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Transcript of - Comparison of the Equatorial Electrojet over American ... Geospace and Radar Science Laboratory,...
General IntroductionObservations
SummaryReferences
Comparison of the Equatorial Electrojet over American, Africanand Asian longitudinal sectors during 2008
1Endalkachew Mengistu (PhD Student in Space Science),2Baylie Damtie,3Mark B. Moldwin, 2Melessew Nigussie, 4Gizaw Mengistu and
2Tsegaye Kassa1Entoto Observatory and Research Center, Space Science Research Division,
Addis Ababa, Ethiopia2Washera Geospace and Radar Science Laboratory, Department of Physics,
College of Science, Bahir Dar University, Ethiopia3Climate and Space Sciences and Technology, University of Michigan, USA
4Department of Physics, Addis Ababa University, Ethiopia
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General IntroductionObservations
SummaryReferences
The ionosphere is related to the time, season, location, andactivity of the Sun, and therefore, the difference of ionosphericeffects on the propagation of radio in different local areas ortime is very large.Satellite observations, for example, have shown significantdifferences in the morphology of ionospheric irregularities overthe equatorial regions at different longitudes [Gentile et al(2006)].Therefore, monitoring of the ionospheric variability isnecessary for improving the performance of communication,navigation, and positioning systems.This is well done in most regions of the world.However, the characteristics of the ionosphere over Africancontinent has still remained a mystery.
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General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
This is due to the sparse distribution of ionospheric sensorsover this vast continent [e.g., Akala et al. (2013)]
So, in order to characterising ionosphere over low latitude inAfrica (to get regional ionospheric specification), we have atleast three options:
install instrument
model and
comparison (with other well known ionospheric region such asSouth America and others)
Here, we present a case study of the observational comparisonof the Equatorial Electrojet (EEJ) over American, African andAsian longitudinal sectors during 2008 inferred from EEJM-2Model.
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General IntroductionObservations
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Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
At Long. 750 W, 250 E, and 1050 E
Figure : Width and periodicity of the EEJ current density signal.
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General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Daily variation, wavelet power spectrum and averagevariance
0 50 100 150 200 250 300 350
−1
0
1
Day number in 2008
Daily
Mea
n EEJ
a) Normalized daily mean variation of the EEJ over American sector (Long. 750 W), 2008
Day number in 2008
Perio
d (da
ys)
b) Wavelet Power Spectrum
0 50 100 150 200 250 300 350
4
8
16
32
64
128
2560 1 2
x 10−3Power (Arb. unit)
c) Global Wavelet Spectrum
SpectrumSignificance
0 50 100 150 200 250 300 350
9
10
11x 10
−5
Day number in 2008
Avg v
arian
ce
d) 10−80 days Scale−average time Series
Mean=9.6169e−05
Figure : American longitudinal sector, 20085 / 24
14th ISEA Conference in Bahir Dar (October 19 to 23, 2015)
General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
0 50 100 150 200 250 300 350
−1
0
1
Day number in 2008
Daily
Mea
n EE
Ja) Normalized daily mean variation of the EEJ over African sector (Long. 250), 2008
Day number in 2008
Perio
d (d
ays)
b) Wavelet Power Spectrum
0 50 100 150 200 250 300 350
4
8
16
32
64
128
2560 1 2 3
x 10−3Power (Arb. unit)
c) Global Wavelet Spectrum
SpectrumSignificance
0 50 100 150 200 250 300 350
1.5
2
2.5
x 10−4
Day number in 2008
Avg
varia
nce
d) 10−80 days Scale−average time Series
Mean=0.00021291
Figure : African sector, 2008
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General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
0 50 100 150 200 250 300 350−2
−1
0
1
Day number in 2008
Daily
Mea
n EE
Ja) Normalized daily mean variation of the EEJ over Asian sector (Long. 1050 E), 2008
Day number in 2008
Perio
d (d
ays)
b) Wavelet Power Spectrum
0 50 100 150 200 250 300 350
4
8
16
32
64
128
2560 0.5 1
x 10−3Power (Arb. unit)
c) Global Wavelet Spectrum
SpectrumSignificance
0 50 100 150 200 250 300 350
7
8
9
x 10−5
Day number in 2008
Avg
varia
nce
d) 10−80 days Scale−average time Series
Mean=8.3304e−05
Figure : Asian sector, 2008
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General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Months of the year
Lo
ca
l T
ime
(in
hr)
Monthly averaged hourly value of EEJ in 2008 (Long. 750 W)
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec579
1113151719
0
0.05
0.1
Months of the year
Lo
ca
l T
ime
(in
hr)
Monthly averaged hourly value of EEJ in 2008 (Long. 250 E)
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec579
1113151719
0
0.05
0.1
Months of the year
Lo
ca
l T
ime
(in
hr)
Monthly averaged hourly value of EEJ in 2008 (Long. 1050 E)
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec579
1113151719
0
0.05
0.1
5 7 9 11 13 15 17 19−0.02
00.020.040.060.08
Jan, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19
00.020.040.060.08
Feb, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19−0.02
00.020.040.060.08
Mar, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19
0
0.05
0.1Apr, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19−0.02
00.020.040.060.08
May, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19−0.02
00.020.040.060.08
Jun, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19
00.020.040.060.08
Jul, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19−0.02
00.020.040.060.08
Aug, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19
00.020.040.060.08
Sept, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19−0.02
00.020.040.060.08
Oct, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19
0
0.05
0.1Nov, 2008
Local Time (in hr)
EE
J (
in A
/m2)
5 7 9 11 13 15 17 19−0.02
00.020.040.060.08
Dec, 2008
Local Time (in hr)
EE
J (
in A
/m2)
Figure : Monthly hourly variation around 750 W, 250 E & 1050 E, 2008.CEJ: like N • N at Asian sector.
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General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Longitudinal symmetry and asymmetry
Figure : Monthly hourly variation around 1050 W, 00 & 1050 E, 2008.. 9 / 2414th ISEA Conference in Bahir Dar (October 19 to 23, 2015)
General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
GPS-IGS: vTEC around the equator
Figure : GPS-IGS vTEC observed around 750W, 2008. 10 / 2414th ISEA Conference in Bahir Dar (October 19 to 23, 2015)
General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Figure : GPS-IGS vTEC observed around 250E, 2008.
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General IntroductionObservations
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Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Figure : GPS-IGS vTEC observed around 1050E, 2008.
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General IntroductionObservations
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Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Figure : ..
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Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Dominating fluctuation period: 12-90 min
200 400 600 80010
20
30
40
50
High frequency residual values, 2008
American sector (750W)
200 400 600 800
20
30
40
50
60
African sector (250E)
200 400 600 800
10
20
30
40
50
Resid
ual (
in fr
eque
ncy u
nit)
Period, min
Asian sector (1050E)
20 40 60 80
15
20
25
30
35
American sector (750W)
High fluctuation, 2008
20 40 60 80
15
20
25
30
35
African sector (250E)
20 40 60 80
15
20
25
30
35
Ampl
itude
Period, min
Asian sector (1050E)
Figure : High frequency residuals.
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General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Seasonal variability
Figure : 750 W (Black broken line), 250 E (Black solid line) and 1050 E(Blue line).
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General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Figure :
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General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Figure :
17 / 2414th ISEA Conference in Bahir Dar (October 19 to 23, 2015)
General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
Figure :
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General IntroductionObservations
SummaryReferences
Equatorial ElectrojetCharacteristics of the normalized daily averaged value of the EEJMonthly hourly variationSpectral AnalysisHigh frequency EEJ
High frequency EEJ: dominating month (elementarycomparison)
At 75o W, 25o E and 105o WSept.Equinox: Aug(-), Sept(-) & [Sept(-) Aug(+)],respectivelyDec solstice: Nov(+), Dec(+) & Jan(+), respectivelyMar Equinox: Apr(+), Mar(+) & Feb(-), respectivelyJun solstice: Jun(+), May(+) & Jul(+), respectively
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Summary
There is a consistently stronger EEJ current density overAmerican and Asian sectors that decreases to African sectorfrom both sides.Larger (wider) widths are found around 75o W & 105o E.Whereas the pronounced narrower on the width of the EEJsignal is observed around 25o E.This implies that higher current densities tend to occur inregions of wider current channels.The power of the signal over African sector is approximatelyhalf of the corresponding values at American or Asian sector.This has been attributed to a fall (valley) in amplitude at 25o
E as one moves from 75o W to 105o E longitudes to the effectof day time EEJ signals.
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SummaryReferences
A monthly and seasonal variations of the EEJ at the threesectors show that the current system is most intense andsymmetrical over American and Asian sectors but not withAfrican sector.The dominating fluctuation periods with reasonable amplitudelies approximately between 20 - 40 min, 25 - 65 min and 20 -35 min at American, African and Asian longitudes,respectively. That means high frequency EEJ fluctuations aredominant at African sector.Furthermore, form vTEC observation, it is evident that theionospheric variation at the three sectors is not restricted toE-region (goes beyond that).
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Acknowledgement
The Author’s are highly indebted to acknowledge PatrickAlken, Department of Physics, University of Colorado,Boulder, Colorado, USA and Stefan Maus, CooperativeInstitute for Research in Environmental Sciences, University ofColorado, Boulder, Colorado, USA, for their efforts to developEEJM-2 model and made it available to the public.GPS-IGS workers.
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Thank you very much forlistening!!
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References
Gentile, L.C. Burke, W.J. and Rich, F.J. (2006). A globalclimatology for equatorial plasma bubbles in the topsideionosphere, Ann. Geophys., 24, 163.
Akala A. O., Seemala G. K., Doherty P. H., Valladares C. E.,Carrano C. S., Espinoza J. , Oluyo S. (2013). Comparison ofequatorial GPS-TEC observations over an African station andan American station during the minimum and ascendingphases of solar cycle 24, Ann. Geophys., 31,2085-2096;doi:10.5194/angeo-31-2085-2013.
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