Scintillation Network Decision Aid Research Articles

Relationship between geomagnetic storms and occurrence of ionospheric irregularities in the west sector of Africa during the peak of the 24th solar cycle

The study of ionospheric irregularities is important since many technological systems might be influenced by the ionosphere. In this work, we use data from the Global Navigation Satellite Systems (GNSS) receiver installed in Abuja, Nigeria, GPS Scintillation Network Decision Aid (SCINDA) TEC data from the Air Force Research Laboratory (AFRL) data archive, and the geomagnetic data from the World Data Center (WDC) in Kyoto, Japan, to investigate the relationship between geomagnetic storm and ionospheric irregularity occurrences using the rate of change of total electron content (TEC) index (ROTI), with a validation using the S4 indices, during the peak of the 24th solar cycle. The occurrences of irregularities were investigated on day-to-day and seasonal bases. The nighttime ionospheric irregularities, which are attributed to ionospheric plasma irregularities in the equatorial ionospheric F-region, were found to be prevalent. To investigate the relationship between the strength of ionospheric irregularities (ROTI) and the geomagnetic storm (Dst), the periodogram power spectral density (PSD) and regression analysis were used. The results showed that there was no correlation, cc = 0.073, between the Dst and ROTI, implying that the strengths of ionospheric irregularities occurring during geomagnetic storms are not strictly decided by the magnitudes of the storms; this was also confirmed using the S4 index. The impact of geomagnetic storms caused enhanced development or inhibition of ionospheric irregularities. We observed that the bulk of the storms occurring during the period of this study is not associated with ionospheric irregularities. Finally, the investigation showed that the correlation between the ROTI and Dst observed during the coronal mass ejection (CME)-driven geomagnetic storms was higher than that during the corotating interaction region (CIR)-driven geomagnetic storms, during the peak of the 24th solar cycle. The results of this work confirm the findings by other researchers.

Correlation analysis of normalized ROTI and S4 as observed during different geomagnetic conditions of the 2013 September equinox over the stations within EIA African sector

It has been a concern of space scientists and engineers for many decades to have a well-defined proxy to characterize the fluctuations experienced by radio-based signals propagating through the ionosphere. Scintillation indices were deduced using the signal intensity to show the level of fluctuations in phase and amplitude of radio signal passing through the ionosphere. Subsequently, more than two decades now, the rate of change of Total Electron Content (TEC) index (ROTI) was as well used to characterize the level of fluctuations associated to ionospheric irregularities on radio signals. This paper examines the level of relationship between the rate of change of TEC index (ROTI) and the ionospheric amplitude scintillation (S4) within the belt of equatorial ionization anomaly of West African sector. The study was carried out using the Scintillation Network Decision Aid (SCINDA) Global Positioning System (GPS) data obtained from ground-based stations located at Dakar (Senegal) and Cape Verde. The comparative analysis of ROTI and S4 was done with normalized ROTI. The results obtained have shown that the magnitude of normalized ROTI and S4 corresponds very well, higher in Cape Verde compared to Dakar. It was observed that the correlation coefficient could be ∼0.6 when all the satellites are used. However, the relationship increases with individual satellite in which the coefficient of correlation could be up to ∼0.97 and R2 ∼ 0.94. It can be concluded that the relationship between the S4 and ROTI depends on the location and the level of ionospheric disturbance condition as observed in this work.

Instantaneous Ionospheric Scintillation Mapping over the East African Region by use of GPS Derived Amplitude Scintillation Proxy

Ionospheric scintillation activity over the East African region is often monitored using measurements from the SCIntillation Network Decision Aid (SCINDA) receivers. Many of the SCINDA receivers over East Africa are currently not archiving data and therefore a large part of the region remain un sampled. We investigated the possibility to use dual frequency receivers of the Global Navigation Satellite System (GNSS) network for scintillation mapping. A proxy for amplitude scintillation was first derived by scaling the rate of change of total electron content index (ROTI). The proxy was validated against S4 derived from nearly collocated SCINDA receivers over the region. A good correlation was observed between the proxy and S4. The proxy was then used to map the occurrence of amplitude scintillation over East Africa based on semivariogram modeling and Kriging interpolation technique. The results indicate that the S4 values had a good positive correlation with *Corresponding author: E-mail: emirant.amabayo@gmail.com; Amabayo et al.; AJR2P, 4(2): 6-20, 2021; Article no.AJR2P.66815 the simulated S4p from the Kriging interpolation. This observation suggests that data from the dual frequency receivers of GNSS may be used to map scintillation over East Africa. These maps can in turn be used to study the evolution of ionospheric scintillation patterns over the region.

GPS derived amplitude scintillation proxy model: A case over a low latitude station in East Africa

Ionospheric scintillation is quite a common phenomenon over the low latitude regions and in East Africa it is often monitored using measurements from the SCIntillation Network Decision Aid (SCINDA) receivers. The SCINDA receivers over East Africa are characterized by long base lines and data paucity thus offering a huge challenge in the long term scintillation characterization over the region. To alleviate this challenge, we implemented the use of data from the dual frequency GPS receivers of the IGS network in combination with data from the SCINDA receiver at Nairobi, Kenya to model amplitude scintillation. The data from the SCINDA (geographic coordinates 36.808oE, −1.274oN) and GPS (geographic coordinates 36.893oE, −1.221oN) receivers were used to derive S4 index and its proxy respectively. Comparison of the S4 and its proxy revealed a high correlation coefficient between the two datasets. Scintillation occurrence was observed to peak during the equinox months of March–April and September–October. The vernal equinox was observed to have less frequent scintillation events than the autumnal equinox. The local time (LT) scintillation occurrence shows a peak between 20:00 LT and 23:00 LT. An empirical hybrid amplitude scintillation occurrence probability model was then developed. The results show that the model predicted values were in good agreement with the observed amplitude scintillation occurrence probabilities from the SCINDA receiver. This observation suggests that the model is a useful tool for approximating amplitude scintillation occurrence probabilities at L-band frequencies at African equatorial latitudes.

Multi-wavelength coordinated observations of ionospheric irregularity structures from an anomaly crest location during unusual solar minimum of the 24th cycle

The present paper reports coordinated ionospheric irregularity measurements at optical as well as GPS wavelengths. Optical measurements were obtained from Tiny Ionospheric Photometer (TIP) sensors installed onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. GPS radio signals were obtained from a dual frequency GPS receiver operational at Calcutta (22.58°N, 88.38°E geographic; geomagnetic dip: 32.96°; 13.00°N, 161.63°E geomagnetic) under the SCIntillation Network Decision Aid (SCINDA) program. Calcutta is located near the northern crest of Equatorial Ionization Anomaly (EIA) in the Indian longitude sector. The observations were conducted during the unusually low and prolonged solar minima period of 2008–2010. During this period, four cases of post-sunset GPS scintillation were observed from Calcutta. Among those cases, simultaneous fluctuations in GPS Carrier-to-Noise ratios (C/No) and measured radiances from TIP over a common ionospheric volume were observed only on February 2, 2008 and September 25, 2008. Fluctuations observed in measured radiances (maximum 0.95 Rayleigh) from TIP due to ionospheric irregularities were found to correspond well with C/N0 fluctuations on the GPS links observed from Calcutta, such effects being noted even during late evening hours of 21:00–22:00 LT from locations around 40° magnetic dip. These measurements indicate the existence of electron density irregularities of scale sizes varying over several decades from 135.6 nm to 300–400 m well beyond the northern crest of the EIA in the Indian longitude sector during late evening hours even in the unusually low solar activity conditions.

A Study of Daytime L‐Band Scintillation in Association With Sporadic E Along the Magnetic Dip Equator

AbstractIn this paper, we present a comprehensive study of occurrence of L‐band scintillation in association with the appearance of sporadic E (Es) along the magnetic dip equator during daytime in 2013. The presence of L‐band scintillation was determined from signals collected with GNSS (Global Navigation Satellite Systems) ground‐based Scintillation Network Decision Aid receivers from five stations situated at the magnetic dip equator. The detection and analysis of Es layers were obtained from GNSS FORMOSAT‐3/Constellation Observing System for Meteorology, Ionosphere, and Climate (F3/C) radio occultation (RO) data. Combining ground‐based data with the limb‐viewing geometry from space provides a unique opportunity to retrieve complementary information about scintillation and association with equatorial E region irregularities (i.e., Es) during daytime. Results for the first time show that daytime scintillation does occur at the magnetic dip equator and the occurrence is associated with the appearance of Es observed using GNSS F3/C RO data.

Characterization of the low latitude plasma density irregularities observed using C/NOFS and SCINDA data

Complex electrodynamic processes over the low latitude region often result in post sunset plasma density irregularities which degrade satellite communication and navigation. In order to forecast the density irregularities, their occurrence time, duration and location need to be quantified. Data from the Communication/Navigation Outage Forecasting System (C/NOFS) satellite was used to characterize the low latitude ion density irregularities from 2011 to 2013. This was supported by ground based data from the SCIntillation Network Decision Aid (SCINDA) receivers at Makerere (Geographic coordinate 32.6°E, 0.3°N, and dip latitude −9.3°N) and Nairobi (Geographic coordinate 36.8°E, −1.3°N, and dip latitude −10.8°N). The results show that irregularities in ion density have a daily pattern with peaks from 20:00 to 24:00 Local Time (LT). Scintillation activity at L band and VHF over East Africa peaked in 2011 and 2012 from 20:00 to 24:00 LT, though in many cases scintillation at VHF persisted longer than that at L band. A longitudinal pattern in ion density irregularity occurrence was observed with peaks over 135–180°E and 270–300°E. The likelihood of ion density irregularity occurrence decreased with increasing altitude. Analysis of C/NOFS zonal ion drift velocities showed that the largest nighttime and daytime drifts were in 270–300°E and 300–330°E longitude regions respectively. Zonal irregularity drift velocities over East Africa were for the first time estimated from L-band scintillation indices. The results show that the velocity of plasma density irregularities in 2011 and 2012 varied daily, and hourly in the range of 50–150ms−1. The zonal drift velocity estimates from the L-band scintillation indices had good positive correlation with the zonal drift velocities derived from VHF receivers by the spaced receiver technique.

Assessment of scintillation proxy maps for a scintillation study during geomagnetically quiet and disturbed conditions over Uganda

The objective of this paper is demonstrate the validity and usefulness of scintillation proxies derived from IGS data, through its comparison with data from dedicated scintillation monitors and its application to GNSS scintillation patterns. The paper presents scintillation patterns developed by using data from the dedicated scintillation monitors of the scintillation network decision aid (SCINDA) network, and proxy maps derived from IGS GPS data for 2011 and 2012 over low latitude stations in Uganda. The amplitude and phase scintillation indicies (S4 and σΦ) were obtained from the Novatel GSV4004B ionospheric scintillation and total electron content (TEC) monitor managed by SCINDA at Makerere (0.340N, 32.570E). The corresponding IGS GPS proxy data were obtained from the receivers at Entebbe (0.040N, 32.440E) and Mbarara (0.600S, 30.740E). The derived amplitude (S4p) and phase (sDPR) scintillation proxy maps were compared with maps of S4 and σΦ during geomagnetic storms (moderate and strong) and geomagnetically quiet conditions. The scintillation patterns using S4 and σΦ and their respective proxies revealed similar diurnal and seasonal patterns of strong scintillation occurrence. The peaks of scintillation occurrence with mean values in the range 0.3<(S4p,sDPR)≤0.6 were observed during nighttime (17:00–22:00 UT) and in the months of March-April and September-October. The results also indicate that high level scintillations occur during geomagnetically disturbed (moderate and strong) and quiet conditions over the Ugandan region. The results show that SCINDA and IGS based scintillation patterns reveal the same nighttime and seasonal occurrence of irregularities over Uganda irrespective of the geomagnetic conditions. Therefore, the amplitude and phase scintillation proxies presented here can be used to fill gaps in low-latitude data where there are no data available from dedicated scintillation receivers, irrespective of the geomagnetic conditions.

A technique for inferring zonal irregularity drift from single‐station GNSS measurements of intensity (S4) and phase (σφ) scintillations

AbstractThe zonal drift of ionospheric irregularities at low latitudes is most commonly measured by cross‐correlating observations of a scintillating satellite signal made with a pair of closely spaced antennas. The Air Force Research Laboratory–Scintillation Network Decision Aid (AFRL‐SCINDA) network operates a small number of very high frequency (VHF) spaced‐receiver systems at low latitudes for this purpose. A far greater number of Global Navigation Satellite System (GNSS) scintillation monitors are operated by the AFRL‐SCINDA network (25–30) and the Low‐Latitude Ionospheric Sensor Network (35–50), but the receivers are too widely separated from each other for cross‐correlation techniques to be effective. In this paper, we present an alternative approach that leverages the weak scatter scintillation theory to infer the zonal irregularity drift from single‐station GNSS measurements of S4, σφ, and the propagation geometry. Unlike the spaced‐receiver technique, this approach requires assumptions regarding the height of the scattering layer (which introduces a bias in the drift estimates) and the spectral index of the irregularities (which affects the spread of the drift estimates about the mean). Nevertheless, theory and experiment suggest that the ratio of σφ to S4 is less sensitive to these parameters than it is to the zonal drift. We validate the technique using VHF spaced‐receiver measurements of zonal irregularity drift obtained from the AFRL‐SCINDA network. While the spaced‐receiver technique remains the preferred way to monitor the drift when closely spaced antenna pairs are available, our technique provides a new opportunity to monitor zonal irregularity drift using regional or global networks of widely separated GNSS scintillation monitors.

Analysis of Longitudinal Advancement of the Peak Total Electron Content in the African Equatorial Anomaly Region Using Data From GPS Receivers and GIS Stations in Kenya

We investigated longitudinal advancement of the peak Total Electron Content (TEC) within the equatorial anomaly region of Kenya, based on the data from the two Scintillation Network Decision Aid (SCINDA) Global Positioning System (GPS) receivers at Jomo Kenyatta University of Agriculture & Technology (JKUAT): latitude ?1.095, longitude 37.015, and at the University of Nairobi: latitude ?1.274, longitude 36.808; and the two Geographical Information System (GIS) stations at Malindi: latitude ?2.996, longitude 40.194, and at the Regional Center for Mapping of Resources for Development (RCMRD): latitude ?1.221, longitude 36.893. The retrieved archived data from these stations were for 17 th December 2009; and for 26 th , 27 th and 28 th August 2010 —just after the solar minimum period of 2008. They were subjected to analysis by the GPS-TEC analysis application software provided by Boston College Research Institute (USA). Results reveal that the peak TEC within the region of study occurs between 8 a.m. and 10 a.m. The Coastal region experiences peak TEC earlier than Nairobi region. Slight variations were also observed on the TEC plots from various stations. It can be concluded that the peak TEC advances westwards within the equatorial anomaly region; these variations are due to plasma bubbles that take place from the east to west within the equatorial region.

Climatology of ionospheric scintillations and TEC trend over the Ugandan region

This study presents results on the investigation of the diurnal, monthly and seasonal variability of Total Electron Content (TEC), phase (σΦ) and amplitude (S4) scintillation indices over Ugandan (Low latitude) region. Scintillation Network Decision Aid (SCINDA) data was obtained from Makerere (0.34°N, 32.57°E) station, Uganda for two years (2011 and 2012). Data from two dual frequency GPS receivers at Mbarara (0.60°S, 30.74°E) and Entebbe (0.04°N, 32.44°E) was used to study TEC climatology during the same period of scintillation study. The results show that peak TEC values were recorded during the months of October–November, and the lowest values during the months of July–August. The diurnal peak of TEC occurs between 10:00 and 14:00 UT hours. Seasonally, the ascending and descending phases of TEC were observed during the equinoxes (March and September) and solstice (June and December), respectively. The scintillations observed during the study were classified as weak (0.1≤S4,σΦ≤0.3) and strong (0.3<S4,σΦ≤1.0). The diurnal scintillation pattern showed peaks between 17:00 and 22:00 UT hour, while the seasonal pattern follows the TEC pattern mentioned above. Amplitude scintillation was more dominant than phase scintillation during the two years of the study. Scintillation peaks occur during the months of March–April and September–October, while the least scintillations occur during the months of June–July. Therefore, the contribution of this study is filling the gap in the current documentation of amplitude scintillation without phase scintillation over the Ugandan region. The scintillations observed have been attributed to wave-like structures which have periods of about 2–3h, in the range of that of large scale travelling ionospheric disturbances (LSTIDs).

A comparison of IRI‐TEC predictions with GPS‐TEC measurements over Nsukka, Nigeria

The International Reference Ionosphere (IRI) model has been widely adopted as the international standard for specifying ionospheric parameters. An evaluation on the performance of the IRI model (version 2007) over Nsukka, Nigeria (Geographic: 6.87°N, 7.38°E; Geomagnetic: 8.47°N, 81.07°E) is presented in this work. We compare Total Electron Content (TEC) values for year 2010 from the IRI model with corresponding TEC data from the SCINDA (Scintillation Network Decision Aid) GPS receiver installed at Nsukka so as to evaluate the performance of the model over the Nsukka region. Given the proliferation of dual‐frequency GPS receivers over the African continent, data from these equipment is proposed for use in TEC modeling over the continent together with the IRI model. Knowledge on the performance of the IRI over various regions of the continent will inform the extent to which the model will be used. The development of more accurate TEC maps find useful applications in enhancing the extent to which ionospheric influences on radio signals (as in single frequency GPS receivers) are corrected. Our results show very good diurnal correlations (above 0.88) between the IRI‐TEC predictions and the GPS‐TEC measurements for the days examined, and so reveal the potential of the IRI model as a good candidate for an enhanced TEC modeling over the African region.

Images of bottomside irregularities observed at topside altitudes

We analyzed plasma and field measurements acquired by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during an eight‐hour period on 13–14 January 2010 when strong to moderate 250 MHz scintillation activity was observed at nearby Scintillation Network Decision Aid (SCINDA) ground stations. C/NOFS consistently detected relatively small‐scale density and electric field irregularities embedded within large‐scale (∼100 km) structures at topside altitudes. Significant spectral power measured at the Fresnel (∼1 km) scale size suggests that C/NOFS was magnetically conjugate to bottomside irregularities similar to those directly responsible for the observed scintillations. Simultaneous ion drift and plasma density measurements indicate three distinct types of large‐scale irregularities: (1) upward moving depletions, (2) downward moving depletions, and (3) upward moving density enhancements. The first type has the characteristics of equatorial plasma bubbles; the second and third do not. The data suggest that both downward moving depletions and upward moving density enhancements and the embedded small‐scale irregularities may be regarded as Alfvénic images of bottomside irregularities. This interpretation is consistent with predictions of previously reported theoretical modeling and with satellite observations of upward‐directed Poynting flux in the low‐latitude ionosphere.

Specification of the occurrence of equatorial ionospheric scintillations during the main phase of large magnetic storms within solar cycle 23

[1] Satellite communication and navigation systems operating at low latitudes suffer outages due to ionospheric scintillations during large magnetic storms that are not currently specified by any model. This paper describes and demonstrates how in the framework of an eastward electric field penetration from high to low latitudes at dusk during the main phase of a large storm, for which the rate of change of Dst ≤ −50 nT/h and the Dst minimum index ≤ −100 nT, it is possible to specify the longitude interval within the low-latitude ionosphere where scintillations and plasma bubbles are most likely to occur. It is known that the eastward prompt penetration electric field becomes enhanced near sunset due to the day-to-night conductivity gradient. Such enhanced eastward electric fields generally set off the Rayleigh-Taylor plasma instability at F region heights and cause the formation of plasma bubbles and irregularities of electron density that give rise to scintillations of satellite signals. We first discuss two individual magnetic storms that satisfy the criterion of large magnetic storms mentioned above and for which the onsets of the main phase are about 15 h apart. We show that the dusk sectors corresponding to these two storms are such that irregularities and scintillations were observed in the Atlantic-Peruvian longitude sector for one storm and in the Pacific sector for the other. We then present a statistical study with 30 large magnetic storms during solar cycle 23 which satisfy the two criteria of large magnetic storms and we attempt to specify the longitude interval of irregularity and scintillation occurrence during the main phase of such storms. We have tracked globally the occurrence of equatorial scintillations during magnetic storms by the use of scintillation observations made by the Air Force Research Laboratory's Scintillation Network Decision Aid (SCINDA) network and the DMSP satellite in situ measurements of plasma bubbles at 840 km. The statistical study reveals that during large magnetic storms, scintillations and plasma bubbles occur over a specific longitude sector for which the local dusk corresponds to the time interval of the main phase of storms. The magnetic storm induced scintillations may enhance the general seasonal/longitudinal pattern of quiet time scintillations at the station but may also occur where it is least expected in accordance with climatology. The storm time response of the equatorial ionosphere discussed in this paper will be implemented in the SCINDA algorithm to enhance its capability to specify scintillations during large magnetic storms.

Extreme longitudinal variability of plasma structuring in the equatorial ionosphere on a magnetically quiet equinoctial day

We investigate the extreme longitudinal variability of equatorial scintillation under quiet magnetic conditions during 22–23 March 2002. Scintillation Network Decision Aid (SCINDA) observations show intense activity in the South American–Atlantic sector during local evening hours, whereas an absence of scintillation is seen in the far east Asian sector. Ground‐ and space‐based measurements from SCINDA, the Global Ultraviolet Imager (GUVI), TOPEX, and a chain of GPS receivers are used in combination with the Utah State University Global Assimilation of Ionospheric Measurements (USU‐GAIM) model to explore the relationship between the large‐scale ionization distribution and small‐scale irregularities at low latitudes in both the scintillating and nonscintillating longitude sectors. Our analysis shows that there are significant differences in the evolution of the ionization distributions during the evening hours, which are likely the result of differences in the daytime and postsunset vertical plasma drift in the two sectors. This study demonstrates the importance of USU‐GAIM as a new tool for investigating longitudinal as well as day‐to‐day variability that is observed in the large‐scale distribution of the ionosphere and how this relates to the occurrence of scintillation.

Longitudinal correlation of equatorial ionospheric scintillation

Studies at the Air Force Research Laboratory are investigating methods for the incorporation of expected data sets from the Communication/Navigation Outage Forecast System (C/NOFS) satellite into existing scintillation specification models for an improved knowledge of the regional scintillation environment. Results from this research will form the basis for ground‐based empirical scintillation forecast algorithms. One such study involves a determination of the extent to which correlations can be made for scintillation over a range of longitudes providing valid upstream (westward) forecasts of scintillation activity based on near real‐time observations. Using archived data collected on Scintillation Network Decision Aid (SCINDA) receivers, a comprehensive study was conducted to numerically evaluate the correlation of scintillation on link pairings separated by varying degrees of longitude representing up to 3 hours in local time.

GPS proxy model for real‐time UHF satellite communications scintillation maps from the Scintillation Network Decision Aid (SCINDA)

In order to provide a more reliable situational awareness of scintillation impacts on users of space‐based communication/navigation systems, L‐band scintillation measurements from GPS satellites are ingested, in real time, to the Scintillation Network Decision Aid (SCINDA) model. SCINDA is a real‐time, data‐driven communication outage forecast and alert system developed by the Air Force Research Laboratory at Hanscom Air Force Base and made operational through a joint effort between the U.S. Air Force and the U.S. Navy. UHF and L‐band scintillation parameters are measured, modeled, and propagated in time to provide a regional specification of the scintillation environment in an effort to mitigate the impacts on the satellite communications (SATCOM) community. In an effort to provide UHF SATCOM users with a more consistent estimation of scintillation impacts on their systems, GPS sensors, measuring S4 at L‐band frequency, are now used as a supplement to the stationary UHF links dramatically increasing the regional coverage at each individual station, particularly those located outside the anomaly crest. Three‐dimensional representations of GPS observed plumes are mapped to the ground from the location of a selected satellite, producing a “scintillation specification map detailing “outage” regions on the globe. In this paper we present results from a validation study of the GPS proxy model and demonstrate its usefulness as an adjunct to the SCINDA model in producing the most accurate and reliable nowcast and forecast scintillation specification products available to UHF SATCOM users.

Equatorial scintillation and systems support

The need to nowcast and forecast scintillation for the support of operational systems has been recently identified by the interagency National Space Weather Program. This issue is addressed in the present paper in the context of nighttime irregularities in the equatorial ionosphere that cause intense amplitude and phase scintillations of satellite signals in the VHF/UHF range of frequencies and impact satellite communication, Global Positioning System navigation, and radar systems. Multistation and multifrequency satellite scintillation observations have been used to show that even though equatorial scintillations vary in accordance with the solar cycle, the extreme day‐to‐day variability of unknown origin modulates the scintillation occurrence during all phases of the solar cycle. It is shown that although equatorial scintillation events often show correlation with magnetic activity, the major component of scintillation is observed during magnetically quiet periods. In view of the day‐to‐day variability of the occurrence and intensity of scintillating regions, their latitude extent, and their zonal motion, a regional specification and short‐term forecast system based on real‐time measurements has been developed. This system, named the Scintillation Network Decision Aid, consists of two latitudinally dispersed stations, each of which uses spaced antenna scintillation receiving systems to monitor 250‐MHz transmissions from two longitudinally separated geostationary satellites. The scintillation index and zonal irregularity drift are processed on‐line and are retrieved by a remote operator on the Internet. At the operator terminal the data are combined with an empirical plasma bubble model to generate three‐dimensional maps of irregularity structures and two‐dimensional outage maps for the region.