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The background

Ionospheric forecast over Europe driven by IMF conditions Tsagouri I. and A. Belehaki National Observatory of Athens. The background. Prölss, G.W., On explaining the local time variation of ionospheric storm effects, Ann. Geophys., 1993.

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The background

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  1. Ionospheric forecast over Europe driven by IMF conditionsTsagouri I. and A. BelehakiNational Observatory of Athens

  2. The background Prölss, G.W., On explaining the local time variation of ionospheric storm effects, Ann. Geophys., 1993. Tsagouri et al., Positive and negative ionospheric disturbances at middle latitudes during geomagnetic storms,GRL, 2000 Belehaki and Tsagouri, On the occurrence of storm-induced nighttime ionization enhancements at ionospheric middle latitudes, JGR, 2002 Tsagouri and Belehaki, A new empirical model of middle latitude ionospheric response for space weather pplications, Advances in Space research, 2006

  3. The aim This contribution aims at: • the introduction of criteria for the on line determination of the storm onset in real time from ACE’s observations, and • the reformulation of the model’s expressions in order to include the latitudinal dependence of the ionospheric response. The data analysis was established on observations concerning 60 intense (Dst < -100 nT) or great (Dst < -250 nT ) storm events (Gonzalez et al., 1999) occurred in the time interval 1998 – 2005.

  4. Determination of the storm disturbance onset based on IMF observations Based on preliminary analysis and previous reports the storm onset is accompanied by: • Increase of the Bmag (first indication). Bmag significant greater than 10 nT. • IMF-Bz < 0. Storm conditions (long lasting southward turning, Bz < - 5 nT). The Dst decrease is triggered by the Bz southward turning.

  5. IMF conditions (introduced criteria) • Based on the detailed analysis of the events the following set of criteria was established: • Rapid increase of the Bmag verified by dB/dt > 5 nT/h • Bmag > 12 nT • IMF-Bz southward turning either simultaneously or at maximum 4 hours later than the increase in Bmag: IMF-Bz < -5 nT for at least two hours. • Fine tuning of the criteria: • Determination of the “end” of an event: northward turning of IMF-Bz (IMF-Bz > -1 nT).

  6. Ionospheric response over Europe The ionospheric observations were organized in eight groups based on: 1. The latitude of the observation point • middle-to-high: latitudes greater than 45º (Chilton, Juliusruh) • middle-to-low: latitudes from 30º to 45º (Athens, Rome, San Vito, Sofia, El Arenosillo and Tortosa) 2. The local time (LT) of the observation point at the storm onset. • Evening (19-00) • Morning (01 – 06) • Prenoon (07 – 12) • Afternoon (13-18)

  7. Ionospheric response: LT of the observation point in the afternoon sector (13 – 18) Strong ionospheric depletion (over median conditions) of 50% maximum intensity is recorded in all latitudes.

  8. Ionospheric response: LT of the observation point in the evening sector (19 – 00) Significant ionospheric disturbances (> 30 %) are recorded at middle-to-high latitudes. In middle-to-low latitudes the disturbances are less intense but greater than 20 %.

  9. Ionospheric response: LT of the observation point in the morning sector (01 – 06) Intense ionospheric depletion (~40%) is detected in middle-to-high latitudes. No significant effects are observed in the middle-to-low latitudes.

  10. Ionospheric response: LT of the observation point in the prenoon sector (07 – 12) Intense ionospheric depletion (~40%) is detected in middle-to-high latitudes. Positive storm effects in the prenoon/afternoon sectors constitutes the ionospheric storm time response in middle-to-low latitudes (~ 30%).

  11. Discussion of the results • According to our results, • Systematic positive storm effects are observed at middle-to-low latitudes during daytime hours and about three hours later than the storm onset (for storm onset in the prenoon sector). The positive phase penetrates to the evening sector. • Negative storm effects are systematically observed in middle-to-high latitudes independently on the LT of the observation point at onset and in the middle-to-low latitudes in the nighttime hours. The negative phase is first detected in the evening sector while it is expanded in the daytime hours as the storm develops and recovers. • All the above, indicate that the ionospheric storm time disturbances that follow the storm onset time as it is determined from ACE observations are consistent with Prölls (1993) and Fuller-Rowell et al. (1994; 1996) phenomenological scenario.

  12. Validation tests (quiet intervals)

  13. Validation tests (disturbed intervals)

  14. Modeling the ionospheric response: Time delay in negative phase onset The time delay in ionospheric negative phase onset in respect to the LT of the observation point at onset. The LT effect is clearly demonstrated.

  15. Modeling the Ionospheric Response: Reformulation of the model’s expressions • Middle-to-high latitudes • Four LT sectors • Predictions are provided for 24 to 40 hours ahead

  16. Modeling the Ionospheric Response: Reformulation of the model’s expressions • Middle-to-low latitudes • Three LT sectors • Predictions are provided for 18 to 24 hours ahead

  17. Application of the model • Determination of the storm onset in UT based on IMF observations from ACE (introduced criteria) • Determination of LT of the observation point at onset • Estimation of the time delay in ionospheric response • Application of the model’s expressions on the quiet ionosphere (monthly medians)

  18. Validation tests for middle-to-high latitudes: Juliusruh station The model’s predictions are satisfactory correlated with actual observations (during quiet and disturbed ionospheric conditions) In general, the model’s predictions underestimates the ionospheric disturbances (30%).

  19. Model’s prediction over climatology (Juliusruh) • N is the number of days • % improvement = ((RMSE(monthly median)-RMSE(model)/RMSE(monthly median))x100 • (Araujo-Pradere and Fuller-Rowell, 2002)

  20. Validation tests for middle-to-low latitudes: Rome station The model’s predictions are satisfactory correlated with actual observations (during quiet and disturbed ionospheric conditions) Once again, the model’s predictions underestimates ionospheric disturbances (slightly greater than 30%).

  21. Model’s prediction over climatology (Rome) • N is the number of days • % improvement = ((RMSE(monthly median)-RMSE(model)/RMSE(monthly median))x100 • (Araujo-Pradere and Fuller-Rowell, 2002)

  22. Summary The proposed method was further improved to anticipate more localized predictions over Europe. In particular, • Quantitative criteria for the determination of the storm onset from IMF observations were introduced, and • the models expressions were reformulated to include the latitudinal dependence of the ionospheric response. Extensive validation test were also performed for two European stations well separated in latitude in order to investigate the methods performance. The results gave evidence for significant improvement over climatology (up to 54%) for all seasons, while the method’s predictions presents satisfactory accuracy in respect to actual observations.

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