- Earth’s Magnetic Field
- Paleomagnetism and Rock Magnetism
- Sun-Earth Relations: Geomagnetic Phenomena
- Middle-Upper Atmosphere
- Sun-Earth Relations: Ionospheric Phenomena
- Ionospheric Tomography
- Ionospheric Scintillation
- Ionospheric Space Weather
- Ionospheric Variability
- Environmental Terrestrial Physics
- Hydrosphere - Geosphere - Atmosphere Interactions
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Irregularly structured ionospheric regions can cause diffraction and scattering of trans-ionospheric radio signals. When received at an antenna, these signals present random temporal fluctuations in both amplitude and phase. This is known as ionospheric scintillation. Ionospheric scintillation may cause problems such as signal power fading, phase cycle slips, receiver loss of lock, etc., and degrade the quality of satellite navigation systems.
The ionospheric irregularities
The ionosphere can deviate from the expected behaviour, as for instance modelled by the Klobuchar model. This is the case when the ionosphere includes irregularities in which the electron density differs significantly from the “ambient” plasma. These irregularities can cause diffraction effects, i.e. scintillations, on the signals passing through them. The formation, evolution and dynamics of such irregularities are ruled by the interplay between the geomagnetic field, the Interplanetary Magnetic Field (IMF) and the solar wind (that is the emission of energetic particles coming from the Sun).
Over the equator the geomagnetic field lines are almost horizontal in respect to the Earth surface, while at polar and auroral latitudes they are almost vertical. This strong characterization in relation to the geomagnetic field configuration makes these regions the most affected by the formation of the ionospheric irregularities potentially dangerous for positioning systems.
The scintillation indices
The widely used ionospheric scintillation indices S4 and σΦ give an indication of the intensity of amplitude and phase scintillation affecting GNSS receivers.
The amplitude scintillation index is called S4 and it is the standard deviation of the intensity of the received signal over a certain interval, typically over 60 seconds.
The phase scintillation index is called sF and it is the standard deviation of the detrended phase of the carrier frequency over a certain interval, typically over 60 seconds.
The ionospheric scintillation monitoring
To monitor transient effects like scintillations it is necessary to rely on high rate sampling GPS receivers. Space weather must include scintillations real time monitoring, this is the reason why INGV is managing a network of specially modified dual-frequency GPS receivers for Ionospheric Scintillation and TEC Monitoring (GISTM) since 2003 (ISACCO project).
The GISTM system is based on a Novatel GSV4004B receiver with the AJ System firmware, able to provide scintillation indices from L1 frequency and TEC from L1 and L2 (minute data) and 50 Hz (20 ms) raw data. Currently the network counts on three GISTM receivers at Svalbard (Norway), and two in Antarctica at MZS (74.7° S, 164.1° E) and on the Antarctic plateau at Concordia Station (Dome C, 75.1° S, 123.4° E). The first GISTM was deployed in September 2003 at the Italian Arctic station “Dirigibile Italia” in Ny Alesund (79.9° N, 11.9° E, Svalbard, Norway).