Jicamarca Radio Observatory Research Articles

On the Magnitude and Variability of Height Gradients in the Equatorial F Region Vertical Plasma Drifts

AbstractPrevious radar studies have shown that magnitude of the vertical component of equatorial ionospheric E×B plasma drifts can vary significantly with height, even within main F region altitudes. These studies, however, were limited to few observation days. In order to properly quantify the height variation of equatorial F region vertical drifts, we examined 559 days of measurements made by the incoherent scatter radar of the Jicamarca Radio Observatory between the years of 1986 and 2017. From the observed profiles of vertical plasma drifts, we determined the mean behavior and variability of the height gradients as a function of local time and two distinct solar flux conditions (mean F10.7 around 80 and 150 SFU). Only observations made under geomagnetically quiet conditions were considered. Our results quantify the enhanced negative height gradients of vertical drifts near sunset that have been reported in the past. More importantly, we also identify and explain an enhancement in positive gradients near sunrise. We discuss the variability of the height gradients in vertical ionospheric E×B drifts at main equatorial F region heights, and the impact of this variability for satellite observations and studies of ionospheric stability and equatorial spread F.

Equatorial Disturbance Dynamo Vertical Plasma Drifts Over Jicamarca: Bimonthly and Solar Cycle Dependence

AbstractWe use extensive incoherent scatter radar observations from the Jicamarca Radio Observatory to study the local time and bimonthly dependence of the equatorial disturbance dynamo vertical plasma drifts on solar flux and geomagnetic activity. We show that the daytime disturbance drifts have generally small magnitudes with largest values before noon and an apparent annual variation. Near dusk, they are downward throughout the year with largest values during the equinoxes and smallest during June solstice. These downward drifts increase strongly with solar flux and shift to later local times. They also increase with increasing geomagnetically active conditions with no apparent local time shift. The equinoctial evening downward disturbance drifts are larger during the autumnal equinox than during the vernal equinox. The nighttime disturbance drifts are upward and have small seasonal and solar cycle dependence but increase strongly with geomagnetic activity, particularly in the late night sector. Our results are in general agreement with those from previous theoretical and experimental studies, except near dusk where our results show much stronger seasonal and solar cycle dependence.

Radar Studies of Height‐Dependent Equatorial F region Vertical and Zonal Plasma Drifts

AbstractWe 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.

On the Genesis of Postmidnight Equatorial Spread F: Results for the American/Peruvian Sector

AbstractPrevious studies of the Earth's low‐latitude ionosphere using in situ measurements made by sensors on the Communication/Navigation Outage Forecasting System (C/NOFS) satellite showed an unexpected predominance of equatorial spread F (ESF) events in the postmidnight sector during June and December solstice months of the 2008–2009 deep solar minimum. It has been suggested that these events might have been driven by the unusual behavior of the equatorial plasma drifts, which showed an abnormal upward peak around midnight during the same period. We use coherent backscatter radar (Jicamarca Unattended Long‐term Investigations of the Ionosphere and Atmosphere ‐ JULIA) measurements made at the Jicamarca Radio Observatory (11.95°S, 76.87°W, ∼1∘ dip lat) in Peru to better understand the origin of the ESF irregularities observed by C/NOFS. The radar observations show that ESF events during December solstice start in the postsunset sector. These ESF events and the conditions for their development are shown to continue through midnight hours. The predominance of postmidnight irregularities on C/NOFS observations during December solstice is caused by the slow vertical development of the ESF structures, which only reach the topside near midnight in most cases. On June solstice, however, JULIA observations show that ESF started predominately in the midnight to postmidnight sector. Collocated digisonde observations provide additional insight on F‐region conditions leading to these ESF events.

Coherent MIMO to Improve Aperture Synthesis Radar Imaging of Field-Aligned Irregularities: First Results at Jicamarca

Multiple-input multiple-output (MIMO) radar techniques make use of multiple transmitters and multiple receivers to improve the spatial characterization of targets. In the case where the Bragg scattering $\vec {k}$ -vector can be assumed to be the same for all transmit–receive paths, MIMO methods can be seen as a way of increasing the number of effective receivers. In the last decades, there has been scientific interest in determining the spatial characteristics of ionospheric and atmospheric irregularities on the subtransmit beam scale, allowing the study of processes in their intrinsic scales, otherwise inaccessible using simple beamforming techniques. Interferometric methods, including aperture synthesis imaging, were used in the past with a single transmitter and multiple receivers [single-input multiple-output (SIMO)]. In this paper, we present the first implementation of MIMO techniques to improve the spatial resolution of aperture synthesis radar imaging of daytime equatorial electrojet irregularities observed using the Jicamarca Radio Observatory (JRO). Our implementation uses two spatially separated transmitters and four spatially separated receivers. In order to separate the contributions of each transmitter, time, code, and polarization diversity experiments have been tested. We find that all three diversity approaches can be used for ionospheric irregularities, but time and polarization diversity are not applicable in all situations due to the range and Doppler width of the echoes, and due to magnetoionic radio propagation effects. The results are evaluated by comparing new MIMO imaging results against the currently used SIMO imaging technique. We present and discuss the theoretical and practical aspects of the MIMO approach, so they can be applied to study other targets not only at JRO but also at other modular coherent scatter radars.

Simultaneous 6300 Å airglow and radar observations of ionospheric irregularities and dynamics at the geomagnetic equator

Abstract. In March 2014 an all-sky imager (ASI) was installed at the Jicamarca Radio Observatory (11.95∘ S, 76.87∘ W; 0.3∘ S MLAT). We present results of equatorial spread F (ESF) characteristics observed at Jicamarca and at low latitudes. Optical 6300 and 7774 Å airglow observations from the Jicamarca ASI are compared with other collocated instruments and with ASIs at El Leoncito, Argentina (31.8∘ S, 69.3∘ W; 19.8∘ S MLAT), and Villa de Leyva, Colombia (5.6∘ N, 73.52∘ W; 16.4∘ N MLAT). We use Jicamarca radar data, in incoherent and coherent modes, to obtain plasma parameters and detect echoes from irregularities. We find that ESF depletions tend to appear in groups with a group-to-group separation around 400–500 km and within-group separation around 50–100 km. We combine data from the three ASIs to investigate the conditions at Jicamarca that could lead to the development of high-altitude, or topside, plumes. We compare zonal winds, obtained from a Fabry–Pérot interferometer, with plasma drifts inferred from the zonal motion of plasma depletions. In addition to the ESF studies we also investigate the midnight temperature maximum and its effects at higher latitudes, visible as a brightness wave at El Leoncito. The ASI at Jicamarca along with collocated and low-latitude instruments provide a clear two-dimensional view of spatial and temporal evolution of ionospheric phenomena at equatorial and low latitudes that helps to explain the dynamics and evolution of equatorial ionospheric/thermospheric processes. Keywords. Ionosphere (equatorial ionosphere; ionospheric irregularities; plasma temperature and density)

Multi-instrumented observations of the equatorial F-region during June solstice: large-scale wave structures and spread-F

Typical equatorial spread-F events are often said to occur during post-sunset, equinox conditions in most longitude sectors. Recent studies, however, have found an unexpected high occurrence of ionospheric F-region irregularities during June solstice, when conditions are believed to be unfavorable for the development of plasma instabilities responsible for equatorial spread-F (ESF). This study reports new results of a multi-instrumented investigation with the objective to better specify the occurrence of these atypical June solstice ESF in the American sector and better understand the conditions prior to their development. We present the first observations of June solstice ESF events over the Jicamarca Radio Observatory (11.95° S, 76.87° W, ∼ 1° dip latitude) made by a 14-panel version of the Advanced Modular Incoherent Scatter Radar system (AMISR-14). The observations were made between July 11 and August 4, 2016, under low solar flux conditions and in conjunction with dual-frequency GPS, airglow, and digisonde measurements. We found echoes occurring in the pre-, post-, and both pre- and post-midnight sectors. While at least some of these June solstice ESF events could have been attributed to disturbed electric fields, a few events also occurred during geomagnetically quiet conditions. The late appearance (22:00 LT or later) of three of the observed events, during clear-sky nights, provided a unique opportunity to investigate the equatorial bottomside F-region conditions, prior to ESF, using nighttime airglow measurements. We found that the airglow measurements (630 nm) made by a collocated all-sky camera show the occurrence of ionospheric bottomside F-region perturbations prior to the detection of ESF echoes in all three nights. The airglow fluctuations appear as early as 1 hour prior to radar echoes, grow in amplitude, and then coincide with ESF structures observed by AMISR-14 and GPS TEC measurements. They also show some of the features of the so-called large-scale wave structures (LSWS) that have been detected, previously, using other types of observations and have been suggested to be precursors of ESF. The bottomside fluctuations have zonal spacings between 300 and 500 km, are aligned with the magnetic meridian, and extend at least a few degrees in magnetic latitude.

June Solstice Equatorial Spread F in the American Sector: A Numerical Assessment of Linear Stability Aided by Incoherent Scatter Radar Measurements

AbstractPrevious studies have suggested that weakening downward plasma drifts can produce favorable conditions for the ionospheric Generalized Rayleigh‐Taylor (GRT) instability and explain the occurrence of postmidnight equatorial spread F (ESF). We evaluated this hypothesis using numerical simulations aided by measurements and attempted to explain ESF events observed in the American sector during June solstice, low solar flux conditions. We analyzed plasma drifts and ESF measurements made by the incoherent scatter radar of the Jicamarca Radio Observatory (11.95° S, 76.87° W, ∼1° dip). We found adequate measurements during a prototypical, quiet time event on 4–5 June 2008 when the downward drifts weakened and a fully developed ESF appeared. The measured drifts were used as input for the SAMI2 model. SAMI2 reproduced an “apparent” uplift of the ionosphere based on h F measurements that was consistent with expectations and observations. SAMI2 also provided parameters for estimation of the flux tube linear growth rates of GRT instability associated with the weakening drift event. We found that the weakening drifts did produce unstable conditions with positive growth rates. The growth rates, however, were slower than those obtained for typical, premidnight ESF events and those obtained for similar drift conditions in other longitude sectors. We show, however, that departures in the wind pattern, from climatological model predictions, can produce favorable conditions for instability development. Following the hypothesis of Huba and Krall (2013) and using SAMI2 simulations, we show that equatorward winds, when combined with weakening drifts, could have contributed to the unstable conditions responsible for the postmidnight ESF events.

Range-Doppler Mapping of Space-Based Targets Using the JRO 50 MHz Radar

The Jicamarca Radio Observatory (JRO) two-dimensional square array radar system operating at ~ 6-m wavelength was used to study the Moon and low Earth orbit satellites using the Range-Doppler inverse synthetic aperture radar technique also known as Delay-Doppler imaging. The radar data was collected on Oct 21, 2015. A circularly polarized coded pulse was transmitted from a quarter-array antenna segment during lunar transit over JRO. Dual-linear polarization receive systems were employed on two quarter-array segments and on two 1/64th array modules giving the longest possible baselines across the transit path. A Range-Doppler mapping technique that uses the rotational motion of the targets and an autofocusing motion and ionospheric delay compensation technique has been implemented to generate the two-dimensional maps of the point-target (Satellite) and range-spread target (Moon). A review of our technique and the maps obtained from these observations is presented herein. Range-Doppler maps of the Moon and satellites are instructive with regards to possible further improvement of the technique, especially regarding ionospheric compensation.

Gravity Wave‐Induced Ionospheric Irregularities in the Postsunset Equatorial Valley Region

AbstractPlasma irregularities in the postsunset equatorial valley region ionosphere are investigated experimentally and through numerical simulation. Coherent radar backscatter observed at the Jicamarca Radio Observatory shows two classes of irregularities in different altitude bands—one mainly below about 125 km and the other mainly above. Irregularities in both bands are organized into wavefronts with wavelengths of a few kilometers. However, only the irregularities in the high‐altitude band exhibit consistent propagation speeds and directions. Some previous observations of irregularities in the nighttime electrojet suggest that gravity waves may sometimes influence their morphology. The possibility that the valley region irregularities are also related to gravity waves (GWs) is therefore investigated numerically. A model of a GW packet propagating through a tidal wind field is used to drive another model which predicts the resulting ionospheric electrodynamics. The combined simulation shows that GWs can induce field‐aligned currents and excite resistive drift waves which could be responsible for the valley region irregularities in the high‐altitude band. The GWs also induce irregularities in the upper E region directly through simple dynamo action which subsequently deform under the influence of shear flow. This may explain the irregularities in the low‐altitude band.

Radar images of the Moon at 6-meter wavelength

We present new range-Doppler images of the Moon using 6-mwavelength. The radar images were obtained using the Jicamarca Radio Observatory 49.92 MHz radar. The observations were performed using circular polarization on transmit and two orthogonal linear polarizations on receive, allowing scattering images to be obtained with the polarization matched to the transmitted wave (polarized), and at a polarization orthogonal to the transmitted wave (depolarized). Due to the long wavelength that penetrates efficiently into the subsurface of the Moon, the radar images are especially useful for studies of subsurface composition. Two antenna interferometry on receive was used to remove the Doppler north-south ambiguity. The images have approximately 10 km resolution in range 20 km resolution in Doppler, allowing many large scale features, including maria, terrae, and impact craters to be identified. Strong depolarized return is observed from relatively new larger impact craters with large breccia and shallow regolith. Terrae regions with less lossy surface material also appear brighter in both depolarized and polarized images. A large region in the area near the Mare Orientale impact basin has overall higher than mean radar backscatter in both polarized and depolaried returns, indicating higher than average presence of relatively newly formed large breccia in this region. Mare regions are characterized by lower polarized and depolarized return, indicating that there is higher loss of the radio wave in the subsurface, reducing the echo. We also report unexpected low polarized and depolarized backscatter from an old impact basin in the Schiller–Schickard region, as well as from the region poleward from Mare Imbrium.

After Decades, High-Altitude Observations Revived at Jicamarca

Recent upgrades to the Jicamarca Radio Observatory in Peru allow it to probe electron densities several thousand kilometers above Earth, a feat it hasn't accomplished in 50 years.

High‐altitude incoherent‐scatter measurements at Jicamarca

AbstractIn an attempt to reproduce experimental results obtained in the early days of operations, electron density profiles have been measured at the Jicamarca Radio Observatory at altitudes reaching L=2. The methodology involves using a combination of pulses, including pulses as long as 4 ms, and processing the data with matched filtering. The modern experiments are complicated by systemic, time‐dependent bias in the noise estimators as well as by clutter from satellites and space debris, including a geosynchronous satellite. Ultimately, experiment performance comparable to what was achieved in the original experiments could be achieved and should be surpassed in future experiments when all four of the Jicamarca transmitters will be utilized.

Unusual Change in Critical Frequency of F<sub>2</sub> Layer during and Prior to Earthquakes

The unusualness in the critical frequency of different layers of earth’s ionosphere is commensurate to be associated with seismic events. We present study of critical frequency of F2 layer (denoted as f0F2) during some major earthquakes in South American region. We use the semi-empirical Barbier’s theorem of air-glow and define a parameter using the critical frequency and virtual height of F2 layer and named it as “F Parameter”. To investigate the variation of this parameter, we consider five large earthquakes in the junction of Nazca plate and South American plate having magnitude greater than M > 6.5 and study the temporal variation of F parameter during these earthquakes. The F Parameter is measured using the ionograms as recorded from the Ionosonde in Jicamarca Radio Observatory (lat. 11.95°S, long 76.87°W) in Chile which lies within the earthquake preparation zones of these five earthquakes. We examine the F Parameter within a span of ±15 days during earthquakes and observed significant change in the evaluated F Parameter in 12 to 3 days prior to the earthquakes. The increment is over +3σ from the normal variation. We also observe significant changes during aftershock events. The solar geomagnetic indices were found to be low which ensures that these anomalies in F Parameter are due to seismic events.

Equatorial E region electric fields at the dip equator: 2. Seasonal variabilities and effects over Brazil due to the secular variation of the magnetic equator

AbstractIn this work, the seasonal dependency of the E region electric field (EEF) at the dip equator is examined. The eastward zonal (Ey) and the daytime vertical (Ez) electric fields are responsible for the overall phenomenology of the equatorial and low‐latitude ionosphere, including the equatorial electrojet (EEJ) and its plasma instability. The electric field components are studied based on long‐term backscatter radars soundings (348 days for both systems) collected during geomagnetic quiet days (Kp ≤ 3+), from 2001 to 2010, at the São Luís Space Observatory (SLZ), Brazil (2.33°S, 44.20°W), and at the Jicamarca Radio Observatory (JRO), Peru (11.95°S, 76.87°W). Among the results, we observe, for the first time, a seasonal difference between the EEF in these two sectors in South America based on coherent radar measurements. The EEF is more intense in summer at SLZ, in equinox at JRO, and has been highly variable with season in the Brazilian sector compared to the Peruvian sector. In addition, the secular variation on the geomagnetic field and its effect on the EEJ over Brazil resulted that as much farther away is the magnetic equator from SLZ, later more the EEJ is observed (10 h LT) and sooner it ends (16 h LT). Moreover, the time interval of type II occurrence decreased significantly after the year 2004, which is a clear indication that SLZ is no longer an equatorial station due to the secular variation of the geomagnetic field.

Simultaneous observations of structure function parameter of refractive index using a high-resolution radar and the DataHawk small airborne measurement system

Abstract. The SOUSY (SOUnding SYstem) radar was relocated to the Jicamarca Radio Observatory (JRO) near Lima, Peru, in 2000, where the radar controller and acquisition system were upgraded with state-of-the-art parts to take full advantage of its potential for high-resolution atmospheric sounding. Due to its broad bandwidth (4 MHz), it is able to characterize clear-air backscattering with high range resolution (37.5 m). A campaign conducted at JRO in July 2014 aimed to characterize the lower troposphere with a high temporal resolution (8.1 Hz) using the DataHawk (DH) small unmanned aircraft system, which provides in situ atmospheric measurements at scales as small as 1 m in the lower troposphere and can be GPS-guided to obtain measurements within the beam of the radar. This was a unique opportunity to make coincident observations by both systems and to directly compare their in situ and remotely sensed parameters. Because SOUSY only points vertically, it is only possible to retrieve vertical radar profiles caused by changes in the refractive index within the resolution volume. Turbulent variations due to scattering are described by the structure function parameter of refractive index Cn2. Profiles of Cn2 from the DH are obtained by combining pressure, temperature, and relative humidity measurements along the helical trajectory and integrated at the same scale as the radar range resolution. Excellent agreement is observed between the Cn2 estimates obtained from the DH and SOUSY in the overlapping measurement regime from 1200 m up to 4200 m above sea level, and this correspondence provides the first accurate calibration of the SOUSY radar for measuring Cn2.

Remote Sensing of Atmospheric and Ionospheric Signals Prior to the Mw 8.3 Illapel Earthquake, Chile 2015

In the present study, a number of atmospheric and some ionospheric anomalies are analyzed, which were recorded prior to the Mw 8.3 Illapel earthquake of September 16, 2015. This very large earthquake occurred in Central Chile, close to the coast, as the result of thrust faulting on the interface between the Nazca Plate and South American continent. Using remotely sensed data extracted from NASA/Giovanni, NOAA/NCEP, and NOAA/NGDC, atmospheric and ionospheric anomalies were observed that co-registered 35–40 and 25–30 days prior to the main shock, respectively. With reference to long-term time series over the epicentral area, significant atmospheric anomalies were recorded for cloud cover, geopotential height, precipitation rates, surface air pressure, omega, stream function, and wind vectors—all in the time window of August 5–10, 2015, 35–40 days prior to the main shock. Anomalous TEC maps were recorded for the same time period. Satellite images indicate the formation of an unusual cyclone, presumably triggered by air turbulences and abnormal atmospheric conditions over the epicentral area, including strong vertical winds. Data from the Jicamarca radio observatory in Peru, more than 2000 km to the North, reveal anomalous ionospheric variations on August 15–20, 2015 with respect to international reference ionosphere thickness parameters and the altitude of the F layer. The observed anomalies are consistent with processes that occur at the ground-to-air interface due to the stress activation of peroxy defects in the hypocentral volume. The flow of positive hole charge carriers to the Earth surface expected to have led to massive air ionization, generating at first primarily positive airborne ions, then negative air ions plus ozone. Understanding the sequence of processes inside the Earth’s crust and at the ground-to-air interface provides information not previously available about the causal and temporal linkages between the various pre-earthquake phenomena and the future seismic event.

High-resolution radar observations of meteoroid fragmentation and flaring at the Jicamarca Radio Observatory

High-resolution radar observations of meteoroid fragmentation and flaring at the Jicamarca Radio Observatory

Generation of a severe convective ionospheric storm under stable Rayleigh–Taylor conditions: triggering by meteors?

Abstract. Here we report on four events detected using the Jicamarca Radio Observatory (JRO) over an 18-year period, in which huge convective ionospheric storms (CISs) occur in a stable ionosphere. We argue that these rare events could be initiated by meteor-induced electric fields. The meteor-induced electric fields map to the bottomside of the F region, causing radar echoes and a localized CIS. If and when a localized disturbance reaches 500 km, we argue that it becomes two-dimensionally turbulent and cascades structure to both large and small scales. This leads to long-lasting structure and, almost certainly, to scintillations over a huge range of latitudes some ±15° wide and to 3 m irregularities, which backscatter the VHF radar waves. These structures located at high altitudes are supported by vortices shed by the upwelling bubble in a vortex street.

Concurrent observations at the magnetic equator of small‐scale irregularities and large‐scale depletions associated with equatorial spread F

AbstractIn 2014 an all‐sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR‐14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large‐scale equatorial spread F irregularities (10–500 km), while AMISR‐14 detects small‐scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 50–200 km scale sizes using the all‐sky imager, at 3 m scale sizes using the JULIA (Jicamarca Unattended Long‐term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR‐14 radar. We compare data from the three instruments on the night of 20–21 August 2014 by locating the radar scattering volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR‐14 had five beams perpendicular to the magnetic field covering ~200 km in the east‐west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at submeter scales by the lower hybrid drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR‐14 and ASI comparison.