Global Electron Content Global Electron Content as a as a New INew Ionospheric Index. onospheric Index.

Comparison With IRI Comparison With IRI Modeling ResultsModeling Results

Institute of Solar-Terrestrial Physics SD RAS, Irkutsk, RussiaInstitute of Solar-Terrestrial Physics SD RAS, Irkutsk, Russia

elliada@iszf.irk.ruelliada@iszf.irk.ru

Elvira I. AstafievaElvira I. Astafieva

It is known that condition of the Earth’s ionosphere is determined mainly by solar radiation within wide range of

wavelengths. A plenty of works have been devoted to study of ionosphere parameters variations depending on

solar activity changes.

We have proposed a new approach for studying and better understanding of sun-earth connection. It lies in

estimation of global electron content (GEC) which is equal to the total number of electrons in the near space environment. An advantage of this approach is in

disappearance of local features of ionosphere and in determining of dynamics of global characteristics.

Besides, new applications of experimental data are necessary for different ionosphere models correction.

Geodetic Survey Division of Natural Resources Canada (EMRG)

[http://www.nrcan rncan.gc.ca/],

Center for Orbit Determination in Europe, University of Berne, Switzerland

(CODG) [http://www.cx.unibe.ch/],

Jet Propulsion Laboratory of California Institute of Technology (JPLG)

[http://www.jpl.nasa.gov/],

Grup Universitat Politecnica de Catalunya (UPCG) [http://www.upc.es/],

European Space Agency Group (ESAG).

TEC GPS,

GEC

Maps

cIonospheri

Global

221122

21

22

21

H

0

λLλLff

ffNdlTEC

2.5° Ii,j

5°

h 2t

3600:Lon

9090- :Lat

(IONEX) GIM

ji,ji, S*IG(t) electrons 10GECU 1 32

ionex/products/ov/pub/gpssfc.nasa.g//cddisa.g:ftp

ji,ji, S*IG(t)

electrons 10GECU 1 32

Geodetic Survey Division of Natural Resources Canada (EMRG) [http://www.nrcan

rncan.gc.ca/],

Center for Orbit Determination in Europe, University of Berne,

Switzerland (CODG) [http://www.cx.unibe.ch/],

Jet Propulsion Laboratory of California Institute of Technology (JPLG) [http://www.jpl.nasa.gov/],

Grup Universitat Politecnica de Catalunya (UPCG)

[http://www.upc.es/],European Space Agency Group

(ESAG).

The objectives of this research are to The objectives of this research are to analyze dynamics of global electron analyze dynamics of global electron content during the 1998-2005 and to content during the 1998-2005 and to

compare the dynamics with changes of compare the dynamics with changes of solar activity and modeled GEC values.solar activity and modeled GEC values.

We compared experimental GEC G(t) values with F10.7 as solar activity index F(t), which is equal to solar radiation flux on the wavelength 10.7 cm in

s.f.u. units (10-22 Wm-2 Hz-1).

We calculated modeled values of GEC M(t) using International Reference Ionosphere 2001.

We smoothed G(t), F(t) and M(t) series with the time window τ of 10 days.

Diurnal variations appear to be averaged and, therefore, important effects of quick GEC changes

cannot be distinguished (such as geomagnetic disturbances).

(а) - M(t), year 2003

hmax= 2000 km,

10000 и 20000 km;

(b) – M(t), hmax= 1000 km и 2000 km и G(t).

Modeled GECModeled GEC

hmax=2000 km

Global Electron Content, Global Electron Content,

1998-20051998-2005

(а) – Experimental GEC;

(b) – Solar Radiation Flux F10.7;

(c) – Modeled GEC;

(d) – G(t), M(t) и F(t); τ = 365 days.

G(t) = 0.5 ÷ 3.5 GECU

G(t), M(t) and F(t) for all the globe are similar

Regression Regression dependenciesdependencies

N=2771 days

(а) - G(t) from M(t); τ = 365 days;

(b) - G(t) from F(t);

(c) - G(t) from F(t); τ = 365 days.

G(F)=0.013[F10.7-60] + 0.5

G(M)=1.056M + 0.1

Global Electron Content,Global Electron Content,

Day and NightDay and Night

For understanding of the physical mechanisms and For understanding of the physical mechanisms and comparison with models it is very important to determine comparison with models it is very important to determine GEC for day GGEC for day Gdd and night G and night Gnn sides of the Earth as well as sides of the Earth as well as

their ratio R =  Gtheir ratio R =  Gdd/G/Gnn

A scheme of A scheme of Estimation of Day Estimation of Day

and Night GECand Night GEC

H=200 km

March 31, 2003

12 UT

We carry out calculation of G(t) only for those GIM

cells that are located inside or outside the solar

terminator border determined for a certain

altitude H in the atmosphere.

1998-20051998-2005

(а) – Experimental GEC;

(c) – Modeled GEC.

GEC of the day and night sides of the Earth for

experimental and modeled GEC are similar

A ratio R(t)=GR(t)=Gdd/G/Gnn of the day and night sides

of the Earth

Maximal values of R(t) correspond to periods of

summer and winter solstices.

M(t) values for the night side are overestimated as

compared to the day side.

Seasonal variations of GECSeasonal variations of GEC

The series of the G(t), M(t) and F(t) were filtered within The series of the G(t), M(t) and F(t) were filtered within the period range from 100 to 300 days and normalized on the period range from 100 to 300 days and normalized on

background values of the G(t), M(t) and F(t).background values of the G(t), M(t) and F(t).

Seasonal variations Seasonal variations

(b) – Relative amplitude of GEC variation dG/G,% and dM/M,%;

(c) – GEC G(t) and F10.7 F(t).

GEC is characterized by seasonal variations.

Relative amplitude of seasonal variations reaches 10% during low solar activity

and it changes up to 30 % during high solar activity.

(а) – relative difference between G(t) and M(t), % during 1998-2005; τ = 81 days;

(b) – (d) - G(t) и М(t) for the 2001, 2003, 2005.

Seasonal variations of G(t) and M(t) are not phased.

Maximum of GEC is related to equinoctial months.

27-day variations27-day variations

The series of the G(t) and F(t) were filtered within the The series of the G(t) and F(t) were filtered within the period range from 20 to 40 days and normalized on period range from 20 to 40 days and normalized on

background values of the G(t) and F(t).background values of the G(t) and F(t).

27-day variations, 27-day variations, 20032003::

(а) – dG/G for the globe and of the lighted and

darken sides;

(b) – dG/G and dF/F;

(c) – G(t) for the globe and of the lighted and darken sides ;

(d) – estimation of the envelope of 27-day variations G27(t).

G(t) lags in time for 2-5 days from F(t).

 It is known that response of the ionosphere to ultraviolet radiation flux changes is determined

by the lag time and the recombination time constants, which is equal to 1 hour. Founded lag

of the 27-day GEC variations relative to corresponding changes of the F10.7 flux can be caused by significantly greater time constants

that characterize thermosphere as GEC variations.

1998 – 2005:1998 – 2005:

(а) – the variations of the 10.7-cm solar radio emission and of sunspot number Rsn;

τ = 365 days;

(b) – the envelope of 27-day variations for F(t) and G(t);

τ = 365 days;

(c) - the same as for (b), but

τ = 81 days;

(d) – the solar hydrogen atom emission of Lyman-alpha irradiance at 121.67 nm (L-alpha), τ = 81 days.

CONCLUSIONCONCLUSION

1. During the period 1998-2005 the average level of GEC varied from 0.5 to 3.5 GECU.

2. 27-day variations of GEC are very similar to the ones of the index F10.7. However G(t) lags in time for 2-5 days from F(t).

3. GEC has seasonal variations with maximum values in equinoctial months. Deep seasonal variations are also typical for a ratio of GEC for the lighted and darken sides of the Earth. Maximal values of this ratio were observed during the periods of summer and winter solstices.

4. Good agreement between observational and modeled data for GEC was found in general, but there are some distinctions: M(t) values for the night side are overestimated as compared to the day side; IRI 2001 does not take into account rotation of the Sun.

Prof. Edward L. Afraimovich,

PhD students Alexey V. Oinatz, Ilya V. Zhivetiev, Yuri V.

Yasukevich.

Co-authorsCo-authors::

We acknowledge academician G.A. Zherebtsov, Drs. V.V. Pipin, V.G. Eselevich, A.V. Mordvinov, L.A.

Plyusnina for their support and interest in our work and E.A. Kosogorov for his help in programming. We are grateful to N. Jakowski, D. Bilitza, S.M. Radicella for their interest in our work and good suggestions.

 We acknowledge for the IONEX data available from the Internet: Geodetic Survey Division of Natural Resources Canada (EMRG), Center for Orbit Determination in Europe, University of Berne, Switzerland (CODG), Jet Propulsion Laboratory of California Institute of Technology (JPLG), Grup Universitat Politecnica de Catalunya (UPCG), European Space Agency Group (ESAG) and others.

Acknowledgements:Acknowledgements:

The results of this work are accepted for publication in

Doklady, Earth SciencesDoklady, Earth Sciences

International Reference Ionosphere NewsInternational Reference Ionosphere News

Thank you for your attentionThank you for your attention!!

GPS Monitoring WorkGroup,GPS Monitoring WorkGroup,Institute of Solar-Terrestrial Physics, Institute of Solar-Terrestrial Physics,

SD RAS, Irkutsk, RussiaSD RAS, Irkutsk, Russia