Browsing by Author "Hysell, D.L."
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Item Open Access Estimation of spectral parameters from oblique Equatorial Electrojet echoes using a double skewed Gaussian model at JRO(2023 CEDAR Workshop, 2023) Flores, Roberto; Milla, M.; Kuyeng, Karim; Hysell, D.L.; Chau, J.L.Coherent echoes from the equatorial electrojet (EEJ) region are detected at the Jicamarca Radio Observatory (JRO) by using an array of 16 Yagi antennas with a main beam pointed obliquely to the west with an elevation of about 35 deg. The spectrum of these observations are composed of two types of EEJ echoes (Type I and Type II)[1] from which we can estimate their main spectral parameters such as Doppler shift and spectral width independently for each type. Previously, the method applied to obtain these parameters was a standard fitting approach based on a double Gaussian model. However, in some cases, the shape of the spectral measurements are not symmetric (resembling the shape of a skewed distribution). Based on simulations, we determined that the skewed shape of the oblique EEJ spectrum comes from the fact that the measured spectrum is the result of the sum of spectral contributions coming from different heights, with different Doppler shifts and spectral widths weighted by the antenna beam shape. The overall result is an asymmetric spectrum with a peak that does not coincide with the average Doppler shift. Thus in order to account for this effect, we have implemented a double skewed Gaussian distribution model to fit the oblique EEJ measurements and estimate their spectral parameters. In this work, we present the results obtained in the simulation showing the skewed shape of the spectrum. Based on our simulations, we have also proved that the shift of the skewed Gaussian model can be interpreted as the Doppler shift of the echoes. In addition, some examples of the new fitting procedure are shown in comparison with the classical Gaussian fitting where it can be seen the better agreement between the data and the double skewed Gaussian model.Item Open Access Full profile incoherent scatter analysis at Jicamarca(European Geosciences Union (EGU), 2008-02-04) Hysell, D.L.; Rodrígues, F.S.; Chau Chong Shing, Jorge Luis; Huba, J.D.Incoherent scatter data from a hybrid longpulse/double-pulse experiment at Jicamarca are analyzed using a full-profile analysis similar to the one implemented by Holt et al. (1992). In this case, plasma density, electron and ion temperatures, and light ion composition profiles in the topside are estimated simultaneously. Full-profile analysis is crucial at Jicamarca, since the long correlation time of the incoherent scatter signal at 50 MHz invalidates conventional gated analysis. Results for a 24 h interval in April of 2006 are presented, covering altitudes through 1600 km with 10 min time resolution, and compared with results from the NRL ionospheric model SAMI2. The analysis provides the first comprehensive assessment of ionospheric conditions over Jicamarca at sunrise as well as the first 24-h record of helium ion layers. Possible refinements to the experiment and the algorithm are discussed.Item Open Access Imaging coherent backscatter radar observations of topside equatorial spread F(American Geophysical Union, 1997-11) Hysell, D.L.; Woodman Pollitt, Ronald FranciscoMultiple baseline interferometric imaging of a large-scale topside spread F depletion has been performed at the Jicamarca Radio Observatory near Lima, Perú. A new imaging technique makes it possible to examine the detailed structure of the scatter from field-aligned irregularities in and around the depletion. A new antenna at Jicamarca, physically separated from the main antenna array, provided very long interferometry baselines up to -94 A long for the observations. High-resolution images of coherent backscatter from title radar plume were computed írom tite interferometry data using tite maximum entropy metltod. These images show that scattering regions with small Doppler velocities lay mainly along the boundary of the depleted region. Meanwhile, regions with high Doppler velocities were located within the depletion itselí and could be seen convecting upward through the depleted channel.Item Open Access Inferring Zonal Wind Profiles in the Equatorial Electrojet From Coherent Scatter(URSI, 2022-10-16) Hysell, D.L.; Chau, J.L.; Conte, J.F.; Flores, Roberto; Milla, M.A.Zonal wind estimates in the equatorial electrojet derived from coherent scatter echoes, specular meteor trail echoes, and optical limb scans are compared. While the three techniques exhibit broad overall agreement, significant differences in the results of the three techniques appear. The differences can be attributed in large part to horizontal inhomogeneity in the winds and the dissimilar averaging kernels of the three techniques.Item Restricted Jicamarca incoherent and coherent scatter radar capabilities for equatorial aeronomy(European Geosciences Union, 2005) Chau Chong Shing, Jorge Luis; Hysell, D.L."The International Symposium on Equatorial Aeronomy is held approximately every three to four years and is typically a major gathering of scientists from around the world interested in the low-latitude atmosphere and ionosphere, as well as coupling with other latitudinal and altitudinal regions. Each ISEA represents an opportunity for researchers to share their most recent results as well as discuss possibilities for future campaigns and experiments. Over 130 scientists attended ISEA-11 from 15 countries, participating in eight different scientific sessions. The sessions were: (1) K. C. Yeh memorial session: F-region irregularities and scintillations, radio occultation and tomographic imaging; (2) Upper atmospheric responses to seismic and volcanic activities; (3) Equatorial and low-latitude studies: ionospheric and thermospheric dynamics; (4) Numerical simulation, modeling and data assimilation; (5) Magnetic storm effects and space weather features at low latitudes; (6) E-region plasma irregularities and instabilities; (7) Equatorial and low-latitude studies: middle atmosphere dynamics and coupling processes; (8) Experimental techniques and recent low-latitude campaigns."Item Open Access Julia radar studies of electric fields in the equatorial electrojet(American Geophysical Union, 1997-07) Hysell, D.L.; Larsen, M.F.; Woodman Pollitt, Ronald FranciscoFirst results from the JULIA radar at Jicamarca are presented. These include coherent scatter observations of the equatorial electrojet and of 150-km echoes. Interferometry is used to measure the zonal drift rate of kilometer scale waves in the electrojet as functions of altitude. A technique for estimating the background zonal electric field from the interferometry data is described. The electric field estimates can be calibrated against the Doppler speed of the 150-km echoes when the latter are present. The kilometer-scale wave drifts sometimes exhibit large-amplitude, periodic height variations with vertical wavelengths of about 10 km. These signatures are reminiscent of the wind profiles measured with chemical release techniques in the lower thermosphere during the Guará campaign.Item Open Access Measuring the equatorial spread F irregularity k-space spectrum with the Jicamarca radar: preliminary results(Instituto Geofísico del Perú, 2008) Chau Chong Shing, Jorge Luis; Hysell, D.L.Diapositivas presentadas en URSI General Assembly, August 7-16, 2008, Chicago, Illinois, USA.Item Open Access Zonal wind velocity profiles in the equatorial electrojet derived from phase velocities of type II radar echoes(American Geophysical Union, 2005-12) Shume, E.B.; Hysell, D.L.; Chau Chong Shing, Jorge LuisZonal wind profiles in the daytime equatorial electrojet are inferred from the Doppler shifts of type II radar echoes observed at the Jicamarca Radio Observatory (JRO) in Perú. The inference is based on a three-dimensional electrostatic potential model. The model includes anomalous effects and is constrained by radar and magnetometer data. The amplitude and phase of the calculated zonal wind profiles are in general agreement with representative wind profiles measured by the WINDII instrument on board the Upper Atmosphere Research Satellite (UARS). The calculated winds also have the same general characteristics as zonal wind profiles measured by rocket-borne chemical release experiments. However, the magnitude of the latter are larger than the former. The temporal behavior of the calculated zonal winds suggests a downward phase progression with a roughly semidiurnal period.