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Ionospheric Space Weather


The term “Space Weather” indicates the changes occurring in the space environment that can affect the near Earth environment. Space Weather processes can include changes in the interplanetary magnetic field, coronal mass ejections from the Sun, and disturbances in Earth’s magnetic field. The effects of space weather can range from damage to satellites to disruption of power grids on Earth.
The investigation of the space weather processes is strongly multidisciplinary including the knowledge of solar physics, magnetospheric physics, ionospheric physics and geomagnetism.
Similarly to the tropospheric weather, the scope of the space weather is to forecast the effects on the geospace, and, in particular, to forecast the effects of corruption on the communication and positioning systems vital for our modern society.
The realization of prediction tools is possible only starting from experimental observations of the geospace and, in this frame, the measurements of the ionospheric plasma can provide fundamental information for the development of forecasting models.
INGV manages different techniques for probing the ionosphere, from radar measurements to GNSS observations, to the acquisition of radio cosmic noise data. Combining these methods provides the ability to study the ionosphere from high in the F-region to the bottom of the D-layer over regions covering high and mid latitudes. The high latitudes ionosphere contains the footprints of processes that have their origin in the interplanetary space, propagate into the magnetosphere and hit the Earth. In this sense the monitoring of the upper atmosphere over the polar regions can be considered as a diagnostic space weather tool. The information acquired at mid latitude can confirm the occurrence of a perturbation effect, integrating the description of the phenomenon that, in some case, can assume dangerous consequences on global scale.

Ionospheric Measurements during Disturbed Conditions due to Space Weather processes

During Space Weather processes the ionosphere may strongly deviate from its normal behaviour, hence the monitoring of the ionospheric plasma dynamics during disturbed conditions becomes crucial, mostly if done in real time. Now three examples of ionospheric measurements will be shown to underline their importance towards the understanding of the Sun-Earth domain as a whole.

Example of Ionospheric Absorption Measurement at high latitudes

Under disturbed conditions, one of the main causes of ionization in the D region (the ionospheric region whose height range is 50 to 80 km) is due to the influx of energetic particles penetrating the atmosphere that increases the electron density and then the ionospheric absorption. Therefore a measurement of the ionospheric absorption is a suitable parameter to disclose the effects on the lower ionosphere due to both the magnetic and the solar activity.
Figure 1 shows an example of ionospheric absorption in the polar region, in absence of a significant magnetic activity, caused by a strong protons emission event, as recorded the 26th February 2004 by two different equipments installed at Mario Zucchelli Station (Terra Nova Bay, Antarctica, 74.7° S, 164.1° E). The top panel illustrates the cosmic noise curve as recorded by a riometer, while the thumbnails of the 48 ionograms (one every 30 minutes) recorded by the AIS-INGV ionosonde are depicted just below. The correspondence between the ionograms recorded at 02:00 and 22:30 UT showing missing echoes and the absorption events highlighted by the cosmic noise curve is clear, and points out how during a significant event of this kind the ionosphere may lose its reflection property.

Figure 1 Example of ionospheric absorption in the polar region caused by a strong protons emission event, as recorded the 26th February 2004. Click on the image to enlarge

 

Example of Ionospheric Storm at mid latitudes

On 3 April 2004, in correspondence to the Earth’s arrival of a coronal mass ejection (CME), the interplanetary magnetic field (IMF) strength changed from ~5 to ~8 nT, the Bx and By components became highly variable, Bz increased to large positive values (~12 nT), then decreased, becoming negative. After the IMF southward turning, ground observations showed the development of a moderate geomagnetic storm.
To visualize the behavior of the ionosphere, in Figure 2 the observed (in red)15-min foF2 values at the Rome station (Italy, 41.8° N, 12.5° E) are drawn in comparison with the long term prediction of the hourly median values (in blue), here assumed as quiet-day values. Pre-storm conditions are illustrated in Figure 2a, 2b, and 2c. Figure 2d shows how the geomagnetic storm onset is followed by a weak, positive ionospheric storm in the afternoon hours of 3 April 2004. Then, through the whole 4 April (Figure 2e), it follows a phase in which foF2 is depressed below its median value (a so-called “negative storm”). These variations of foF2 (also called the “decrease type”) usually accompany geomagnetic disturbances at mid latitudes. These values are very similar to those caused by neutral composition changes at mid latitudes. Hence, it is possible to attribute the negative phase effects in Figure 2e to the composition changes of the neutral atmosphere, specifically in the atomic/molecular ratio that alters the balance of the production and loss processes of the ionised plasma. However, we need to take into account that other processes, in particular dynamic processes, such as electric field drifts and thermospheric neutral winds, contribute to the complexity of ionospheric storms. It is worth noting also the missing data in Figure 2e between 06:00 UT and 13:00 UT on 4 April, due to an absorption phenomenon that is typical, as said in the previous paragraph, for such a disturbed condition, because of D-layer ionization by precipitating charged particles.

Figure 2 Behavior of the ionosphere during a Ionospheric Storm

Figure 3a shows instead the vertical total electron content (TEC) measurements deduced from GPS signals using a European network of the international GPS service (IGS) stations for the time interval 2–5 April 2004 above Northern Italy at geographic coordinates of 45° N and 10° E. In Figure 3b, 3c, and 3d the diurnal TEC variation of the geomagnetically quiet day 2 April 2004 (in black), is compared with the different disturbance phases characterizing the three subsequent days (in red). This comparison shows a “positive storm phase” on 3 April, followed by a “negative storm phase” during about one and a half days on 4–5 April, after which a smaller, positive disturbance re-establishes at about 11:00 UT on 5 April.

Figure 3 Example of vertical total electron content (TEC) measurements deduced from GPS signals using a European network of the international GPS service (IGS) stations

 In order to compare the ionospheric plasma behavior at mid latitude with that at high latitude, also the slant TEC measurements performed by the GPS receiver installed at the Svalbard (Norway, 78.9° N, 11.9° E) are considered. Figure 4 shows the slant TEC variation recorded at Svalbard, between 06:00 and 12:00 UT, of the geomagnetically quiet day 2 April 2004 (top panel), compared with the one recorded on 4 April (bottom panel). This comparison highlights that also at high latitude the TEC is characterized by a significant “negative storm phase” occurring the 4 April (please note the y axis change of scale).

Figure 4 Slant TEC variation recorded at Svalbard of the geomagnetically quiet day 2 April 2004 (top panel), compared with the one recorded on 4 April (bottom panel)

The Halloween storms of 2003

In late 2003, the Sun produced an X17 flare on October 28, quickly followed by an X10 flare on October 29. There were two distinct very intense geomagnetic storms (Halloween storms) associated with these flares. Both these storms rank as the largest geomagnetic storms of Cycle 23. The X17 storm on October 28 is number 6 on the Top 30 list, which dates back to 1936.
Figure 5 shows, together with the vertical TEC (in black), the significant phase and amplitude scintillations (in blue and in red, respectively) suffered by the signal recorded at the Svalbard (Norway, 78.9° N, 11.9° E) GPS receiver, between 21:00 and 22:00 UT of 30 October 2003, from the GPS satellite ‘PRN 31’. This to highlight that severe ionospheric disturbances originating from intense solar flares have significant effects on the propagation of radio waves over the entire radio spectrum, on which radio communications and navigation systems critically depend.

 

Figure 5 Vertical TEC (in black) and the significant phase and amplitude scintillations (in blue and in red, respectively)

 

Real Time Data at INGV

As previously said, the real time monitoring of the ionospheric plasma is very important for Space Weather purposes.
Vertical soundings are performed and elaborated in real time at the ionospheric stations of Rome (Italy, 41.8° N, 12.5° E), Gibilmanna (Italy, 37.9° N, 14.0° E), and Tucumán (Argentina, 26.9° S, 294.6° E).
The data recorded at Rome is used within the GIFINT, DIAS, and MIRTO projects.
At the high latitude observatories of Mario Zucchelli Station (Baia Terra Nova, Antarctica, 74.7° S, 164.1° E), Dome C (75.1° S, 123.4° E), Ny Alesund (Svalbard, Norway, 78.9° N, 11.9° E), and Longyearbean (Svalbard, Norway, 78.2° N, 16.0° E) scintillation and TEC measurements are carried out and available in real time or near real time.
The data recorded at polar stations is used within the ISACCO, PNRA, SCAR, MAE, and Royal Society projects.
The data is stored in a relational database and published on the Web within the eSWua project.


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