Heelis, Roderick A.

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Roderick Heelis holds the Distinguished Chair in Natural Sciences and Mathematics and is the Director of the William B. Hanson Center for Space Sciences. Dr. Heelis’s research interests focus on understanding the interaction of planetary environments with the Sun. For the Earth this interaction is influenced by the atmosphere and the magnetic field and directly affects the successful operation of space-based communication and navigation systems.

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Now showing 1 - 14 of 14
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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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    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.
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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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    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.
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    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.
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    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.
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    Daytime Zonal Drifts in the Ionospheric 150km and E Regions Estimated Using Ear Observations
    (Amer Geophysical Union, 2017-08-31) Pavan Chaitanya, P.; Patra, A. K.; Otsuka, Y.; Yokoyama, T.; Yamamoto, M.; Stoneback, Russell A.; Heelis, R. A.; 0000 0000 3175 0999 (Heelis, RA); 0000-0001-7216-4336 (Stoneback, RA); 0000-0002-5543-5357 (Heelis, RA); Stoneback, Russell A.; Heelis, R. A.
    Multibeam observations of the 150km echoes made using the Equatorial Atmosphere Radar (EAR), located at Kototabang, Indonesia, provide unique opportunity to study both vertical and zonal ExB plasma drifts in the equatorial ionosphere. In this paper, we focus on estimating daytime zonal drifts at the 150km (140-160km) and E (100-110km) regions using multibeam observations of 150km and E region echoes made using the EAR and study the daytime zonal drifts covering all seasons not studied before from Kototabang. Zonal drifts in the 150km and E regions are found to be westward and mostly below -80ms⁻¹ and -60ms⁻¹, respectively. While the zonal drifts in the 150km and E regions do not go hand in hand on a case-by-case basis, the seasonal mean drifts in the two height regions are found to be in good agreement with each other. Zonal drifts at the 150km region show seasonal variations with three maxima peaking around May, September, and January. The zonal drifts at the 150km region are found to be smaller than the F region drifts obtained from Coupled Ion Neutral Dynamics Investigation (CINDI) onboard Communication and Navigation Outage Forecasting System (C/NOFS) by about 25ms⁻¹ consistent with the height variations of F region zonal drifts observed by the Jicamarca radar. These results constitute the first comprehensive study of zonal drifts at the 150km and E regions from Kototabang, Indonesia, and the results are discussed in the light of current understanding on the low-latitude electrodynamics and coupling.
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    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⁺.
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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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    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.
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    Topside Equatorial Zonal Ion Velocities Measured by C/NOFS During Rising Solar Activity
    (Copernicus Gesellschaft Mbh, 2014-02-04) Coley, W. R.; Stoneback, Russell A.; Heelis, Rodney A.; Hairston, M. R.; 0000 0000 3175 0999 (Heelis, RA); 88021080‏ (Heelis, RA); Coley, W. R.; Stoneback, Russell A.; Heelis, Rodney A.; Hairston, M. R.
    The Ion Velocity Meter (IVM), a part of the Coupled Ion Neutral Dynamic Investigation (CINDI) instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft, has made over 5 yr of in situ measurements of plasma temperatures, composition, densities, and velocities in the 400-850 km altitude range of the equatorial ionosphere. These measured ion velocities are then transformed into a coordinate system with components parallel and perpendicular to the geomagnetic field allowing us to examine the zonal (horizontal and perpendicular to the geomagnetic field) component of plasma motion over the 2009-2012 interval. The general pattern of local time variation of the equatorial zonal ion velocity is well established as westward during the day and eastward during the night, with the larger nighttime velocities leading to a net ionospheric superrotation. Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually increased from around 70 sfu to levels in the 130-150 sfu range. The comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us to examine variations of the topside zonal ion velocity over a wide level of solar activity as well as the dependence of the zonal velocity on apex altitude (magnetic latitude), longitude, and solar local time. It was found that the zonal ion drifts show longitude dependence with the largest net eastward values in the American sector. The pre-mid-night zonal drifts show definite solar activity (F10.7) dependence. The daytime drifts have a lower dependence on F10.7. The apex altitude (magnetic latitude) variations indicate a more westerly flow at higher altitudes. There is often a net topside subrotation at low F10.7 levels, perhaps indicative of a suppressed F region dynamo due to low field line-integrated conductivity and a low F region altitude at solar minimum.
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    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.
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    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.

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