Research

Electric and magnetic detectors provide complementary information on electromagnetic phenomena, even if incomplete regarding their coupling with objects. CIEN was therefore equipped with meteorological stations and other instruments to measure the mobility of electric charges.

Thunderstorms

Rain is electrically charged, so when it strikes electrodes, it generates intense signals on the electric apparatus. Typical electrical recordings are shown in the following pictures reporting spectrograms.

A 2.5 hour recording in the ELF band of a

couple of perpendicular electrodes for a

thunderstorm at the Camerino Station of

CIEN, is shown in the Figure above. The

time evolution moves rightward on the plot.

Being so, it is possible to see that the arrival

of a thunderstorm (light blue) is preceded by

a moderate rain event (in blue) associated

with an increase in the spherics number

(vertical lines). Such increases are

determined by lightning bolts and inter-cloud

discharges that approach the station. When

rainfall begins at the Camerino Station, a 30

dB increase in power continuously fills the

whole ELF band until the end of rainfall. This

is due to the electrical charge of raindrops

striking the wires. The polarity of such

charges change many times, as shown by

the white-colored amplitude into the upper

blue band. Note that the ELF band has a

logarithmic scale. Strong meteorological

perturbations can also influence the radio

transmissions in VLF band, here with a

linear scale. For example this occurred in

Perugia on 27 July 2011, in the early

afternoon, when an intense rainfall swept

the area as shown in Figure on the right. In

this spectrogram which is relative to one

electrode only, a high-intensity rainfall

event is associated with ELF band in the

bottom, where power increased to 50 dB. VLF is also shown on the top, where strong signals are nearly absent. Here, one can observe the surprising disappearance of the signal at 16 kHz at about 16:35LT, which is produced by the photovoltaic power supply and suggesting that the sun was obscured for some minutes by the intense precipitations. During the same time interval, the yellow belt fades as do the carrier waves of several transmitters indicated by horizontal lines (from Fidani, 2011).

Schumann Resonances

The resonances of the earth-ionosphere cavity are also

evidenced by yellow horizontal bands in the lower part of

the ELF band, on the right. This picture represents about

50' of recordings at the Camerino Station. The frequency

resonances occur at about 8, 14, 20, 26, 32, 37 and 43

Hz. Principal excitation source of Schumann Resonances

are cloud-to-ground discharges, with the peak currents on

the order of 20,000–30,000 A and the discharge rates of

100 times per second. Because of such high discharge

rates and a remarkably small propagation loss, the

associated electromagnetic radiations from individual

lightning overlap to form a stationary background

electromagnetic noise. However, once in a while, the

middle atmospheric electrical current between the cloud

tops and the ionosphere causes sufficiently large

transients called ELF transients and excite the

earth-ionosphere cavity to amplitudes that may exceed

the background by factors of 10–20 or more. ELF

transients have been found to be coincident with transient

optical events, such as red sprites and elves. Other

sources include: (1) the vertical component of intercloud

and intracloud discharges; (2) a fluctuating auroral electrojet that flows horizontally within the upper boundary of the cavity at altitudes of approximately 100 km; and (3) ELF whistlers, which are narrow signals believed to originate as plasma drift waves in the dayside magnetosheath and to enter the earth-ionosphere cavity through the polar cusp. Investigations have been performed on Schumann Resonance regarding its possible link between geo-electromagnetic activity and human health effects (see Price, 2016).

Electric Oscillations

Spectrograms elaborated from the signals of the two electrodes are usually equal to each other, less than for the presence of spots with high intensity in the power spectrum that makes them appear red. Spots are electromagnetic phenomena characterized by well-defined frequencies and represent measures of electric oscillations. These oscillations have frequencies usually ranging between 20 and 400Hz, often starting and ending at lower frequencies. Moreover, the duration of the signals ranges from several minutes to several hours. Their intensities can be evaluated in comparison with those of Schumann Resonances intensities, resulting in electric field intensities of 1 - 10 micro Volts/m. Electric oscillations from one electrode appear near always different in shapes and times from those detected in the perpendicular electrode of the same station. Furthermore, electric oscillations appear different at different stations.

Magnetic pulses

Two independent ULF magnetic recording

systems utilizing the same magnetic coil,

were collocated inside the CIEN stations,

in an attempt to characterize and cross-

correlate the different instruments of the

network. The systems were realized by

Labview and Spectrumlab software, which

produced remarkably similar pulse series

and spectral responses. An example of

24 hours of pulse number (in red) detected

at the Fermo Station is shown on the right,

where characteristic frequencies (green),

amplitudes (blue) and effective values

(violet) are plotted together. These pulses

were investigated to found their physical origin and their possible correlation with seismic activity. The software at all of the CIEN stations is able to automatically send warning emails if the pulse number overcome a fixed threshold, which depends on the station position and noise around.

Radon detection

Recently, a new instrument for the measurement of the Radon gas was realized by the Novara Geophysical Observatory and was installed in a box underground at the CIEN Fermo Station. From the beginning of 2020, this detector has produced a time series of decay counts linked to the Radon flow through the soil, look down.