1. Storm-time total electron content and its response to penetration electric fields over South America P. M. de Siqueira, E. R. de Paula, M. T. A. H. Muella, C. M. Paulo, L. C. Viera 09/11/2011

2. Introduction We present the response of the ionosphere due to the severe magnetic storm of 7–10 November 2004. GPS Total Electron Content (TEC) maps of South America region were analyzed. Ionospheric vertical drift data obtained from Jicamarca ISR are used in the analysis in order to verify the disturbed zonal electric fields during the superstorm. The vertical drifts were also inferred from H magnetometer data (Jicamarca-Piura) following the methodology presented by Anderson et al. (2004).

3. Introduction Penetration electric fields were observed by comparing the equatorial vertical drifts and the Interplanetary Electric Field (IEF). TEC maps reveal unexpected plasma distributions and TEC levels during the main phase of the superstorm on 7 November. The results also reveal well known characteristics of the plasma distributions on 8, 9, and 10 November. The emphasized features are the expansion and intensification of EIA due to prompt penetration electric fields on November 9 and the inhibition of EIA during post- sunset hours on November 7, 8, and 10.

4. General Scenario of the Superstorm First increase in Sym-H: around 12 UT on Nov. 07. Minimum Sym-H: -394 nT on Nov. 08, 05:55UT.

5. TEC responses on November 07, 2004.

6. Black line (third panel) is referred to modeled vertical drifts (using H Jicamarca- Piura data in a neural network). Vertical drifts are smaller compared to quiet time before 15 UT and before the SSC. Jicamarca: LT = UT – 5 hours

7. Jicamarca: LT = UT – 5 hours Prompt Penetration Electric Field (PPEF) event occurs from 15 to 17 UT. Vertical drifts are negative from 17 to 18 UT. SSC occurs around 18:30 UT. Pre-reversal enhancement (PRE) is present (dh’F/dt from Jicamarca digisonde). Daytime negative vertical drifts (DD)

8. TEC maps  denotes the geographic positions of GPS receptors. Nov. 06 is the quiet time reference. Top: 16:00 UT (13 LT at Brazil) Bottom: 16:30 UT (13:30 LT). Higher TEC absolute values on Nov. 07 after the PPEF event. No significant differences. Nov. 06 Nov. 07

9. Nov. 06 (19 LT Brazil) Nov. 07 (19 LT Brazil) During PRE hours (after sunset). Smaller TEC on Nov. 07 at 19 LT (Brazil) EIA crests are diminished.

10. Nov. 06 (20 LT Brazil) Nov. 07 (20 LT Brazil) EIA is developed on Nov. 06 at 20 LT (quiet time reference). EIA disappears on Nov. 07 from 20 LT on (even though the occurrence of PRE). This is probably due to the smaller vertical drifts on Nov. 07 during daytime (being negative in some hours).

11. TEC responses on November 08, 2004.

12. Flat IEF Ey (IMF Bz near zero during this period). Daytime vertical drifts near zero during daytime (sometimes negative). Second panel: green line is referred to sunset hours denoting a weak PRE (~20m/s). These vertical drifts reflect the action of disturbance dynamo fields. Jicamarca: LT = UT – 5 hours Daytime drifts

13. Nov. 06 (12 LT Brazil) Nov. 08 (12 LT Brazil) Nov. 06 – quiet time reference. TEC enhancement confined to the geomagnetic equator and magnetic low- latitude. Typical effect of disturbance dynamo electric fields.

14. Nov. 06 (18:30 LT Brazil) Nov. 08 (18:30 LT Brazil) EIA starting to develop at 18:30 LT (Brazil) on Nov. 06. EIA absent on Nov. 08 and TEC enhancement prevails over the geomagnetic equator.

15. Nov. 06 (19:30 LT Brazil) Nov. 08 (19:30 LT Brazil) EIA developed at 19:30 LT (Brazil) on Nov. 06. EIA also developed on Nov. 08 (19:30 LT Brazil). The weak PRE occurred on Nov. 08 was efficient to develop EIA after 19:30 LT.

16. TEC responses on November 09-10, 2004.

17. Second Panel: green line is referred to vertical drifts measured at Jicamarca ISR. Great PPEF event occurs on Nov. 09, from ~19:30 UT to 21 UT (vertical drifts reach ~120m/s) during a recurrent and very intense magnetic storm. Jicamarca: LT = UT – 5 hours

18. Vertical drifts quite disturbed on Nov. 10 (nighttime). Daytime vertical drifts (after 12 UT on Nov. 10) present a partial recovery to quiet time patterns. Absence of PRE on Nov. 10. Jicamarca: LT = UT – 5 hours nighttime Nov. 09Nov. 10

19. Nov. 06 (12 LT Brazil) Nov. 09 (12 LT Brazil) TEC strongly increased on Nov. 09 (12 LT). No significant PPEF is identified at this time.

20. Nov. 06 (17 LT Brazil) Nov. 09 (17 LT Brazil) TEC strongly increased on Nov. 09 (17 LT). At this time occurs the strong PPEF event.

21. Nov. 06 (18 LT Brazil) Nov. 09 (18 LT Brazil) Anomalous development of EIA due to the PPEF. Intensified crests displaced to higher latitudes.

22. Nov. 06 (18:30 LT Brazil) Nov. 09 (18:30 LT Brazil) Anomalous development of EIA due to the PPEF.

23. Nov. 06 (20 LT Brazil) Nov. 09 (20 LT Brazil) Anomalous development of EIA due to the PPEF prevails until the end of Nov. 09. And on Nov. 10...

24. Nov. 06 (13 LT Brazil) Nov. 10 (13 LT Brazil) Anomalous TEC distribution on Nov. 10 (during partial recovery of vertical drifts). Negative phase of ionospheric storm is observed at mid-latitudes. Distribution of ionization is related to the decrease of O/N 2 ratio at mid-latitudes.

25. Nov. 06 (19 LT Brazil) Nov. 10 (19 LT Brazil) Negative phase of ionospheric storm is still observed at mid-latitudes. This result prevailed during the whole day.

26. Composition changes add to electrodynamics forcing. Nov. 08: Expansion at high latitudes causes decreasing in the O/N 2 ratio resulting in TEC decreases at high to mid-latitudes. Nov. 10: Decrease of O/N 2 ratio over mid-latitudes at South America region causing TEC decreases at this region. From Mannucci et al. 2009 (JGR)

27. Final remarks EIA is inhibited on Nov. 07 even though the occurrence of PRE then it is probably due to the disturbed daytime vertical drifts (smaller compared to quiet time). Storm time TEC responses are well known on: – Nov. 08 (denoted by disturbance dynamo patterns), – Nov. 09 (denoted by strongly developed EIA due to PPEF), – Nov. 10 (denoted by the late negative phase of ionospheric storms over mid-latitudes). LISN added to RBMC (IBGE/Brazil) GPS receptors provide a good distribution over South America which is extremely important for this type of research at this region characterized by the SAMA and large declination differences.