Behavior of the ionosphere over Europe during two geomagnetic storms which caused Tongues of Ionization over North America.

Marta Rodríguez-Bouza (1), Miguel Herraiz (1,2),Gracía Rodriguez-Caderot (3,4) , and Sandro M. Radicella (5)

(1) Departamento de Física de la Tierra, Astronomía y Astrofísica I (Geofísica y Meteorología), Facultad de Ciencias Físicas, Universidad Complutense de Madrid (UCM), Spain (mrodriguezbouza@ucm.es) (2) Instituto de Geociencias, (UCM, CSIC), Spain. (3) Sec. Dptal. Astronomía y Geodesia, Facultad de Matemáticas, UCM, Spain. (4) Instituto de Matemáticas Interdisciplinar UCM, Spain.

(5) Telecommunications/ICT Development Laboratory (T/ICT4D), Abdus Salam International Centre for Theoretical Physics (ICTP), Italy.

Figure 1. Station distribution.

DATA AND METHODOLOGY

TEC has been obtained by processing GPS/GLONASS observations from RINEX files fromGNSS stations belonging to EUREF Permanent Network and International GPS Service,IGS, networks (Figure 1). Data have been divided into two groups according to theirorigin: Europe and North America. For each group we have used all the availablestations.

Processing technique (Ciraolo, 2012) assumes the thin shell model of the ionosphere toobtain vertical TEC (vTEC) and slant TEC (sTEC) at the Ionospheric Pierce Point, IPP. Thispoint is defined as the place where the line-of-sight between the satellite and theground receiver intersects the ionosphere. Data were obtained at 1 minute sampling inperiods of the geomagnetic storms and during quiet days around the storm days forcomparison. Values at IPP points have been interpolated using the Kriging method inorder to obtain the maps over the two regions.

INTRODUCTION

GEOMAGNETIC STORMS IONOSPHERIC STORMS

Storm of 15 July 2013 Storm of 19 February 2014

Storm of 15 July 2013

Storm of 19 February 2014

The value of Dst index decreasedto a minimum of -72 nT, on 15thJuly 2013. According to thecriteria of Gonzalez et al.,(1994)this geomagnetic storm isclassified as Moderate.

In the second storm, the Dst indexdropped to a value of -112nT, on19th February 2014. Thereforethe geomagnetic storm isclassified as Intense following thesame criteria.

Ciraolo, L. (2012) Ionospheric Total Electron Content (TEC) from the Global Positioning System, Personal communication.Foster, J. C., Coster, A. J., Erickson, P. J., Holt, J. M., Lind, F. D., Rideout, W., McCready, M., van Eyken, A., Barnes, R. J., Greenwald, R. A., Rich, F. J. (2005), Multiradar observations of thepolar tongue of ionization, J. Geophys. Res., 110, A09S31 doi:10.1029/2004JA010928Gonzalez, W.D., Joselyne, J.A., Kamide, Y., Kroehl, H . W., Rostoker, G., Tsurutani, B. T., Vasyliunas, V.M. (1994) What is a Geomagnetic Storm?, Journal of Geophysical Research, 99 5771–5792Stankov, S.M., Warnant, R., Stegen, K. (2009) Trans-ionospheric GPS signal delay gradients observed over mid-latitude Europe during the geomagnetic storms of October-November2003. Advances in Space Research 43 1314-1324 doi: 10.1016/j.asr.2008.12.012Yizengaw, E., Moldwin, M.B., Galvam, D.A. (2006) Ionospheric signatures of a plasmaspheric plume over Europe. Geophysical Research Letters, Vol. 33, L17103,doi:10.1029/2006GL026597

ACKNOWLEDGMENTS: REFERENCES:

CONCLUSIONS

This work presents the effect of two geomagnetic storms on the ionospheric Total Electron Content (TEC) over Europe.These geomagnetic events occurred on July 2013 and February 2014 and have been chosen because in both cases aTongue of Ionization (ToI) appeared over North America.

A ToI is a local density enhancement of low-temperature plasma in the F region polar ionosphere occurred in disturbedconditions as a consequence of rapid sunward convection from the postnoon midlatitude (Foster et al., 2005). Theionosphere produces a delay in the satellite signals when they cross it. Strong ionospheric disturbances are capable ofcausing large variability in the ionospheric delay. Anomalous ionospheric spatial gradients, characterized by sharpincrease/decrease in ionospheric delays over relatively short horizontal distance, as those caused in ToIs, are of particularconcern. This is due to their sudden appearance, like a wave with a steep front or like a moving ‘ionospheric wall’, theirrelatively fast propagation and their changing patterns (Stankov et al., 2009). There are many observations of ToIs in theNorth America sector but in Europe this phenomenon is much less frequent and ToIs have been observed for the first timein September 2005 (Yizengaw et al, 2006).

Figure 2. Dst index for July 8-17, 2013

Figure 3. Dst index for July 12-21, 2014

Figure 4. Ionospheric total electron content in a quiet day (left) and during the geomagnetic storm (right). Figure 6. Ionospheric total electron content in a quiet day (left) and during the geomagnetic storm (right).

Figure 5. Ionospheric total electron content in a quiet day (left) and during the geomagnetic storm (right). Figure 7. Ionospheric total electron content in a quiet day (left) and during the geomagnetic storm (right).

Both geomagnetic storms caused a ToI over North America but the shape ofthese ToIs is clearly different. While in the first storm the ToI extended fromSoutheast to the Northwest , the second ToI was propagated in the Westernregion part from South to North and spread to the East upon its arrival to higherlatitudes.

The behavior of the ionospheric storms over Europe is also very different. InJuly’s storm there was a general decrease of TEC over the entire region while. InFebruary’s storm, there was a strong increase of TEC below 50º latitude and apronounced decrease between 50º and 60º.

ToIs in North America appears in local dusk, while the European ToI wasobserved in the morning sector.

In both cases the origin of the geomagnetic storm was a Coronal Mass Ejection combined with a South component of the interplanetary magnetic field.

North AmericaNorth America

Europe Europe

This work is part of the research activities of the "Ionospheric Studies andSatellite Positioning Techniques (GNSS) Group" funded by UCM.The authors are very grateful to L. Ciarolo and F. J Sánchez Dulcet for theirvaluable collaboration and want to thank EUREF Permanent Network andInternational GPS Service, IGS, networks for providing the GNSS data, andWorld Data Center for Geomagnetism, Kyoto, for Dst index data.M.H. thanks the grant from the Spanish Ministry of Education, Culture andSports for a sabbatical leave at T/ICT4D, Trieste.