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We report the proposal and results of a low‐cost, easy‐to‐build GPS‐based sensor for detection and monitoring ionospheric irregularities through the detection of amplitude scintillation. The system is based on the Raspberry Pi single‐board computer combined with an Adafruit Ultimate GPS peripheral, which is capable of measuring (at 10‐Hz rate) the intensity of the L1 signals transmitted by GPS satellites. We introduce and discuss results of short‐ and long‐term observations obtained with a prototype of this system deployed in Presidente Prudente, a low magnetic latitude site in Brazil. The deployment and observations were carried out to test the ability of the system to detect ionospheric scintillations and, therefore, monitor the occurrence of ionospheric irregularities associated with equatorial spread F. Our results show that this low‐cost sensor is indeed capable of detecting scintillation events associated with equatorial spread F. Comparison with simultaneous, collocated measurements made by a commercial scintillation monitor are also presented. The joint observations allowed us to quantify the performance of the low‐cost monitor and to identify sources of potential limitations. While the sensor cannot (and it was not intended to) substitute commercial scintillation monitors, the low cost allows its use in studies of ionospheric irregularities (space weather) that require observations made by distributed arrays of small instruments (DASI). Furthermore, the simplicity of the sensor design stimulates its use in educational and citizen science initiatives.

We present results of an effort to evaluate the ability of an analytic model to describe the behavior of the equatorial zonal plasma drifts given inputs provided by readily available climatological models of thermospheric and ionospheric parameters. In a data-model fusion approach, we used vertical drift measurements to drive the model and zonal drift measurements to evaluate its output. Drift measurements were made by the Jicamarca incoherent scatter radar, and model results were evaluated for different seasons and two distinct solar flux conditions. We focused, in particular, on model results for different versions of the Horizontal Wind Model (HWM 97, 07, and 14). We found that, despite its simplicity, the analytic model can reproduce fairly well most of the features in the observed zonal plasma drifts, including the vertical shear associated with the evening plasma vortex. During daytime hours the model predicts similar results for the zonal drifts independently of the HWM used to drive the model. More importantly, the modeled daytime drifts match exceptionally well the behavior and magnitude of the observed drifts for all seasons and solar flux conditions considered. The nighttime results drive the overall performance of the analytic model, and we found that a single HWM cannot provide the best results for all seasons and solar flux conditions. We also examined the main sources of zonal drift variability. Most of the morphology is controlled by the zonal wind dynamo term of the analytic model, but with non-negligible contribution from the vertical drift term. Finally, we examined the contribution from the E- and F-region to the zonal wind dynamo. The morphology of the zonal drifts in the region of observation (240–560 km altitude) is controlled mostly by the F-region winds, but with significant contributions from the daytime E-region particularly during December solstice and low solar flux conditions.

Nighttime airglow images observed at the low-latitude site of Sao Joao do Cariri (7.4S, 36.5W) showed the presence of a medium-scale atmospheric gravity wave (AGW) associated with the...

We present the results of an effort to model quiet-time vertical plasma drifts in the low-latitude F-region ionosphere using the random forest machine learning technique. The model is capable of describing the climatological variation of the drifts as a function of universal time, day of the year, solar flux, and altitude (200–600 km). The model has been trained using measurements of the vertical plasma drifts made by the incoherent scatter radar of the Jicamarca Radio Observatory ($$11.95^\circ \hbox { S}$$ 11 . 95 ∘ S , $$76.87^\circ$$ 76 . 87 ∘ W, $$\sim 1^\circ$$ ∼ 1 ∘ dip lat). In our analysis, we compare our machine learning model results with the Scherliess and Fejer (J Geophys Res 104:6829–6842, 1999) model (SF99 model), a widely used empirical model of the vertical drifts developed using a different set of Jicamarca measurements. We find that the machine learning model is able to capture the overall features of the diurnal variation of the equatorial drifts for different seasonal and solar flux conditions. The model is also capable of capturing the mean height variation of the drifts, particularly the height gradient enhancements that have been observed near sunrise and sunset. Finally, the model can easily be expanded and improved as more drift measurements are made and become available for training.

We demonstrate scintillation analysis from a network of geodetic Global Positioning System (GPS) receivers which provide data at 1-second resolution. We introduce proxy phase (σ TBC ) and amplitude (SNR 4 ) scintillation indices and validate them against the rate of change of TEC index (ROTI) and S 4 . Additionally, we validate scintillation observations against a Connected Autonomous Space Environment Sensor scintillation receiver. We develop receiver-dependent scintillation event thresholding using hardware-dependent noise variance. We analyze 6 days adjacent to the 7–8 September 2017 geomagnetic storm, using 169 receivers covering magnetic latitudes between 15° and 65° in the American longitude sector. We leverage the available spatial sampling coverage to construct 2-D maps of scintillation and present episodic evolution of scintillation intensifications during the storm. We show that low-latitude and high-latitude scintillation morphology match well-established scintillation climatology patterns. At midlatitudes, spatiotemporal evolution of scintillation partially agrees with known scintillation patterns. Additionally, the results reveal previously undocumented midlatitude scintillation-producing structures. The results provide an unprecedented view into the spatiotemporal development of scintillation-producing plasma irregularities and provide a resource to further exploit scintillation evolution at large spatial scales.

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.

We present results of Capon's method for estimation of in-beam images of ionospheric scattering structures observed by a small, low-power coherent backscatter interferometer. The radar interferometer operated in the equatorial site of São Luís, Brazil (2.59° S, 44.21° W, −2.35° dip latitude). We show numerical simulations that evaluate the performance of the Capon method for typical F region measurement conditions. Numerical simulations show that, despite the short baselines of the São Luís radar, the Capon technique is capable of distinguishing localized features with kilometric scale sizes (in the zonal direction) at F region heights. Following the simulations, we applied the Capon algorithm to actual measurements made by the São Luís interferometer during a typical equatorial spread F (ESF) event. As indicated by the simulations, the Capon method produced images that were better resolved than those produced by the Fourier method. The Capon images show narrow (a few kilometers wide) scattering channels associated with ESF plumes and scattering regions spaced by only a few tens of kilometers in the zonal direction. The images are also capable of resolving bifurcations and the C shape of scattering structures.

We present long-overdue details about the intensity and spectral characteristics of 150-km echoes observed by the São Luís radar in Brazil. The São Luís 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 m s−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-of-view of the radar and the spatial distribution of the scatterers within the radar beam.

We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of São Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) onboard the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18:00–18:30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.

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.

We report and discuss interesting observations of the variability of electric fields and ionospheric densities near sunrise in the equatorial ionosphere made by instruments onboard the Communications/Navigation Outage Forecasting System (C/NOFS) satellite over six consecutive orbits. Electric field measurements were made by the Vector Electric Field Instrument (VEFI), and ionospheric plasma densities were measured by Planar Langmuir Probe (PLP). The data were obtained on 17 June 2008, a period of solar minimum conditions. Deep depletions in the equatorial plasma density were observed just before sunrise on three orbits, for which one of these depletions was accompanied by a very large eastward electric field associated with the density depletion, as previously described by de La Beaujardière et al. (2009), Su et al. (2009) and Burke et al. (2009). The origin of this large eastward field (positive upward/meridional drift), which occurred when that component of the field is usually small and westward, is thought to be due to a large-scale Rayleigh–Taylor process. On three subsequent orbits, however, a distinctly different, second type of relationship between the electric field and plasma density near dawn was observed. Enhancements of the eastward electric field were also detected, one of them peaking around 3 mV m−1, but they were found to the east (later local time) of pre-dawn density perturbations. These observations represent sunrise enhancements of vertical drifts accompanied by eastward drifts such as those observed by the San Marco satellite (Aggson et al., 1995). Like the San Marco measurements, the enhancements occurred during winter solstice and low solar flux conditions in the Pacific longitude sector. While the evening equatorial ionosphere is believed to present the most dramatic examples of variability, our observations exemplify that the dawn sector can be highly variable as well.

Previous 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, low-power 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.

This brief report presents unique day-time F region coherent scatter echoes observed by the 30 MHz radar over Sao Luis in eastern Brazil. The radar observation was part of the July 2011 radar campaign designed to detect echoes from day-time F region irregularities. These rare day-time F region radar echoes, scattered from short wavelength plasma irregularities, have quasi patchy features. They are characterized by large upward Doppler velocities ( ∼ 100 – 200 m / s ). They are very weak (by more than 10 dB) when compared to radar echoes observed over Sao Luis scattered from the night-time F plasma irregularities known as equatorial spread F. Simultaneous GPS vertical total electron content (TEC), and F2 peak frequency ( f ○ F 2 ) and F2 peak height ( h m F 2 ) estimated from ionosonde measurements over Sao Luis have provided additional evidence that the received day-time F region radar echoes were from genuine ionospheric scatterers. This report suggests physical explanations for the day-time radar echoes in terms of the generalized Rayleigh–Taylor instability mechanism operating on large magnetic declination ( ∼ 20 ° westward) of the geomagnetic field geometry in Sao Luis, conductivity distribution in the winter southern hemisphere and summer northern hemisphere, and the resulting magnetic flux tube electric field configurations.

Interferometric radar imaging of F-region spread F irregularities is used to determine the distribution of scatterers within the radar field of view. In this study, we investigate the use of the Capon's spectral method for estimating the distribution of equatorial spread F (ESF) irregularity structures observed by a small, low power coherent backscatter radar interferometer located at the equatorial site of Sao Luis (2.59°S, 44.21°W, −2.35° dip.), Brazil. To evaluate the performance of the method, we show numerical simulations for typical F-region measurement conditions. Results for the Fourier imaging method are also shown for comparison. The simulation shows that, despite the short baselines of the Sao Luis radar, the Capon technique is capable of distinguishing features with km scale sizes (in the zonal direction) at F-region heights. We also investigated the application of the Capon algorithm to actual measurements made by the Sao Luis radar, and obtained high resolution images of equatorial spread F (ESF) scattering structures. In this presentation, we will show results of the Capon images during different types of equatorial spread F events, and will compare the results with images obtained using the conventional Fourier method. As predicted by the numerical simulations, we are able to distinguish features of the scattering structures with resolution of a few km in the zonal direction. We have been able, in particular, to identify the morphology of scattering structures during bottom-type layers. Signatures of underlying deca-kilometric waves, similar to those observed by [3] and [7] were detected. The observations suggest the action of the so-called collisional shear instability.

The 30 MHz coherent backscatter radar located at the equatorial observatory in São Luís, Brazil (2.59° S, 44.21° W, −2.35° dip lat) has been upgraded to perform coherent backscatter radar imaging. The wide field-of-view of this radar makes it well suited for radar imaging studies of ionospheric irregularities. Radar imaging observations were made in support to the spread F Experiment (SpreadFEx) campaign. This paper describes the system and imaging technique and presents results from a bottom-type layer that preceded fully-developed radar plumes on 25 October 2005. The radar imaging technique was able to resolve decakilometric structures within the bottom-type layer. These structures indicate the presence of large-scale waves (~35 km) in the bottomside F-region with phases that are alternately stable and unstable to wind-driven gradient drift instabilities. The observations suggest that these waves can also cause the initial perturbation necessary to initiate the Generalized Rayleigh-Taylor instability leading to spread F. The electrodynamic conditions and the scale length of the bottom-type layer structures suggest that the waves were generated by the collisional shear instability. These results indicate that monitoring bottom-type layers may provide helpful diagnostics for spread F forecasting.

In 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 (10s-100s km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 10-100 km scales using the all sky-imager, at 3 m scales 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 sub-meter 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., Comment: 35 pages (unformatted manuscript), 8 figures, 2 tables, accepted for publication in JGR Space Physics

On 11 April 2001, a large magnetic storm occurred with SSC at 13:43UT, and Dst reached below -200nT after two southward Bz excursions. The Kp index during this storm reached 8 and remained high (>4) for about 21h, and the São Luís magnetometer H component presented simultaneous oscillations and decreased substantially relative to the previous magnetically quiet days. This storm triggered strong ionospheric irregularities, as observed by a recently installed 30MHz coherent scatter radar, a digisonde, and a GPS scintillation receiver, all operating at the São Luís equatorial station (2.33° S, 44° W, dip latitude 1.3° S). The ionospheric conditions and the characteristics of the ionospheric irregularities observed by these instruments are presented and discussed. The VHF radar RTI (Range Time Intensity) echoes and their power spectra and spectral width for the storm night 11-12 April 2001, were used to analyse the nature and dynamics of the plasma irregularities and revealed the coexistence of many structures in the altitudinal range of 400-1200km, some locally generated and others that drifted from other longitudinal sectors. The radar data also revealed that the plumes had periodic eastward and westward zonal velocities after 22:20UT, when well-developed quiet-time plumes typically drift eastward. Another interesting new observation is that the F-layer remained anomalously high throughout the 11-12 April 2001 storm night (21:00UT to 09:00UT next day) (the LT at São Luís isUT -3h), as indicated by the digisonde parameters hmF2 and h'F, which is a condition favourable for spread F generation and maintenance. The AE auroral index showed enhancements (followed by decreases) that are indicative of magnetospheric convection enhancements at about 15:00UT, 20:00UT and 22:00UT on 11 April 2001 and at 00:20UT (small amplitude) on 12 April 2001, associated with many Bz fluctuations, including clear two southward incursions that gave rise to large and long lasting Kp values and large negative Dst values. This intense auroral activity generated disturbance dynamo and prompt penetration electric fields that were responsible for the maintenance of the F-layer at a high altitude along the night of 11-12 April 2001. The short-lived F-region height rise seen between 16:00 to 18:00UT on 11April 2001 is probably due to the prompt penetration eastward electric fields of magnetospheric origin during the first IMF Bz turning to south around 15:00UT.

GPS ionospheric scintillation data collected at four stations in the United Kingdom and Norway were analyzed during periods of high solar flux, with ionospheric pierce points covering magnetic latitudes from about 40° to 75°. Maps of scintillation activity and total electron content (TEC) fluctuations for Northern Europe were generated. A detailed analysis of such maps enables us to infer the extension of the disturbed ionosphere controlled by the expansion and contraction of the auroral oval due to the varied geomagnetic conditions. Statistical distributions of phase scintillation magnitudes (based on the 60 s sφ scintillation index), amplitude scintillation magnitudes (based on the 60 s S4 scintillation index), and rate of change of TEC values (dTEC/dt computed for 15 s time bins) are presented in this paper. The statistical distributions were computed for each observation station and for the different geomagnetic activity conditions. Correlation with GPS user errors is also investigated, and possible implications for users are discussed.

In a collaborative study, INPE and Cornell University have installed several Global Positioning System (GPS) based scintillation monitors over the Brazilian territory in order to study L Band scintillation. These scintillation monitors were developed by Cornell University to measure the amplitude scintillation observed at L1 (1.575 GHz) GPS signal and are sensitive to ionospheric irregularities of about 400 meters scale size. This paper describes some characteristics of the intensity of scintillations observed at three observation sites in Brazil: (1) Sao Luis (2.33 ° S, 44 ° W, dip latitude 1.3 ° S), located at magnetic equator, (2) Sao Jose dos Campos (23.21 ° S, 45.86 ° W, dip latitude 17.8 ° S), located under the equatorial anomaly peak and (3) Cuiaba (15.33 ° S, 56.46 ° W, dip latitude 6.1 ° S), an intermediate observation site located in between the magnetic equator and the equatorial anomaly peak. Analysis of data from January to March of 2000 showed that the occurrence percentage as well as the magnitude of the L Band scintillation increase with latitude from the magnetic equator to the equatorial anomaly crest as previously reported by Basu et al. (1988). Strong scintillation with S4 index exceeding 0.5 only has been observed under equatorial anomaly peak while at magnetic equator scintillation intensity (S4 index) did not exceed 0.3. Such studies from the network of stations set up by INPE and Cornell University in Brazil, where the effect of large declination controls the ESF statistics, will be very useful for developing a regional scintillation model for use in IRI.

[1] The evolution of the pre-reversal enhancement in the vertical ion drift in the equatorialFregion is described via an examination of the current systems determined from a coupled ionosphere thermosphere model. We find that the pre-reversal enhancement is produced by a reversal in theF region zonal wind that results in an additional upward current where the E region Pedersen conductivity is declining across the dusk sector. The continuity of the total current is maintained through an enhancement in the eastward zonal current and an associated upward drift of the ions.

[1] HF Doppler sounders represent a low-cost and low-maintenance solution for monitoring wave activity in theF region ionosphere. HF Doppler sounders together with modern data analysis techniques can provide comprehensive traveling ionospheric disturbance (TID) characteristics, including both horizontal and vertical TID velocities and wavelengths across the entire spectrum from periods of 1 min to over an hour. Atmospheric and Space Technology Research Associates LLC has developed a new system called “TIDDBIT” (TID Detector Built in Texas), and data will be presented from a TIDDBIT system deployed in Virginia. These results reinforce the relationship between atmospheric gravity waves (AGWs) and TIDs. The TID propagation azimuths rotate through 360° in 24 h, mimicking the rotation of the thermospheric winds but with approximately a 90° offset. The rotation of TID azimuths and thermospheric winds in Virginia is similar to that observed previously by other Northern Hemisphere systems and opposite from the direction observed in Antarctica. These results illustrate the filtering effects that thermospheric neutral winds can have on the propagation of AGW. The completeness of the wave information obtained from the TIDDBIT system makes it possible to reconstruct the vertical displacement of isoionic contours over the ∼200 km horizontal dimension of the sounder array. Such information will be relevant for understanding the seeding of irregularities, as well as for several operational needs involving navigation, communication, and surveillance systems.

[1] We present new results of a study of the interferometric coherent backscatter radar imaging technique applied to Sao Luis observations made on the night of 1 December 2005. The range-time-intensity (RTI) map of the observations shows echoes occurring near theF region peak and topside heights followed by echoing layers confined to bottomside F region heights. Analyses of the measurements made on this night allowed us to investigate the ability of the Sao Luis radar interferometer to provide information about the morphology of the scattering structures responsible for different types of equatorial spread Fechoing layers. Results show that topside echoes were produced by a vertically elongated, horizontally narrow scattering channel of irregularities associated with a large-scale plasma depletion (“bubble”) as evidenced by colocated GPS scintillation measurements. Bottomside echoes were caused by structured, eastward drifting scattering regions with limited vertical development. Bottom-type echoes, on the other hand, were detected at heights below the minimum altitude of the bottomside echoes and were caused by an undifferentiated scattering region. Our imaging results are discussed in light of current equatorial spreadFtheories and previous higher-resolution imaging observations made at the Jicamarca Radio Observatory.

[1] We present new observations made by the Coupled Ion Neutral Dynamics Investigation (CINDI) Ion Velocity Meter (IVM) instrument onboard the Communication/Navigation Outage Forecasting System (C/NOFS) satellite that show the effects of the January 2009 sudden stratospheric warming (SSW) event on equatorial electric fields. We have used IVM observations to construct composite curves of mean equatorial vertical plasma drifts as a function of local time and longitude sector. These curves show large upward vertical drifts during morning hours and downward drifts during afternoon. Our analysis indicates that this pattern could be observed over the range of longitudes where adequate IVM measurements were available, from approximately 165°E to about 315°E longitude. A clear day-to-day, quasi-deterministic variability in the drifts is also observed, with the transition from upward to downward drifts occurring at increasing local times from 25 to 30 January 2009. The analysis also suggests some level of longitudinal variability in the magnitude of the drifts. These in-situ observations are in good agreement with previous ground-based measurements of the response of equatorial electric fields to SSW events. In particular, we found that IVM drift measurements centered around 285°E depart significantly from climatological values but agree exceptionally well with ground-based measurements of vertical drifts made by the Jicamarca incoherent backscatter radar. Overall, the results agree well with previous studies of SSW events, demonstrate the usefulness of the IVM observations and motivate further studies of the variability of the equatorial ionosphere using C/NOFS.

[1] The development of a convective ionospheric storm is studied using three radars, the C/NOFS satellite, airglow instrumentation, and a numerical model. First detected in the form of convective plumes over the Eastern Pacific, plasma irregularities, airglow signatures, plumes, and irregularities were also detected over Brazil and then Peru. Dynamo conditions were such that a modest prereversal enhancement was recorded at both Christmas Island and Peru and probably over Brazil as well. No prereversal enhancement occurred during the next two days and no plumes were detected. The numerical model reproduced the results quite well over Peru. Evidence for seeding by both gravity waves and the Kelvin-Helmholtz instability is presented.

Incoherent scatter data from a hybrid long-pulse/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.

[1] Multitechnique observations may considerably improve our understanding of factors responsible for the generation, growth, and dynamics of the destabilized nighttime equatorial F region plasma irregularities. In order to investigate the dynamics of plasma density irregularities of different scale sizes, a campaign of observations was conducted during 11–20 November 2001 at the Brazilian magnetic equatorial station Sao Luis (2.57°S, 44.21°W, dip latitude 1.73°S). We carried out observations using VHF coherent backscatter radar, two spaced GPS-based scintillation monitors, and one digisonde. Range type spread F on ionograms and radar plume signatures on range-time-intensity maps of the VHF radar started at similar times. In order to compare GPS L1 (1.575 GHz) scintillations and radar plumes we used the scintillation S4 index computed for the signal transmitted by the highest elevation satellite. GPS scintillations were not observed during the initial bottom-type layer shown by the radar; however, stronger scintillations (higher S4 values) were observed concurrently to stronger radar echoes. Although the time duration of GPS scintillation is longer than the duration of the plumes observed by the radar, ionosonde spread F is still much longer than scintillation occurrence, confirming that smaller scale-size irregularities decay faster. Zonal and vertical velocities of 5-m irregularities measured by the radar were analyzed jointly with the apparent zonal velocity of ∼400-m irregularities measured by the spaced-receiver scintillation method. Larger values of the zonal velocity measured by the scintillation technique were found during the explosive growth phase of radar plumes associated with large values of vertical drifts measured by the radar.

The Communication/Navigation Outage Forecasting System (C/NOFS) satellite was launched into orbit in April 2008 as part of an ongoing effort to understand and identify plasma irregularities that adversely impact the propagation of radio waves in the upper atmosphere. Combined with recent improvements in radar, airglow, and ground-based studies, as well as state-of-the-art modeling techniques, the C/NOFS mission has led to new insights into equatorial ionospheric electrodynamics. In order to document these advances, the C/NOFS Results and Equatorial Dynamics Technical Interchange Meeting was held in Albuquerque, New Mexico from 12 to 14 March 2013. The meeting was a great success with 55 talks and 22 posters, and covered topics including the numerical simulations of plasma irregularities, the effects of atmospheric tides, stratospheric phenomena, and magnetic storms on the upper atmosphere, causes and predictions of scintillation-causing ionospheric irregularities, current and future instrumentation efforts in the equatorial region. The talks were broken into the following three topical sessions: A. Ambient Ionosphere and Thermosphere B. Transient Phenomena in the Low-Latitude Ionosphere C. New Missions, New Sensors, New Science and Engineering Issues. The following special issue was planned as a follow-up to the meeting. We would like to thank Mike Pinnock, the editors and staff of Copernicus, and our reviewers for their work in bringing this special issue to the scientific community. Our thanks also go to Patricia Doherty and the meeting organizing committee for arranging the C/NOFS Technical Interchange Meeting.

We provide here an overview of, and a summary of results arising from, an extensive experimental campaign (the Spread F Experiment, or SpreadFEx) performed from September to November 2005, with primary measurements in Brazil. The motivation was to define the potential role of neutral atmosphere dynamics, specifically gravity wave motions propagating upward from the lower atmosphere, in seeding Rayleigh-Taylor instability (RTI) and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12, and the GUVI instrument aboard the TIMED satellite. Initial results of our SpreadFEx analyses are described separately by Fritts et al. (2009). Further analyses of these data provide additional evidence of 1) gravity wave (GW) activity near the mesopause apparently linked to deep convection predominantly to the west of our measurement sites, 2) small-scale GWs largely confined to lower altitudes, 3) larger-scale GWs apparently penetrating to much higher altitudes, 4) substantial GW amplitudes implied by digisonde electron densities, and 5) apparent influences of these perturbations in the lower F-region on the formation of equatorial spread F, RTI, and plasma bubbles extending to much higher altitudes. Other efforts with SpreadFEx data have also yielded 6) the occurrence, locations, and scales of deep convection, 7) the spatial and temporal evolutions of plasma bubbles, 8) 2-D (height-resolved) structures in electron density fluctuations and equatorial spread F at lower altitudes and plasma bubbles above, and 9) the occurrence of substantial tidal perturbations to the large-scale wind and temperature fields extending to bottomside F-layer and higher altitudes. Collectively, our various SpreadFEx analyses suggest direct links between deep tropical convection and large GW perturbations at large spatial scales at the bottomside F-layer and their likely contributions to the excitation of RTI and plasma bubbles extending to much higher altitudes.