C. Manoj*, S. Maus and Patrick Alken NGDC/CIRES, Boulder, Colorado, USA
description
Transcript of C. Manoj*, S. Maus and Patrick Alken NGDC/CIRES, Boulder, Colorado, USA
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%.