http://hdl.handle.net/2122/2860 2013-05-21T07:12:37Z http://hdl.handle.net/2122/8598 Title: On the multi-scale nature of large geomagnetic storms: an empirical mode decomposition analysis Authors: De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Consolini, G.; INAF – Istituto di Astrofisica e Planetologia Spaziali, 00133 Roma, Italy; Tozzi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Complexity and multi-scale are very common properties of several geomagnetic time series. On the other hand, it is amply demonstrated that scaling properties of geomagnetic time series show significant changes depending on the geomagnetic activity level. Here, we study the multiscale features of some large geomagnetic storms by applying the empirical mode decomposition technique. This method, which is alternative to traditional data analysis and is designed specifically for analyzing nonlinear and nonstationary data, is applied to long time series of Sym-H index relative to periods including large geomagnetic disturbances. The spectral and scaling features of the intrinsic mode functions(IMFs) into which Sym-H time series can be decomposed, as well as those of the Sym-H time series itself, are studied considering different geomagnetic activity levels. The results suggest an increase of dynamical complexity and multi-scale properties for intermediate geomagnetic activity levels. 2012-10-31T23:00:00Z http://hdl.handle.net/2122/8500 Title: Space weather challenges of the polar cap ionosphere Authors: Moen, J.; Department of Physics, University of Oslo, P.O. Box 1048 Blindern, NO-0316 Oslo, Norway; Oksavik, K.; Department of Physics and Technology, University of Bergen, P.O. Box 7803, NO-5020 Bergen, Norway; Alfonsi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Daabakk, Y.; Department of Physics, University of Oslo, P.O. Box 1048 Blindern, NO-0316 Oslo, Norway; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Spogli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: This paper presents research on polar cap ionosphere space weather phenomena conducted during the European Cooperation in Science and Technology (COST) action ES0803 from 2008 to 2012. The main part of the work has been directed toward the study of plasma instabilities and scintillations in association with cusp flow channels and polar cap electron density structures/patches, which is considered as critical knowledge in order to develop forecast models for scintillations in the polar cap. We have approached this problem by multi-instrument techniques that comprise the EISCAT Svalbard Radar, SuperDARN radars, in-situ rocket, and GPS scintillation measurements. The Discussion section aims to unify the bits and pieces of highly specialized information from several papers into a generalized picture. The cusp ionosphere appears as a hot region in GPS scintillation climatology maps. Our results are consistent with the existing view that scintillations in the cusp and the polar cap ionosphere are mainly due to multi-scale structures generated by instability processes associated with the cross-polar transport of polar cap patches. We have demonstrated that the SuperDARN convection model can be used to track these patches backward and forward in time. Hence, once a patch has been detected in the cusp inflow region, SuperDARN can be used to forecast its destination in the future. However, the high-density gradient of polar cap patches is not the only prerequisite for high-latitude scintillations. Unprecedented highresolution rocket measurements reveal that the cusp ionosphere is associated with filamentary precipitation giving rise to kilometer scale gradients onto which the gradient drift instability can operate very efficiently. Cusp ionosphere scintillations also occur during IMF BZ north conditions, which further substantiates that particle precipitation can play a key role to initialize plasma structuring. Furthermore, the cusp is associated with flow channels and strong flow shears, and we have demonstrated that the Kelvin- Helmholtz instability process may be efficiently driven by reversed flow events. 2012-12-31T23:00:00Z http://hdl.handle.net/2122/7287 Title: Structure and Dynamics of Ionospheric Plasma Authors: Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Liu, L.; Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Abstract: The selection of the topics included in this issue is far from being exhaustive, but it contributes to demonstrate how many questions arise from the investigation of the coupling between ionized and neutral atmosphere and from the solarterrestrial relationship. We would like to thank the authors for their excellent contributions and patience in assisting us. Finally, the fundamental work of all reviewers on these papers is also very warmly acknowledged. 2011-12-03T23:00:00Z http://hdl.handle.net/2122/7259 Title: Automatic scaling of polar ionograms Authors: Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The Istituto Nazionale di Geosifica e Vulcanologia (INGV) software for automatic scaling of ionograms (Autoscala) was improved by introducing a system to identify D region absorption events, spread-F condition (frequency spreading in the F region), and Z-ray propagation. The algorithm was applied to a series of ionograms recorded by the AIS-INGV (Advanced Ionospheric Sounder-INGV) ionosonde installed at the Mario Zucchelli Station (74.78S, 164.18E), Terra Nova Bay, Antarctica. Critical cases are shown to illustrate the behaviour of the software. 2012-01-31T23:00:00Z http://hdl.handle.net/2122/7239 Title: Unusual nighttime impulsive foF2 enhancement below the southern anomaly crest under geomagnetically quiet conditions Authors: Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Fagundes, P. R.; Ciraolo, L.; Correia, E.; Cabrera, M. A.; Ezquer, R. G. Abstract: An unusual nighttime impulsive electron density enhancement was observed on 6 March 2010 over a wide region of South America, below the southern crest of the equatorial anomaly, under low solar activity and quiet geomagnetic conditions. The phenomenon was observed almost simultaneously by the F2 layer critical frequency ( foF2) recorded at three ionospheric stations which are widely distributed in space, namely Cachoeira Paulista (22.4°S, 44.6°W, magnetic latitude 13.4°S), São José dos Campos (23.2°S, 45.9°W, magnetic latitude 14.1°S), Brazil, and Tucumán (26.9°S, 65.4°W, magnetic latitude 16.8°S), Argentina. Although in a more restricted region over Tucumán, the phenomenon was also observed by the total electron content (TEC) maps computed by usingmeasurements from 12 GPS receivers. The investigated phenomenon is very particular because besides being of brief duration, it is characterized by a pronounced compression of the ionosphere. This compression was clearly visible both by the virtual height of the base of the F region (h′F) recorded at the aforementioned ionospheric stations, and by both the vertical electron density profiles and the slab thickness computed over Tucumán. Consequently, neither an enhanced fountain effect nor plasma diffusion from the plasmasphere can be considered as the single cause of this unusual event. A thorough analysis of isoheight and isofrequency ionosonde plots suggest that traveling ionospheric disturbances (TIDs) caused by gravity wave (GW) propagation could have likely played a significant role in causing the phenomenon. 2011-12-08T23:00:00Z http://hdl.handle.net/2122/6707 Title: ASTER temperature and emissivity validation on volcano Teide Authors: Amici, Stefania; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Piscini, Alessandro; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Buongiorno, Fabrizia; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Editors: IEEE IGARSS Abstract: The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER ) has operated since 19 December 1999 from NASA’s Terra Earth-orbiting, sun synchronous satellite. Emissivity and temperature standard products are based on the TES algorithms and require periodical validation campaign. In the frame of the EC project PREVIEW (http://www.preview-risk.com/) a field campaign on Volcano Teide was carried on, from the 16th to 24th of September 2007, to validate and to integrate the satellite derived products services. 2010-06-30T22:00:00Z http://hdl.handle.net/2122/5943 Title: Improving the GNSS positioning stochastic model in the presence of ionospheric scintillation Authors: Aquino, M.; Institute of Engineering Surveying and Space Geodesy (IESSG), University of Nottingham, Nottingham, UK; Monico, J. F. G.; Department of Cartography, Sao Paulo State University, Pres. Prudente, São Paulo, SP, Brazil; Dodson, A. H.; Institute of Engineering Surveying and Space Geodesy (IESSG), University of Nottingham, Nottingham, UK; Marques, H.; Department of Cartography, Sao Paulo State University, Pres. Prudente, São Paulo, SP, Brazil; De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Andreotti, M.; Geospatial Research Center Ltd., Christchurch, New Zealand Abstract: Ionospheric scintillations are caused by timevarying electron density irregularities in the ionosphere, occurring more often at equatorial and high latitudes. This paper focuses exclusively on experiments undertaken in Europe, at geographic latitudes between ~50°N and ~80°N, where a network of GPS receivers capable of monitoring Total Electron Content and ionospheric scintillation parameters was deployed. The widely used ionospheric scintillation indices S4 and бφ represent a practical measure of the intensity of amplitude and phase scintillation affecting GNSS receivers. However, they do not provide sufficient information regarding the actual tracking errors that degrade GNSS receiver performance. Suitable receiver tracking models, sensitive to ionospheric scintillation, allow the computation of the variance of the output error of the receiver PLL (Phase Locked Loop) and DLL (Delay Locked Loop), which expresses the quality of the range measurements used by the receiver to calculate user position. The ability of such models of incorporating phase and amplitude scintillation effects into the variance of these tracking errors underpins our proposed method of applying relative weights to measurements from different satellites. That gives the least squares stochastic model used for position computation a more realistic representation, vis-a-vis the otherwise ‘equal weights’ model. For pseudorange processing, relative weights were computed, so that a ‘scintillation-mitigated’ solution could be performed and compared to the (non-mitigated) ‘equal weights’ solution. An improvement between 17 and 38% in height accuracy was achieved when an epoch by epoch differential solution was computed over baselines ranging from 1 to 750 km. The method was then compared with alternative approaches that can be used to improve the least squares stochastic model such as weighting according to satellite elevation angle and by the inverse of the square of the standard deviation of the code/carrier divergence (sigma CCDiv). The influence of multipath effects on the proposed mitigation approach is also discussed. With the use of high rate scintillation data in addition to the scintillation indices a carrier phase based mitigated solution was also implemented and compared with the conventional solution. During a period of occurrence of high phase scintillation it was observed that problems related to ambiguity resolution can be reduced by the use of the proposed mitigated solution. 2009-02-28T23:00:00Z http://hdl.handle.net/2122/5259 Title: Imaging of the Antarctic ionosphere: Experimental results Authors: Yin, P.; College of Electronic Information Engineering,Civil Aviation University of China,Tianjin,China; Mitchell, C. N.; Department of Electronic and Electrical Engineering, University of Bath, Bath BA2 7AY,UK; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pinnock, M.; British Antarctic Survey, UK; Spencer, P.; Department of Electronic and Electrical Engineering, University of Bath, Bath BA2 7AY, UK; De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Newell, P.; Johns Hopkins University, Applied Physics Laboratory, USA; Sarti, P.; Istituto Radio Astronomia (IRA)-INAF, Bologna, Italy; Negusini, M.; Istituto Radio Astronomia (IRA)-INAF, Bologna, Italy; Capra, A.; Università di Modena e Reggio Emilia, Italy Abstract: Ground-based dual-frequency GPS observations can be used to create images of electron density.This is well established for the Arctic ionosphere; here one of the first results is presented for the Antarctic. In this study, the GPS receivers in the Antarctic are supplemented with another GPS receiver onboard CHAMP. The aim of the study is to demonstrate the technique for investigating geophysical events, for example, an ionospheric disturbance period on 11 February 2004. The images have been validated by in-situ measurements from DMSP and CHAMP satellites, as well as Super Dual Auroral Radar Network (SuperDARN) convection patterns, which are able to confirm the location, presence, and transportation of large-scale plasma patches. This study indicates that although the convection still dominates in the high-latitude ionosphere, soft precipitation within the polar cap may play a role in the evolution of the polar patches. It also illustrates the potential for future multi-instrument studies of the Antarctic. 2009-10-31T23:00:00Z http://hdl.handle.net/2122/5214 Title: Climatology of GNSS ionospheric scintillation at high latitudes Authors: Spogli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Aquino, M.H.O.; Institute of Engineering Surveying and Space Geodesy (IESSG), University Park Nottingham, NG7 2RD, United Kingdom; Dodson, A.; Institute of Engineering Surveying and Space Geodesy (IESSG), University Park Nottingham, NG7 2RD, United Kingdom Editors: University of Padova Abstract: We analyse GNSS ionospheric scintillation data in the polar areas of both hemispheres to develop a climatology over a large geomagnetic quiet period. The conditions of the near-Earth environment leading to scintillation scenarios are investigated via scintillation occurrence. Within this scope we realize maps of scintillation occurrence as a function of the magnetic local time(MLT) and of the altitude adjusted corrected geomagnetic coordinates (AACGM). The maps are realized merging observations from a network of four GISTM (GPS Ionospheric Scintillation and TEC Monitor) in the Northern Europe and two GISTM in Antarctica during the year 2008. The results highlight the possibility to investigate the impact of ionospheric irregularities on the phase and amplitude of GNSS signals, evidencing the auroral and cusp/cap contributions. This works aims to contribute to development of nowcasting and forecasting tools for GNSS ionospheric scintillation. 2009-10-13T22:00:00Z http://hdl.handle.net/2122/5193 Title: Electron density profile calculation technique for Autoscala ionogram analysis Authors: Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: An electron density profile model with free parameters is introduced. Initially the parameters are calculated on the basis of the ionospheric characteristics automatically obtained from the ionograms by Autoscala and considering the helio- geophysical conditions. The technique used to adjust the free parameters to the particular ionograms recorded is presented. 2009-09-14T22:00:00Z