Browsing by Author "Kudeki, Erhan"
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Item Restricted A causal relationship between lightning and explosive spread F(American Geophysical Union, 1984-12) Woodman Pollitt, Ronald Francisco; Kudeki, ErhanExperimental evidence for a causal relationship between lightning and explosive equatorial spread F is presented. It is proposed that explosive spread F is produced by rapidly growing plasma instabilities, which are triggered by sudden increases of the F region ambient electric fields due to the penetration of lightning fields into regions of weak or marginal instability.Item Restricted A multi-beam incoherent scatter radar technique for the estimation of ionospheric electron density and Te/Ti profiles at Jicamarca(Elsevier, 2013-12) Milla, Marco; Kudeki, Erhan; Reyes, Pablo M.; Chau Chong Shing, Jorge LuisA multi-beam incoherent scatter radar technique has been developed at the Jicamarca Radio Observatory in order to maximize the number of ionospheric parameters that can be estimated simultaneously. The technique interleaves radar observations with antenna beams pointing perpendicular and oblique to the Earth's magnetic field. For the estimation of the ionospheric parameters, we have modeled the magnetic aspect angle variations of the signal power and cross-correlation data measured in multiple directions. The data model, formulated in terms of soft-target radar equations, was built based on the theories of incoherent scattering and magneto-ionic propagation. Applying a nonlinear least-squares inversion algorithm, we have succeeded in measuring simultaneously ionospheric electron densities Ne, electronto-ion temperature ratios Te=Ti as well as vertical and zonal plasma drifts. In the past, radar users had to choose between either perpendicular-to-B or oblique modes, thus, the application of this technique extends the current capabilities of the Jicamarca radar.Item Restricted A poststatistics steering technique for MST radar applications(American Geophysical Union, 1990-07) Kudeki, Erhan; Woodman Pollitt, Ronald FranciscoA new interferometric data analysis procedure equivalent to software beam synthesis and scanning is introduced. It is shown that the self- and cross-spectra of interferometric multiple-receiver signals can be linearly combined to obtain the self- and cross-spectra of radar returns from selected viewing directions within the two-way radar beam pattern.Item Restricted An investigation of equatorial 150-km irregularities(University of Illinois at Urbana-Champaign, 1999) Fawcett, Clinton Douglas; Kudeki, ErhanWe performed experiments using the 50-MHz Jicamarca radar to study the equatorial 3-m scale plasma irregularities which are responsible for the radar backscatter called 15-km echoes observed at upper E-region heights from approximately 140 to 170 km. These studies were motivated by the search for a generation mechanism and the potential for using backscatter from 150-km irregularities to make vertical drift estimates over long time periods for enhancing the databases used in space weather prediction tools. Based on our observations of a counter-electrojet event, we have determined that the zonal component of the electric field is not the main factor in the generation of these plasma irregularities. We observe no significant altitudinal shears in the zonal drifts, but we do observe intensity and Doppler velocity modulations that indicate the presence of gravity waves. Our power-map shift analyses indicate a predominantly meridioanal propagation direction for these waves. The brief interval during which we observe modulations in the vertical drift estimates indicates the presence of a purely zonally propagating wave. The wave parameters extracted from our observations allow us to estimate the zonal wind U for this short time. The differential between the computed U and the measured zonal drift is large enough to consider the associated 2.5-mv / m vertical electric field as a possible driver for the generation of the 150-km irregularities, themselves. Howewer, the absence of observed velocity perturbations at other times on the same day and the other two days means that we have not yet established a generation mechanism for all times. With regard to our aspect width measurements, we conclude that aspect widths of the 150-km echoes are smaller than those of those electrojet and larger than those of F-region irregularities. With regard to zonal interferometry, we conclude that scatterers observed using an east-west baseline appear diffuse and fill the beam.Item Restricted Aspect sensitivity of equatorial electrojet irregularities and theoretical implications(American Geophysical Union, 1989-01-01) Kudeki, Erhan; Farley, Donald T.We used a multi baseline 50-MHz radar interferometer at the Jicamarca Radio Observatory to study the dependence of echo strength on the aspect angle, the angle of arrival relative to normal to the geomagnetic field. We observed rms values of this angle in the range 0.1–0.4, which implies an aspect sensitivity somewhat greater than the nominal 10 dB/deg often quoted for auroral echoes. The technique has sufficient resolution to allow deviations from normal of less than 0.1 to be measured fairly easily, and we were able to determine variations of the aspect sensitivity with altitude, Doppler shift, and electrojet conditions. During weakly driven periods, when only type 2 echoes were observed, the width, or rms angular deviation from normal, decreased monotonically with increasing altitude, as simple linear theory would suggest, but the variation was less rapid than the variation of νe/Ωe, especially on the bottomside of the electrojet. A particularly interesting observation was that, during strongly driven type 1 conditions, there was a pronounced variation of width with Doppler shift. The width for small phase velocities was sometimes more than twice that at the ion-acoustic velocity. We believe that this broadening is due to nonlinear three-wave mode coupling which produces a reverse cascade of energy from short wavelengths to long and an increase in the mean aspect angle. Such a cascade represents an increase in the effective diffusion coefficient for the short wavelength waves and so could provide an explanation alternative to that of the anomalous collision process of Sudan (1983) for the limitation of the type 1 phase velocity at the ion-acoustic velocity.Item Restricted Calibration of Jicamarca radar using F-region incoherent scatter for measurements of D-region backscatter RCS(University of Illinois at Urbana-Champaign, 2007) Akgiray, Ahmed H.; Kudeki, ErhanEl propósito de esta tesis es describir las mediciones del radar calibrado de absoluta retrodispersión a traves de las secciones mesososféricas de los ecos del radar observados en el Radio Observatorio de Jicamarca en Perú. La calibración del sistema de radar se lleva a cabo mediante la simulación de la propagación de ondas de radio transmitidas y retrodispersados a través de la ionosfera y la comparación de los rendimientos simulados de alimentación a las mediciones. El modelo directo utilizado en el algoritmo de calibración se basa en la dispersión magnetoionica, incoherente (IS) y de las teorías de la antena.Item Open Access Dynamics of the equatorial mesosphere observed using the Jicamarca MST radar during June and August 1987(American Meteorological Society, 1992-12) Fritts, David C.; Yuan, Li; Hitchman, Matthew H.; Coy, Lawrence; Kudeki, Erhan; Woodman Pollitt, Ronald FranciscoThe Jicamarca MST radar was used in two campaigns during June and August 1987 to measure wave influences, flow variability, and mean structure in the equatorial stratosphere and mesosphere. This paper presents observations of motions and momentum fluxes in the mesosphere during each campaign. A companion paper by Hitchman et al. addresses the mean structure and fluxes as well as comparisons with other datasets. Results presented here indicate that the equatorial mesosphere is dynamically very active, with considerable gravity-wave and tidal motions and persuasive evidence of inertial instability and wave-filtering processes. Vertical velocities at high frequencies are comparable to those observed at other locations. Hourly mean horizontal motions and momentum fluxes are Iikewise large and variable, exhibiting enormous vertical shears and strong modulation of the wave spectrum and momentum fluxes at higher frequencies. Daily mean profiles revea! persistent structures with vertical scales of -6-10 km, vertical shears ofthe meridional velocity of -0.03 s-1, and large mean momentum fluxes. Also discussed are the implications of these observations for wave forcing and instability in the equatorial middle atmosphere.Item Open Access Efectos de propagación magneto-iónica en las mediciones de dispersión incoherente del radar de Jicamarca(Instituto Geofísico del Perú, 2010) Milla, Marco; Kudeki, Erhan; Chau Chong Shing, Jorge LuisDiapositivas presentadas en el XIII Encuentro Científico Internacional, (ECI 2010i), realizado del 2 al 6 de agosto de 2010 en la ciudad de Lima, Perú.Item Restricted Equatorial F-region plasma density estimation with incoherent scatter radar using a transverse-mode differential-phase method(University of Illinois at Urbana-Champaign, 2002) Feng, Zhaomei; Kudeki, ErhanEsta tesis presenta un método de adquisición y análisis de datos novedoso para radar de dispersión incoherente Jicamarca para medir derivas de alta precisión y la densidad ionosférica simultáneamente en las alturas de la región F. Dado que las mediciones de deriva de alta precisión a favor de las señales de retorno de radar con los espectros de frecuencia estrecha posible, Jicamarca derivas observaciones se llevaron a cabo utilizando las ondas de radar transversal polarizadas lineales. la señal vuelve transversal de las vigas se recogen usando un par ortogonal de antenas polarizadas lineales, y la potencia media, así como la diferencia de fase de las salidas de antena están instalados en los modelos de datos adecuados, desarrollados sobre la base de la teoría de dispersión incoherente y la teoría de la magneto-iónico. El modelo de fase diferencial de crudo cuando Bo se caracteriza en términos de campos de las líneas rectas se aplica a los datos de enero de 2000. El modelo de fase diferencial más completa, que tiene en cuenta el ángulo desalineada entre los ejes dipolares de las matrices de Jicamarca ortogonales y noreste geomagnético y direcciones sureste, así como la anchura del haz de radar y la variación de los campos magnéticos, se aplica a la 01 2000 datos de 2002 y junio de datos. Presentamos y comparar los resultados obtenidos con la inversión de diferentes versiones de los modelos de datos y concluir que los detalles geométricos sólo tienen un impacto menor en la inversión. También nos encontramos con que funciona el método de fase diferencial mejor para el 15-min de datos integrada de enero de 2000 al 5-min integrado de junio de 2002, los datos ya que el primero tiene las mayores densidades de electrones, mayor SNR de las señales de retrodispersión, y datos de la fase más usables. Nuestros resultados de la inversión se comparan con los datos ionosonda, y que muestran un acuerdo razonable.Item Restricted Equatorial spread-F initiation: Post-sunset vortex, thermospheric winds, gravity waves(Elsevier, 2007-12) Kudeki, Erhan; Akgiray, Ahmed; Milla, Marco; Chau Chong Shing, Jorge Luis; Hysell, David L.We present experimental evidence and modeling results which indicate that eastward thermospheric wind is the primary controlling factor of equatorial spread-F initiation in the post-sunset ionosphere. Eastward wind-driven Pedersen currents are able to polarize F-region density perturbations with westward tilting wavefronts into rapidly growing modes to trigger the formation of spread-F bubbles. The described process is so rapid that seeding requirements of spread-F initiation by external factors such as gravity waves are effectively eliminated.Item Restricted Estimating daytime vertical ExB drift velocities in the equatorial F‐region using ground‐based magnetometer observations(American Geophysical Union, 2002-06-28) Anderson, David; Anghel, Adela; Yumoto, Kiyohumi; Ishitsuka, Mutsumi; Kudeki, ErhanThe daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100 to 120 km altitude region within ±2° latitude of the dip equator. A unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the Horizontal (H) component between a magnetometer placed directly on the magnetic equator and one displaced 6 to 9 degrees away. The difference between these measured H values provides a direct measure of the daytime electrojet current, and in turn, the magnitude of the vertical ExB drift velocity in the F region ionosphere. This paper discusses a recent study that has established the quantitative relationship between the vertical ExB drift velocity in the ionospheric F region and the daytime strength of the equatorial electrojet in the South American (west coast) longitude sector.Item Restricted F region plasma density estimation at Jicamarca using the complex cross‐correlation of orthogonal polarized backscatter fields(American Geophysical Union, 2004-06-16) Feng, Zhaomei; Kudeki, Erhan; Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge Luis; Milla, MarcoThe differential‐phase method for Jicamarca F region density measurements has been modified to fit the real and imaginary components of the cross‐correlation of orthogonally polarized radar returns. The original method [Kudeki et al., 2003; Feng et al., 2003] based on fitting the cross‐correlation phase could only make use of correlation data from lower F region heights since the phase noise in low‐SNR upper F region returns is typically non‐Gaussian. However, upper F region correlation data become useful in the modified method since the fluctuations in real and imaginary parts of cross‐correlation remain Gaussian even under low‐SNR conditions.Item Open Access F-region electron density and Te / Ti measurements using incoherent scatter power data collected at ALTAIR(European Geosciences Union (EGU), 2006-07) Milla, Marco; Kudeki, ErhanThe ALTAIR UHF radar was used in an incoherent scatter experiment to observe the low-latitude ionosphere during the Equis 2 rocket campaign. The measurements provided the first high-resolution electron density maps of the low-latitude D- and E-region in the Pacific sector and also extended into the F-region and topside ionosphere. Although the sampling frequency was well below the Nyquist frequency of F-region returns, we were able to estimate Te/Ti ratio and infer unbiased electron density estimates using a regularized inversion technique described here. The technique exploits magnetic aspect angle dependence of ISR cross-section for Te>Ti.Item Restricted Height variation of gaps in 150‐km echoes and whole atmosphere community climate model electron densities suggest link to upper hybrid resonance(American Geophysical Union, 2020-01) Lehmacher, Gerald A.; Wu, Haonan; Kudeki, Erhan; Reyes, Pablo M.; Hysell, David L.; Milla, MarcoRadar echoes from the daytime lower F region near the magnetic equator, so-called 150-km echoes, have been puzzling researchers for decades. Neither the mechanisms that generate the enhanced backscatter at very high frequencies (typically 30–50 MHz), the sharp lower cutoff height, the intricate layering with multiple echo layers separated by narrow gaps, nor the modulation of the echoes by short-period gravity waves is well understood. Here we focus on the diurnal variation of the echo layers specifically, certain wide gaps in the vertical structure—which apparently descend in the morning, reach their lowest altitude near local noon, and ascend in the afternoon, sometimes described as necklace structure based on the appearance of the layers in range-time-intensity diagrams. Analyzing high-resolution data obtained with the Jicamarca radar between 2005 and 2017, spanning more than one solar cycle, we find that (a) wide gaps and narrow lines occur in vertically stacked, systematically repeating pattern; (b) the gap heights vary with season and solar cycle; and (c) the gap heights can be associated with specific contours of plasma frequencies or electron densities. The last two findings are supported by simultaneous observations of VIPIR ionosonde reflection heights and by comparison of gap heights with electron density contours obtained with the WACCM-X 2.0 global model. Finally, the wide gaps appear to coincide with the double resonance condition, where the upper hybrid frequency equals integer multiples of the electron gyrofrequency. This may explain why field-aligned plasma irregularities are suppressed and enhanced radar backscatter is not observed inside the gaps.Item Open Access Incoherent backscatter radar measurements at Jicamarca with a beam pointed perpendicular to(Editor no identificado, 2000) Kudeki, Erhan; Woodman Pollitt, Ronald FranciscoDoppler spectra of 50 MHz F-region incoherent backscattered signals detected at Jicamarca will be presented. The measurements were conducted with the Jicamarca radar beams pointed perpendicular to the ambient magnetic field B. Consequently, the Doppler spectra contain a sharp cusplike feature centered about the bulk Ex B velocity of the ionospheric plasma [Kudeki et al. 1999]. The overall shape of the spectrum about the mean Doppler velocity represents a beam weighted superposition of incoherent scatter spectra corresponding to small magnetic aspect angles. Incoherent scatter theory based models for the measured spectra indicate that the spectral width is regulated by the electron temperature Te , However, unless electron Coulomb collisions are included in the model, unrealistically low Te estimates are obtained via model fitting of the measured spectra. The collisions broaden the incoherent scatter spectra at very small magnetic aspect angles (due to cross-:field diffusion), but reduce the spectral width at larger aspect angles by reducing the rate of parallel diffusion as pointed out first by Sulzer and Gonzales [1999]. Spectral width reduction due to electron collisions is particularly important in measurements made close to perpendicularity to the ambient magnetic field. As a consequence, estimation of Te from incoherent scatter spectra measured at small magnetic aspect angles requires the knowledge of electron collision frequency and plasma density profiles in F-region. Recent multi-receiver (north-south antenna separation) and dual-polarization (0- and X-mode) F-region incoherent scatter measurements conducted at Jicamarca will be presented. The north-south and O-X cross-spectra of the backscattered signals provide · additional information about the ionospheric plasma. Differential phase information extracted from O-X cross-spectra provides estimates of the absolute electron density profiles near the F-region peak. The normalized magnitude of the north-south cross-spectra (coherence) is sensitive to Te/Ti. Therefore, joint inversions of the incoherent scatter self- and cross-spectra holds the potential for the estimation of ali the state parameters describing the F-region plasma at low-latitudes.Item Restricted Incoherent scatter radar - spectral signal model and ionospheric applications(IntechOpen, 2012-04-05) Kudeki, Erhan; Milla, MarcoThe chapter is organized as follows: The working principles of ISR’s and the general theory of incoherent scatter spectrum are described in Sections 2 and 3. ISR spectral features in unmagnetized and magnetized plasmas are examined in Sections 4 and 5, respectively. Coulomb collision process operating in magnetized ionosphere is described in Section 6. Effects of Coulomb collisions on particle trajectories and ISR spectra are discussed in Sections 7 and 8. Finally, Section 9 discusses the magnetoionic propagation effects on incoherent scattered radar signals. The chapter ends with a brief summary in Section 10.Item Open Access Incoherent scatter radar plasma density measurements at Jicamarca using a transverse-mode differential-phase method(American Geophysical Union, 2003) Kudeki, Erhan; Woodman Pollitt, Ronald Francisco; Feng, ZhaomeiThe 50 MHz Jicamarca incoherent scatter radar can be used to make very high precision F-region plasma drift measurements with less than a m/s uncertainty and 5 min/ 15 km time/height resolutions. In such measurements the transmitting antenna beam is pointed perpendicular to the geomagnetic field ~ B [e.g., Kudeki et al. , 1999] and backscattered fields consist of magneto-ionic O- and X- components with unequal phase retardations. Detecting the fields with an orthogonal pair of linear-polarized antennas and fitting the average power and differential- phase of the antenna outputs to an appropriate data model we have succeeded in making F-region electron density measurements with data collected during Jicamarca drifts experiments. This procedure provides Jicamarca with a new capability for simultaneous drifts and density measurements at F-region heights.Item Restricted Incoherent Scatter Spectral Theories—Part I: A General Framework and Results for Small Magnetic Aspect Angles(Institute of Electrical and Electronics Engineers, 2010-10-07) Kudeki, Erhan; Milla, MarcoA general framework for the incoherent scatter radar spectral theories is presented in terms of the generalized Nyquist theorem, Kramers-Kronig relations, and the characteristic functions of random charge-carrier displacements in the ionosphere. Specific spectral models for typical ionospheric conditions are derived and discussed. The discussions focus on the effect of Coulomb collisions in magnetized plasmas, which is a topic of current interest treated in further detail in the companion paper by the authors, as well as on different combinations of physical principles that can be invoked in the derivation of incoherent scatter spectral models.Item Restricted Incoherent Scatter Spectral Theories—Part II: Modeling the Spectrum for Modes Propagating Perpendicular to B(Institute of Electrical and Electronics Engineers, 2011-10-07) Milla, Marco; Kudeki, ErhanIncoherent scatter (IS) spectral models for collisional and magnetized F-region plasmas are developed based on a general framework described in part I of this paper and on the statistics of simulated particle trajectories. In the simulations, a Langevin update equation is used to describe the motion of charge carriers undergoing Coulomb collisions. It is shown that random displacements of oxygen ions in the F-region can be characterized as a Brownian-motion process with Gaussian distributed displacement vectors. Electron displacements, on the other hand, are non-Brownian, and their statistics exhibit a dependence on the magnetic aspect angle. A numerical library of characteristic functions of electron displacements was constructed from the simulation data obtained for a set of plasma parameters typical of the equatorial F-region. Spectral models for the IS radar signals from F-region heights are constructed with one-sided Fourier transforms of the characteristic functions of electron and ion displacements. The models are valid at all magnetic aspect angles, including the zero aspect angle that corresponds to radar observations perpendicular to the ambient geomagnetic field B.Item Open Access Incoherent scatter spectrum theory for modes propagating perpendicular to the geomagnetic field(American Geophysical Union, 2006-06-20) Kudeki, Erhan; Milla, MarcoThe short‐term relationship of the equatorial peak electron density and the solar short‐wavelength irradiance is examined using foF2 observations from Jicamarca, Peru and recent solar irradiance measurements from satellites. Solar soft X‐ray measurements from both the Student Nitric Oxide Explorer (SNOE) (1998–2000) and Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) (2002–2004) satellites as well as extreme ultraviolet (EUV) measurements from the TIMED satellite are used. Soft X‐rays show similar or higher correlation with foF2 at short timescales (27 days or less) than EUV does, although the EUV correlation is higher for longer periods. For the short‐term variations, both SNOE and TIMED observations have a higher correlation in the morning (∼0.46) than in the afternoon (∼0.1). In the afternoon, SNOE observations have a higher correlation (∼0.2) with foF2 than the TIMED observations (∼0.1 correlation), which may be due to differences in the solar cycle. At morning times, foF2 has a ∼27‐day variation, consistent with the solar rotation rate. After noon, but not in the morning, a ∼13.5‐day variation consistently appears in foF2. This ∼13.5‐day variation is attributed to geomagnetic influences.