The EISCAT (European Incoherent SCATer) Scientific Association has provided versatile incoherent scatter (IS) radar facilities on the mainland of northern Scandinavia (the EISCAT UHF and VHF radar systems) and on Svalbard (the electronically scanning radar ESR (EISCAT Svalbard Radar) for studies of the high-latitude ionised upper atmosphere (the ionosphere). The mainland radars were constructed about 30 years ago, based on technological solutions of that time. The science drivers of today, however, require a more flexible instrument, which allows measurements to be made from the troposphere to the topside ionosphere and gives the measured parameters in three dimensions, not just along a single radar beam. The possibility for continuous operation is also an essential feature. To facilitatefuture science work with a world-leading IS radar facility, planning of a new radar system started first with an EU-funded Design Study (2005-2009) and has continued with a follow-up EU FP7 EISCAT_3D Preparatory Phase project (2010-2014). The radar facility will be realised by using phased arrays, and a key aspect is the use of advanced software and data processing techniques. This type of software radar will act as a pathfinder for other facilities worldwide. The new radar facility will enable the EISCAT_3D science community to address new, significant science questions as well as to serve society, which is increasingly dependent on space-based technology and issues related to space weather. The location of the radar within the auroral oval and at the edge of the stratospheric polar vortex is also ideal for studies of the long-term variability in the atmosphere and global change. This paper is a summary of the EISCAT_3D science case, which was prepared as part of the EU-funded Preparatory Phase project for the new facility. Three science working groups, drawn from the EISCAT user community, participated in preparing this document. In addition to these working group members, who are listed as authors, thanks are due to many others in the EISCAT scientific community for useful contributions, discussions, and support.

The paper reviews the current state of GNSS-based detection, monitoring and forecasting of ionospheric perturbations in Europe in relation to the COST action ES0803 ''Developing Space Weather Products and Services in Europe''. Space weather research and related ionospheric studies require broad international collaboration in sharing databases, developing analysis software and models and providing services. Reviewed is the European GNSS data basis including ionospheric services providing derived data products such as the Total Electron Content (TEC) and radio scintillation indices. Fundamental ionospheric perturbation phenomena covering quite different scales in time and space are discussed in the light of recent achievements in GNSS-based ionospheric monitoring. Thus, large-scale perturbation processes characterized by moving ionization fronts, wave-like travelling ionospheric disturbances and finally small-scale irregularities causing radio scintillations are considered. Whereas ground and space-based GNSS monitoring techniques are well developed, forecasting of ionospheric perturbations needs much more work to become attractive for users who might be interested in condensed information on the perturbation degree of the ionosphere by robust indices. Finally, we have briefly presented a few samples illustrating the space weather impact on GNSS applications thus encouraging the scientific community to enhance space weather research in upcoming years.

10 11The Ionospheric Weather Assessment and Forecast (IWAF) system is a computer software package 12 designed to assess and predict the world-wide representation of 3-D electron density profiles from the 13 Global Ionospheric Maps of Total Electron Content (GIM-TEC). The unique system products include 14 daily-hourly numerical global maps of the F2 layer critical frequency (foF2) and the peak height 15 (hmF2) generated with the International Reference Ionosphere extended to the plasmasphere, IRI-Plas, 16 upgraded importing the daily-hourly GIM-TEC as a new model driving parameter. Since GIM-TEC 17 maps are provided with one-or two-days latency, the global maps forecast for one day and two days 18 ahead is envisaged using the harmonic analysis applied to the temporal changes of TEC, foF2 and 19 hmF2 at 5112 grid points of a map encapsulated in IONEX format (-87.5º:2.5º:87.5ºN in latitude, -20 180º:5º:180ºE in longitude). The system provides online the ionospheric disturbance warnings in the 21 global W-index map establishing categories of the ionospheric weather from the quiet state (W=±1) to 22 intense storm (W=±4) according to the thresholds sets for instant TEC perturbations regarding quiet 23 reference median for the preceding 7 days. The accuracy of IWAF system predictions of TEC, foF2 24 and hmF2 maps is superior than the standard persistence model with prediction equal to the most 25 recent 'true' map. The paper presents outcome of the new service expressed by the global ionospheric 26 2 foF2, hmF2 and W-index maps demonstrating process of origin and propagation of positive and 27 negative ionosphere disturbances in space and time and their forecast under different scenarios. 28 29

International Reference Ionosphere extended to the plasmasphere (IRI-Plas) is upgraded analytically for assimilative mode of operation using GPS-derived Total Electron Content (TEC) for reconstruction of instantaneous ionospheric critical frequency and topside scale height at magnetic conjugate hemisphere. The performance of IRI-Plas code is examined with TEC gps retrieved from Global Ionospheric Maps compared with the F 2 -layer critical frequency at eight ionosonde locations in East Asia region on both hemispheres during the space weather storms at solar maximum (2000) and solar minimum (2006). Missing ionosonde data are completed by cloning of critical frequency. Decomposition of TEC gps in electron density profile with IRI-Plas code reveals the opposite relative changes of critical frequency and the topside scale height depending on solar activity. The ionospheric weather W index is computed for the desired locations in conjugate hemispheres and consistent results are obtained indicating the departure of instantaneous values of ionospheric parameters from their respective median varying from quiet state to intense storm.

Abstract. The planetary ionospheric storm index, W p , is deduced from the numerical global ionospheric GPS-IONEX maps of the vertical total electron content, TEC, for more than half a solar cycle, 1999-2008. The TEC values are extracted from the 600 grid points of the map at latitudes 60 • N to 60 • S with a step of 5 • and longitudes 0 • to 345 • E with a step of 15 • providing the data for 00:00 to 23:00 h of local time. The local effects of the solar radiant energy are filtered out by normalizing of the TEC in terms of the solar zenith angle χ at a particular time and the local noon value χ 0 . The degree of perturbation, DTEC, is computed as log of TEC relative to quiet reference median for 27 days prior to the day of observation. The W-index map is generated by segmentation of DTEC with the relevant thresholds specified earlier for foF2 so that 1 or −1 stands for the quiet state, 2 or −2 for the moderate disturbance, 3 or −3 for the moderate ionospheric storm, and 4 or −4 for intense ionospheric storm at each grid point of the map. The planetary ionospheric storm W p index is obtained from the W-index map as a latitudinal average of the distance between maximum positive and minimum negative W-index weighted by the latitude/longitude extent of the extreme values on the map. The threshold W p exceeding 4.0 index units and the peak value W p max≥6.0 specify the duration and the power of the planetary ionosphere-plasmasphere storm. It is shown that the occurrence of the W p storms is growing with the phase of the solar cycle being twice as much as the number of the magnetospheric storms with D st ≤−100 nT and A p ≥100 nT.