Evaluation of the STORM model storm-time corrections for middle latitude

1. Evaluation of the STORM model storm-time corrections for middle latitude D. Buresova(1), L-A. McKinnell(2), T.Sindelarova(1), I. Blanco Alegre(3) and B. De La Morena(3) (1) Institute of Atmospheric Physics, Prague, Czech Republic (2) Hermanus Magnetic Observatory, Hermanus, South Africa (3) Ionospheric observatory, El Arenosillo, Huelva, Spain

2. Outline: IRI simulation of ionospheric storm effects: STORM model design and results of the previous validations Occurrence of the positive and negative effects of ionospheric storms over European middle latitudes Evaluation of the quality of the STORM model ionospheric storm-time corrections over middle latitudes New results Conclusions

3. The STORM model design: • The updated IRI-2001 version contains a geomagnetic activity dependence option based on Time Empirical Ionospheric Correction Model (STORM) (Araujo-Pradere et al., 2002) • The STORM was developed using data from 75ionosonde stations, incoherent scatter radars, the ISIS and Alouette topside sounders, and in situ instruments on several satellites and rockets for 43 storms. • The design of the STORM relies on the theory that long-living negative storm effects are due to regions in which the neutral composition is changed. The prevailing thermospheric summer-to-winter circulation, which transports the molecular rich gas equatorward, explains the seasonal dependence : appearance of the prevailing negative phase in summer and characteristic positive storms in winter (Prolss, 1993, Fuller-Rowell et al., 1996). • The STORM was designed to be a function of the intensity of the storm and depend on latitude and season. It was based on an extensive database of ionosonde observations, guided by simulations using a coupled thermosphere-ionosphere model. (Fuller-Rowell et al., 1996, 1998)

4. Results of the previous STORM model validation: • Model validation was carried out by Araujo-Pradere et al., (2002; 2003). The model output has been compared with the observed ionospheric response at 15 selected NH and SH stations during 14 strong storms in the years 2000-2001. • The accuracy of the model has been quantified by evaluating the daily RMSE between the model and observations and compared with the predictions using the monthly median (IRI prediction with STORM option switched-off) using equations: • The comparison showed that the model captures the decrease in electron density particularly well in summer and equinox at mid-latitudes and high latitudes, but is less accurate in winter.

5. Results of the previous STORM model validation: • Visually, the prediction given by the STORM model follows the observed changes for many of the cases, but does not do sufficiently well in the summer hemisphere. • The results showed that the model is on average 33% improved over the monthly mean. • Miro et al.(2007) compared the STORM corrections with ionosonde data obtained at 15 stations during two severe storms of October and November 2003. The results also showed that the model simulates quite well the negative effects above SH stations (improvement 60-70%). For NH stations the model predictions were significantly worse (improvement 12-23%)

7. Data sources The created database incorporates 65 strong-to-severe magnetic storms occurred within the period from 1995 to 2005. The study is carried out using F2 region peak parameters available in the World Data Centre for Solar-Terrestrial Physics at Chilton (WDC1) http://www.ukssdc.ac.uk/wdcc1,inthe Digital Ionogram Database of the Centre for Atmospheric Research, UMass, Lowell http://ulcar.uml.edu/DIDBase/, in the COST 271 databasehttp://www.wdc.rl.ac.uk/cgi-gin/ionosondes/cost_database.pl. and provided by ionospheric stations. Parameters used are hourly interval resolution manually checked foF2 values for the initial, main and partly for recovery phases of the analysed magnetic storms (at least for a 5-day period) for each station and corresponding monthly medians. The parameters simulation has been performed by running online model available at the IRI web site http://omniweb.gsfc.nasa.gov/vitmo/iri_vitmo.html. ·        Sudden storm commencement (SSC) has been chosen as an indicator of the storm onset. The storm main phase is defined by the decrease of Dst (decrease in magnetic field strength) and the subsequent recovery phase by its gradual reversal to quiet conditions. ·      Strong storm conditions were defined when Dst ≤ -100 nT for at least 2 consecutive hours. Storm conditions prevail till Dst < -50 nT.

8. Our results show that the changeover from one type of the effect to the other is more common for winter than for summer, and the occurrence of such behaviour increases with decreasing latitude. • During summer all three stations display more frequent appearance of only negative effect during the entire main phase of the analysed storms. (Buresova et al, 2007).

10. May 1997 magnetic storm Observed values and output of the STORM model as foF2 ratio for May 1997 storm. The dashed line shows the output of the IRI model, the black line is the observation. An empty square represents the daily RMSE for STORM, and the cross is the IRI with STORM option switched off.

11. 7-12 November 2004 magnetic storm

12. July 2004 magnetic storm

13. (McKinnell and Oyeyemi, 2008)

14. Conclusions: • Present results of the STORM model evaluation show that: • In general, the STORM model improves a storm-time foF2 representation over middle latitudes. At the peak of the disturbance the model gives best results for summer storms and for European higher-middle latitudes At the NH the effectiveness of the model storm-time corrections is decreasing with decreasing latitude. For the SH the trend seems to be opposite (larger investigation is necessary). • The model partially fails in capturing an alternation of the storm positive and negative effects. • The STORM model is not able to reproduce correctly the storm-induced rapid changes in the daily course of the foF2 (e.g. initial rapid positive ionospheric response on the storm onset) and the foF2 behaviour in the case of more complicated magnetic storm development. • The largest differences between the observed and model-reproduced magnitude of the storm effect was obtained for the negative phases. • Acknowledgements • This work has been supported by Grant 1QS300120506 of the Academy of Sciences of the Czech Republic and by Grant 205/08/1356 of the Grant Agency of the Czech Republic. We also thank all data centers and ionospheric observatories for supplying us with data.

15. Outline of current activities: • To analyse the storm-time behavior of main ionospheric parameters (e.g. foF2, foF1, hmF2) above single localities. • To compare the IRI-calculated and observed monthly medians. • To use the created database for other ionospheric model validation. • To use the database for NN training.

16. References: Araujo-Pradere, E. A., andT. J.Fuller-Rowell: A model of a perturbed ionosphere using the auroral power as the input, Geof. Int., 39(1), 29--36, 2000. Araujo-Pradere E.A, Fuller-Rowell T.J, M.V. Codrescu: STORM: An empirical storm-time ionospheric correction model –1. Model description, Radio Sci., 37 (5), doi: 10.1029/2001RS002467, 2002. Araujo-Pradere E.A, T.J. Fuller-Rowell: Storm: An empirical storm-time ionospheric correction model – 2. Validation, Radio Sci., 37 (5), 1071, 2002. Araujo-Pradere E.A, Fuller-Rowell T.J, M.V. Codrescu, A.Anghel: Evaluation and prospects for storm-time corrections in the International Reference Ionosphere, Adv. Space Res, 33, 908-909, 2004. Bilitza D.: International reference ionosphere 2002: Examples of improvements and new features, Adv. Space Res, 31 (3), 757-767, 2003. Buresova, D., J. Lastovicka, and G. de Franceschi: Manifestation of strong geomagnetic storms in the ionosphere above Europe. Space Weather Research towards Applications in Europe, pp. 185-202, ed. J. Lilensten, Springer, Dordrecht, 2007. Fuller-Rowell, T.J., D. Rees, S. Quegan, R.J. Moffett, M.V. Codrescu, and G.H. Millward: A coupled thermosphere-ionosphere model (CTIM), in STEP: Handbook of Ionosphereic Models, ed. by R. Schunk, 239-279, 1996. Miro Amarante, G., Cueto Santamaria, M., Alazo, K., and Radicella, S.M.: Validation of the STORM model used in IRI with ionosonde data, Adv. Space Res., 39, 681-686, 2007. Prölss, G.W.: On explaining the local time variation of ionospheric storm effects, Ann. Geophys. 11, 1-9, 1993.