by electrical currents flowing in space. These currents, which can be 10,000 times greater than domestic electrical supplies, can flow along the Earth's magnetic field and into the upper atmosphere and are linked to aurora. The size of this current depends on atmospheric conditions, with the upper atmosphere being a better conductor when it is sunlit, and the interaction between particles flowing from the Sun and the Earth's magnetic field. During space weather events known as substorms, which happen several times per day on average, the aurora brightens massively and the currents flowing into the upper atmosphere increase. Using data from the Iridium communications satellites, the increase in this current can be measured. While the strength of the day-to-day current varies with season, as expected from simple models of the system, the increases due to these space weather events are the same throughout the year.
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    Plasma Dynamics Associated with Equatorial Ionospheric Irregularities
    (Blackwell Publishing Ltd) Smith, Jonathon Matthew; Heelis, Roderick A.; 0000 0000 3175 0999 (Heelis, RA); 0000-0002-5543-5357 (Heelis, RA); Smith, Jonathon Matthew; Heelis, Roderick A.
    The Communication/Navigation Outage Forecasting System satellite was operational from 2008, a period of deep solar minimum, to 2015, a period of moderate solar conditions. The behavior of the vertical plasma drift and the distribution of plasma depletions during the deep solar minimum of 2009 deviated substantially from the behavior that was observed during the solar moderate conditions encountered by the Communication/Navigation Outage Forecasting System satellite in 2014, which are typical of previous observations. Presented here are observations of the vertical drift of plasma depletions and the background plasma in which they are embedded. We find that depletions detected at local times after 2100 hr during solar minimum are typically found in background drifts that are weakly downward compared to the strongly downward background drifts observed during moderate solar activity levels. Additionally, at solar minimum, the drift within the depletions is upward with respect to the background as compared with observations at the same local times during solar moderate conditions for which the depleted plasma more nearly drifts with the background. We note that weak background plasma drifts observed throughout the night during solar minimum promote the continued growth of depletions that may evolve more slowly or be continuously generated to appear in the topside in the postmidnight hours. ©2018. American Geophysical Union. All Rights Reserved.
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    The Ion/Electron Temperature Characteristics of Polar Cap Classical and Hot Patches and their Influence on Ion Upflow
    (Blackwell Publishing Ltd) Ma, Y. -Z; Zhang, Q. -H; Xing, Z. -Y; Heelis, Roderick A.; Oksavik, K.; Wang, Y.; 0000-0002-5543-5357 (Heelis, RA); Heelis, Roderick A.
    The term of “polar cap hot patch” is a newly identified high-density plasma irregularity at high latitudes, which is associated with high electron temperature and particle precipitation, while a classical polar cap patch has lower electron temperature. To investigate characteristics of hot patches versus classical patches, five years of in situ database of plasma observations from the DMSP satellites was analyzed. For the first time, we show how the ion/electron temperature ratio (or temperature difference) can be used to distinguish between classical and hot patches. For classical patches (Ti/Te > 0.8 or Te Ti + 600 K), the vertical ion flux is generally upward. The highest upflow occurrence was found near the polar cap boundary, associated with hot patches, particle precipitation, strong convection speed, and localized field-aligned currents. This result shows that the polar cap hot patches may play a very important role in solar wind-magnetosphere-ionosphere coupling processes. ©2018. American Geophysical Union. All Rights Reserved.
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    Quantifying Extremely Rapid Flux Enhancements of Radiation Belt Relativistic Electrons Associated with Radial Diffusion
    (Amer Geophysical Union) Liu, Si; Yan, Qi; Yang, Chang; Zhou, Qinghua; He, Zhaoguo; He, Yihua; Gao, Zhonglei; Xiao, Fuliang; 0000-0001-8465-9395 (Liu, S); 0000-0001-9178-5920 (He, Z); Liu, Si; He, Zhaoguo
    Previous studies have revealed a typical picture that seed electrons are transported inward under the drive of radial diffusion and then accelerated via chorus to relativistic energies. Here we show a potentially different process during the 2-3 October 2013 storm when Van Allen Probes observed extremely rapid (by about 50 times in 2h) flux enhancements of relativistic (1.8-3.4 MeV) electrons but without distinct chorus at lower L-shells. Meanwhile, Time History of Events and Macroscale Interactions during Substorms satellites simultaneously measured enhanced chorus and fluxes of energetic (~100- 300keV) seed electrons at higher L-shells. Numerical calculations show that chorus can efficiently accelerate seed electrons at L ~8.3. Then radial diffusion further increased the phase space density of relativistic electrons throughout the outer radiation belts, with a remarkable agreement with the observation in magnitude and timescale. The current results provide a different physical scenario on the interplay between radial diffusion and local acceleration in outer radiation belt.
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    Study of the Equatorial and Low-Latitude Electrodynamic and Ionospheric Disturbances during the 22–23 June 2015 Geomagnetic Storm Using Ground-Based and Spaceborne Techniques
    (Blackwell Publishing Ltd) Astafyeva, E.; Zakharenkova, I.; Hozumi, K.; Alken, P.; Coïsson, P.; Hairston, Marc R.; Coley, William R.; 0000-0003-4524-4837 (Hairston, MR); Hairston, Marc R.; Coley, William R.
    We use a set of ground-based instruments (Global Positioning System receivers, ionosondes, magnetometers) along with data of multiple satellite missions (Swarm, C/NOFS, DMSP, GUVI) to analyze the equatorial and low-latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22-23 June 2015, which is the second largest storm in the current solar cycle. Our results show that at the beginning of the storm, the equatorial electrojet (EEJ) and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields (PPEF). The PPEF were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside, and downward drift on the nightside. Furthermore, about 45 min after the storm commencement, the interplanetary magnetic field (IMF) Bz component turned northward, leading to the EEJ changing sign to westward, and to overall decrease of the vertical total electron content (VTEC) and electron density on the dayside. At the end of the main phase of the storm, and with the second long-term IMF Bz southward turn, we observed several oscillations of the EEJ, which led us to conclude that at this stage of the storm, the disturbance dynamo effect was already in effect, competing with the PPEF and reducing it. Our analysis showed no significant upward or downward plasma motion during this period of time; however, the electron density and the VTEC drastically increased on the dayside (over the Asian region). We show that this second positive storm was largely influenced by the disturbed thermospheric conditions. ©2018. The Authors.
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    An Auroral Boundary-Oriented Model of Subauroral Polarization Streams (SAPS)
    (Amer Geophysical Union) Landry, Russell G.; Anderson, Phillip C.; 0000-0003-1320-4064 (Landry, RG); Landry, Russell G.; Anderson, Phillip C.
    An empirical model of subauroral polarization stream (SAPS) electric fields has been developed using measurements of ion drifts and particle precipitation made by the Defense Meteorological Satellite Program from 1987 to 2012 and Dynamics Explorer 2 as functions of magnetic local time (MLT), magnetic latitude, the auroral electrojet index (AE), hemisphere, and day of year. Over 500,000 subauroral passes are used. This model is oriented in degree magnetic latitude equatorward of the aurora and takes median values instead of the mean to avoid the contribution of low occurrence frequency subauroral ion drifts so that the model is representative of the much more common, latitudinally broad, low-amplitude SAPS field. The SAPS model is in broad agreement with previous statistical efforts in the variation of the SAPS field with MLT and magnetic activity level, although the median field is weaker. Furthermore, we find that the median SAPS field is roughly conjugate in both hemispheres for all seasons, with a maximum in SAPS amplitude and width found for 1800-2000 MLT. The SAPS amplitude is found to vary seasonally only from about 1800-2000 MLT, maximizing in both hemispheres during equinox months. Because this feature exists despite controlling for the AE index, it is suggested that this is due to a seasonal variation in the flux tube averaged ionospheric conductance at MLT sectors where it is more likely that one flux tube footprint is in darkness while the other is in daylight.
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    Coincident Observations by the Kharkiv IS Radar and Ionosonde, DMSP and Arase (ERG) Satellites, and FLIP Model Simulations: Implications for the NRLMSISE-00 Hydrogen Density, Plasmasphere, and Ionosphere
    (Blackwell Publishing Ltd) Kotov, D. V.; Richards, P. G.; Truhlík, V.; Bogomaz, O. V.; Shulha, M. O.; Maruyama, N.; Hairston, Marc R.; Miyoshi, Y.; Kasahara, Y.; Kumamoto, A.; Tsuchiya, F.; Matsuoka, A.; Shinohara, I.; Hernández-Pajares, M.; Domnin, I. F.; Zhivolup, T. G.; Emelyanov, L. Y.; Chepurnyy, Y. M.; 0000-0003-4524-4837 (Hairston, MR); Hairston, Marc R.
    This paper reports the results of ionosphere and plasmasphere observations with the Kharkiv incoherent scatter radar and ionosonde, Defense Meteorological Satellite Program, and Arase (ERG) satellites and simulations with field line interhemispheric plasma model during the equinoxes and solstices of solar minimum 24. The results reveal the need to increase NRLMSISE-00 thermospheric hydrogen density by a factor of ~2. For the first time, it is shown that the measured plasmaspheric density can be reproduced with doubled NRLMSISE-00 hydrogen density only. A factor of ~2 decrease of plasmaspheric density in deep inner magnetosphere (L ≈ 2.1) caused by very weak magnetic disturbance (D_{st} > -22 nT) of 24 December 2017 was observed in the morning of 25 December 2017. During the next night, prominent effects of partially depleted flux tube were observed in the topside ionosphere (~50% reduced H⁺ ion density) and at the F2-layer peak (~50% decreased electron density). The likely physical mechanisms are discussed.
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    Effects of Electric Field and Neutral Wind on the Asymmetry of Equatorial Ionization Anomaly
    (Blackwell Publishing Ltd) Khadka, S. M.; Valladares, Cesar E.; Sheehan, R.; Gerrard, A. J.; Valladares, Cesar E.
    The zonal electric field and the meridional neutral wind are the principal drivers that define the geometry and characteristics of the equatorial ionization anomaly (EIA). Here we present the response of the EIA to the variability of the zonal electric field based on measurements of the equatorial electrojet (EEJ) currents and trans-equatorial neutral winds for the generation and control of the asymmetries of the EIA crests of total electron content (TEC) in the western side of the South American continent. The EEJ strengths are determined using a pair of magnetometers. The 24-hr trans-equatorial neutral wind profile is measured using the Second-Generation, Optimized, Fabry-Perot Doppler Imager (SOFDI) located near the geomagnetic equator. The EIA is evaluated using TEC data measured by Global Positioning System (GPS) receivers from the Low-Latitude Ionospheric Sensor Network and several other networks in South America. A physics-based numerical model, Low-Latitude Ionospheric Sector, and SOFDI data are used to study the effects of daytime meridional neutral winds on the consequent evolution of an asymmetry in equatorial TEC anomalies during the afternoon and onward for the first time. We find that the configuration parameters such as strength, shape, amplitude, and latitudinal width of the EIAs are affected by the eastward electric field associated with the EEJ under undisturbed conditions. The asymmetries of EIA crests are observed more frequently during solstices and the September equinox than in the March equinox season. Importantly, this study indicates that the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. This result suggests that a precise observation of the latitudinal TEC profile at low latitudes can be used to derive the meridional wind. ©2018. American Geophysical Union. All Rights Reserved.
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    The Plasma Environment Associated with Equatorial Ionospheric Irregularities
    (Amer Geophysical Union) Smith, Jonathon M.; Heelis, Roderick A.; 0000-0002-8191-4765 (Smith, JM); 0000-0002-5543-5357 (Heelis, RA); Smith, Jonathon M.; Heelis, Roderick A.
    We examine the density structure of equatorial depletions referred to here as equatorial plasma bubbles (EPBs). Data recorded by the Ion Velocity Meter as part of the Coupled Ion Neutral Dynamics Investigation (CINDI) aboard the Communication/Navigation Outage Forecasting System (C/NOFS) satellite are used to study EPBs from 1600 to 0600 h local time at altitudes from 350 to 850 km. The data are taken during the 7 years from 2008 to 2014, more than one half of a magnetic solar cycle, that include solar minimum and a moderate solar maximum. Using a rolling ball algorithm, EPBs are identified by profiles in the plasma density, each having a depth measured as the percent change between the background and minimum density (ΔN/N). During solar moderate activity bubbles observed in the topside postsunset sector are more likely to have large depths compared to those observed in the topside postmidnight sector. Large bubble depths can be observed near 350 km in the bottomside F region in the postsunset period. Conversely at solar minimum the distribution of depths is similar in the postsunset and postmidnight sectors in all longitude sectors. Deep bubbles are rarely observed in the topside postsunset sector and never in the bottomside above 400 km in altitude. We suggest that these features result from the vertical drift of the plasma for these two solar activity levels. These drift conditions affect both the background density in which bubbles are embedded and the growth rate of perturbations in the bottomside where bubbles originate.
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    The Radiation Belt Electron Scattering by Magnetosonic Wave: Dependence on Key Parameters
    (Amer Geophysical Union, 2018-10-22) Lei, Mingda; Xie, Lun; Li, Jinxing; Pu, Zuyin; Fu, Suiyan; Ni, Binbin; Hua, Man; Chen, Lunjin; Li, Wen; Chen, Lunjin
    Magnetosonic (MS) waves have been found capable of creating radiation belt electron butterfly distributions in the inner magnetosphere. To investigate the physical nature of the interactions between radiation belt electrons and MS waves, and to explore a preferential condition for MS waves to scatter electrons efficiently, we performed a comprehensive parametric study of MS wave-electron interactions using test particle simulations. The diffusion coefficients simulated by varying the MS wave frequency show that the scattering effect of MS waves is frequency insensitive at low harmonics (f < 20 f(cp)), which has great implications on modeling the electron scattering caused by MS waves with harmonic structures. The electron scattering caused by MS waves is very sensitive to wave normal angles, and MS waves with off 90 degrees wave normal angles scatter electrons more efficiently. By simulating the diffusion coefficients and the electron phase space density evolution at different L shells under different plasma environment circumstances, we find that MS waves can readily produce electron butterfly distributions in the inner part of the plasmasphere where the ratio of electron plasma-to-gyrofequency (f(pe)/f(ce)) is large, while they may essentially form a two-peak distribution outside the plasmapause and in the inner radiation belt where f(pe)/f(ce) is small.
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    Testing Nowcasts of the Ionospheric Convection from the Expanding and Contracting Polar Cap Model
    (Amer Geophysical Union, 2017-04-20) Walach, M. -T; Milan, S. E.; Yeoman, T. K.; Hubert, B. A.; Hairston, Marc R.; Hairston, Marc R.
    The expanding/contracting polar cap (ECPC) model, or the time-dependent Dungey cycle, provides a theoretical framework for understanding solar wind-magnetosphere-ionosphere coupling. The ECPC describes the relationship between magnetopause reconnection and substorm growth phase, magnetotail reconnection and substorm expansion phase, associated changes in auroral morphology, and ionospheric convective motions. Despite the many successes of the model, there has yet to be a rigorous test of the predictions or nowcasts made regarding ionospheric convection, which remains a final hurdle for the validation of the ECPC. In this study we undertake a comparison of ionospheric convection, as measured in situ by ion drift meters on board DMSP (Defense Meteorological Satellite Program) satellites and from the ground by SuperDARN (Super Dual Auroral Radar Network), with motions nowcasted by a theoretical model. The model is coupled to measurements of changes in the size of the polar cap made using global auroral imagery from the IMAGE FUV (Imager for Magnetopause to Aurora Global Exploration Far Ultraviolet) instrument, as well as the dayside reconnection rate, estimated using the OMNI data set. The results show that we can largely nowcast the magnitudes of ionospheric convection flows using the context of our understanding of magnetic reconnection at the magnetopause and in the magnetotail. Plain Language Summary We test a physics-based model which describes flows in the ionosphere near the magnetic poles due to solar wind driving of the activity within the Earth's magnetic environment using spacecraft and radar measurements of the flows. The results of this comparison show that our knowledge of the interactions of the solar wind, the Earth's magnetic environment, and ionosphere encompasses the general pattern of flows well, as well as the flow strengths. Further work is required to expand our understanding of asymmetric flows and to be able to model them better.
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    Duskside Enhancement of Equatorial Zonal Electric Field Response to Convection Electric Fields During the St. Patrick's Day Storm on 17 March 2015
    (Blackwell Publishing Ltd, 2016-01-11) Tulasi Ram, S.; Yokoyama, T.; Otsuka, Y.; Shiokawa, K.; Sripathi, S.; Veenadhari, B.; Heelis, Roderick A.; Ajith, K. K.; Gowtam, V. S.; Gurubaran, S.; Supnithi, P.; Le Huy, M.; 0000 0000 3175 0999 (Heelis, RA); Heelis, Roderick A.
    The equatorial zonal electric field responses to prompt penetration of eastward convection electric fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F layer to >550 km and development of intense equatorial plasma bubbles (EPBs) were observed. These EPBs were found to extend up to 27.13⁰N and 25.98⁰S magnetic dip latitudes indicating their altitude development to ~1670 km at apex. In contrast, at few degrees east in the premidnight sector (Thailand-Indonesian longitudes), no significant height rise and/or EPB activity has been observed. The eastward electric field perturbations due to PPEF are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo (IDD) fields, whereas they were mostly counter balanced by the IDD fields in the premidnight sector. In situ observations from SWARM-A and SWARM-C and Communication/Navigation Outage Forecasting System satellites detected a large plasma density depletion near Indian equatorial region due to large electrodynamic uplift of F layer to higher than satellite altitudes. Further, this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator. This study brings out the significantly enhanced equatorial zonal electric field in response to PPEF that is uniquely confined to dusk sector. The responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field B_z.
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    Ionosphere-Thermosphere (IT) Response to Solar Wind Forcing During Magnetic Storms
    (EDP Sciences S A, 2016-01-25) Huang, Cheryl Yu-Ying; Huang, Yanshi; Su, Yi-Jiun; Sutton, Eric K.; Hairston, Marc Rotan; Coley, William Robin
    During magnetic storms, there is a strong response in the ionosphere and thermosphere which occurs at polar latitudes. Energy input in the form of Poynting flux and energetic particle precipitation, and energy output in the form of heated ions and neutrals have been detected at different altitudes and all local times. We have analyzed a number of storms, using satellite data from the Defense Meteorological Satellite Program (DMSP), the Gravity Recovery and Climate Experiment (GRACE), Gravity field and steady-state Ocean Circulation Explorer (GOCE), and Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission. Poynting flux measured by instruments on four DMSP spacecraft during storms which occurred in 2011-2012 was observed in both hemispheres to peak at both auroral and polar latitudes. By contrast, the measured ion temperatures at DMSP and maxima in neutral density at GOCE and GRACE altitudes maximize in the polar region most frequently with little evidence of Joule heating at auroral latitudes at these spacecraft orbital locations.
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    Radar and Satellite Investigations of Equatorial Evening Vertical Drifts and Spread F
    (Copernicus Gesellschaft Mbh, 2015-11-11) Smith, J. M.; Rodrigues, Fabiano S.; de Paula, E. R.; Smith, J. M.; Rodrigues, Fabiano S.
    We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of Sao Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) on-board the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18: 00-18: 30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.
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    Observations of the Generation of Eastward Equatorial Electric Fields near Dawn
    (Copernicus Gesellschaft Mbh, 2014-09-19) Kelley, M. C.; Rodrigues, Fabiano S.; Pfaff, R. F.; Klenzing, J.; Kelley, M. C.; Rodrigues, Fabiano S.
    We report and discuss interesting observations of the variability of electric fields and ionospheric densities near sunrise in the equatorial ionosphere made by instruments onboard the Communications/Navigation Outage Forecasting System (C/NOFS) satellite over six consecutive orbits. Electric field measurements were made by the Vector Electric Field Instrument (VEFI), and ionospheric plasma densities were measured by Planar Langmuir Probe (PLP). The data were obtained on 17 June 2008, a period of solar minimum conditions. Deep depletions in the equatorial plasma density were observed just before sunrise on three orbits, for which one of these depletions was accompanied by a very large eastward electric field associated with the density depletion, as previously described by de La Beaujardiere et al. (2009), Su et al. (2009) and Burke et al. (2009). The origin of this large eastward field (positive upward/meridional drift), which occurred when that component of the field is usually small and westward, is thought to be due to a large-scale Rayleigh-Taylor process. On three subsequent orbits, however, a distinctly different, second type of relationship between the electric field and plasma density near dawn was observed. Enhancements of the eastward electric field were also detected, one of them peaking around 3 mV m⁻¹, but they were found to the east (later local time) of pre-dawn density perturbations. These observations represent sunrise enhancements of vertical drifts accompanied by eastward drifts such as those observed by the San Marco satellite (Aggson et al., 1995). Like the San Marco measurements, the enhancements occurred during winter solstice and low solar flux conditions in the Pacific longitude sector. While the evening equatorial ionosphere is believed to present the most dramatic examples of variability, our observations exemplify that the dawn sector can be highly variable as well.