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Hāgere Hiywet, Ethiopia

This paper presents the performance of the latest version of the International Reference Ionosphere (IRI-2012) model in estimating the Vertical Total Electron Content (VTEC) variation over equatorial and low latitude East Africa regions during the period of 2012-2013. This has been conducted by comparing the ground-based Global Positioning System (GPS) VTEC inferred from nine dual frequency GPS receivers installed at different regions in the continent. In this work, the diurnal, monthly and seasonal variation in the measured VTEC have been analyzed and compared with the VTEC obtained from IRI-2012 model. It is depicted that the lowest diurnal peaks of the modeled and measured VTEC values are observed in the June solstice months, whereas the highest values are observed in the equinoctial months. The variability of the diurnal GPS-VTEC is also found to be minimal nearly at 03:00 UT and maximal mostly between 09:00 and 14:00 UT. Moreover, the maximum and minimum monthly mean hourly measured VTEC values inferred from both the Arba Minch and Entebbe stations are observed in October and July, respectively. Similarly, the highest and the lowest seasonal mean hourly measured VTEC values are observed in the September equinox and in the June solstice, respectively. The model predictions generally follow the diurnal variations of the measured VTEC, with minimum value at predawn hours and maximum at noontime hours (10:00-13:00 UT). It has been shown that the model better estimates the diurnal VTEC values mostly just after midnight hours (00:00-03:00 UT). Good agreements between the modeled and measured monthly and seasonal mean hourly VTEC values obtained from Arba Minch station are also observed in the equinoctial months. But, for the Entebbe station, the modeled monthly and seasonal VTEC values are larger than the corresponding measured VTEC values by about 75% and 60%, respectively. In addition, there are large discrepancies observed between the diurnal measured and modeled VTEC values (especially in the equinoctial months) in the time interval between 09:00 and 14:00 UT. © 2015 COSPAR. Published by Elsevier Ltd. All rights reserved. Source


Asmare Y.,University of Ambo | Kassa T.,Bahir Dar University | Nigussie M.,Bahir Dar University
Advances in Space Research | Year: 2014

This paper investigates the capacity of the latest version of the International Reference Ionosphere (IRI-2012) model in predicting the vertical Total Electron Content (vTEC) over Ethiopian regions during solar minimum (2009) and solar maximum (2013) phases. This has been carried out by comparing the IRI-2012 modeled and experimental vTEC inferred from eight ground based dual frequency GPS (Global Positioning System) receivers installed recently at different regions of the country. In this work, the diurnal, monthly and seasonal variation in the measured vTEC have been analyzed and compared with the IRI-2012 modeled vTEC. During the solar minimum phase, the lowest and highest diurnal peak of the experimental vTEC are observed in July and October, respectively. In general, the diurnal variability of vTEC has shown minimum values around 0300 UT (0600 LT) and maximum values between around 1000 and 1300 UT (1300 and 1600 LT) during both solar activity phases. Moreover, the maximum and minimum monthly and seasonal mean hourly vTEC values are observed in October and July and in the March equinox and June solstice, respectively. It is also shown that the IRI-2012-model better predicts the diurnal vTEC in the time interval of about 0000-0300 UT (0300-0600 LT) during the solar minimum phase. However, the model generally overestimates the diurnal vTEC except in the time interval of about 0900-1500 UT (1200-1800 LT) during the solar maximum phase. The overall result of this work shows that the diurnal vTEC prediction performance of the model is generally better during the solar minimum phase than during solar maximum phase. Regarding the monthly and seasonal prediction capacity of the model, there is a good agreement between the modeled and measured monthly and seasonal mean hourly vTEC values in January and December solstice, respectively. Another result of the work depicts that unlike the GPS-TEC the IRI-2012 TEC does not respond to the effect resulted from geomagnetic storms. © 2014 COSPAR. Published by Elsevier Ltd. All rights reserved. Source


This paper deals with the pattern of the variability of the Global Positioning System vertical total electron content (GPS VTEC) and the modeled vertical total electron content (IRI 2012 TEC) over American mid-latitude regions during the rising phase of solar cycle 24 (2009-2011). This has been conducted employing ground-based dual frequency GPS receiver installed at Mississippi County Airport (geographic lat. 36.85°N and long. 270.64°E). In this work, the monthly and seasonal variations in the measured VTEC have been analyzed and compared with the VTEC inferred from IRI-2012 model. It has been shown that the monthly and seasonal mean VTEC values get decreased mostly between 05:00 and 10:00. UT and reach their minimal nearly at around 10:00. UT for both the experimental and the model. The VTEC values then get increased and reach the peak values at around 20:00. UT and decrease again. Moreover, it is depicted that the model better estimates both the monthly and seasonal mean hourly VTEC values mostly between 15:00 and 20:00. UT. The modeled monthly and seasonal VTEC values are smaller than the corresponding measured values as the solar activity decreases when all options for the topside electron density are used. However, as the Sun goes from a very low to a high solar activity, the overestimation performance of the VTEC values derived from the model increases. The overall results show that it is generally better to use the model with IRI-2000 option for the topside electron density in estimating the monthly and seasonal VTEC variations, especially when the activity of the Sun decreases. © 2016 COSPAR. Source


Tariku Y.A.,University of Ambo
Journal of Geophysical Research A: Space Physics | Year: 2015

This paper examines the capacity of the latest version of the International Reference Ionosphere (IRI-2012) model in predicting the vertical total electron content (VTEC) variation over Uganda during a very low solar activity phase (2009) and a high solar activity (2012) phase. This has been carried out by comparing the ground-based Global Positioning System (GPS) VTEC inferred from dual-frequency GPS receivers installed at Entebbe (geographic latitude 0.038N and longitude 32.44E; geomagnetic latitude -9.53N and longitude 104.06E) and Mbarara (geographic latitude -0.60N and longitude 30.74E; geomagnetic latitude -10.02N and longitude 102.36E). In this work, the diurnal, monthly, and seasonal variations in the measured VTEC have been analyzed and compared with the VTEC derived from IRI-2012 model. It has been shown that the lowest diurnal peak GPS-VTEC values are observed in the June solstice months during both the low and the high solar activity phases. Similarly, the highest diurnal peak IRI-2012 VTEC values are observed in equinoctial months during both phases. The variability of the VTEC in both the experimental and model is minimal nearly at 03:00 UT (06:00 LT) and maximal mostly between 10:00 and 13:00 UT (13:00-16:00 LT) during both phases. The diurnal highest peak modeled VTEC value observed during the high solar activity phase is almost twice larger than the diurnal highest peak modeled VTEC value depicted during the low solar activity phase. Moreover, the highest monthly mean hourly measured VTEC value observed in October during the high solar activity phase is larger by more than twice the corresponding highest monthly mean hourly measured VTEC value observed in November during the low solar activity phase. Similarly, the lowest monthly measured VTEC value observed in July during the high solar activity phase is larger by more than twice the corresponding lowest measured monthly VTEC value observed in the same month during the low solar activity phase. It has also been shown that the highest measured seasonal mean hourly VTEC values are observed in the December solstice and the March equinox, respectively, during the low and the high solar activity phases, while the corresponding lowest measured VTEC values are observed in the June solstice during both phases. The model prediction generally follows the monthly and seasonal variations of measured VTEC, with the highest and the lowest monthly values being observed in equinoctial and solstice months, respectively, during both phases. The overall results show that the modeled diurnal, monthly, and seasonal VTEC values are generally larger than those corresponding measured VTEC values observed during both the low and the high solar activity phases, with the largest deviations being observed during the low solar activity phase. Moreover, the model does not respond to the effects resulting from the storm. Hence, unlike the measured VTEC values, the modeled VTEC values are unaffected by the storm. © 2015. American Geophysical Union. All Rights Reserved. Source


This paper discusses the performance of the latest version of the International Reference Ionosphere (IRI-2012) model for estimating the vertical total electron content (VTEC) variation over Ethiopian regions during the rising phase of solar cycle 24 (2009-2011). Ground-based Global Positioning System (GPS) VTEC data, inferred from dual-frequency GPS receivers installed at Bahir Dar (geographic latitude 11.6°N and longitude 37.35°E, geomagnetic latitude 2.64°N and longitude 108.94°E), Nazret (geographic latitude 8.57°N and longitude 39.29°E, geomagnetic latitude -0.25°N and longitude 111.01°E), and Robe (geographic latitude 7.11°N and longitude 40.03°E, geomagnetic latitude -1.69°N and longitude 111.78°E), are compared to diurnal, monthly, and seasonal VTEC variations obtained with the IRI-2012 model. It is shown that the variability of the diurnal VTEC is minimal at predawn hours (near 0300 UT, 0600 LT) and maximal between roughly 1000 and 1300 UT (1300-1600 LT) for both the experimental data and the model. Minimum seasonal VTEC values are observed for the June solstice during the period of 2009-2011. Moreover, it is shown that the model better estimates diurnal VTEC values just after the midnight hours (0000-0300 UT, 0300-0600 LT). The modeled monthly and seasonal VTEC values are larger than the corresponding measured values during the period of 2009-2010 when all options for the topside electron density are used. An important finding of this study is that the overestimation of VTEC values derived from the model decreases as the Sun transitions from very low to high solar activity. Moreover, it is generally better to use the model with the NeQuick option for the topside electron density when estimating diurnal, monthly, and seasonal VTEC variations. © 2015 Tariku. Source

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