Browsing by Author "Heelis, Roderick A."
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Item Changes in Thermospheric Temperature Induced by High-Speed Solar Wind Streams(American Geophysical Union, 2012-12-08) Gardner, Larry; Sojka, Jan J.; Schunk, Robert W.; Heelis, Roderick A.; Heelis, Roderick A.During high-speed stream (HSS) events the solar wind speed increases, and the cross polar cap potential increases, leading to increased Joule heating at high latitudes. The heat input at high latitudes heats the polar regions, which then conducts to lower latitudes, producing global heating. The heating occurs during the risetime of the cross polar cap potential and throughout the period of high cross polar cap potential as seen in our simulation. These simulations are performed using the Utah State University global thermosphere model driven by Joule heating rates that are consistent with electric fields observed by DMSP-15 observations of HSS events. Cooling occurs as the cross polar cap potential decreases and continues for several days after the cross polar cap potential has returned to background values. Polar cap ionospheric observations are compared to model simulations of heating and cooling, providing evidence that the thermospheric model is capturing the HSS energy input and the post-HSS multiday return to pre-HSS conditions. The HSS heating can be as high as 100 K (as seen from both the model and the data) at high latitudes, with a corresponding, but lower, global increase in thermospheric temperature.Item Coordinated Satellite Observations of the Very Low Frequency Transmission through the Ionospheric D Layer at Low Latitudes, Using Broadband Radio Emissions from Lightning(Amer Geophysical Union) Jacobson, Abram R.; Holzworth, Robert H.; Pfaff, Robert; Heelis, Roderick A.; 0000-0002-5543-5357 (Heelis, RA); Heelis, Roderick A.Both ray theory and full-wave models of very low frequency transmission through the ionospheric D layer predict that the transmission is greatly suppressed near the geomagnetic equator. We use data from the low-inclination Communication/Navigation Outage Forecast System satellite to test this semiquantitatively, for broadband very low frequency emissions from lightning. Approximate ground-truthing of the incident wavefields in the Earth-ionosphere waveguide is provided by the World Wide Lightning Location Network. Observations of the wavefields at the satellite are provided by the Vector Electric Field Instrument aboard the satellite. The data set comprises whistler observations with the satellite at magnetic latitudes < 26 degrees. Thus, our conclusions, too, must be limited to the near-equatorial region and are not necessarily predictive of midlatitude whistler properties. We find that in most broadband recordings of radio waves at the satellite, very few of the lightning strokes result in a detectable radio pulse at the satellite. However, in a minority of the recordings, there is enhanced transmission of very low frequency lightning emissions through the D layer, at a level exceeding model predictions by at least an order of magnitude. We show that kilometric-scale D-layer irregularities may be implicated in the enhanced transmission. This observation of sporadic enhancements at low magnetic latitude, made with broadband lightning emissions, is consistent with an earlier review of D-layer transmission for transmission from powerful man-made radio beacons.Item Coupling Physical Measurement with Machine Learning for Holistic Environmental Sensing(2021-05-01T05:00:00.000Z) Wijeratne, Lakitha Omal Harindha; Lary, David J.; Stefan, Mihaela C.; Glosser, Robert; Chen, Lunjin; Slinker, Jason D.; Heelis, Roderick A.The interest in characterizing the abundance and nature of airborne particulates has been increasing over the last decade, driven in large part by the rising awareness of the manifold health impacts of airborne particulates. Since regulatory observations of airborne particulates are usually made with expensive instruments, the number of sensors that can be deployed is naturally limited by the costs involved. This dissertation describes the substantial progress we have made in the physical sensing of airborne particulates by providing low-cost, high-quality observations of airborne particulates by utilizing advances in low-cost laser-based sensors, that can be deployed at scale, coupled with machine learning used for accurate calibration of these low-cost sensors. The abundance of airborne particulates is usually quantified by an integrated mass density in µg/m3 over the airborne aerosol size distribution (e.g. PM2.5, the integrated mass density of all airborne particulates with a diameter of up to 2.5 microns). A persistent feature of all airborne observations of particulates is the variability over small temporal and spatial scales. This persistent and ubiquitous variability underscores the value of being able to deploy a large number of low-cost sensors that can make accurate measurements every few seconds, 24/7. Taking this into account, I have built, calibrated, and deployed a large number of sensors across the Dallas-Fort Worth (DFW) Metroplex in Texas as a part of my dissertation work. Other physical measurements can also be utilized in accurate assessment of airborne particulates. Just as weather RADARs are used to examine the spatial and temporal distribution of atmospheric precipitation, we show that if we use machine learning, we can also employ the weather RADARs to examine the spatial distribution of airborne particulates. CO2 has gained a lot of attention in recent years due to global warming. It is considered the principal anthropogenic greenhouse gas driving global warming. As a result, CO2 levels must be monitored and controlled. The present study describes how machine learning can be used to calibrate a low-cost CO2 sensor which is already part of the sensor systems that I have built and deployed. This dissertation provides an overview of how low-cost physical sensing can be combined with machine learning to provide environmental sensing systems at scale, thus using physics in service of society.Item 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.Item Effects of Electric Field Methods on Modeling the Midlatitude Ionospheric Electrodynamics and Inner Magnetosphere Dynamics(Amer Geophysical Union, 2017-05-22) Yu, Yiqun; Jordanova, Vania K.; Ridley, Aaron J.; Toth, Gabor; Heelis, Roderick A.; 0000-0002-5543-5357 (Heelis, RA); Heelis, Roderick A.We report a self-consistent electric field coupling between the midlatitude ionospheric electrodynamics and inner magnetosphere dynamics represented in a kinetic ring current model. This implementation in the model features another self-consistency in addition to its already existing self-consistent magnetic field coupling with plasma. The model is therefore named as Ring current-Atmosphere interaction Model with Self-Consistent magnetic (B) and electric (E) fields, or RAM-SCB-E. With this new model, we explore, by comparing with previously employed empirical Weimer potential, the impact of using self-consistent electric fields on the modeling of storm time global electric potential distribution, plasma sheet particle injection, and the subauroral polarization streams (SAPS) which heavily rely on the coupled interplay between the inner magnetosphere and midlatitude ionosphere. We find the following phenomena in the self-consistent model: (1) The spatially localized enhancement of electric field is produced within 2.5 < L < 4 during geomagnetic active time in the dusk-premidnight sector, with a similar dynamic penetration as found in statistical observations. (2) The electric potential contours show more substantial skewing toward the postmidnight than the Weimer potential, suggesting the resistance on the particles from directly injecting toward the low-L region. (3) The proton flux indeed indicates that the plasma sheet inner boundary at the dusk-premidnight sector is located further away from the Earth than in the Weimer potential, and a "tongue" of low-energy protons extends eastward toward the dawn, leading to the Harang reversal. (4) SAPS are reproduced in the subauroral region, and their magnitude and latitudinal width are in reasonable agreement with data.Item Heat Exchange Processes in the Topside Ionosphere at Low to Middle Latitudes(2018-05) Hsu, Chih Te; 0000-0003-3261-5176 (Hsu, CT); Heelis, Roderick A.Plasma temperatures in the ionosphere are fundamental indicators of the heat balance between the charged and neutral species and are associated with both the dynamics and structure of the upper atmosphere. At low and middle latitudes the temperatures are determined by solar energy inputs and energy exchange between charged particles and neutrals. During the daytime the thermal electrons are heated by photoelectrons and cooled by conduction and collisions with ions. The ions are heated principally by collisions with electrons and ions and cooled by conduction to lower altitudes. During the nighttime, when the source of photoionization is absent, both ions and electrons are cooled by conduction to lower altitudes where heat is lost to the neutral gas. Thus, variations in both electron temperature and ion temperatures can be used to explore the heat exchange processes in the topside ionosphere. A numerical model called Sami2 is Another Model of the Ionosphere (SAMI2) and measurements from the Defense Meteorological Satellite Program (DMSP) F15 satellite are used in this study of plasma temperatures in the topside ionosphere. The effects of ion composition on the ion and electron temperatures in the mid-latitude topside ionosphere during daytime are examined by using data that has been previously derived from the DMSP F15 measurements in 2004–2006. The heat exchanged between the different constituent ions and the role played by the solar zenith angle and the solar ionizing flux (F10.7) is suggested from the variations of electron and ion temperature with electron number density and composition. The SAMI2 model adds further interpretation of the electron and ion temperature distribution by capturing the major mechanisms that control the heat flow in the topside ionosphere at middle latitudes. Due to the absence of constituent ion temperature information in the original DMSP dataset, this model study is also used to retrieve both TH+ and TO+ and verify the observed dependence of ion temperature on ion composition. The model calculation shows that topside TH+ should reside between TO+ and Te, and further confirms the preferential heat transfer from the electrons to H+ in the topside. Finally, an implementation of a more sophisticated analysis procedure to extract constituent ion temperatures from the Retarding Potential Analyzer (RPA) measurements is utilized to reexamine the DMSP F15 dataset. The result shows that in the daytime, when electrons are actively heated, TH+ is a few hundred degrees higher than TO+ at all longitudes. The nighttime temperature difference between TH+ and TO+ is indicative of mass dependent adiabatic heating and cooling processes across the equatorial region. These adiabatic processes present clear longitudinal variations in the ion temperatures and measured plasma flows that are associated with season and magnetic declination.Item Identifying Equatorial Ionospheric Irregularities using In Situ Ion Drifts(Copernicus Gesellschaft Mbh, 2014-04-15) Stoneback, Russell A.; Heelis, Roderick A.; 0000 0000 3175 0999 (Heelis, RA); 88021080 (Heelis, RA)Previous climatological investigations of ionospheric irregularity occurrence in the equatorial ionosphere have utilized in situ measurements of plasma density to identify the presence of an irregularity. Here we use the Morlet wavelet and C/NOFS to isolate perturbations in meridional ion drifts and generate irregularity occurrence maps as a function of local time, longitude, season, and solar activity. For the low solar activity levels in 2008, the distributions identified by velocity perturbations follow normalized density perturbation (Delta N/N) maps with large occurrences after midnight into dawn over all longitudes. The velocity and normalized density occurrence maps contract in both local time and longitude with increasing solar activity. By 2011 irregularities are confined to particular longitudes expected by alignment and a few hours of local time after sunset. The variation in the occurrence of the late night irregularities with solar activity is consistent with the presence of gravity wave seeding.Item Magnetic Storm Effects on the Occurrence and Characteristics of Plasma Bubbles(May 2023) Adhya, Purbi 1993-; McKeown, Stephen; Anderson, Phillip C.; Heelis, Roderick A.; Valladares, Cesar; Lary, David J.; Glosser, RobertDuring geomagnetic storms actions of prompt penetration electric fields (PPEF) during the main phase disturbs the equatorial ionosphere. In addition, disturbance dynamo electric fields (DDEF) can follow during the recovery phase to further modify the plasma dynamics of the low-latitude ionosphere. The eastward PPEF and westward DDEF cause sudden or ongoing upward and downward plasma drifts that can cause changes in seasonal-longitudinal occurrence patterns of plasma bubbles. Ionospheric irregularities like plasma bubbles occur all around the year within equatorial latitudes, but their occurrence varies seasonally and with changes in solar activity. The short-term changes in the plasma vertical drift during storms cause enhancement or suppression in the occurrence and intensity of plasma bubbles. Our study investigates the changes in the plasma bubble occurrence pattern and characteristics during different phases of storms. The Communications/Navigation Outages Forecast System (C/NOFS) satellite mission was designed to investigate the ionospheric conditions that lead to the formation of plasma irregularities. We have studied the effects of magnetic storms on the formation and evolution of plasma bubbles during the satellite’s lifetime (2008-2014). During this period encompassing solar minimum and maximum conditions, many magnetic storms of varying intensity developed. Each storm was isolated and divided into initial, main, and recovery phases based on the SYM-H index data observed from geomagnetic observatories. Interplanetary Magnetic Field (IMF) data measured by the Advanced Composition Explorer (ACE) satellite was used to observe fluctuations in magnetic fields during storms. Measurements of plasma density from the Plasma Langmuir Probe (PLP) were used to identify plasma bubble occurrences, and determine their local times, depths, widths, etc. A bubble detection algorithm was developed to detect bubbles from the plasma density data. Measurements of plasma vertical velocities from the Ion Velocity Meter (IVM) were used to determine evening PRE peak velocities and bubble internal vertical velocities. Analysis of 109 storms of varying intensities with available bubble and PRE data between May 2008 and August 2014 has revealed that the most intense plasma bubbles occur during a storm’s main phase when Bz turns southwards as PRE velocities tend to increase during those times. New bubbles develop with large PRE values and the bubble lifetime extends into the recovery phase. Comparisons of bubble depths and internal vertical velocities between the storm’s main phases and quiet periods before have shown significant improvement during storms. The augmentation of the plasma bubbles’ depth and internal velocity become more prominent when the bubble intensities were low during the quiet period before the storms. Furthermore, bubble intensities decrease by the end of the recovery phase along with the decline in the PRE velocities. The growth and decline of the bubble occurrence and characteristics signify the important roles of PPEF and DDEF during storms on the low-latitude ionosphere.Item Measurement of Individual H⁺ and O⁺ Ion Temperatures in the Topside Ionosphere(Amer Geophysical Union) Hsu, Chih-Te; Heelis, Roderick A.; 0000 0000 3175 0999 (Heelis, RA); 0000-0002-5543-5357 (Heelis, RA); Hsu, Chih-Te; Heelis, Roderick A.Plasma temperatures in the ionosphere are associated with both the dynamics and spatial distribution of the neutral and charge particles. During the daytime, temperatures are determined by solar energy inputs and energy exchange between charged and neutral particles. Plasma transport parallel to the magnetic field adds another influence on temperatures through adiabatic processes that are most evident during the nighttime. Previous observations suggest that the topside H⁺ temperature (T_{H⁺+}) should reside between the O⁺ temperature (T_{O+}) and the electron temperature (T_e), and further calculations confirm the preferential heat transfer from the electrons to H⁺ in the topside. In this work we implement a more sophisticated analysis procedure to extract individual mass-dependent ion temperatures from the retarding potential analyzer measurements on the DMSP F15 satellite. The results show that the daytime T_{H+} is a few hundred degrees higher than T_{O+} at all longitudes. The nighttime temperature difference between T_{H+} and T_{O+} is indicative of mass-dependent adiabatic heating and cooling processes across the equatorial region. The ion temperatures and measured plasma flows present clear longitudinal variations that are associated with magnetic declination.Item Mesoscale Plasma Convection Perturbations In The High-latitude Ionosphere(Blackwell Publishing Ltd) 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.An investigation of flow perturbations with spatial scale sizes between 100 and 500 km in the high-latitude ionosphere is presented. These localized flow perturbations are deviations from the large-scale background convection, expected to give us new insights into the magnetosphere-ionosphere coupling process. Ion drift measurements from the Defense Meteorological Satellite Program F17 are utilized to identify these mesoscale flow perturbations. Our intent is to discover the properties of these perturbations in terms of perturbation flow speeds, location, scale size, and occurrence frequency as well as their dependence on the interplanetary magnetic field (IMF) and underlying large-scale convection pattern. Observation suggests that flow perturbation locations strongly depend on the IMF orientation as does the occurrence frequency of the flow perturbations. For southward IMF, more flow perturbations occur in regions of sunward background flow than in regions of antisunward background flow. For flow perturbations with speeds over 300 m/s, an asymmetry in the preferred direction and scale size is seen for those embedded in sunward and antisunward background flows. Significantly less asymmetry is present for flow perturbations with speeds between 100 and 300 m/s. The flow perturbations exceeding 300 m/s are most likely closed locally with lower magnitude return flows or with adjacent flows across the convection reversal boundary and representing additional sources of frictional heating and momentum transfer to the thermosphere. The perturbation flow speed is almost independent of the scale size and underlying convection speed, but the largest speeds are preferentially seen at scale sizes between 200 and 300 km.Item Modeling the Daytime Energy Balance of the Topside Ionosphere at Middle Latitudes(Amer Geophysical Union, 2018-08-20) Hsu, Chih-Te; Heelis, Roderick A.; Hsu, Chih-Te; Heelis, Roderick A.Recently reported measurements from the Defense Meteorological Satellite Program (DMSP) indicate that the O⁺ temperature in the topside ionosphere is dependent on the fractional H⁺ density. This finding indicates that the mass-dependent energy exchange rate between O⁺ and H⁺ plays an important role in the thermal balance of the topside ionosphere. In this study we utilize the SAMI2 model to retrieve both T_{H⁺} and T_{O⁺} and verify the previously observed dependence of ion temperature on ion composition. The model shows that in the topside at middle latitudes when a single ion is dominant, O⁺ or H⁺ is heated by electron collisions and cooled by conduction as expected. However, in the intervening altitude region where both O⁺ and H⁺ are present, O⁺ is heated by collisions with H⁺ and cooled by conduction, while H⁺ is heated by collisions with electrons and cooled by collisions with O⁺.Item Motions of the Convection Reversal Boundary and Local Plasma in the High-Latitude Ionosphere(Amer Geophysical Union) 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.We present results from a systematic study of multisatellite samplings from the Defense Meteorological Satellite Program F13, F15, F16, F17, and F18 satellites over the period from 2007 to 2015 that describe the motion of the convection reversal boundary (CRB) and the local plasma flow across it. Focusing on the cases with continuous poleward and equatorward CRB motion sampled by three consecutive satellites within 50 min, 45% of the time the CRB motion may deviate from the local plasma motion near dawn and dusk where the reconnection process is unlikely to be present. Differences in the inferred CRB motion and the local plasma motion may arise from apparent motion induced by the local time displacement of consecutive samples across the CRB that is tilted with respect to a line of constant latitude. The presence of a viscous- like interaction across the CRB can also contribute to the difference in the CRB and plasma motion. Accounting for these processes, the CRB motion and the motion of the plasma at the CRB are consistent only if a back and forth motion over a timescale of a few minutes is superimposed on a monotonic migration of the CRB over longer time periods.Item 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.Item Propagation of Very Low Frequency Transmitter Signals in the Inner Magnetosphere(2022-05-01T05:00:00.000Z) Gu, Wenyao; Chen, Lunjin; Balanov, Zalman; Heelis, Roderick A.; Anderson, Phillip C.; Rodrigues, Fabiano Da Silveira; Shi, XiaoyanSignals from ground-based very low frequency (VLF) transmitters can leak through the ionosphere and propagate in the inner magnetosphere as whistler-mode waves. They interact with energetic electrons from the Earth’s radiation belts, and precipitate them into the ionosphere. The effect of wave-particle interactions is affected by signal propagations, which depend on the spatial variation of the cold plasma population (as the propagation medium). Therefore, a further understanding of transmitter signal propagation and cold plasma medium is essential for investigating wave-particle interactions. First, a case study is performed on Russian Alpha transmitter signals observed by the Van Allen Probes. The signals are in ducted propagation, experience multiple reflections, and excite triggered emissions. The ducted propagation is justified by a ray-tracing technique, and the nonlinear cyclotron resonance theory is tested by the observed triggered emissions. Second, we perform a statistical study on the distribution of the two propagation modes, ducted and nonducted, by the use of observed Russian Alpha transmitter signals. The statistics show the dominance of nonducted signals in the plasmasphere in terms of both occurrence and power. The proportion of ducted signals is enhanced at higher L-shells and during active geomagnetic conditions. Finally, we statistically analyze the spatial and temporal distributions of inner-magnetospheric cold plasma density irregularities, which are responsible for ducted propagation. The density irregularities deep inside the plasmasphere are dominant in the night and dusk sectors and show no significant variation with geomagnetic conditions. In contrast, the density irregularities in and near the plasmasphere boundary layer occur at post-midnight during quiet times and expand throughout the night sector during active times.Item Response of Low-Latitude Ionosphere to Medium-Term Changes of Solar and Geomagnetic Activity(2012-08-28) Kutiev, I.; Otsuka, Y.; Pancheva, D.; Heelis, Roderick A.; Heelis, Roderick A.The paper presents the medium-term quasi periodic (∼9-27 day) response of middle and low-latitude ionosphere to solar F10.7) and geomagnetic (Kp-index) forcing. The ionospheric response is examined by wavelet analysis of the relative deviations of TEC over Japan for the period of time 2000-2008. It is found that the ∼27-day rTEC oscillations correlate well with the same oscillations of the solar index F10.7 particularly in the solar maximum and its early declining phase (2001-2005). During the declining phase of solar activity (for example, year of 2005) the Kp-index variability exhibits additionally strong oscillations with periods 13.5- and 9-days. Similar oscillations are found in rTEC as well but they do not follow the geomagnetic forcing as faithfully as those associated with F10.7. During solar minimum the quasi periodic rTEC variability is shaped mainly by the recurrent geomagnetic activity. An attempt is made to investigate the latitudinal dependence of the ∼9-27-day rTEC response over Japan as well as the phase relationship between the forcing and response. © 2012. American Geophysical Union. All Rights Reserved.Item Satellite Observations of Evolving Properties of Equatorial Ionospheric Plasma Structures(2018-05) Smith, Jonathon M; 0000-0002-8191-4765 (Smith, JM); Heelis, Roderick A.The Earth’s atmosphere contains a layer of plasma created primarily by photo-ionization of neutral species between 80 km and 1,000 km called the ionosphere. There are many complex processes near the equator where the Earth’s magnetic field is approximately horizontal. In this region large scale irregularities, sometimes referred to as equatorial plasma bubbles (EPBs), in the plasma density occur. Data recorded by the Ion Velocity Meter (IVM) 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 during nightside local times at altitudes from 350 to 850 km. The data are taken during the seven years from 2008 to 2014, more than one half of a magnetic solar cycle, that include a deep solar minimum and a moderate solar maximum. EPB data are divided into four longitude sectors and two local time regions to determine seasonal and solar cycle variability. During solar minimum EPBs occur late in local time, primarily after midnight in all longitude sectors. Conversely, by the solar moderate conditions of 2014, EPB occurrence after midnight diminishes in all seasons and longitude sectors with the exception of the sector extending from 15˚ to 60˚. An examination of the widths of bubbles indicates that all longitudes show similar distributions between 115 km and 460 km with a prominent peak near 200 km during all levels of solar activity. This suggests that seeding conditions are independent of solar activity. Among these widths is a distinct width that belongs to discrete individual bubbles with no substructure. We suggest that many bubbles are actually combinations of these individual bubbles; however, in the later phase of the mission there is a population of bubbles that do not conform to this description, perhaps due to the influence of large-scale plasma motions affecting the background density in which they are embedded. Each EPB has a depth measured as the percent change between the background and minimum density (∆N/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.Item 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.Item The Characterization of Ionospheric Convection Reversal Boundaries in the High-Latitude Region Using DMSP Data(2017-08) Chen, Yun-Ju; 0000 0000 3175 0999 (Heelis, RA); Heelis, Roderick A.The characteristics of the convection reversal boundary (CRB) in the high latitude ionosphere are investigated by using Defense Meteorological Satellite Program (DMSP) ion drift and particle precipitation measurements from 2000 to 2015. A statistical study shows that the CRB location is well organized by the magnitude and direction of the Interplanetary Magnetic Field (IMF) components Bz and By. Observation also suggests that the average latitudinal movement of the CRB associated with By changes is comparable to that associated with Bz changes. Inspection of the CRB locations as a function of magnetic local time (MLT) shows that the CRB has a general spiral shape with a latitudinal gap at the dayside boundary. An observed uneven boundary expansion between the dawn and dusk side reveals that an initial reconfiguration of the boundary near local noon is redistributed around the dawn or dusk side dependent on the direction of By. Two halves of ellipses with different lengths for the semi-major axes are produced to represent the boundary location. The properties of the plasma motion at the CRB and its dependence on the location of the CRB and the IMF orientation are then investigated. A smaller variability in plasma drifts across the CRB is seen over a 4 h segment in MLT around dawn and dusk for stable southward IMF compared to that for variable IMF. Across these segments, a total potential drop ~10 kV is found, suggesting that the CRB behaves much like an adiaroic line, for which the plasma and the boundary move together. Considering a full range of IMF orientations with no stability constraint, a relatively narrow distribution of plasma drifts across the CRB is seen only between the 6-7 h and between 17-18 h MLT, and equatorward/poleward motions of the CRB are observed when the CRB is located at the highest/lowest latitudes. The smaller local time extent of the adiaroic line for variable IMF (~1 h) may be associated with rotation of the dayside merging gap in local time or local contractions and expansions of the polar cap boundary. A systematic case study of the relationship between the motion of the convection reversal boundary and the plasma motion from multi-satellite samplings is performed. Focusing on the cases with continuous poleward and equatorward CRB motion sampled by three consecutive satellites, the CRB usually moves at approximately the same speed and in the same direction as the local plasma flow. Differences in the inferred CRB motion and the local plasma motion may arise from the presence of a viscous-like interaction across the boundary, apparent motion induced by the local time displacement of consecutive samples across the CRB that is tilted with respect to a line of constant latitude and the merging or reconnection processes. The observations also suggest that monotonic migrations of the CRB over time scales of a half hour take place episodically with time scales shorter than the typical sample time of 15 minutes available from sequential measurements.Item 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.Item 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.