- Comparison of the Equatorial Electrojet over American ... Geospace and Radar Science Laboratory, Department of Physics, College of Science, Bahir Dar University, Ethiopia 3Climate

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

1 / 24


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.

2 / 2414th ISEA Conference in Bahir Dar (October 19 to 23, 2015)


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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At Long. 750 W, 250 E, and 1050 E

Figure : Width and periodicity of the EEJ current density signal.



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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)


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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)


0 50 100 150 200 250 300 350

4

8

16

32

64

128

2560 1 2 3




0 50 100 150 200 250 300 350

1.5

2

2.5

x 10−4

Day number in 2008

Avg

varia

nce


Mean=0.00021291

Figure : African sector, 2008



SummaryReferences


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)


0 50 100 150 200 250 300 350

4

8

16

32

64

128

2560 0.5 1




0 50 100 150 200 250 300 350

7

8

9

x 10−5

Day number in 2008

Avg

varia

nce


Mean=8.3304e−05

Figure : Asian sector, 2008



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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)


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)


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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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)


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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)


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Figure : GPS-IGS vTEC observed around 250E, 2008.



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Figure : GPS-IGS vTEC observed around 1050E, 2008.



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Figure : ..



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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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Seasonal variability

Figure : 750 W (Black broken line), 250 E (Black solid line) and 1050 E(Blue line).



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Figure :



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Figure :



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Figure :



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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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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.


Documents

- Comparison of the Equatorial Electrojet over American ... Geospace and Radar Science Laboratory, Department of Physics, College of Science, Bahir Dar University, Ethiopia 3Climate