Papers presented at European Geosciences Union (EGU) 1st General Assembly, Nice, 26-30 April 2004 Guest Editors: Dr. Bruno Zolesi and Dr. Ljiliana Cander. Special issue.

M. Cueto, P. Coisson, S. M. Radicella, L. Ciraolo, M. Herraiz. INCLUDING THE GALLAGHER PLASMASPHERIC MODEL IN THENEQUICK IONOSPHERIC MODEL
Abstract. The NeQuick ionospheric electron density model has a very simple topside formulation which allows to take into account the electron content up to 20000 km. In the present work Gallagher model has been used in connection with NeQuick to provide a more realistic representation of the electron concentration distribution in the plasmasphere. Electron density profiles and TEC values obtained by NeQuick alone and by NeQuick+Gallagher have been compared. ISIS-2 topside sounder profiles have been used for comparison of electron density at 1300 km. In addition, GPS vertical TEC values obtained from data of the San Fernando IGS station (36.46 N, 353.79 E) have been compared with the NeQuick and NeQuick+Gallagher vertical TEC values.
Key words: ionosphere, plasmasphere, electron density, total electron content

A. Krankowski, I.I. Shagimuratov, L.W. Baran, G.A. Yakimova, A.V. Radievsky. STORM-TIME CHANGES IN IONOSPHERIC TEC DURING THE DISTURBANCES ON THE NOVEMBER 5-7, 2001 STORM
Abstract. This paper presents the response of the ionospheric total electron content over Europe to the severe storm on November 5-7, 2001 (S Kp = 54). Spatial and temporal changes in TEC we analyzed on the basis of TEC maps. The maps were compiled using GPS measurements from 70 – 90 stations of the International GPS Service (IGS) / EUREF Permanent Network (EPN). Our estimation technique provided TEC maps with 15 min intervals and spatial resolution of 150 – 300 km. One of the features of the developing winter storm over Europe was a positive effect observed at night, at its early stage. This positive effect was recorded only at latitudes higher than 50N. TEC enhancements exceeded 150% relative to a quiet day. The strong enhancement of TEC was probably connected with particle precipitation. A long-lasting negative perturbation was registered in the daytime on November 6 and 7, 2001. The depression of TEC reached 70 – 100%. TEC maps showed that the spatial distribution of TEC underwent dramatic variations. In the ionosphere large- and medium-scale structures, including both increases and decreases in TEC, develop during the storm. TEC maps were used for an analysis of the dynamics of latitude profiles. The latitude dependence of TEC is significantly modified during a storm. The latitudinal profiles very well represent the dynamics of a mean ionospheric trough (MIT). During the storm the trough was displayed at a latitude of about 48N.
Key words: ionosphere, TEC, geomagnetic storms, GPS.

S. Heise, N. Jakowski. COMBINED ASSIMILATION OF GPS BASED TEC DATA FROM CHAMP AND SAC-C FOR IONOSPHERE/PLASMASPHERE IMAGING
Abstract. Space based GPS observations onboard LEO satellites provide a valuable new data source for ionospheric remote sensing. The paper deals with application of GPS navigation measurements from CHAMP and SAC-C for reconstruction of 3d electron density distributions of the upper ionosphere and plasmasphere by assimilation of link related TEC measurements into an initial model prediction. We describe data processing and retrieval technique. Reconstruction results for selected assimilation examples are presented. We validate our results with CHAMP Langmuir Probe data and compare reconstructions based on data from only one and from both satellites.
Key words: ionosphere, plasmasphere, CHAMP, SAC-C, GPS.

K. V. Polimeris, V. Romano, S.S. Kouris, B. Zolesi. THE WITHIN THE HOUR VARIABILITY IN TEC: SOME PRELIMINARY RESULTS
Abstract. Using 10-minutes TEC daily data measured at Matera (Italy) the within-the-hour variability in TEC is investigated. It is found that this type of variability is negligible except at sunrise and sometimes at sunset where it reaches values as 0.20 higher or lower over the corresponding standard hourly value.
Key words: Total Electron Content, ionospheric variability.

B. Forte. IONOSPHERIC SCINTILLATION OBSERVED DURING OCTOBER 2003 STORM
Abstract. Rapid fluctuations in the amplitude and phase of radio waves propagating through the ionosphere may be caused by small-scale plasma density irregularities. Ionospheric scintillation events have been observed on signals from GPS satellites during successive phases of October 2003 storm. Those observations have been made by means of a commercial single frequency GPS receiver, suitably operated in order to carry out the measurements of those fluctuations caused by small-scale electron density irregularities. The relationship between scintillation and TEC fluctuations is also investigated by means of dual frequency data from a close geodetic receiver. Structures of enhanced electron density have been observed during occurrence of scintillation and high TEC fluctuations events. Phase scintillation is characterized by means of a recently new proposed estimator, which provides a more robust information than classical phase scintillation index against data detrending effects.
Key words: radiowaves scintillation, TEC fluctuations, GPS scintillation monitors, auroral oval, magnetic storm.

V. Romano, J. B. Arokiasamy, F. Doumaz, M. Pezzopane, U. Sciacca, E. Zuccheretti. THE NEW AIS-INGV IONOSONDE AT ITALIAN ANTARCTIC OBSERVATORY
Abstract. The Italian Ionospheric Antarctic Observatory of Terra Nova Bay (74.70S, 164.11E) was recently equipped with the AIS-INGV ionosonde developed at the Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, (Italy). This paper aims to describe briefly which are the main characteristics of the instrument and show the good quality and reliability of the recorded ionograms.
Key words: ionosonde, antarctic ionospheric observatory, ionospheric data, vertical soundings.

E. Tulunay, Y. Tulunay, E.T. Senalp, Lj.R. Cander. FORECASTING GPS TEC USING THE NEURAL NETWORK TECHNIQUE “A Further Demonstration”
Abstract. The use of the Middle East Technical University Neural Networks (METU-NN) technique to forecast 10 minute values of the total electron content (TEC), one hour ahead, during high solar activity in the current solar cycle has been demonstrated. Being a data based approach, the METU-NN is trained with the total electron content data evaluated from GPS measurements at Chilbolton (51.8oN; 1.26oW) receiving station for January and February 2000 and 2001. An independent validation data set of the GPS-TEC values for Hailsham (50.9oN; 0.3oE) receiving station for the selected months in 2002 is used as an additional validation to forecast the TEC values one hour in advance.
Key words: Total Electron Content, forecast, Neural Networks, near Earth space, disturbed space weather