1. May 23, 2008 16:45ISEA, 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 Alken NGDC/CIRES, Boulder, Colorado, USA (* On leave from, NGRI-Hyderabad, India) H. Lühr GeoForschungsZentrum-Potsdam, Germany

2. May 23, 2008 16:45ISEA, 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

3. May 23, 2008 16:45ISEA, 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?

4. May 23, 2008 16:45ISEA, 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 Data during 2001 to 2008 Interplanetary electric field (IEF) data Equatorial ionospheric electric field (EEF) data

5. May 23, 2008 16:45ISEA, 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). * manuscript in preparation Example of data processing

6. May 23, 2008 16:45ISEA, 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.

7. May 23, 2008 16:45ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects Coherence between IEF and EEF 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 minutesPeriod in hours

8. May 23, 2008 16:45ISEA, 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. 10 17 25 -100 -50 0 50 100 150 200 250 phase difference (degrees) 6102030 1 2 4 610 |<-->|-> | <-Period in minutesPeriod in hours 0 Delay in Minutes 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.

9. May 23, 2008 16:45ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects Dependence on local time Using 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

10. May 23, 2008 16:45ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects Dependence on IMF Bz The whole data set is divided into two groups. Prompt penetration shows no significant dependence on IMF Bz polarity.

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

12. May 23, 2008 16:45ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects Dependence on solar flux level 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).

13. May 23, 2008 16:45ISEA, Crete, Greece. S10 Ionospheric storms and space weather effects 0.178 0.100 0.056 0.032 0.018 0.010 0.006 0.003 0.002 Ratio of EEF/IEF Signal Transfer Function 6102030 1 2 4 610 -50 0 50 100 |<-->|-> | <-Period in minutesPeriod in hours phase difference (degrees) 0.1 110 Frequency (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 study Nicolls 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.

14. May 23, 2008 16:45ISEA, 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%.