E. Yizengaw - Academia.edu (original) (raw)

Papers by E. Yizengaw

Journal of Atmospheric and Solar-Terrestrial Physics, 2013

ABSTRACT We report on Pc5 wave related electric field and vertical drift velocity oscillations at... more ABSTRACT We report on Pc5 wave related electric field and vertical drift velocity oscillations at the equator as observed by ground magnetometers for an extended period on 9 August 2008. We show that the magnetometer-estimated equatorial E x B drift oscillates with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. We also show ionospheric density fluctuations during the period when we observed ULF wave activity. At the same time, we detect the ULF activity on the ground using ground-based magnetometer data from the African Meridian B-field Education and Research (AMBER) and the South American Meridional B-field Array (SAMBA). From space, we use magnetic field observations from the GOES 12 and the Communication/Navigation Outage and Forecast System (C/NOFS) satellites. Upstream solar wind conditions are provided by the ACE spacecraft. We find that the wave power observed on the ground also occurs in the upstream solar wind and in the magnetosphere. All these observations demonstrate that Pc5 waves with a likely driver in the solar wind can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. While no direct drift measurements from equatorial radars exist for the 9 August 2008 event, we used JULIA 150 km radar drift velocities observed on 2 May 2010 and found similar fluctuations with the period of 5-8 min, as a means of an independent confirmation of our magnetometer derived drift dynamics.

Les observatoires magnétiques de Médéa (Réseau AMBER) implanté au nord de l'Algérie (2,72°E, ... more Les observatoires magnétiques de Médéa (Réseau AMBER) implanté au nord de l'Algérie (2,72°E, 36,29°N) et de Tamanrasset (réseau INTERMAGNET) implanté au sud (5,52°E, 22,79°N) fournissent des enregistrements continues du Champ Magnétique Terrestre. Les données minutes, récoltée durant l'année 2010, ont servies au calcul et à l’analyse de la variation solaire journalière et saisonnière des composantes horizontale Sq(H) et verticale Sq(Z). Ces dernières ont été corrigées des variations non-cycliques. La moyenne de la variation solaire est prise sur les valeurs moyennes horaires des jours les plus calmes de tous les mois et des trois saisons de l'année 2010(minimum du cycle solaire 24). les variation Sq(H) et Sq(Z) conserve pratiquement la même allure de mois en mois. Néanmoins, du fait de la situation géographique des deux observatoires, elle présente des amplitudes différentes. En effet l'amplitude maximale atteinte aux alentours de midi (heure locale) est de 20 nT à M...

nationalacademies.org

Satellite observations (see Figure 1) show unique equatorial ionospheric structures only in the A... more Satellite observations (see Figure 1) show unique equatorial ionospheric structures only in the African sector [Hei et al., 2005; Su, 2005; Burke et al., 2006; Yizengaw et al., 2010]. It has been observed that in this region the bubbles are much deeper and occur more frequently than ...

Journal of Atmospheric and Solar-Terrestrial Physics, 2015

1. As (1) above, but E-mail E-mail: P.dyson@latrobe.edu.au (3) As (1) above, but ABSTRACT This pa... more 2) As (1) above, but E-mail E-mail: P.dyson@latrobe.edu.au (3) As (1) above, but ABSTRACT This paper describes the experimental procedures of tomographic imaging techniques that have been developed and used at La Trobe University. Tomographic imaging provides a powerful technique for obtaining images of the ionospheric electron density distribution, and is a relatively new technique which has promising features to supplement the most expensive ground-based vertical sounding instruments such as ionosonde and incoherent radar. The technique, which involves monitoring radio transmission from Global Positioning System (GPS) along a meridional chain of ground based receivers, has particular potential for complementing temporal measurements by other observing techniques such as ionosondes. The tomographic inversion algorithm has been applied to actual GPS-based total electron content (TEC) measurements obtained during two severe magnetic storm periods (18 August 2003 and 31 March 2001). The tomographic reconstruction presented here revealed important features in ionospheric structure such as ionization troughs and quasi-wave formations. Electron density profiles obtained by the tomographic reconstruction method are in excellent agreement with profiles obtained by ionosondes at or near the GPS receiver stations, confirming the validity of the tomographic algorithm that has been developed. Geophysical interpretations of the observations are also presented.

On 07 September 2001 the Cluster spacecraft observed a "bursty bulk flow" event in the near-Earth... more On 07 September 2001 the Cluster spacecraft observed a "bursty bulk flow" event in the near-Earth central plasma sheet. This paper presents a detailed study of the coincident ground-based observations and attempts to place them within a simple physical framework. The event in question occurs at ∼22:30 UT, some 10 min after a southward turning of the IMF. IMAGE and SAMNET magnetometer measurements of the ground magnetic field reveal perturbations of a few tens of nT and small amplitude Pi2 pulsations. CUTLASS radar observations of ionospheric plasma convection show enhanced flows out of the polar cap near midnight, accompanied by an elevated transpolar voltage. Optical data from the IMAGE satellite also show that there is a transient, localised ∼1 kR brightening in the UV aurora. These observations are consistent with the earthward transport of plasma in the tail, but also indicate the absence of a typical "large-scale" substorm current wedge. An analysis of the field-aligned current system implied by the radar measurements does suggest the existence of a small-scale current "wedgelet", but one which lacks the global scale and high conductivities observed during substorm expansions.

This study investigates the performances of the NeQuick 2 empirical model in the East-African reg... more This study investigates the performances of the NeQuick 2 empirical model in the East-African region by assisting this model with Global Positioning System (GPS) measurements obtained from a single station. First we calculate an effective ionization level that drives NeQuick 2 to reproduce TEC that fits the least square sense to the measurements. We then quantify the performances of the NeQuick 2 in reproducing the topside in situ ion density observed by Communication/ Navigation Outage Forecast System (C/NOFS) satellite after modifying the model's input parameter. This is done by inputting the effective ionization level calculated from the slant total electron content (sTEC) measurements obtained from the single GPS receiver to the model. The performances of the model before and after data ingestion are then investigated by comparing the model results with the topside in situ ion density observation. One-month data during low solar activity conditions were used in this study. W...

The occurrence of Equatorial Plasma Bubbles (EPBs) has become an important research topic in the ... more The occurrence of Equatorial Plasma Bubbles (EPBs) has become an important research topic in the field of space science in recent years, due to the adverse influence of EPBs on many important technological applications. One such application is the use of Global Navigation Satellite System (GNSS) signals, such as the Global Positioning System (GPS). The seasonal/longitudinal variability in EPB occurrence is relatively well understood, following decades of EPB observations spanning around the globe. A key unresolved issue is the daily variability in the occurrence of EPBs. To address this issue, an analysis of the daily GPS scintillation occurrence variability in several locations was conducted, and was complimented by coupled ionosphere-thermosphere modeling. It was found that the coupled ionosphere-thermosphere model, which was run independently of ionospheric observations, exhibited a daily variability that closely matched the observations. Further investigation found that the mode...

Geophysical Research Letters, 2014

ABSTRACT The feasibility of predicting the daily occurrence of Global Positioning System scintill... more ABSTRACT The feasibility of predicting the daily occurrence of Global Positioning System scintillation events using forecasts of common geophysical indices to drive a physics-based model of the system is demonstrated over a 5-month period for the African and Asian longitude sectors. The output from the Wing Kp model, which uses solar wind data to predict the geomagnetic activity level up to four hours in advance, was used to drive the NCAR thermosphere/ionosphere model (TIEGCM), from which the strength of the Rayleigh-Taylor instability growth rate was calculated to determine the likelihood of scintillation. It is found that the physics-based model demonstrates superior skill to an empirical scintillation model (WBMOD) in forecasting scintillation suppression events during seasons when scintillation is common. However, neither of the models driven in this way possess the ability to forecast isolated scintillation events during transitional and off-peak seasons.

Applications that heavily rely on trans-ionospheric radio signals are subjected to many space wea... more Applications that heavily rely on trans-ionospheric radio signals are subjected to many space weather phenomena that can adversely affect their operations. Perhaps the most significant space weather phenomenon affecting GNSS in particular is the generation of ionospheric plasma irregularities (or plasma waves) at locations close to the magnetic equator during the night time. As the GNSS signals pass through the ionosphere, they are effectively diffracted by the ionospheric irregularities, causing random fluctuations in the measured amplitude and phase of the signal; i.e., amplitude and phase scintillation. These ionospheric irregularities are associated with large plasma depletions, called Equatorial Plasma Bubbles (EPBs) that develop during the night time near the magnetic equator. The physical mechanism that drives the generation of these EPBs is the generalised Rayleigh-Taylor instability. The seasonal/longitudinal occurrence climatology of the EPBs is well documented, following decades of ground-based and space-based remote sensing and in-situ observations. However, there are still significant questions as to what exactly controls the day-to-day EPB occurrence. In this study, a multi-instrument approach is used to investigate the mechanisms driving the generation of EPBs in the Australian longitude sector during the equinox months, when EPBs are typically rather common. The results are then discussed in the context of formulating a GNSS scintillation event prediction capability.

ABSTRACT Global Positioning System (GPS) navigation measurements have become useful in observing ... more ABSTRACT Global Positioning System (GPS) navigation measurements have become useful in observing the ionospheric spatial electron density distribution TEC from ground-based receivers are biased by the high density around the F2 peak and therefore it is difficult to extract information about the topside ionosphere and plasmasphere. GPS measurements onboard Low Earth Orbiting (LEO) satellites provide more detailed observations of the ionospheric electron density distribution from the orbit height of the LEO satellite to GPS orbit heights. We use GPS TEC measurements onboard COSMIC satellites to reconstruct the topside ionosphere and plasmasphere electron density distribution for both geomagnetically quiet and disturbed conditions during over-flights of the American and African mid-latitude regions by the COSMIC spacecraft using algebraic tomographic reconstruction technique (ART). The reconstructions provide more detailed information of the longitudinal and vertical spatial structure of topside ionosphere and plasmasphere during both geomagnetically quiet and disturbed conditions, and indicate the great potential of evaluating ionospheric models in the topside ionosphere/plasmasphere altitude range.

ABSTRACT Much of our understanding of this complex equatorial electrodynamics and ionospheric den... more ABSTRACT Much of our understanding of this complex equatorial electrodynamics and ionospheric density distribution has been primarily based on observation from the only equatorial Jicamarca incoherent scatter radar (ISR) instrument (even though satellite observation telling us differently) which is located in the region where fairly large excursion between the geomagnetic and geographic equator is available. In the African sector, where there is currently no incoherent (or coherent) scatter radar, the geomagnetic and geodetic equators are reasonably parallel, separated by at most 10 degrees. Data from satellites (e.g. ROCSAT, C/NOFS, DMSP) have indicated that the equatorial ionosphere in the African sector responds differently than other sectors. For example, ionospheric bubbles have been observed to be much deeper and to occur more frequently in the African sector. It has also been reported that ionospheric depletions more frequently rise to higher altitudes (up to 1000+ km) in the African sector than those in other longitude sectors. However, these observations have not been confirmed, validated or studied in detail by observations from the ground due to lack of suitable ground-based instrumentation in Africa. Thus, the causes or driving mechanisms of the unique density irregularities, bubbles, and depletions in the African sector remain unresolved. To address these issues, the U.S. National Science Foundation has recently sponsored a workshop that has been held at Boston College to consider the possibility of relocating an Advanced Modular Incoherent Scatter Radar (AMISR) to Ethiopia. Adding a single ISR to the recently growing number of ground-based space science instruments in the continent, such as GPS, magnetometers, VHF, and Ionosonde, would be of significant scientific benefit. The primary purpose of this workshop was to define the science goals motivating such a move and to examine the technical and logistical issues involved. This talk will summarize the findings of this workshop.

ABSTRACT Although Satellite observations in the African sector show unique equatorial ionospheric... more ABSTRACT Although Satellite observations in the African sector show unique equatorial ionospheric structures that can severely impact navigation and communication systems, the study of ionospheric disturbances in this region is difficult due to the lack of ground-based instruments. This has created a gap in global understanding of the physics behind the evolution and formation of plasma irregularities in the equatorial region, which imposes limitations on ionospheric density modeling efforts. Therefore, in order to have a more complete global understanding of equatorial ionosphere motion, the international space science community has begun to develop an observational infrastructure in the African sector. This includes the deployment of a number of arrays of small instruments, including the AMBER magnetometer array, through the International Heliophysical Year (IHY) cooperative program with the United Nations Basic Space Science (UNBSS) program. Two AMBER magnetometers have been deployed successfully at Adigrat (~6°N magnetic) in Ethiopia and at Medea in Algeria (28°N magnetic), and became fully operational on 03 August 2008. The remaining two AMBER magnetometers will be deployed soon in Cameroon and Namibia. One of the prime scientific objectives of AMBER is to understand the processes governing electrodynamics of the equatorial ionosphere as a function of latitude, local time, magnetic activity, and season in the African region. The most credible driving mechanism of ionospheric plasma (E × B drift) can be estimated using two magnetometers, one right at the equator and the other about 6 off the equator. Therefore, using the AMBER magnetometer at Adigrat and the INTERMAGNET magnetometer located at Addis Ababa (0.9°N magnetic) in Ethiopia, the equatorial electrojet (E × B drift) activities in that longitudinal sector of the African continent is estimated. The paper also presents the comparison between the estimated vertical drift and the drift values obtained from the vector electric field instrument observation onboard the C/NOFS satellite. The evolution of equatorial ionospheric irregularities will also be presented using data from the growing number of ground- and space-based (on Low-Earth-Orbit (LEO) satellites) GPS receivers in the African region.

Journal of Atmospheric and Solar-Terrestrial Physics, 2013

ABSTRACT We report on Pc5 wave related electric field and vertical drift velocity oscillations at... more ABSTRACT We report on Pc5 wave related electric field and vertical drift velocity oscillations at the equator as observed by ground magnetometers for an extended period on 9 August 2008. We show that the magnetometer-estimated equatorial E x B drift oscillates with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. We also show ionospheric density fluctuations during the period when we observed ULF wave activity. At the same time, we detect the ULF activity on the ground using ground-based magnetometer data from the African Meridian B-field Education and Research (AMBER) and the South American Meridional B-field Array (SAMBA). From space, we use magnetic field observations from the GOES 12 and the Communication/Navigation Outage and Forecast System (C/NOFS) satellites. Upstream solar wind conditions are provided by the ACE spacecraft. We find that the wave power observed on the ground also occurs in the upstream solar wind and in the magnetosphere. All these observations demonstrate that Pc5 waves with a likely driver in the solar wind can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. While no direct drift measurements from equatorial radars exist for the 9 August 2008 event, we used JULIA 150 km radar drift velocities observed on 2 May 2010 and found similar fluctuations with the period of 5-8 min, as a means of an independent confirmation of our magnetometer derived drift dynamics.

Les observatoires magnétiques de Médéa (Réseau AMBER) implanté au nord de l'Algérie (2,72°E, ... more Les observatoires magnétiques de Médéa (Réseau AMBER) implanté au nord de l'Algérie (2,72°E, 36,29°N) et de Tamanrasset (réseau INTERMAGNET) implanté au sud (5,52°E, 22,79°N) fournissent des enregistrements continues du Champ Magnétique Terrestre. Les données minutes, récoltée durant l'année 2010, ont servies au calcul et à l’analyse de la variation solaire journalière et saisonnière des composantes horizontale Sq(H) et verticale Sq(Z). Ces dernières ont été corrigées des variations non-cycliques. La moyenne de la variation solaire est prise sur les valeurs moyennes horaires des jours les plus calmes de tous les mois et des trois saisons de l'année 2010(minimum du cycle solaire 24). les variation Sq(H) et Sq(Z) conserve pratiquement la même allure de mois en mois. Néanmoins, du fait de la situation géographique des deux observatoires, elle présente des amplitudes différentes. En effet l'amplitude maximale atteinte aux alentours de midi (heure locale) est de 20 nT à M...

nationalacademies.org

Satellite observations (see Figure 1) show unique equatorial ionospheric structures only in the A... more Satellite observations (see Figure 1) show unique equatorial ionospheric structures only in the African sector [Hei et al., 2005; Su, 2005; Burke et al., 2006; Yizengaw et al., 2010]. It has been observed that in this region the bubbles are much deeper and occur more frequently than ...

Journal of Atmospheric and Solar-Terrestrial Physics, 2015

1. As (1) above, but E-mail E-mail: P.dyson@latrobe.edu.au (3) As (1) above, but ABSTRACT This pa... more 2) As (1) above, but E-mail E-mail: P.dyson@latrobe.edu.au (3) As (1) above, but ABSTRACT This paper describes the experimental procedures of tomographic imaging techniques that have been developed and used at La Trobe University. Tomographic imaging provides a powerful technique for obtaining images of the ionospheric electron density distribution, and is a relatively new technique which has promising features to supplement the most expensive ground-based vertical sounding instruments such as ionosonde and incoherent radar. The technique, which involves monitoring radio transmission from Global Positioning System (GPS) along a meridional chain of ground based receivers, has particular potential for complementing temporal measurements by other observing techniques such as ionosondes. The tomographic inversion algorithm has been applied to actual GPS-based total electron content (TEC) measurements obtained during two severe magnetic storm periods (18 August 2003 and 31 March 2001). The tomographic reconstruction presented here revealed important features in ionospheric structure such as ionization troughs and quasi-wave formations. Electron density profiles obtained by the tomographic reconstruction method are in excellent agreement with profiles obtained by ionosondes at or near the GPS receiver stations, confirming the validity of the tomographic algorithm that has been developed. Geophysical interpretations of the observations are also presented.

On 07 September 2001 the Cluster spacecraft observed a "bursty bulk flow" event in the near-Earth... more On 07 September 2001 the Cluster spacecraft observed a "bursty bulk flow" event in the near-Earth central plasma sheet. This paper presents a detailed study of the coincident ground-based observations and attempts to place them within a simple physical framework. The event in question occurs at ∼22:30 UT, some 10 min after a southward turning of the IMF. IMAGE and SAMNET magnetometer measurements of the ground magnetic field reveal perturbations of a few tens of nT and small amplitude Pi2 pulsations. CUTLASS radar observations of ionospheric plasma convection show enhanced flows out of the polar cap near midnight, accompanied by an elevated transpolar voltage. Optical data from the IMAGE satellite also show that there is a transient, localised ∼1 kR brightening in the UV aurora. These observations are consistent with the earthward transport of plasma in the tail, but also indicate the absence of a typical "large-scale" substorm current wedge. An analysis of the field-aligned current system implied by the radar measurements does suggest the existence of a small-scale current "wedgelet", but one which lacks the global scale and high conductivities observed during substorm expansions.

This study investigates the performances of the NeQuick 2 empirical model in the East-African reg... more This study investigates the performances of the NeQuick 2 empirical model in the East-African region by assisting this model with Global Positioning System (GPS) measurements obtained from a single station. First we calculate an effective ionization level that drives NeQuick 2 to reproduce TEC that fits the least square sense to the measurements. We then quantify the performances of the NeQuick 2 in reproducing the topside in situ ion density observed by Communication/ Navigation Outage Forecast System (C/NOFS) satellite after modifying the model's input parameter. This is done by inputting the effective ionization level calculated from the slant total electron content (sTEC) measurements obtained from the single GPS receiver to the model. The performances of the model before and after data ingestion are then investigated by comparing the model results with the topside in situ ion density observation. One-month data during low solar activity conditions were used in this study. W...

The occurrence of Equatorial Plasma Bubbles (EPBs) has become an important research topic in the ... more The occurrence of Equatorial Plasma Bubbles (EPBs) has become an important research topic in the field of space science in recent years, due to the adverse influence of EPBs on many important technological applications. One such application is the use of Global Navigation Satellite System (GNSS) signals, such as the Global Positioning System (GPS). The seasonal/longitudinal variability in EPB occurrence is relatively well understood, following decades of EPB observations spanning around the globe. A key unresolved issue is the daily variability in the occurrence of EPBs. To address this issue, an analysis of the daily GPS scintillation occurrence variability in several locations was conducted, and was complimented by coupled ionosphere-thermosphere modeling. It was found that the coupled ionosphere-thermosphere model, which was run independently of ionospheric observations, exhibited a daily variability that closely matched the observations. Further investigation found that the mode...

Geophysical Research Letters, 2014

ABSTRACT The feasibility of predicting the daily occurrence of Global Positioning System scintill... more ABSTRACT The feasibility of predicting the daily occurrence of Global Positioning System scintillation events using forecasts of common geophysical indices to drive a physics-based model of the system is demonstrated over a 5-month period for the African and Asian longitude sectors. The output from the Wing Kp model, which uses solar wind data to predict the geomagnetic activity level up to four hours in advance, was used to drive the NCAR thermosphere/ionosphere model (TIEGCM), from which the strength of the Rayleigh-Taylor instability growth rate was calculated to determine the likelihood of scintillation. It is found that the physics-based model demonstrates superior skill to an empirical scintillation model (WBMOD) in forecasting scintillation suppression events during seasons when scintillation is common. However, neither of the models driven in this way possess the ability to forecast isolated scintillation events during transitional and off-peak seasons.

Applications that heavily rely on trans-ionospheric radio signals are subjected to many space wea... more Applications that heavily rely on trans-ionospheric radio signals are subjected to many space weather phenomena that can adversely affect their operations. Perhaps the most significant space weather phenomenon affecting GNSS in particular is the generation of ionospheric plasma irregularities (or plasma waves) at locations close to the magnetic equator during the night time. As the GNSS signals pass through the ionosphere, they are effectively diffracted by the ionospheric irregularities, causing random fluctuations in the measured amplitude and phase of the signal; i.e., amplitude and phase scintillation. These ionospheric irregularities are associated with large plasma depletions, called Equatorial Plasma Bubbles (EPBs) that develop during the night time near the magnetic equator. The physical mechanism that drives the generation of these EPBs is the generalised Rayleigh-Taylor instability. The seasonal/longitudinal occurrence climatology of the EPBs is well documented, following decades of ground-based and space-based remote sensing and in-situ observations. However, there are still significant questions as to what exactly controls the day-to-day EPB occurrence. In this study, a multi-instrument approach is used to investigate the mechanisms driving the generation of EPBs in the Australian longitude sector during the equinox months, when EPBs are typically rather common. The results are then discussed in the context of formulating a GNSS scintillation event prediction capability.

ABSTRACT Global Positioning System (GPS) navigation measurements have become useful in observing ... more ABSTRACT Global Positioning System (GPS) navigation measurements have become useful in observing the ionospheric spatial electron density distribution TEC from ground-based receivers are biased by the high density around the F2 peak and therefore it is difficult to extract information about the topside ionosphere and plasmasphere. GPS measurements onboard Low Earth Orbiting (LEO) satellites provide more detailed observations of the ionospheric electron density distribution from the orbit height of the LEO satellite to GPS orbit heights. We use GPS TEC measurements onboard COSMIC satellites to reconstruct the topside ionosphere and plasmasphere electron density distribution for both geomagnetically quiet and disturbed conditions during over-flights of the American and African mid-latitude regions by the COSMIC spacecraft using algebraic tomographic reconstruction technique (ART). The reconstructions provide more detailed information of the longitudinal and vertical spatial structure of topside ionosphere and plasmasphere during both geomagnetically quiet and disturbed conditions, and indicate the great potential of evaluating ionospheric models in the topside ionosphere/plasmasphere altitude range.

ABSTRACT Much of our understanding of this complex equatorial electrodynamics and ionospheric den... more ABSTRACT Much of our understanding of this complex equatorial electrodynamics and ionospheric density distribution has been primarily based on observation from the only equatorial Jicamarca incoherent scatter radar (ISR) instrument (even though satellite observation telling us differently) which is located in the region where fairly large excursion between the geomagnetic and geographic equator is available. In the African sector, where there is currently no incoherent (or coherent) scatter radar, the geomagnetic and geodetic equators are reasonably parallel, separated by at most 10 degrees. Data from satellites (e.g. ROCSAT, C/NOFS, DMSP) have indicated that the equatorial ionosphere in the African sector responds differently than other sectors. For example, ionospheric bubbles have been observed to be much deeper and to occur more frequently in the African sector. It has also been reported that ionospheric depletions more frequently rise to higher altitudes (up to 1000+ km) in the African sector than those in other longitude sectors. However, these observations have not been confirmed, validated or studied in detail by observations from the ground due to lack of suitable ground-based instrumentation in Africa. Thus, the causes or driving mechanisms of the unique density irregularities, bubbles, and depletions in the African sector remain unresolved. To address these issues, the U.S. National Science Foundation has recently sponsored a workshop that has been held at Boston College to consider the possibility of relocating an Advanced Modular Incoherent Scatter Radar (AMISR) to Ethiopia. Adding a single ISR to the recently growing number of ground-based space science instruments in the continent, such as GPS, magnetometers, VHF, and Ionosonde, would be of significant scientific benefit. The primary purpose of this workshop was to define the science goals motivating such a move and to examine the technical and logistical issues involved. This talk will summarize the findings of this workshop.

ABSTRACT Although Satellite observations in the African sector show unique equatorial ionospheric... more ABSTRACT Although Satellite observations in the African sector show unique equatorial ionospheric structures that can severely impact navigation and communication systems, the study of ionospheric disturbances in this region is difficult due to the lack of ground-based instruments. This has created a gap in global understanding of the physics behind the evolution and formation of plasma irregularities in the equatorial region, which imposes limitations on ionospheric density modeling efforts. Therefore, in order to have a more complete global understanding of equatorial ionosphere motion, the international space science community has begun to develop an observational infrastructure in the African sector. This includes the deployment of a number of arrays of small instruments, including the AMBER magnetometer array, through the International Heliophysical Year (IHY) cooperative program with the United Nations Basic Space Science (UNBSS) program. Two AMBER magnetometers have been deployed successfully at Adigrat (~6°N magnetic) in Ethiopia and at Medea in Algeria (28°N magnetic), and became fully operational on 03 August 2008. The remaining two AMBER magnetometers will be deployed soon in Cameroon and Namibia. One of the prime scientific objectives of AMBER is to understand the processes governing electrodynamics of the equatorial ionosphere as a function of latitude, local time, magnetic activity, and season in the African region. The most credible driving mechanism of ionospheric plasma (E × B drift) can be estimated using two magnetometers, one right at the equator and the other about 6 off the equator. Therefore, using the AMBER magnetometer at Adigrat and the INTERMAGNET magnetometer located at Addis Ababa (0.9°N magnetic) in Ethiopia, the equatorial electrojet (E × B drift) activities in that longitudinal sector of the African continent is estimated. The paper also presents the comparison between the estimated vertical drift and the drift values obtained from the vector electric field instrument observation onboard the C/NOFS satellite. The evolution of equatorial ionospheric irregularities will also be presented using data from the growing number of ground- and space-based (on Low-Earth-Orbit (LEO) satellites) GPS receivers in the African region.