Browsing by Author "Hysell, D. L."
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Item Restricted A multistatic HF beacon network for ionospheric specification in the Peruvian sector(American Geophysical Union, 2016-05-04) Hysell, D. L.; Milla, Marco; Vierinen, J.A small network of HF beacon transmitters and receivers has been deployed in Peru for specifying the F region ionosphere in the sector. The effort is motivated by ionospheric disturbances associated with equatorial spread F (ESF) and specifically disturbances arising under inauspicious conditions for ESF as determined by numerical simulations. The beacons operate at dual frequencies (2.72 and 3.64 MHz). They are CW but incorporate pseudorandom noise (PRN) coding so that the group delays of the links can be measured. Other observables are power, Doppler shift, bearing, and polarization. A transmitter is currently deployed at Ancon (11∘46’37’’S, 77∘09’1’’W, 51 m above sea level (asl)), while receivers are at Jicamarca (11∘57’5.8’’S, 76∘52’27’’W, 510 m asl) and Huancayo (12∘02’30’’S, 75∘19’15’’W, 3315 m asl). An algorithm for inverting the beacon data combined with electron density profiles from Jicamarca is described. Data and representative solutions from an experimental campaign held in August 2015 are presented and evaluated.Item Open Access A renormalization group approach to estimation of anomalous diffusion in the unstable equatorial F region(American Geophysical Union, 1998-11-01) Hysell, D. L.; Seyler, C. E.An expression is derived for the anomalous diffusion coefficient associated with collisional interchange turbulence in the equatorial F region ionosphere. Waves with ω ≪ Vin ≪ Ωi are considered. The calculation makes use of the renormalization group method, following closely that of Kichatinov [1985]. The calculation is applied to the problem of plasma waves in the equatorial F region ionosphere generated by the ionospheric interchange instability. Approximations appropriate for the geometry of that problem are incorporated into the calculation. Using a model spectrum of the irregularities based on in situ satellite observations, we calculate that the anomalous diffusion seen by large‐scale plasma waves can be 5 orders of magnitude larger than the ambipolar diffusion coefficient.Item Open Access AMISR contributions to equatorial aeronomy(Instituto Geofísico del Perú, 2004) Hysell, D. L.; Chau Chong Shing, Jorge LuisPresentación incluida en CEDAR (Coupling, Energetics and Dynamics of Atmospheric Regions) Workshop for 2004 (Santa Fe, Nuevo México, 2004).Item Restricted An overview and synthesis of plasma irregularities in equatorial spread F(Elsevier, 2000-10-06) Hysell, D. L.A unified picture of plasma irregularities in equatorial spread F is developed from the analysis of satellite, sounding rocket, and coherent scatter radar observations. The coherent scatter data are analyzed using a new in-beam radar imaging technique that permits direct comparison between radar data, in situ data, and computer simulations of the irregularities. Three varieties of irregularities, all produced by ionospheric interchange instabilities, are found to occur. Thin bottom-type layers are composed of waves with primary transverse wavelengths less than about 1 km and with significant parallel wavenumbers. These exist on magnetic flux tubes controlled by the E region dynamo and drift westward in the postsunset ionosphere. A nonlocal analysis is used to calculate their linear growth rate. When the F region dynamo takes control of the flux tube, bottomside irregularities can emerge. These are more robust irregularities with longer primary wavelengths and which exhibit greater vertical development. Nonlinear analyses explain the appearance of steepened structures in rocket observations and solitary waves in satellite observations of bottomside layers. The one-dimensional spectra of these irregularities obey power laws but are anisotropic and have variable spectral indices and spectral breaks. Very strong polarization electric fields can eject large regions of deeply depleted plasma through the F peak and form topside irregularities. Theoretical calculations supported by satellite data show that ion inertia may become important for topside irregularities. The one-dimensional spectra of irregularities in the inertial regime obey a k−5/3 power law, but strong plasma inhomogeneity implies that Kolmogorov weak turbulence is not the explanation. Topside depletions are shown to bifurcate and also to pinch off from the bottomside.Item Restricted Aperture synthesis radar imaging for upper atmospheric research(IntechOpen, 2012-04) Hysell, D. L.; Chau Chong Shing, Jorge LuisRadars used for upper-atmospheric applications can be engineered to measure the Doppler spectra of their targets adequately for most intents and purposes, the spectral resolution being limited only by the observing time and the constraints of stationarity. Likewise, they can measure the range to their targets adequately for most intents and purposes, range resolution being limited by system bandwidth, the power budget, and the constraints of stationarity. Problems arise for “overspread” targets, where range and frequency aliasing cannot simultaneously be avoided using pulse-to-pulse methodologies, and more complicated pulse-to-lag or aperiodic pulsing methods are required (see for example (Farley, 1972; Huuskonen et al., 1996; Lehtinen, 1986; Sulzer, 1986; Uppala, 1993)). Important examples of this situation include incoherent scatter experiments (Farley, 1969), observations of meteor head echoes (Chau & Woodman, 2004), and observations of plasma density irregularities present in certain rapid flows, as are found in the equatorial ionosphere during so-called “equatorial spread F” (Woodman, 2009; Woodman & La Hoz, 1976).Item Restricted Aperture-synthesis radar imaging with compressive sensing for ionospheric research(American Geophysical Union, 2019-06) Hysell, D. L.; Sharma, P.; Urco, M.; Milla, MarcoInverse methods involving compressive sensing are tested in the application of two-dimensional aperture-synthesis imaging of radar backscatter from field-aligned plasma density irregularities in the ionosphere. We consider basis pursuit denoising, implemented with the fast iterative shrinkage thresholding algorithm, and orthogonal matching pursuit (OMP) with a wavelet basis in the evaluation. These methods are compared with two more conventional optimization methods rooted in entropy maximization (MaxENT) and adaptive beamforming (linearly constrained minimum variance or often “Capon's Method.”) Synthetic data corresponding to an extended ionospheric radar target are considered. We find that MaxENT outperforms the other methods in terms of its ability to recover imagery of an extended target with broad dynamic range. Fast iterative shrinkage thresholding algorithm performs reasonably well but does not reproduce the full dynamic range of the target. It is also the most computationally expensive of the methods tested. OMP is very fast computationally but prone to a high degree of clutter in this application. We also point out that the formulation of MaxENT used here is very similar to OMP in some respects, the difference being that the former reconstructs the logarithm of the image rather than the image itself from basis vectors extracted from the observation matrix. MaxENT could in that regard be considered a form of compressive sensing.Item Open Access Bottom-type scattering layers and equatorial spread F(European Geosciences Union (EGU), 2004-12) Hysell, D. L.; Chun, J.; Chau Chong Shing, Jorge LuisJicamarca radar observations of bottom-type coherent scattering layers in the post-sunset bottomside F-region ionosphere are presented and analyzed. The morphology of the primary waves seen in radar images of the layers supports the hypothesis of Kudeki and Bhattacharyya (1999) that wind-driven gradient drift instabilities are operating. In one layer event when topside spread F did not occur, irregularities were distributed uniformly in space throughout the layers. In another event when topside spread F did eventually occur, the irregularities within the pre-existing bottom-type layers were horizontally clustered, with clusters separated by about 30 km. The same horizontal periodicity was evident in the radar plumes and large-scale irregularities that emerged later in the event. We surmise that horizontal periodicity in bottom-type layer irregularity distribution is indicative of large-scale horizontal waves in the bottomside F-region that may serve as seed waves for large-scale Rayleigh Taylor instabilities.Item Restricted Collisional shear instability in the equatorial F region ionosphere(American Geophysical Union, 2004-11-03) Hysell, D. L.; Kudeki, E.A collisional shear instability in a magnetized plasma is described and evaluated. The instability is related to electrostatic Kelvin Helmholtz but operates in inhomogeneous plasmas in the collisional regime. Boundary value analysis predicts that the linear growth rate for the instability could be comparable to that of the collisional interchange instability in the equatorial F region ionosphere under ideal conditions. An initial value simulation of a nonlinear model of the instability run under realistic conditions produces growing waves with a relatively long growth time (50 min) and with an initial wavelength of about 30 km. The simulation results are consistent with recent radar observations showing large‐scale plasma waves in the bottomside equatorial ionosphere at sunset prior to the onset of spread F conditions. The role of shear instability in preconditioning the F region for interchange instabilities to occur after sunset is discussed.Item Open Access Comparing F region ionospheric irregularity observations from C/NOFS and Jicamarca(American Geophysical Union, 2009-07-11) Hysell, D. L.; Hedden, R. B.; Chau Chong Shing, Jorge Luis; Galindo, F. R.; Roddy, P. A.; Pfaff, R. F.Observations of plasma density irregularities associated with equatorial spread F (ESF) have been made using the Jicamarca Radio Observatory and the Plasma Langmuir Probe (PLP) and Vector Electric Field Instrument (VEFI) instruments on the Communications Navigation Outage Forecast System (C/NOFS) satellite during a close spatio-temporal conjunction. The radar data resolution is of the order of 1 km and a few sec. in space and time, respectively. We find that coherent scatter intensifications at these scales are coincident and collocated with plasma density depletions as determined by C/NOFS. The Doppler shifts of the localized echoes are also comparable to the vertical components of the E × B plasma drifts. The strongest backscatter does not necessarily come from the deepest or most rapidly convecting depletions. This implies a complex relationship between coherent backscatter and the underlying state parameters in the ionospheric plasma.Item Open Access Comparing Jicamarca and C/NOFS (PLP, VEFI): observations of equatorial spread F irregularities(Instituto Geofísico del Perú, 2009) Hysell, D. L.; Hedden, R. B.; Chau Chong Shing, Jorge Luis; Galindo, F. R.; Roddy, P. A.; Pfaff, R. F.Diapositivas presentadas en The Meeting of the Americas, 2009 Joint Assembly, organizadas por la American Geophysical Union del 24 al 27 mayo de 2009 en Ontario, Canada.Item Restricted Comparison of topside equatorial parameters derived from DMSP, Jicamarca, and Another Model of the Ionosphere (SAMI2)(American Geophysical Union, 2005-01-19) Venkatraman, Sarita; Heelis, R. A.; Hysell, D. L.Comparison is made of topside equatorial parameters obtained from DMSP satellites with those measured from Jicamarca radar and those calculated from Another Model of the Ionosphere (SAMI2). To determine acceptable limits for this volume, knowledge of the spatial and temporal gradients in the parameters must be defined. Those can be obtained independently from each data source and are dependent on local time and season. Having described the spatial gradients, a comparison of the ionospheric variables can be made. The present study focuses on simultaneous ground‐based and satellite data obtained for June 2002. Data for days 11, 12, and 13 are compared in this study. Satellite data are obtained from the DMSP satellites F13 (0600–1800 LT) and F15 (0900–2100 LT), respectively. Ground‐based data are obtained from the Jicamarca radar. These are then compared with numerical computations performed by the SAMI2 model for the same period. Good agreement between observation and model is achieved for the total ion concentration during daytime and nighttime, while the ion and electron temperatures agree well at night. The light ion fraction is usually <20% from all three sources except during sunrise where the light ion content can be higher. Accounting for the variables H+ and He+ concentrations in the topside appears to be the major factor affecting the different data sources.Item Restricted Data-driven numerical simulations and forecasts of equatorial spread F in the Peruvian sector(Instituto Geofísico del Perú, 2014-08) Hysell, D. L.; Milla, Marco"Ionospheric state parameters including plasma number density and vector drift profiles were measured at the Jicamarca Radio Observatory during campaigns throughout 2013. Neutral winds were measured by the redline Fabry Perot interferometer at Jicamarca. Coherent radar backscatter from plasma irregularities associated with equatorial spread F (ESF) was also recorded. Radar imagery of the morphology of the large-scale ESF irregularities is also available from simultaneous measurements. A 3D numerical simulation of ionospheric irregularities, initialized and forced using parametrizations derived from a combination of measurements and empirical models, has been used to reproduce the ESF activity that occurred on a number of different, representative campaign nights. The simulations were able to recover many of the most salient features of the irregularities that formed in each case. The campaign data, numerical simulations, and protocols used to associate them are presented."Item Open Access Data-driven numerical simulations of equatorial spread F in the Peruvian sector 3: Solstice(American Geophysical Union, 2015-11-19) Hysell, D. L.; Milla, Marco; Condori, L.; Vierinen, J.We present results from a continuing effort to simulate equatorial spread F (ESF) using observations from the Jicamarca Radio Observatory near Lima, Peru. Jicamarca measures vertical and zonal plasma drifts along with plasma number density profiles overhead. The number density profiles are used to initialize a three-dimensional regional model of the ionosphere capable of simulating plasma density irregularities produced during ESF conditions. The vertical drifts measurements are used to drive the numerical simulation continuously. Neutral winds are derived from the new Horizontal Wind Model '14 (HWM-14) model, and the zonal winds are scaled so as to make the zonal plasma flows at the start of the simulation agree with the ISR profile measurements. Coherent scatter radar imagery from Jicamarca is used to validate the simulation results. Campaign data were collected in April and December, 2014, and a few events representative of low and high ESF activity were selected for analysis. The numerical simulations are able to reproduce the level of activity observed along with the gross features of the ESF irregularities and radar plumes. Data from a network of HF beacons are being incorporated into the forecast analysis in order to elucidate radar plumes which sometimes appear even when the simulation fails to predict them.Item Open Access Data‐driven numerical simulations of equatorial spread F in the Peruvian sector: 2. Autumnal equinox(American Geophysical Union, 2014-08-11) Hysell, D. L.; Milla, Marco; Condori, L.; Meriwether, J. W.An ongoing effort to simulate plasma instability in the equatorial ionosphere leading to equatorial spread F (ESF) in the American sector is described. Ionospheric state parameters including plasma number density and vector drift velocity profiles were measured at the Jicamarca Radio Observatory in the period between 20 September and 3 October 2013. Coherent radar backscatter from plasma irregularities was recorded simultaneously, and images of the irregularities were calculated using aperture synthesis methods. Neutral winds were measured by the red line Fabry‐Perot interferometers at Jicamarca and Arequipa, Peru. A fully 3‐D numerical simulation of ionospheric irregularities, initialized and forced using parameterizations derived from measurements and empirical models, was used to reproduce the ESF activity observed. Simulations were able to recover many of the features of the irregularities, although some important anomalies can be noted. ESF events in which the first appearance of radar plumes occurred either very early or very late were not reproduced in simulation and may be indicative of nonlocal influence.Item Restricted Eddy turbulence parameters inferred from radar observations at Jicamarca(European Geosciences Union (EGU), 2007-03-08) Vlasov, M. N.; Kelley, M. C.; Hysell, D. L.Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007). In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1×103 m2/s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007) is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density.Item Open Access Effects of large horizontal winds on the equatorial electrojet(American Geophysical Union, 2002-08) Hysell, D. L.; Chau Chong Shing, Jorge Luis; Fesen, C.G.The effects of large winds on the low-latitude E region ionosphere and the equatorial electrojet in particular are analyzed theoretically, computationally, and experimentally. The principles that govern the relationship between electric fields, currents, and winds in steady flows in the ionosphere are reviewed formally. A three-dimensional numerical model of low-latitude ionospheric electrostatic potential is then described. Scaled wind profiles generated by the National Center for Atmospheric Research (NCAR) thermosphere/ionosphere/mesosphere electrodynamics general circulation model (TIME-GCM) are used as inputs for the potential model. The model shows that the horizontal wind component drastically modifies the vertical polarization electric field in the electrojet and drives strong zonal and meridional currents at higher dip latitudes outside the electrojet region. Comparison between the model output and coherent scatter radar observations of plasma irregularities in the electrojet indicate that strong winds and wind shears are present in the E region over Jicamarca that are roughly consistent with NCAR model wind predictions if the amplitudes of the latter are increased by about 50%.Item Open Access Electron density profiles in the equatorial E region ionosphere derived from a bistatic coherent scatter radar experiment in Perú(American Geophysical Union, 2005-01-14) Shume, E. B.; Hysell, D. L.; Chau Chong Shing, Jorge LuisA new bistatic radar system has been developed at the Jicamarca Radio Observatory. The system is a permanent addition to the facility designed to monitor electron density profiles in the equatorial electrojet region using a coherent scatter radar technique that utilizes the Faraday rotation of the scattered signal. A series of radar experiments has been conducted at Jicamarca since March, 2004. In this report, representative E region electron density profiles of the equatorial ionosphere are presented. We compare our electron density estimates with: theoretical electron densities derived from the Chapman production function, electron densities measured by rocket experiments, the International Reference Ionosphere (IRI‐2001) model, and peak electron density estimates from the Jicamarca Digisonde. Overall, the radar measured density profiles have magnitudes and shapes comparable to the electron density estimators mentioned above. However, the measured and IRI‐2001 model density profiles disagree significantly below the E region peak.Item Restricted Electrostatic plasma turbulence in the topside equatorial F region ionosphere(American Geophysical Union, 2002-10-03) Hysell, D. L.; Shume, E. B.Two‐dimensional, turbulent plasma flows in the topside equatorial F region ionosphere associated with fully developed equatorial spread F are analyzed and simulated numerically. In the inertially dominated flow regime, the governing equations of motion resemble the Navier Stokes equation but are cubicly nonlinear. Large amplitude density irregularities are prerequisite for inertial effects to be important, but when these are present, the third‐order nonlinear effects become significant, mean‐squared velocity and vorticity cease to be conserved by nonlinear mode coupling, and the foundations of the turbulent cascade theory of Kraichnan [1967] are undermined. Nonetheless, one‐dimensional, angle‐averaged velocity spectra computed from simulated flows exhibit similarity ranges with k−5/3 and k−3 power laws, resembling inertial ranges and suggesting turbulent cascades. Invariants of the flow (quantities conserved by nonlinear mode coupling) are found which are generalizations of the quadratic forms of kinetic energy and enstrophy and which are dimensionally equivalent to them. Statistical properties of the flow appear to permit turbulent cascades to arise.Item Restricted Equatorial zonal electric fields inferred from a 3‐D electrostatic potential model and ground‐based magnetic field measurements(American Geophysical Union, 2009-06-06) Shume, E. B.; De Paula, E. R.; Maus, S.; Hysell, D. L.; Rodrigues, F. S.; Bekele, A.We present a new technique to infer quiet time zonal electric fields in the daytime equatorial ionosphere. The electric field inference technique utilizes a three‐dimensional (3‐D) electrostatic potential model of the low‐latitude ionosphere constrained by ground‐based magnetic field measurements. To test this technique, inferred zonal electric fields for the Peruvian sector in Jicamarca (11.95°S, 283.13°E, 0.6°N dip latitude) were compared with zonal electric field (vertical drift) measurements made by the Jicamarca Incoherent Scatter Radar. The comparison shows a good agreement between the inferred and measured electric fields. An example of electric field estimation for Davao (7.4°N, 125.4°E, 0.58°S dip latitude) in the Philippines sector is also presented in this report. Inferred electric fields for Davao are in good agreement with F region vertical plasma drifts measured by drift sensors onboard the AE‐E and ROCSAT‐1 satellites on that longitude sector. Our results suggest that realistic estimates of quiet time zonal electric fields for the equatorial ionosphere can be obtained from the 3‐D potential model whenever observatory magnetic field measurements are available.Item Open Access Evaluation of topside equatorial spread F spectra estimators using Monte Carlo simulations(Instituto Geofísico del Perú, 2008) Galindo, F. R.; Kuyeng, K. M.; Chau Chong Shing, Jorge Luis; Hysell, D. L.Radar observations typically employ periodic pulses to study any target. This scheme allows a simple processing of the data but the results frequently shows range or frequency aliasing. In order to solve this problem Uppala and Sahr [1] introduced the aperiodic technique (AT) in the radio science community. The AT is based on transmitting pulses at non uniform intervals and allows to study moderately overspread targets. Some equatorial Spread F (ESF) echoes belong to this category, particularly those from the topside. Using this idea Jicamarca Radio Observatory (JRO) has done a couple of experiments to study ESF echoes. Chau et al [2] used the Fast Fourier Transform (FFT) to compute spectra from those experiments and developed some criteria to remove clutter due to the aperiodic sequence. A second scheme of work was introduced by Hysell et al [3] and this scheme uses a Bayesian method to compute the spectra. Continuing this line of research a Monte Carlo simulations of typical echoes from equatorial ionospheric irregularities as well as ground clutter has been done to evaluate different aperiodic pulsing and inversion techniques to estimate the spectra or its corresponding AutoCorrelation Function (ACF). Our main objective is the estimation of the moderately overspread topside equatorial spread F (ESF) spectra. The optimal spectra estimators combined with radar imaging techniques might represent the unique means to estimate the irregularity power and energy spectral density versus wavenumber from the ground.