2,884 research outputs found
Polar cap absorption events of November 2001 at Terra Nova Bay, Antarctica
Polar cap absorption (PCA) events recorded during November 2001 are investigated by observations of ionospheric absorption of a 30MHz riometer installed at Terra Nova Bay (Antarctica), and of solar proton flux, monitored by the NOAA-GOES8 satellite in geo-synchronous orbit. During this period three solar proton events (SPE) on 4, 19 and 23 November occurred. Two of these are among the dozen most intense events since 1954 and during the current solar cycle (23rd), the event of 4 November shows the greatest proton flux at energies &gt;10MeV. Many factors contribute to the peak intensity of the two SPE biggest events, one is the Coronal Mass Ejection (CME) speed, other factors are the ambient population of SPE and the shock front due to the CME. During these events absorption peaks of several dB (~20dB) are observed at Terra Nova Bay, tens of minutes after the impact of fast halo CMEs on the geomagnetic field. </p><p style="line-height: 20px;"> Results of a cross-correlation analysis show that the first hour of absorption is mainly produced by 84–500MeV protons in the case of the 4 November event and by 15–44MeV protons for the event of 23 November, whereas in the entire event the contribution to the absorption is due chiefly to 4.2–82MeV (4 November) and by 4.2–14.5MeV (23 November). Good agreement is generally obtained between observed and calculated absorption by the empirical flux-absorption relationship for threshold energy <i>E<sub>0</sub></i>=10MeV. From the residuals one can argue that other factors (e.g. X-ray increases and geomagnetic disturbances) can contribute to the ionospheric absorption.<br><br><b>Key words.</b> Ionosphere (Polar Ionosphere, Particle precipitation) – Solar physics (Flares and mass ejections
Dynamic PRA: an Overview of New Algorithms to Generate, Analyze and Visualize Data
State of the art PRA methods, i.e. Dynamic PRA
(DPRA) methodologies, largely employ system
simulator codes to accurately model system dynamics.
Typically, these system simulator codes (e.g., RELAP5 )
are coupled with other codes (e.g., ADAPT,
RAVEN that monitor and control the simulation. The
latter codes, in particular, introduce both deterministic
(e.g., system control logic, operating procedures) and
stochastic (e.g., component failures, variable uncertainties)
elements into the simulation. A typical DPRA analysis is
performed by:
1. Sampling values of a set of parameters from the
uncertainty space of interest
2. Simulating the system behavior for that specific set of
parameter values
3. Analyzing the set of simulation runs
4. Visualizing the correlations between parameter values
and simulation outcome
Step 1 is typically performed by randomly sampling
from a given distribution (i.e., Monte-Carlo) or selecting
such parameter values as inputs from the user (i.e.,
Dynamic Event Tre
MIRTO: a prototype for real-time ionospheric imaging over the Mediterranean area
MIRTO (Mediterranean Ionosphere with Real-time TOmography) is a collaborative project between Istituto
Nazionale di Geofisica (INGV) of Rome, the University of Bath (U.K.) and the Istituto Fisica Applicata «Nello
Carrara»-Consiglio Nazionale delle Ricerche (IFAC-CNR) of Florence. The goal of the project is the development
of a prototype for real-time imaging of the ionosphere over the Italian region with extension to the Mediterranean
Sea. MIRTO uses an original imaging technique developed at the University of Bath and upgraded for
real-time use in cooperation with IFAC. The prototype makes use of the data acquired by the real-time ionospheric
and geodetic instrumentation operated by INGV. Such measurements drive the imaging algorithm to produce
the image of electron density as well as maps and movies of the Total Electron Content (TEC) over the considered
area
GNSS data filtering optimization for ionospheric observation
In the last years, the use of GNSS (Global Navigation Satellite Systems) data has been gradually increasing, for both scientific studies
and technological applications. High-rate GNSS data, able to generate and output 50-Hz phase and amplitude samples, are commonly
used to study electron density irregularities within the ionosphere. Ionospheric irregularities may cause scintillations, which are rapid and
random fluctuations of the phase and the amplitude of the received GNSS signals.
For scintillation analysis, usually, GNSS signals observed at an elevation angle lower than an arbitrary threshold (usually 15 , 20 or
30 ) are filtered out, to remove the possible error sources due to the local environment where the receiver is deployed. Indeed, the signal
scattered by the environment surrounding the receiver could mimic ionospheric scintillation, because buildings, trees, etc. might create
diffusion, diffraction and reflection.
Although widely adopted, the elevation angle threshold has some downsides, as it may under or overestimate the actual impact of
multipath due to local environment. Certainly, an incorrect selection of the field of view spanned by the GNSS antenna may lead to
the misidentification of scintillation events at low elevation angles.
With the aim to tackle the non-ionospheric effects induced by multipath at ground, in this paper we introduce a filtering technique,
termed SOLIDIFY (Standalone OutLiers IDentIfication Filtering analYsis technique), aiming at excluding the multipath sources of
non-ionospheric origin to improve the quality of the information obtained by the GNSS signal in a given site. SOLIDIFY is a statistical
filtering technique based on the signal quality parameters measured by scintillation receivers. The technique is applied and optimized on
the data acquired by a scintillation receiver located at the Istituto Nazionale di Geofisica e Vulcanologia, in Rome. The results of the
exercise show that, in the considered case of a noisy site under quiet ionospheric conditions, the SOLIDIFY optimization maximizes
the quality, instead of the quantity, of the data.Published2552–25622A. Fisica dell'alta atmosferaJCR Journa
GPS positioning errors during the space weather event of October 2003
Due to the configuration of the Earth’s magnetic field and its reconnection with the Interplanetary Magnetic Field (IMF), the high latitudes ionosphere is directly connected with outer space and, consequently, highly sensitive to the enhancement of the electromagnetic radiation and energetic particles coming from the Sun. Under such conditions the ionosphere may show the presence of small-scale structures or irregularities imbedded in the large-scale ambient plasma. These irregularities can produce short term phase and amplitude fluctuations in the carrier frequency of the radio waves which pass through them, commonly called ionospheric phase and amplitude scintillations. Since September 2003 a GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver has been deployed at the Italian Arctic station “Dirigibile Italia” in Ny Alesund (79.9° N, 11.9° E, Svalbard, Norway), in the frame of the ISACCO (Ionospheric Scintillations Arctic Campaign Coordinated Observation) project. The receiver computes and records GPS phase and amplitude scintillation parameters, as well as TEC (Total Electron Content). The measurements made by ISACCO during the superstorm of October 2003 have been here used to assess the positioning errors affecting GNSS (Global Navigation Satellite Systems, such as GPS and the European Galileo) users and their correlation with the occurrence of observed levels of scintillation
L'osservatorio ionosferico in Artide e Antartide: osservazioni sperimentali e risultati scientifici
The Italian Upper Atmosphere Observatory at polar latitude was firstly established during
the Antarctic campaign 1990-1991 to support the telecommunication logistic activity of
the National Program for Antarctic Research (PNRA). The Istituto Nazionale di
Geofisica e Vulcanologia (INGV), formerly Istituto Nazionale di Geofisica (ING), was
involved in this action as the long time experience in HF radar, ionospheric sounding and
ionospheric prediction services for radio communication purposes, managing two of the
most important and historical ionospheric observatories all over the world: Rome (41.8N,
12.5E) and Gibilmanna (37.9 N, 14.0 E). Since that time, starting from 1993 up to now,
several research projects have been carried on focusing on the multi instruments upper
atmosphere observations in Arctic and Antarctica with the aim to study the polar
ionosphere in different time and space domains, contributing both to the Global Change
and to the emerging Space Weather needs. Here we briefly report on the experimental
activities as well on the main scientific results obtained highlighting the latest findings in
the field of bipolar GNSS (Global Navigation Satellite Systems) ionospheric scintillation
measurements and investigation
Proper orthogonal decomposition of solar photospheric motions
The spatio-temporal dynamics of the solar photosphere is studied by
performing a Proper Orthogonal Decomposition (POD) of line of sight velocity
fields computed from high resolution data coming from the MDI/SOHO instrument.
Using this technique, we are able to identify and characterize the different
dynamical regimes acting in the system. Low frequency oscillations, with
frequencies in the range 20-130 microHz, dominate the most energetic POD modes
(excluding solar rotation), and are characterized by spatial patterns with
typical scales of about 3 Mm. Patterns with larger typical scales of 10 Mm, are
associated to p-modes oscillations at frequencies of about 3000 microHz.Comment: 8 figures in jpg in press on PR
Space weather challenges of the polar cap ionosphere
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
Long-term trends in the ionosphere and upper atmosphere parameters
The first part of the paper is directed to the investigation of the practical importance of possible longterm trends in the F2-layer for ionospheric prediction models. Using observations of about 50 different ionosonde stations with more than 30 years data series of foF2 and hmF2, trends have been derived with the solar sunspot number R12 as index of the solar activity. The final result of this trend analysis is that the differences between the trends derived from the data of the individual stations are relatively large,
the calculated global mean values of the foF2 and hmF2 trends, however, are relatively small. Therefore, these small global trends can be neglected for practical purposes and must not be considered in ionospheric prediction models. This conclusion is in agreement with the results of other investigations
analyzing data of globally distributed stations. As shown with the data of the ionosonde station Tromsø, however, at individual stations the ionospheric trends may be markedly stronger and lead to essential effects in ionospheric radio propagation. The second part of the paper deals with the reasons for possible
trends in the Earth’s atmo- and ionosphere as investigated by different methods using characteristic parameters of the ionospheric D-, E-, and F-regions. Mainly in the F2-region different analyses have
been carried out. The derived trends are mainly discussed in connection with an increasing greenhouse effect or by long-term changes in geomagnetic activity. In the F1-layer the derived mean global trend
in foF1 is in good agreement with model predictions of an increasing greenhouse effect. In the E-region the derived trends in foE and h´E are compared with model results of an atmospheric greenhouse effect,
or explained by geomagnetic effects or other anthropogenic disturbances. The trend results in the D-region derived from ionospheric reflection height and absorption measurements in the LF, MF and HF
ranges can at least partly be explained by an increasing atmospheric greenhouse effect
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