Relativistic Electrons, Geomagnetic Indices, and ULF wave activity in the

Terrestrial Magnetosphere

N. Romanova, V Pilipenko, O. Kozyreva, and N. Yagova romanova@ifz.ru, pilipenk@augsburg.edu

“Killer” electrons and satellite anomalies

1988 1989 1990 1991 1992 1993 19940

0.2

0.4

0.6

0.8

1

r pe

1988 1989 1990 1991 1992 1993 19940

2000

4000

6000

GEO elec tons flux E > 2 MeV

Increase of solar activity Decrease of solar activity Maximum of solar activity

rpe

(t) - correlation function between

the anomalities frequency and electrons flux(Е > 2 Мev)in during 22nd solar cycle

(c

m2

se

c s

r)-1

Relativistic electrons fluxes are known to be one of the main

factors responsible for the high-orbit satellites

malfunctions. Thus, the prediction of relativistic electron

fluxes is very important for the space industry.

1 32 63 94

10-2

10-1

100

101

day of 1994 year

(

cm

2 K

eV

se

c s

r)-1

noon-flux electons E = (1.8-3.5) MeV

anomalies at geostationary satellites

Particles Particles energyThreshold value of flux

density

Average value of the flux density for the period

1987–1995.

electrons above 2  MeV 3000  300 (cm2·s·sr)–1 1350  (cm2·s·sr)–1

electrons 1,8 – 3,5 MeV 1,5  0,5 (cm2keVssr)

–1 0,7 (cm2keVssr)–1

electrons 0,3 – 1,5 MeV 500  100 (cm2keVss

r)–1 200 (cm2keVssr)–1

Threshold electron

fluxes for the

increased risk of the

GEO anomaly

occurrence

Geosynchrotron: ULF waves = intermediary between the solar

windand “killer” electrons during magnetic storms?

Mechanism of the acceleration of ~100 keV electrons supplied by substorms is revival of the idea of magnetospheric geosynchrotron. Pumping of energy into seed electrons is provided by large-scale MHD waves in a resonant way, when the wave period matches the multiple of the electron drift period, e.g.

Appearance at GEO of relativistic electrons following storms resists definitive explanation. These electron events are not merely a curiosity for scientists, but they can have disruptive consequences for spacecrafts. While it has been known a general association between the solar wind velocity and electron enhancements, the wide variability of the response and the puzzling time delay (~1-2 days) between storm main phase and the response has frustrated the identification of responsible mechanisms.

Some intermediary must more directly provide energy to the electrons?

Rather surprisingly, ULF waves in the Pc5 band (~few mHz) have been suggested as a possible energy reservoir: the presence of Pc5 wave power after minimum Dst may be a good indicator of relativistic electron response [O’Brien et al., 2001]. Thus, in a laminar, non-turbulent magnetosphere the “killer” electrons would not appear!? dm

Algorithm of the ULF wave index construction• For any UT, magnetic stations in the MLT sector 05 – 15, and in the latitudinal

range 60 - 75 CGM are selected. • Spectra of two detrended (cut-off 0.5 mHz) horizontal components are calculated

with Filon’s method in 1-h time window. • The frequency range for the index definition is the Pc5 band (fL=3 mHz,

fH=7mHz) – the range of the most intense fluctuations. • In order to discriminate broad-band and narrow-band variations we applied an

algorithm based on the determination of “bump” above the linear fit to background “colored-noise” spectra in the range 1-8 mHz.

As a result one obtains: Noise spectral power (N) - the band-integrated area beneath the background spectra;

Signal spectral power (S) - the area of the bump above the background spectra;

Total spectral power (T) - T=S+N

210

1,

1log

fH

INDEX fi N fL

ULF df BN

Global ULF wave indexGlobal ULF wave index::The summation is performed with respect to all N stations where the signal amplitude is above K*Bmax

-200-150-100

-500

n

T

1994 Ds t

0

5

10

15

(c

m2 K

eV

se

c s

r)-1

LANL e lectron noon-recons tructed flux (1.8-3.5 МэВ)

60 91 12202468

10x 10

4

day of year

(c

m2

se

c s

r)-1

GOES-7 e lectron flux E>2MeV

0

1

2

U

LF

new ULF-index

April-May 1994

Surprisingly, the sustained intense increase of the relativistic electrons (E>2 MeV) fluxes up to ~104 is observed after the weak storm (Dst~-100nT), whereas the increase after the strong storm (Dst~-200nT) is much shorter and less intense (up to ~103 only). The electron behavior matches well the variations of the global ULF-index: after the first weak storm this index increases much more substantially and for a longer period than after the second strong storm!

During the March-April 1994

storms geostationary satellites

suffered numerous anomalies

from the “killer” electrons.

Relativistic electron flux has a

time delay ~1-2 days with

respect to the ULF-index. Thus,

this index could be used as a

“precursor” of the risk of GEO

satellite anomalies?!

Space weather events in 1994Space weather events in 1994

?

““Killer” electrons, Killer” electrons, solar wind velocity and ULF indexsolar wind velocity and ULF index

The interconnection between the relativistic electron fluxes and ULF wave index is high throughout all phases of solar cycle. However, the relevant correlation coefficient always appears to be lower than the correlation coefficient between the electron flux and solar wind velocity.

The ULF wave index and solar wind velocity are highly correlated

1994 1995 1996 1997 1998 19990

0.2

0.4

0.6

0.8

r

Corre lation be twe e n e le ctron flux (GOES-7,8) s o lar wind s pe e d and ULF-inde x

ULF-indexVsw

-6 -4 -2 0 2 4 6

0.0

0.2

0.4

0.6

0.8

Co

rre

lati

on

co

eff

icie

nt

Offset, days

Cross-correlation ULF -Vsw

Cross-correlation between the electron flux Cross-correlation between the electron flux variations, ULF-index, and solar wind velocityvariations, ULF-index, and solar wind velocity

-96 -72 -48 -24 0 24 48 72 960.0

0.2

0.4

0.6

0.8

1.0

Vsw Vsw) ULF-index

Co

rre

lati

on

co

eff

icie

nt

Offset, hours

cross-correlation functions for GOES-noon electron flux

The cross-correlation function shows that the electron flux increases about a day after the enhancements of ULF wave activity and solar wind velocity

-4 -2 0 2 40.0

0.2

0.4

0.6

0.8

no integration =2 days

Co

rre

lati

on

co

eff

icie

nt

Offset, days

Cross-correlation ULF-index with electron flux

F=F0exp(-t/)

Correlation between the ULF-index and electron flux somewhat increases for the time-integrated over pre-history ULF index values:

( ) ( ') exp[ ( ') / ] 't

J t J t t t dt

Increase of correlation probably implies the occurrence

of the cumulative effect, that is, the the long-lasting (with

characteristic time ) ULF wave activity is important for

the electron flux increase, but not just instant values!

Relationship between the relativistic electron flux Relationship between the relativistic electron flux and geomagnetic activity indicesand geomagnetic activity indices

The electron flux is also highly correlated with the Dst and AE indices. The electron flux is also highly correlated with the Dst and AE indices. SometimesSometimes the correlation with Dst is even higher than that with the ULF index.the correlation with Dst is even higher than that with the ULF index.

Geomagnetic disturbances, as well as an elevated level of ULF wave activity, precede the growth of relativistic electron flux for about two days on average

-4 -2 0 2 40.0

0.2

0.4

0.6

0.8

1.0

AE - Dst ULF

Co

rre

lati

on

co

eff

icie

nt

Offset, days

Cross-correlation between electrons flux variations, ULF-index and geomagnetic activite in 1994

-4 -2 0 2 40.0

0.2

0.4

0.6

0.8

1.0

Co

rre

lati

on

co

eff

icie

nt

Offset, days

-Dst Vsw ULF

Cross-correlation between electrons flux variations, ULF-index and main geomagnetic indexes in 1999-2000.

We acknowledge the provision of Noon-reconstructed electron fluxes provided by P. O’Brien. GOES data from NOAA NSDC; Ground magnetic data from INTERMAGNET, CPMN, MACCS, and

Greenland arrays; OMNI-2 database from NASA NSSDC;

The The new ULF wave index, analogous to geomagnetic indices, derived from ground-new ULF wave index, analogous to geomagnetic indices, derived from ground-

based and satellite observations in the Pc5 frequency band – the range of natural based and satellite observations in the Pc5 frequency band – the range of natural

MHD resonators and waveguides, characterizes the turbulent level of the solar MHD resonators and waveguides, characterizes the turbulent level of the solar

wind-magnetosphere-ionosphere system. wind-magnetosphere-ionosphere system.

The database for interval 1994-2001 is freely available to space community via anonymous FTP site for testing and validation:

space.augsburg.edu

folder: /pub/MACCS/ULF_Index/

CD with ULF index database may be requested!