Browsing by Author "Rodrigues, F. S."
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Item Open Access AMISR-14: Observations of equatorial spread F(American Geophysical Union, 2015-06-11) Rodrigues, F. S.; Nicolls, M. J.; Milla, Marco; Smith, J. M.; Varney, R. H.; Strømme, A.; Martinis, C.; Arratia, J. F.A new, 14-panel Advanced Modular Incoherent Scatter Radar (AMISR-14) system was recently deployed at the Jicamarca Radio Observatory. We present results of the first coherent backscatter radar observations of equatorial spread F (ESF) irregularities made with the system. Colocation with the 50 MHz Jicamarca Unattended Long-term studies of the Ionosphere and Atmosphere (JULIA) radar allowed unique simultaneous observations of meter and submeter irregularities. Observations from both systems produced similar Range-Time-Intensity maps during bottom-type and bottomside ESF events. We were also able to use the electronic beam steering capability of AMISR-14 to “image” scattering structures in the magnetic equatorial plane and track their appearance, evolution, and decay with a much larger field of view than previously possible at Jicamarca. The results suggest zonal variations in the instability conditions leading to irregularities and demonstrate the dynamic behavior of F region scattering structures as they evolve and drift across the radar beams.Item Restricted Climatology of Equatorial F-Region UHF Coherent Backscatter Radar Echoes and Comparison with Collocated VHF Radar Observations(IEEE, Institute of Electrical and Electronics Engineers, 2024) Massoud, A. A.; Rodrigues, F. S.; Sousasantos, J.; Milla, M. A.; Scipión, Danny; Apaza, J. M.; Kuyeng, Karim; Padin, C.Equatorial ionospheric irregularities at meter scale sizes have been well-studied using Very High Frequency (VHF) radar systems at the Jicamarca Radio Observatory (JRO). For example, the Jicamarca Unattended Long-Term Studies of the Ionosphere and Atmosphere (JULIA) is a 50 MHz coherent scatter radar system and has operated routinely since 1996. Radio waves transmitted by JULIA reflect off of field-aligned irregularities with scale sizes of ~3-meters due to Bragg scattering. Recently, the deployment and later repair of an Ultra High Frequency (UHF) radar system at the JRO provided an opportunity for coherent backscatter radar studies of irregularities with sub-meter scale sizes. The 14-panel version of the Advanced Modular Incoherent Scatter Radar (AMISR-14) system makes measurements at 445 MHz, corresponding to measurements of previously unobserved ~34-centimeters equatorial irregularities.Item Open Access Coherent and incoherent scatter radar study of the climatology and day-to-day variability of mean F-region vertical drifts and equatorial spread F(American Geophysical Union, 2016-02) Smith, J. M.; Rodrigues, F. S.; Fejer, B. G.; Milla, MarcoWe conducted a comprehensive analysis of the vertical drifts and equatorial spread F (ESF) measurements made by the Jicamarca incoherent scatter radar (ISR) between 1994 and 2013. The ISR measurements allowed us to construct not only updated climatological curves of quiet-time vertical plasma drifts but also time-versus-height maps of ESF occurrence over the past two solar cycles. These curves and maps allowed us to better relate the observed ESF occurrence patterns to features in the vertical drift curves than previously possible. We identified an excessively high occurrence of post-midnight F region irregularities during December solstice and low solar flux conditions. More importantly, we also found a high occurrence of ESF events during sudden stratospheric warming (SSW) events. We also proposed and evaluated metrics of evening enhancement of the vertical drifts and ESF occurrence, which allowed us to quantify the relationship between evening drifts and ESF development. Based on a day-to-day analysis of these metrics, we offer estimates of the minimum pre-reversal enhancement (PRE) peak (and mean PRE) values observed prior to ESF development for different solar flux and seasonal conditions. We also found that ESF irregularities can reach the altitudes at least as high as 800 km at the magnetic equator even during low solar flux conditions.Item Open Access Daytime ionospheric equatorial vertical drifts during the 2008–2009 extreme solar minimum(American Geophysical Union, 2015-01-13) Rodrigues, F. S.; Smith, J. M.; Milla, Marco; Stoneback, R. A.One of the most interesting observations made by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite mission was the detection of average equatorial ionospheric vertical drifts that largely differed from model predictions. C/NOFS measurements showed, in particular, downward drifts in the afternoon sector, and upward drifts around local midnight hours during the 2008 and 2009 extreme solar minimum. The unexpected behavior of the drifts has important implications for ionospheric modeling and suggests the necessity for a better understanding of the low‐latitude electrodynamics. We used ground‐based radar measurements to quantify the seasonal and solar flux variability of daytime equatorial drifts at lower altitudes (∼150 km) than those probed by C/NOFS (above ∼400 km). We found that average vertical drifts at 150 km altitude are in good agreement with model predictions of F region drifts and did not show the signatures of an enhanced semidiurnal pattern, as seen by C/NOFS. Comparison of the 150 km echo drifts with model predictions also shows that the increase (decrease) with height of the vertical drifts in the morning (afternoon) hours is a regular feature of the equatorial ionosphere. It occurred in all seasons and solar flux conditions between 2001 and 2011.Item Open Access Equatorial 150 km echoes and daytime F-region vertical plasma drifts in the Brazilian longitude sector(European Geosciences Union, 2013-10-31) Rodrigues, F. S.; Shume, E. B.; De Paula, E. R.; Milla, MarcoPrevious studies showed that conventional coherent backscatter radar measurements of the Doppler velocity of the so-called 150 km echoes can provide an alternative way of estimating ionospheric vertical plasma drifts during daytime hours (Kudeki and Fawcett, 1993; Chau and Woodman, 2004). Using observations made by a small, lowpower 30 MHz coherent backscatter radar located in the equatorial site of São Luís (2.59◦ S, 44.21◦ W; −2.35◦ dip lat), we were able to detect and monitor the occurrence of 150 km echoes in the Brazilian sector. Using these measurements we estimated the local time variation of daytime vertical ionospheric drifts in the eastern American sector. Here, we present a few interesting cases of 150 km-echoes observations made by the São Luís radar and estimates of the diurnal variation of vertical drifts. These cases exemplify the variability of the vertical drifts in the Brazilian sector. Using same-day 150 km-echoes measurements made at the Jicamarca Radio Observatory in Peru, we also demonstrate the variability of the equatorial vertical drifts across the American sector. In addition to first estimates of the absolute vertical plasma drifts in the eastern American (Brazilian) sector, we also present observations of abnormal drifts detected by the São Luís radar associated with the 2009 major sudden stratospheric warming event.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 Estimating E region density profiles from radio occultation measurements assisted by IDA4D(American Geophysical Union, 2009-10-23) Nicolls, M. J.; Rodrigues, F. S.; Bust, G. S.; Chau Chong Shing, Jorge LuisThe Gordeyev integral for plasma particles colliding with neutrals is obtained using a particle dynamics formalism in which the collisions are modeled as a discrete Poisson process. The result leads to an electron density fluctuation spectrum model for partially ionized plasmas which is identical with the spectral model obtained from BGK plasma kinetic equations. This isomorphism between the Poisson process and the BGK operator is analogous to a similar relation between the Brownian motion process and the Fokker-Planck operator with constant coefficients. We take advantage of this analogy to derive a collisional ISR spectrum model that takes into account collisions with both neutrals and charged species.Item Open Access Full profile incoherent scatter analysis at Jicamarca(Instituto Geofísico del Perú, 2008) Hysell, D. L.; Rodrigues, F. S.; Chau Chong Shing, Jorge Luis; Huba, J. D.Diapositivas presentadas en URSI General Assembly, August 7-16, 2008, Chicago, Illinois, USA.Item Restricted Improved electron density measurements at Jicamarca(American Geophysical Union, 2007-11-27) Rodrigues, F. S.; Nicolls, M. J.; Hysel, D. L.Taking into account the effects of electron Coulomb collisions, incoherent scatter (IS) radar cross sections for probing angles close to perpendicular to the magnetic field have been calculated and used to correct backscattered power profiles measured with the Jicamarca incoherent scatter radar so that they accurately represent the height variation of the ionospheric electron density. The corrected power profiles are compared with simultaneous Faraday rotation measurements of electron density. The profiles agree within the measurements uncertainties. This result improves electron density measurements at Jicamarca, since power measurements are less sensitive to clutter and interference than Faraday rotation measurements. The results can be used to correct Jicamarca long‐term IS power measurements.Item Open Access Ion gyroresonance observations at Jicamarca revisited(American Geophysical Union, 2007-07-12) Rodrigues, F. S.; Nicolls, M. J.; Woodman Pollitt, Ronald Francisco; Hysell, D. L.; Chau Chong Shing, Jorge Luis; Gonzáles, S. A.This paper presents recent observations of the proton gyroresonance over Jicamarca. In October 2006, a single-polarization double-pulse experiment was set up to measure the first gyroresonance peak in the incoherent scatter (IS) auto-correlation function (ACF). Despite the clutter caused by Spread-F and artificial satellites, it was possible to measure the first proton gyroresonance peak of the ACF in the topside ionosphere. For the first time, least-squares fits of theoretical IS ACFs to gyroresonance measurements are reported. Theoretical ACFs that best fit the measurements were found using the H+ fraction and temperature (assuming Te = Ti) as fitting parameters. Uncertainties for the estimated fraction of H+ were as low as 12%, while uncertainties for estimated temperatures were around 30%. These are the first successful gyroresonance measurements since the early observations of Farley (1967), and it is the first time measurements of this type have been used to obtain least squares estimates of ion composition and temperatures.Item Open Access On the characteristics of 150-km echoes observed in the Brazilian longitude sector by the 30 MHz São Luís radar(European Geosciences Union (EGU), 2011-10-28) Rodrigues, F. S.; De Paula, E. R.; Chau Chong Shing, Jorge LuisWe present long-overdue details about the intensity and spectral characteristics of 150-km echoes observed by the Sao Lu ıs radar in Brazil. The Sao Lu ıs observations show that the echoes usually come from multiple scattering layers that descend in altitude before local noon, and ascend during afternoon hours, similar to what has been found in observations made in other longitude sectors. The layers are usually 3–5 km thick and located, mostly, between 130 and 170 km altitude. The measurements also show variations in echo intensity that are similar to observations made at other equatorial and off-equatorial sites. Analysis of observations made during 2008 shows significant (>37 %) monthly occurrence rates for every month. Reduced occurrence rates were observed around March Equinox. We associate this reduction in occurrence rate, however, to a non-geophysical factor. An increase in the daytime sky noise in the months around March Equinox causes a decrease in the signal-to-noise ratio (SNR) of the echoes, which makes them less distinguishable in our analysis. A higher occurrence of weaker echoes around March Equinox was confirmed by an statistical analysis of the seasonal variation of echo intensities. Strong, long-lasting and, therefore, more noticeable echoing layers, however, were observed between June and early September compared to other months in 2008. Spectral analyses show that most of the echoes have negative mean Doppler shifts indicating upward velocities. The echoes also have narrow spectral widths of only a few ms−1. Finally, we also found that the mean Doppler shift of the observed echoes can vary noticeably with altitude at times. Using spaced antenna measurements we show that this is caused by the wide field-ofview of the radar and the spatial distribution of the scatterers within the radar beam.Item Open Access Preliminary AMISR-14 radar observations of F-region incoherent backscatter echoes at the Jicamarca Radio Observatory (JRO)(2022 CEDAR Workshop, 2022-06) Apaza, Joab; Kuyeng, Karim; Flores, Roberto; Milla, M.; Rodrigues, F. S.; Scipión, DannyA 14-panel Advanced Modular Incoherent Scatter Radar (AMISR-14) was installed at the Jicamarca Radio Observatory (IGP- JRO) in 2014. Because of its size, this radar was mainly used to observe coherent echoes such as those produced by the Equatorial Electrojet (EEJ) and Equatorial Spread F (ESF). However, the radar operation was intermittent until 2019 when repairs started to make the radar fully operational. Now, AMISR-14 runs regularly in parallel with the main Jicamarca radar in the JULIA (Jicamarca Unattended Long-term studies of the Ionosphere and Atmosphere) mode to monitor the Equatorial Spread F activity. More recently, we found that running these experiments with a more stable peak power, we have been able to detect not only coherently scatter (CS) signals but also what seems to be incoherently scattered (IS) echoes from the F-region ionosphere. In this poster, we will present some examples of the experiments we have been conducting with AMISR-14. More specifically, we will present and discuss examples of these interesting ISR-like echoes observed with AMISR-14 pointing in different directions along the E-W plane.Item Restricted Radar studies of height-dependent equatorial F region vertical and zonal plasma drifts(American Geophysical Union, 2019-03) Shidler, S. A.; Rodrigues, F. S.; Fejer, B. G.; Milla, MarcoWe present the results of an analysis of long-term measurements of ionospheric F region E × B plasma drifts in the American/Peruvian sector. The analysis used observations made between 1986 and 2017 by the incoherent scatter radar of the Jicamarca Radio Observatory. Unlike previous studies, we analyzed both vertical and zonal components of the plasma drifts to derive the geomagnetically quiet time climatological variation of the drifts as a function of height and local time. We determine the average behavior of the height profiles of the drifts for different seasons and distinct solar flux conditions. Our results show good agreement with previous height-averaged climatological results of vertical and zonal plasma drifts, despite that they are obtained from different sets of measurements. More importantly, our results quantify average height variations in the drifts. The results show, for example, the solar flux control over the height variation of the vertical drifts. The results also show the weak dependence of the daytime zonal drift profiles on solar and seasonal variations. We quantify the effects of seasonal and solar flux variations on the morphology of the vertical shear in the zonal plasma drifts associated with the evening plasma vortex. Assuming interchangeability between local time and longitude, we tested the curl-free condition for the F region electric fields with very good results for all seasons and solar flux conditions.We envision the use of our results to aid numerical modeling of ionospheric electrodynamics and structuring and to assist with the interpretation of satellite observations of low-latitude plasma drifts.Item Open Access Topside equatorial ionospheric density, temperature, and composition under equinox, low solar-flux conditions(American Geophysical Union, 2015-12) Hysell, D. L.; Milla, Marco; Rodrigues, F. S.; Varney, R. H.; Huba, J. D.We present observations of the topside ionosphere made at the Jicamarca Radio Observatory in March and September 2013, made using a full-profile analysis approach. Recent updates to the methodology employed at Jicamarca are also described. Measurements of plasma number density, electron and ion temperatures, and hydrogen and helium ion fractions up to 1500 km altitude are presented for 3 days in March and September. The main features of the observations include a sawtooth-like diurnal variation in ht, the transition height where the O+ ion fraction falls to 50%, the appearance of weak He+ layers just below ht, and a dramatic increase in plasma temperature at dawn followed by a sharp temperature depression around local noon. These features are consistent from day to day and between March and September. Coupled Ion Neutral Dynamics Investigation data from the Communication Navigation Outage Forecast System satellite are used to help validate the March Jicamarca data. The SAMI2-PE model was able to recover many of the features of the topside observations, including the morphology of the plasma density profiles and the light-ion composition. The model, forced using convection speeds and meridional thermospheric winds based on climatological averages, did not reproduce the extreme temperature changes in the topside between sunrise and noon. Some possible causes of the discrepancies are discussed.