May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Penetration Characteristics of the Interplanetary Electric Field to

the Day-time Equatorial Ionosphere

C. Manoj*, S. Maus and Patrick AlkenNGDC/CIRES, Boulder, Colorado, USA

(* On leave from, NGRI-Hyderabad, India)

H. Lühr GeoForschungsZentrum-Potsdam, Germany

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

The ionospheric equatorial electric field (EEF) exhibits large day-to-day variability.

– Wind forced diurnal variations (~50% of the variance)

– Influence of interplanetary variations on EEF

• Wind forced (disturbance dynamo)

• Prompt penetration

– Other

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Prompt penetration, some questions

- Frequency dependence of the prompt penetrating electric field?- Coherence, phase relation

- Does the prompt penetration depend on local time, solar flux, season, polarity of IMF Bz, etc ?

- What is the period range of prompt penetration effect on EEF?

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

1. Advance Composition Explorer (ACE) satellite at L1 point

2. Time-shifted to the magnetosphere’s bow-shock nose by OMNI

1. Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere (JULIA) radar, Peru.

2. 1002 days

06:00 09:00 12:00 15:00 18:000

500

1000

Local Time (hours)

days

ava

ilabl

e

Data during 2001 to 2008

Interplanetary electric field (IEF) data

Equatorial ionospheric electric field (EEF) data

120 W 90

W 60

W 30

W

30 S

0

30 N

JULIA radar

dip equator

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

1. Diurnal variation of JULIA data is removed using the model by *Alken (2008)

2. Eastward electric field at JULIA is calculated as,

3. The ionospheric field variations are correlated with the interplanetary E-field (IEF).

15:00 18:00 21:00-101

UT (hours)

IEF

Ey

mV

/m

0

5

10

15

20

Vz (

m/s

)

Date - 2006-10-01

B zy vE

* manuscript in preparation

Example of data processing

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Average power spectra of IEF and JULIA electric fields

Spectra are estimated from pairs of daily EEF and IEF data, each 6 hours long.

265 pairs of data.

The power spectra and cross spectra are computed by Welch's averaged periodogram method (Welch, 1967).

Both power spectra show monotonous increase in power with period.

Dependence on activity level (Ap). Power is higher by factor of 3.

10-1

100

101

10-1

100

101

102

103

period in hours

mV

2/m

2/[H

z]

JULIA, EEF

All daysAp < 20Ap > 20

10-1

100

101

101

102

103

104

105

period in hours

mV

2/m

2/[H

z]

ACE, IEF

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Coherence between IEF and EEF

)().(

|)(|)(

2

EEFEEFIEFIEF

EEFIEFEEFIEF PP

PC

6 10 20 30 1 2 4 6 100

0.2

0.4

0.6

0.8

1

cohe

ren

ce

All days (265 days)

0.1110Frequency (Cycles per hour)

0.1110Frequency (Cycles per hour)

Ap<20 (220 days)Ap>20 (45 days)

Coherence is significant for periods above 20 minutes.

It peaks around 2 hours (0.5 cycles / hour).

Coherence is slightly higher during active days

Significance level (Thompson, 1979)

|<- ->|-> | <-Period in minutes Period in hours

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Cross Phase spectra

A process that causes coherent EEF signals over the whole range is prompt penetration.

In the subsequent analysis, we always delay IEF data by 17 min.

101725

-100

-50

0

50

100

150

200

250

ph

ase

diff

ere

nce

(d

eg

ree

s)

6 10 20 30 1 2 4 6 10|<- ->|-> | <-Period in minutes Period in hours

0

Delay in Minutes

)( EEFIEFPofangle

2πf.Δt Δt = 17 min

Cross-phase spectra is the IEF phase minus the EEF phase as a function of frequency. Unshifted IEF data show monotonous decrease.

When delayed by 17 minutes, the phase spectra have negligible values for all the periods we consider.

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Dependence on local time

6 10 20 30 1 2 4 6 100

0.2

0.4

0.6

0.8

1

cohe

renc

e

|<- ->|-> | <-Period in minutes Period in hours|<- ->|-> | <-Period in minutes Period in hours

09-1210-1311-1412-1513-16

JULIA LTUsing 3-hour long windows of EEF and IEF data.

Coherence is maximum for a window centered on local noon.

Coherence at 40 minutes period seems to be independent of LT

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Dependence on IMF Bz

6 10 20 30 1 2 4 6 100

0.2

0.4

0.6

0.8

1

cohe

renc

e

|<- ->|-> | <-Period in minutes Period in hours

IMF Bz < 0 (119 days)IMF Bz > 0 (146 days)

The whole data set is divided into two groups.

Prompt penetration shows no significant dependence on IMF Bz polarity.

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Dependence on season

6 10 20 30 1 2 4 6 100

0.2

0.4

0.6

0.8

1

cohe

renc

e

|<- ->|-> | <-Period in minutes Period in hours|<- ->|-> | <-Period in minutes Period in hours

Nov-Feb (101 days)Mar-Apr (23 days)May-Aug (92 days)Sep-Oct (47 days)The coherence functions for

June and Dec. solstice are almost identical. The coherence functions during the two equinox periods are slightly different. (small sample number)

No significant dependence on season is observed

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Dependence on solar flux level

6 10 20 30 1 2 4 6 100

0.2

0.4

0.6

0.8

1

cohe

renc

e

|<- ->|-> | <-Period in minutes Period in hours

All days (265 days)EUVAC > 120 (75 days)EUVAC < 120 (190 days)

EUVAC (Extreme Ultraviolet (EUV) flux model for aeronomic calculations (Richards et al., 1994).

EUVAC = 0.5*(F10.7+F10.7A), where F10.7A is the 81-day moving average of F10.7

The coherence between IEF and JULIA electric fields is lower for high solar flux (EUVAC > 120).

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

6 10 20 30 1 2 4 6 10-55

-50

-45

-40

-35

-30

-25

-20

-15

Mag

nitu

de (

dB)

|<- ->|-> | <-Period in minutes Period in hours

0.178

0.100

0.056

0.032

0.018

0.010

0.006

0.003

0.002

Rat

io o

f EE

F/IE

F

Signal Transfer Function

)(

)()(

IEFIEF

IEFEEFEEFIEF P

PT

6 10 20 30 1 2 4 6 10-50

0

50

100

|<- ->|-> | <-Period in minutes Period in hours

phas

e di

ffere

nce

(deg

rees

)

0.1110Frequency (Cycles per hour)

To predict EEF variations from interplanetary electric field (IEF) data

Maximum admittance around 2 hours.

The transfer function does not introduce a phase modulations.

The magnitude of our transfer function is higher than that by Nicolls et al. (2007). The difference increases towards shorter periods.

This studyNicolls et al. (2007)

Transfer function magnitude is ratio of EEF to IEF as a function of frequency. TF phase is the EEF phase minus the IEF phase.

May 23, 2008 16:45 ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects

Conclusions• The coherence between IEF and EEF peaks around 2 hours period at a

magnitude squared coherence of 0.6.

• The lack of a frequency-dependent phase shift between IEF and EEF indicates that the coupling process between IEF and EEF signals is prompt penetration.

• Coherence peaks at local noon, Coherence is lower on days with high solar flux.

• We find that the penetration of interplanetary electric fields to the equatorial ionosphere shows no significant dependence on the polarity of IMF Bz.

• The transfer function can be used to predicted the non-diurnal variations of equatorial electric fields up to 38%.