Time variations of the ionosphere at the northern tropical crest of ionization at Phu Thuy, Vietnam

Thu, H. Pham Thi; Amory‐Mazaudier, Christine

doi:10.5194/angeo-29-197-2011

Cited by 17 publications

(10 citation statements)

References 30 publications

(39 reference statements)

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“…In fact, Pham Thi Thu et al . [] obtained a positive 0.025 MHz/yr trend which is qualitatively in agreement with the expected trend due to the EIA pattern secular displacement.…”

Section: Discussionsupporting

confidence: 84%

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Long‐term trend of f_oF₂ at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement

2013

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[1] Long-term variability of f o F 2 at Ouagadougou station (12.4°N, 358.5°E; dip, 1.45°), a West African equatorial station, is studied, analyzing an annual mean data series at 12 LT for the period 1966-1998. After filtering the solar activity effect using Rz as a solar activity proxy, a downward trend of À0.015 MHz/yr is obtained, that is a~5% decrease during the period of 33 years here considered, equivalent to a~0.2%/yr. The downward trend is qualitatively consistent with a decreasing trend expected from increasing greenhouse gas concentration but greater than the~0.003%/yr that would result from the 20% increase in CO 2 that actually took place during the period of analysis. The f o F 2 decreasing trend is not in agreement with the trend expected from the secular variation of the dip angle at the location of Ouagadougou, but here an additional mechanism is considered, that is the secular movement of the dip equator toward Ouagadougou. This implies an approaching of the trough of the equatorial ionization anomaly and thus an f o F 2 decrease at Ouagadougou that is qualitatively in agreement with the observed trend.Citation: Gnabahou, D. A., A. G. Elias, and F. Ouattara (2013), Long-term trend of f o F 2 at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement,

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“…In fact, Pham Thi Thu et al . [] obtained a positive 0.025 MHz/yr trend which is qualitatively in agreement with the expected trend due to the EIA pattern secular displacement.…”

Section: Discussionsupporting

confidence: 84%

“…This last argument can also explain results for two other stations under the EIA, Huancayo (12.0°S, 284.7°E) and Phu Thuy (21.3°N, 106.0°E), obtained by Upadhyay and Mahajan [] and Pham Thi Thu et al . [], respectively.…”

Section: Discussionmentioning

confidence: 99%

Long‐term trend of f_oF₂ at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement

2013

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“…The The obtained correlation value are in accordance with those determined by Ouattara et al (2009) in Africa and which lay between 0.948 and 0.977 for the solar cycles 20, 21, 22. In contrary the three results are those obtain by Pham et al (2011) in Asia which lay between 0.836 and 0.848 for the same solar cycles and unclear the same conditions.…”

Section: Seasonal Variationcontrasting

confidence: 76%

Transient variations of vertical total electron content over some African stations from 2002 to 2012

Shimeis¹,

Amory‐Mazaudier²,

Fleury³

et al. 2014

Advances in Space Research

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International audienceThis paper presents the vertical total electron content vTEC variations for three African stations, located at mid-low and equatorial latitudes, and operating since more than 10 years. The vTEC of the middle latitude GPS station in Alexandria, Egypt (31.2167°N; 29.9667°E, geographic) is compared to the vTEC of two others GPS stations: the first one in Rabat/Morocco (33.9981°N; 353.1457°E, geographic), and the second in Libreville/Gabon (0.3539°N; 9.6721°E, geographic). Our results discussed the diurnal, seasonal, and solar cycle dependences of vTEC at the local ionospheric conditions, during different phases of solar cycle in the light of the classification of Legrand and Simon. The vTEC over Alexandria exhibits the well-known equinoctial asymmetry which changes with the phases of the solar cycle; the spring vTEC is larger than that of autumn during the maximum, decreasing and minimum phases of solar cycle 23. During the increasing phase of solar cycle 24, it is the contrary. The diurnal variation of the vTEC presents multiple maxima during the equinox from 2005 to 2008 and during the summer solstice from 2006 to 2012. A nighttime vTEC enhancement and winter anomaly are also observed. During the deep solar minimum (2006–2009) the diurnal variation of the vTEC observed over Alexandria is similar to the diurnal variation observed during quiet magnetic period at equatorial latitudes. We observed also that the amplitude of vTEC at Libreville is larger than the amplitude of vTEC observed at Alexandria and Rabat, indeed Libreville is near the southern crest of the Equatorial Ionization anomaly. Finally, the correlation coefficient between vTEC and the sunspot number Rz is high and changes with solar cycle phases

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“…Correlation coefficients between the monthly average number of sunspot and the monthly average amplitude of anomaly crest are 0.909 and 0.897 in the northern and southern crests, respectively. These coefficients show better correlation than the correlation between the critical frequency of F 2 layer in Phu Thuy and the sunspot number, which is equal to ~0.84 (Pham Thi Thu H. et al, 2011). The correlation coefficients of moving average values of 13 months are 0.995 and 0.994 in the northern and southern crests, respectively.…”

Section: Resultsmentioning

confidence: 82%

Continuous GPS Network in Vietnam and Results of Study on the Total Electron Content in the South East Asian Region

Lân

Mazaudier

et al. 2016

TCCKHVTD

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This study presents the continuous GPS network in Vietnam and the results of study on time variations of the total electron content (TEC) in the South East Asian equatorial ionization anomaly (EIA) for the 2006-2013 period. In each year we observe a semiannual pattern of amplitude of the EIA crests with its maximum amplitude at equinox. In both hemispheres, the amplitude of the crest is larger in northern spring equinox than in autumn from 2006 to 2008 (descending phase of solar cycle) and smaller in spring than in autumn from 2009 to 2011 (increasing phase of solar cycle), from 2012-2013 (maximum period of solar cycle) the amplitudes of the crests in spring and autumn are equivalent. We also observe an asymmetry between the amplitude and the position of the two crests of ionization. There is a very high level of correlation between the amplitude of the TEC at the two crests and the sunspot number is approximately equal to 0.9. During the deep solar minimum 2008-2009, the amplitude of crests of ionization becomes small during several months in summer and winter (about 20 TECu). The results show that both crests move more significantly equatorward in winter than in other seasons and there is a tendency for both crests to appear earlier in winter and later in summer. In the solar minimum years, the amplitudes of the crests are minimal; the positions of the crests are nearer the magnetic equator and the crests appear earlier than in other years.

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Time variations of the ionosphere at the northern tropical crest of ionization at Phu Thuy, Vietnam

Cited by 17 publications

References 30 publications

Long‐term trend of f_oF₂ at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement

Long‐term trend of f_oF₂ at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement

Transient variations of vertical total electron content over some African stations from 2002 to 2012

Continuous GPS Network in Vietnam and Results of Study on the Total Electron Content in the South East Asian Region

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Time variations of the ionosphere at the northern tropical crest of ionization at Phu Thuy, Vietnam

Cited by 17 publications

References 30 publications

Long‐term trend of foF2 at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement

Long‐term trend of foF2 at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement

Transient variations of vertical total electron content over some African stations from 2002 to 2012

Continuous GPS Network in Vietnam and Results of Study on the Total Electron Content in the South East Asian Region

Contact Info

Product

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Long‐term trend of f_oF₂ at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement

Long‐term trend of f_oF₂ at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement