Browsing by Author "Omondi, George"

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    Application of Classical Kalman filtering technique in assimilation of multiple data types to NeQuick model
    (EDP Sciences, 2022-03-03) Mungufeni, Patrick; Migoya-Orué, Yenca; Matamba, Tshimangadzo Merline; Omondi, George
    This study attempts to improve estimation of ionospheric electron density profiles over Korea and adjacent areas by employing classical Kalman filtering technique to assimilate Total Electron Content (TEC) data from various sources into the NeQuick model. Successive corrections method was applied to spread the effect of TEC data assimilation at a given location to others that lacked TEC observations. In order to reveal that the assimilation results emulate the complex ionospheric changes during geomagnetic storms, the selected study days included both quiet (Kp ≤ 3) and disturbed geomagnetic conditions in the year 2015. The results showed that assimilation of TEC data derived from ground-based GPS receivers can improve the root mean squared error (RMSE) associated with the NeQuick model estimation of ionospheric parameters by ≥ 56 %. The improvement of RMSE achieved by assimilating TEC data that were measured using ionosondes was ~50 %. The assimilation of TEC observations made by the COSMIC radio occultation technique yielded results that depicted RMSE improvement of > 10 %. The assimilation of TEC data measured by GPS receiver onboard Low Earth Orbiting satellites yielded results that revealed 1 deterioration of RMSE. This outcome might be due to either the fact that the receivers are on moving platforms and these dynamics might have not been accounted for during TEC computation or limitation of the assimilation process. Validation of our assimilation results with global ionosphere TEC data maps as processed at the center for orbit determination in Europe (CODE) revealed that both depicted similar TEC changes, showing response to a geomagnetic storm.
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    Comparison of ionospheric irregularities observed by the COSMIC satellites with ground-basedscintillationobservationsoverthelowlatitudeAfricanRegion
    (Elsevier, 2026-04-07) Mungufeni, Patrick; Migoya-Orue, Yenca; Aol, ItalySharon; Omondi, George
    This study compared the ionospheric irregularities as observed using two different techniques, namely; the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites and the scintillation intensity index(S4) data measured by the Scintillation Network and Decision Aid (SCINDA) receiver which operated at Nairobi University (geog lon 36.8 E, geog lat 1.3 S, dip lat−24.1, Kenya. The data compared were those of the years 2009 (low solar activity) and2011(ascending phase of solar cycle24), for both quiet (Kp3) and disturbed(Kp5) geomagnetic conditions. For the cases of Global Positioning System (GPS)satelliteswithelevationangle0as observed by the COSMIC satellites, a geo-location of the COSMIC S4 data associated with the link between GPS and COSMIC satellites was proposed at the tangent point. The COSMIC S4 data whose geo-locations fall in the vicinity of Nairobi were compared with the S4 data measured by the SCINDA receiver. The coefficient of determination which represents the percentage of the variation in COSMIC S4 data associated with the variation in SCINDA S4 was 50 %. The two data sets depict that scintillation occurs mostly in the seasons of March and September equinoxes of high solar activity conditions. However, there was a moderate positive correlation (Pearson correlation coefficient, r=0.52 on quiet days) between COSMIC and SCINDA S4 data. The results presented signify that the COSMIC S4 could be analyzed to study ionospheric irregularities (which cause scintillations) over locations such as deserts and oceans where it is usually difficult to deploy equipment.
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    The correlation between equatorial electrojet and equatorial ionisation anomaly over the East African region during the solar minimum period 2008-2009
    (East African Journal Of Science, Technology and Innovation, 2023-09-29) Xiong, Mengqiu; Milimu, Hannington; Omondi, George; Mungufeni, Patrick
    This study analyzed the correlation between the equatorial electrojet (EEJ) and the occurrence of equatorial ionisation anomaly (EIA) over the East African region. The study was carried out during both geomagnetically quiet and disturbed conditions when Kp index values were < 2+ and > 5+, respectively. The EEJ data were obtained using a pair of magnetometers located at Adis Ababa (geographic 9.04°N, 38.77°E, geomagnetic 0.17°N, 110.47°E) and Adigrat (geographic 14.281°N, 39.46°E, geomagnetic 6.0°N, 111.06°E), both in Ethiopia while the EIA data were derived from the total electron content (TEC) data that were obtained using a set of Global Navigation Satellite System (GNSS) receivers within the East African region. The data used were for the years 2008 and 2009. The TEC data over the crest of EIA were divided by those over the trough to quantify EIA strength over the region. The EEJ intensity was estimated from the difference in the horizontal component of the geomagnetic field observed by the pair of magnetometers. The results during quiet geomagnetic conditions showed that peak values of EEJ which range from 48nT - 110nT occurred between 10:00 and 14:00 LT. The EIA’s peak which varies from 1.20 to 1.45 occurs between 20:00 to 22:00 LT. The correlation coefficients were found to vary from moderate (0.58) to strongest (0.74). During geomagnetically disturbed conditions, the correlation coefficient ranges from 0.28 to 0.45. The increased eastward electric field and photo-ionization on TEC are responsible for the strong link between EEJ and EIA. This study reveals the trend in the variation of the strength of EEJ and EIA over the East African region which can be used as a basis for developing regional models to forecast or nowcast scintillations and the ionospheric space weather prediction over this region.
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    Solar wind, IMF data analysis and interpretation
    (2023-09-29) Omondi, George
    This presentation introduced concepts on the solar wind, interplanetary magnetic field, coordinate systems based on the Sun-Earth line, data sources, analysis and interpretation.