Outage Forecasting System Satellite Research Articles

Identification of Penetration and Disturbance Dynamo Electric Fields and Their Effects on the Generation of Equatorial Plasma Bubbles

AbstractA very challenging task in ionospheric studies is to determine the separate contributions of penetration and disturbance dynamo processes in the generation of equatorial plasma drift during magnetic storms. In this study, we analyze the ion drift measured by the Communications/Navigation Outage Forecasting System satellite during the magnetic storm on 15–16 July 2012. A unique feature of this storm is the exceptionally long period of continuous southward interplanetary magnetic field (IMF) for 32 hr. The storm‐induced net change of the meridional/vertical ion drift, the difference drift between the storm time and the quiet time, is derived during the storm main phase and the first 20 hr of the recovery phase with southward IMF. The difference drift during the recovery phase cannot be explained by the disturbance dynamo effect alone. A new method is used to separate the drifts caused by the penetration and disturbance dynamo processes. The penetration drift is represented by an empirical pattern of penetration electric field and depends on the IMF magnitude, and the disturbance dynamo drift is obtained by subtracting the penetration drift from the measured difference drift. The derived disturbance dynamo drift is in good agreement with previous statistical pattern. This is the first effort to identify the separate contributions of the penetration and disturbance dynamo processes to the total drift from observed data. The results have important implications in identifying storm‐time penetration and disturbance dynamo electric fields and their effects on the generation and evolution of plasma bubbles.

Space Diversity Mitigation Effects on Ionospheric Amplitude Scintillation With Basis on the Analysis of GNSS Experimental Data

Ionospheric density irregularities embedded in Equatorial Plasma Bubbles, with scale sizes varying from several hundred kilometers to several tens of meters, may cause amplitude and phase scintillation of transionospheric radio waves, degrading the performance and availability of space-based communication and navigation systems. A recent computer simulation study, based on ionospheric irregularities detected by the Planar Langmuir Probe onboard the Communication/ Navigation Outage Forecasting System satellite, analyzed the mitigation effects from space diversity on amplitude scintillation of transionospheric signals received on the ground. The present work, based on experimental data, will confirm and extend the previous results, indicating, in statistically quantitative terms, how space diversity, effective on uplink and downlink ground-satellite paths, particularly in the strong and saturated scintillation regimes, depends on Ionospheric Pierce Point dip-latitude and distance intervals, as well as on a well-known amplitude scintillation index.

Fading of Wideband Signals Due to Propagation Through Equatorial Plasma Bubbles and Diversity Mitigation Effects

Equatorial Plasma Bubbles (EPBs) and their ionospheric density irregularities exhibit structures with scale sizes that can vary from several hundred kilometers to tens of meters. These random irregularities degrade both the performance and the availability of space-based communication and navigation systems, in different ways. As examples of effects to be analyzed, wideband UHF (360 MHz – 380 MHz) transmissions received by Ascension Island (7.93°S, 14.25°W) monitors during an observational campaign in October 2016 displayed flat-fading and frequency-selective fading conditions. In this report, the ionospheric structures that are responsible for the harmful observed behavior (flat and frequency-selective fading) will initially be identified, through the application of a discrete version of the single phase-screen formulation to low-and high-resolution in-situ ion density data recorded by the Planar Langmuir Probe (PLP) onboard the Communications/ Navigation Outage Forecasting System (C/NOFS) satellite. Next, the resulting hypothesis will be confirmed, by the application of the continuous version of the same formulation to single-scale irregularities with different scale sizes. Finally, mitigation effects from space and frequency diversity on the observed behavior will be discussed, with basis on the application of the initial formulation to the high-resolution C/NOFS PLP data.

Interhemispheric Transport of the Ionospheric F Region Plasma During the 2009 Sudden Stratosphere Warming

AbstractThe field‐aligned plasma drift in the equatorial ionosphere drives the interhemispheric transport of the ionospheric F region plasma between the Northern and Southern Hemispheres. We use the Communication/Navigation Outage Forecasting System satellite measurements, for the first time, to present the responses of the equatorial field‐aligned drift during the 2009 sudden stratosphere warming (SSW). The observations show that the equatorial field‐aligned drift presents a southward disturbance in the morning sector and a large northward disturbance in the afternoon sector and gradually shifts to later local time during the SSW. Further, this new finding of semidiurnal disturbance in field‐aligned drift can well explain the hemispheric differences of the responses of the total electron content to the SSW. Based on the whole atmosphere model Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy, it is suggested that the meridional wind can contribute to the disturbance field‐aligned drift. Our results give a new perspective for understanding the ionospheric perturbations during SSWs.

Ion Cyclotron Resonant Absorption Lines in ELF Hiss Power Spectral Density in the Low‐Latitude Ionosphere

AbstractThe effects of multiple ion species have been observed in electromagnetic wave spectra in both the ionosphere and the magnetosphere. Here we report an event from Communication/Navigation Outage Forecast System satellite, showing a new imprint of various ion species in observations of extremely low frequency (ELF) hiss wave spectra near the equatorial ionosphere, which presents minima in the power spectral density at gyrofrequencies and their harmonics of multiple ion species (e.g., O and He ). Cyclotron harmonic resonant absorption is proposed to account for the observed spectral and polarization properties. Furthermore, the implication of using those wave power spectral minima to identify minor ion species in the ionosphere is discussed.

Low‐Latitude Whistler‐Wave Spectra and Polarization From VEFI and CINDI Payloads on C/NOFS Satellite

AbstractThe Communication/Navigation Outage Forecast System (C/NOFS) satellite's VEFI payload performed frequent recordings of the vector electric field in the band 0–16 kHz during the epoch 2008–2014. The Vector Electric Field Instrument (VEFI) was supported by ion‐composition data from the Coupled Ion Neutral Dynamics Investigation (CINDI) instrument. We focus here on statistics of these “burst‐mode” recordings, of which 6,890 (mostly ~12‐s duration) records meet stringent quality‐control criteria, allowing inference of the wave vector k and its orientation relative to the Earth's magnetic field B0. The 6,890 records occur between ±13° (geographic) latitude and between ~ 400‐ and 850‐km altitude, mostly in the topside ionosphere. The wave activity is dominated by terrestrial lightning. We analyze the whistler‐wave intensity and polarization for each pixel in the time‐frequency spectrogram for each record. We then gather weighted statistics on wave polarization, naturally weighted by wave intensity. In this manner we arrive at statistical results that represent the bulk of the energy flow due to whistler waves. Despite rather nonstationary statistics, we can reach three empirical results. We see no evidence of a low‐latitude suppression of whistler‐wave activity, in contrast to the predictions of models of transmission through a laminar ionosphere. The wave vector polar angle is always in the range 40° to 90° from parallel to B0. This indicates that the propagation at low latitudes is dominated by oblique, not ducted, whistlers. At the lowest magnetic latitudes, the wave vector polar angle with respect to B0 becomes nearly 90°.

A neutral wind instrument for nano-satellite platforms.

Here we describe the first neutral wind sensor developed specifically for use on resource limited nano-satellite platforms. The instrument is a next generation redesign of the ram wind sensor flown on the Communications/Navigation Outage Forecasting System satellite for measurements of neutral velocity, temperature, and composition. Results of subsystem tests in vacuum conditions show low-power operation, promising design, and good resolution of measured parameters over the operational pressure and energy ranges expected in the low Earth orbit environment.

Plasma Dynamics Associated With Equatorial Ionospheric Irregularities

AbstractThe Communication/Navigation Outage Forecasting System satellite was operational from 2008, a period of deep solar minimum, to 2015, a period of moderate solar conditions. The behavior of the vertical plasma drift and the distribution of plasma depletions during the deep solar minimum of 2009 deviated substantially from the behavior that was observed during the solar moderate conditions encountered by the Communication/Navigation Outage Forecasting System satellite in 2014, which are typical of previous observations. Presented here are observations of the vertical drift of plasma depletions and the background plasma in which they are embedded. We find that depletions detected at local times after 2100 hr during solar minimum are typically found in background drifts that are weakly downward compared to the strongly downward background drifts observed during moderate solar activity levels. Additionally, at solar minimum, the drift within the depletions is upward with respect to the background as compared with observations at the same local times during solar moderate conditions for which the depleted plasma more nearly drifts with the background. We note that weak background plasma drifts observed throughout the night during solar minimum promote the continued growth of depletions that may evolve more slowly or be continuously generated to appear in the topside in the postmidnight hours.

Statistics of Durations and Spacings of Equatorial Plasma Depletions Detected by the C/NOFS Planar Langmuir Probe

AbstractThe Planar Langmuir Probe onboard the Communication/Navigation Outage Forecasting System satellite monitored ionospheric plasma densities and their irregularities with high resolution almost seamlessly for approximately five years since May 2008. Planar Langmuir Probe data from two different years (1 October 2008 to 30 September 2009 and 5 June 2012 to 4 June 2013) were selected for analysis. The first data set corresponds to solar minimum conditions, and the second one is as close to solar maximum conditions of solar cycle 24 as possible, with basis on their continuous availability. The results from a level‐crossing analysis applied to detrended evening‐time data from a fixed altitude range show how depletion durations and spacings between consecutive depletions are statistically distributed as functions of solar activity and longitude sector. In quantitative terms, they show that (i) the fewer depletions observed in the solar‐minimum year are also shorter, shallower, and closer together than those detected in the more active one and (ii) great similarities exist between structures of depletion durations and spacings between consecutive depletions observed in the South American and African longitude sectors, which are more noticeable than those associated with in the Indian‐Asian longitude sector.

Effects of Geomagnetic Storms on the Postsunset Vertical Plasma Drift in the Equatorial Ionosphere

AbstractIt has been observed that geomagnetic storms cause suppression of the occurrence of equatorial spread F or plasma bubbles in the evening sector. In this study, we use ion drift data measured by the Communication/Navigation Outage Forecasting System satellite over 6 years (2008–2014) to derive the dependence of the vertical ion drift at the prereversal enhancement peak on the strength of magnetic storms (the Dst index). It is found that the average vertical ion drift does not change much for Dst in the range between 0 and −60 nT but decreases approximately linearly with the increasing magnitude of Dst for Dst < −60 nT. The net decrease in the average vertical ion drift is ~30 m/s when Dst changes from −60 to −90 nT. This result is derived when the ion drift data during the storm main phase are excluded, so the decrease of the vertical ion drift is caused by storm time disturbance dynamo. A possible interpretation of this phenomenon is that geomagnetic activity must be strong enough (e.g., Dst < −60 nT) so disturbance winds can reach the equatorial region and change plasma drifts there. The storm time disturbance dynamo becomes dominant in the equatorial ionospheric dynamics near the end of the storm main phase, ~4.7 hr after the storm onset. The postsunset vertical ion drift is significantly decreased during the early stage of the storm recovery phase but becomes almost fully recovered when Dst increases close to −60 nT.

Coordinated Satellite Observations of the Very Low Frequency Transmission Through the Ionospheric D Layer at Low Latitudes, Using Broadband Radio Emissions From Lightning

AbstractBoth ray theory and full‐wave models of very low frequency transmission through the ionospheric D layer predict that the transmission is greatly suppressed near the geomagnetic equator. We use data from the low‐inclination Communication/Navigation Outage Forecast System satellite to test this semiquantitatively, for broadband very low frequency emissions from lightning. Approximate ground‐truthing of the incident wavefields in the Earth‐ionosphere waveguide is provided by the World Wide Lightning Location Network. Observations of the wavefields at the satellite are provided by the Vector Electric Field Instrument aboard the satellite. The data set comprises whistler observations with the satellite at magnetic latitudes <26°. Thus, our conclusions, too, must be limited to the near‐equatorial region and are not necessarily predictive of midlatitude whistler properties. We find that in most broadband recordings of radio waves at the satellite, very few of the lightning strokes result in a detectable radio pulse at the satellite. However, in a minority of the recordings, there is enhanced transmission of very low frequency lightning emissions through the D layer, at a level exceeding model predictions by at least an order of magnitude. We show that kilometric‐scale D‐layer irregularities may be implicated in the enhanced transmission. This observation of sporadic enhancements at low magnetic latitude, made with broadband lightning emissions, is consistent with an earlier review of D‐layer transmission for transmission from powerful man‐made radio beacons.

First Results From the Ionospheric Extension of WACCM‐X During the Deep Solar Minimum Year of 2008

AbstractNew ionosphere and electrodynamics modules have been incorporated in the thermosphere and ionosphere eXtension of the Whole Atmosphere Community Climate Model (WACCM‐X), in order to self‐consistently simulate the coupled atmosphere‐ionosphere system. The first specified dynamics WACCM‐X v.2.0 results are compared with several data sets, and with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM), during the deep solar minimum year. Comparisons with Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite of temperature and zonal wind in the lower thermosphere show that WACCM‐X reproduces the seasonal variability of tides remarkably well, including the migrating diurnal and semidiurnal components and the nonmigrating diurnal eastward propagating zonal wavenumber 3 component. There is overall agreement between WACCM‐X, TIE‐GCM, and vertical drifts observed by the Communication/Navigation Outage Forecast System (C/NOFS) satellite over the magnetic equator, but apparent discrepancies also exist. Both model results are dominated by diurnal variations, while C/NOFS observed vertical plasma drifts exhibit strong temporal variations. The climatological features of ionospheric peak densities and heights (NmF2 and hmF2) from WACCM‐X are in general agreement with the results derived from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) data, although the WACCM‐X predicted NmF2 values are smaller, and the equatorial ionization anomaly crests are closer to the magnetic equator compared to COSMIC and ionosonde observations. This may result from the excessive mixing in the lower thermosphere due to the gravity wave parameterization. These data‐model comparisons demonstrate that WACCM‐X can capture the dynamic behavior of the coupled atmosphere and ionosphere in a climatological sense.

The characteristics and generation mechanism of small‐amplitude and large‐amplitude ESF irregularities observed by the C/NOFS satellite

AbstractIt is well understood that equatorial plasma bubbles are initiated in the bottomside F region and grow into the topside F region, producing equatorial spread F (ESF) irregularities in both bottomside and topside F regions. However, it is not known whether small‐amplitude and large‐amplitude irregularities have the same occurrence pattern and how the generation of small‐amplitude and large‐amplitude irregularities is related to the postsunset vertical plasma drift and potential seeding processes. In this study, we use ion density and velocity data measured by the Communications/Navigation Outage Forecasting System satellite during May 2008 to July 2014 to derive the longitude‐month distributions of the occurrence probability of ESF irregularities at different amplitudes. It is found that the occurrence probability of large‐amplitude irregularities is well correlated with the postsunset vertical plasma drift and that small‐amplitude irregularities do not show a clear pattern at low solar activity but is anticorrelated with that of large‐amplitude irregularities at moderate solar activity. That is, the months and longitudes with high occurrence probability of large‐amplitude irregularities are exactly those with low occurrence probability of small‐amplitude irregularities, and vice versa. ESF irregularities are mostly limited below 500 km during low solar activity in 2008–2010, but large‐amplitude irregularities can reach 700–800 km in altitude during moderate solar activity in 2011–2014. The generation of large‐amplitude ESF irregularities is controlled by the postsunset vertical plasma drift at both low and moderate solar activities. In contrast, small‐amplitude ESF irregularities at moderate solar activity occur more frequently in the areas where the postsunset vertical plasma drift is small.

Further refinements to the spatiotemporal forecast model for L‐band scintillation based on comparison with C/NOFS observations

AbstractThe model‐generated spatiotemporal maps to forecast the occurrence pattern of plasma density irregularities in the nightside equatorial F region that are responsible for the L‐band scintillations have been put to test, in both space and time, by comparing it with actual observations by the Communication/Navigation Outage Forecasting System satellite. The forecast model is based on (i) the temporal variations of the density perturbations during daytime in the Nmax region and (ii) the a priori knowledge of zonal velocity of the perturbations in the postsunset hours. The present study not only substantiates the hypothesis used for the generation of the scintillation forecast but also suggests that the equatorial plasma bubbles remain tied‐up with the initial perturbations which trigger the primary Rayleigh‐Taylor instability. The outcome highlights the need to take into account the altitudinal profile of the topside F region electron density as it could modify the zonal extent of the plasma bubbles that support the generation of the density irregularities and the consequent L‐band scintillations. The present study takes us one more step closer toward the realization of an operational forecast system for satellite‐based navigation.

Study of the effect of 17–18 March 2015 geomagnetic storm on the Indian longitudes using GPS and C/NOFS

AbstractThe largest geomagnetic storm in solar cycle 24 occurred during 17–18 March 2015 where the main phase of the storm commenced from 07:00 UT of 17 March 2015 and reached the Dst negative minimum at 22:00 UT. The present paper reports observations of total electron content (TEC), amplitude, and phase scintillations from different GPS stations of India during the storm of 17 March and highlights its effects on GPS. It also presents the global equatorial spread F (ESF) occurrence during the storm using total ion density drift measurements from Communication and Navigation Outage Forecast System (C/NOFS) satellite. TEC enhancements were noted from stations along 77°E meridian around 10:00 UT on 17 March compared to 16 and 18 March indicating positive storm effects arising out of equatorward neutral wind in the local morning to noon sector of the main phase. Intense scintillation observations from Calcutta were most extensive during 15:00–16:00 UT, 17 March, and the receiver recorded a longitude deviation of 5.2 m during this time. Cycle slips of the order of 8 s could be observed during periods of intense phase scintillations on the same night. Intense scintillation observation from Palampur is an exceptional phenomenon attributed to the dramatic enhancement of the electric field due to prompt penetrating (undershielded) electric leading to a very high upward ion velocity over the magnetic equator as recorded by C/NOFS. The total ion density measured globally by C/NOFS reveals two distinct longitude regions of ESF occurrence during the storm: (i) East Pacific sector and (ii) Indian longitude during the storm. The time and longitude of ESF occurrence could be predicted using the time of southward turning of interplanetary magnetic field Bz.

Ionospheric storm effects and equatorial plasma irregularities during the 17–18 March 2015 event

AbstractThe intense magnetic storm on 17–18 March 2015 caused large disturbances of the ionosphere. Based on the plasma density (Ni) observations performed by the Swarm fleet of satellites, the Gravity Recovery and Climate Experiment mission, and the Communications/Navigation Outage Forecasting System satellite, we characterize the storm‐related perturbations at low latitudes. All these satellites sampled the ionosphere in morning and evening time sectors where large modifications occurred. Modifications of plasma density are closely related to changes of the solar wind merging electric field (Em). We consider two mechanisms, prompt penetration electric field (PPEF) and disturbance dynamo electric field (DDEF), as the main cause for the Ni redistribution, but effects of meridional wind are also taken into account. At the start of the storm main phase, the PPEF is enhancing plasma density on the dayside and reducing it on the nightside. Later, DDEF takes over and causes the opposite reaction. Unexpectedly, there appears during the recovery phase a strong density enhancement in the morning/prenoon sector and a severe Ni reduction in the afternoon/evening sector, and we suggest a combined effect of vertical plasma drift, and meridional wind is responsible for these ionospheric storm effects. Different from earlier studies about this storm, we also investigate the influence of storm dynamics on the initiation of equatorial plasma irregularities (EPIs). Shortly after the start of the storm main phase, EPIs appear in the postsunset sector. As a response to a short‐lived decline of Em, EPI activity appears in the early morning sector. Following the second start of the main phase, EPIs are generated for a few hours in the late evening sector. However, for the rest of the storm main phase, no more EPIs are initiated for more than 12 h. Only after the onset of recovery phase does EPI activity start again in the postmidnight sector, lasting more than 7 h. This comprehensive view of ionospheric storm effects and plasma irregularities adds to our understanding of conditions that lead to ionospheric instabilities.

Automated identification of discrete, lightning‐generated, multiple‐dispersed whistler waves in C/NOFS‐VEFI very low frequency observations

AbstractAutomated wave feature detection is required to efficiently analyze large archives of very low frequency broadband recordings for discrete whistler identification and feature extraction. We describe a new method to do this, even in the presence of simultaneous, multiple whistler phase dispersions. Previous techniques of whistler identification were unable to deal with simultaneous, multiple phase dispersions. We demonstrate the new method with data from the Vector Electric Field Investigation (VEFI) payload on the Communication/Navigation Outage Forecast System (C/NOFS) satellite, from the mission years 2008–2014.

Validation of NeQuick TEC data ingestion technique against C/NOFS and EISCAT electron density measurements

AbstractThis paper investigates a technique to estimate near‐real‐time electron density structure of the ionosphere. Ground‐based GPS receiver total electron content (TEC) at low and high latitudes has been used to assist the NeQuick 2 model. First, we compute model input (effective ionization level) when the modeled slant TEC (sTEC) best fits the measured sTEC by single GPS receiver (reference station). Then we run the model at different locations nearby the reference station and produce the spatial distribution of the density profiles of the ionosphere in the East African region. We investigate the performance of the model, before and after data ingestion in estimating the topside ionosphere density profiles. This is carried out by extracting in situ density from the model at the corresponding location of C/NOFS (Communication/Navigation Outage Forecast System) satellite orbit and comparing the modeled ion density with the in situ ion density observed by Planar Langmuir Probe onboard C/NOFS. It is shown that the performance of the model after data ingestion reproduces the topside ionosphere better up to about 824 km away from the reference station than that before adaptation. Similarly, for high‐latitude region, NeQuick 2 adapted to sTEC obtained from high‐latitude (Tromsø in Norway) GPS receiver and the model used to reproduce parameters measured by European Incoherent Scatter Scientific Association (EISCAT) VHF radar. It is shown that the model after adaptation shows considerable improvement in estimating EISCAT measurements of electron density profile, F2 peak density, and height.

Spectral signatures of the ionospheric Alfvén resonator to be observed by low‐Earth orbit satellite

AbstractInterference of an incident and reflected Alfvén pulses propagating inside the ionospheric Alfvén resonator (IAR) is studied on the basis of a simple one‐dimensional model. Particular emphasis has been placed on the analysis of spectral features of ultralow frequency (∼1–15 Hz) electric perturbations recently observed by Communications/Navigation Outage Forecasting System satellite. This “fingerprint” multiband spectral structure was observed when satellite descended in the terminator vicinity. Among factors affecting spectral structure the satellite position and distance from the IAR boundaries are most significant. It is concluded that the observed spectrograms exhibit modulation with “period” depending on propagation delay time of reflected Alfvén pulses in such a way that this effect can mask a spectral resonance structure resulted from excitation of IAR eigenmodes. The proposed interference effect is capable to produce a spectral pattern resembling a fingerprint which is compatible with the satellite observations.

Effects of solar and geomagnetic activities on the zonal drift of equatorial plasma bubbles

AbstractEquatorial plasma bubbles are mostly generated in the postsunset sector and then move in the zonal direction. Plasma bubbles can last for several hours and move over hundreds of kilometers (even more than 1000 km). In this study, we use measurements of ion density by the Communication/Navigation Outage Forecasting System satellite to determine the orbit‐averaged drift velocity of plasma bubbles. The objective of the study is to identify the dependence of the bubble drift on the solar radio flux and geomagnetic activities. In total, 5463 drift velocities are derived over May 2008 to April 2014, and a statistical analysis is performed. The average pattern of the bubble drift is in good agreement with the zonal drift of the equatorial F region plasma. The zonal drift velocity of plasma bubbles increases with the solar radio flux. However, the increase shows different features at different local times. Geomagnetic activities cause a decrease of the eastward drift velocity of plasma bubbles, equivalent to the occurrence of a westward drift, through disturbance dynamo process. In particular, the decrease of the eastward drift velocity appears to become accelerated when the Dst index is smaller than −60 nT or Kp is larger than 4.