Low Frequency (LF) radio signals lie in the band 30-300 kHz. The electric field of three LF broadcasting stations-CLT (f = 189 kHz, Sicily, Italy), MCO (f = 216 kHz, France) and CZE (f = 270 kHz, Czech Republic)-has been monitored since 1997 with a sampling frequency of ten minutes at a site named AS and located in central Italy. During September-November 2002, we observed significant decreases in the electric field strength of the CLT broadcasting station. A similar effect did not appear on the MCO and CZE radio signals. On September 6 an earthquake with M = 5.6 occurred offshore, about 40 kin far from Palermo city (Sicily), starting an intense seismic crisis for more than one month. On October 27, the Etna volcano (Sicily) started an eruption that in January 2003 was still active. On October 31, an earthquake with M = 5.4 occurred at the border between Molise and Puglia regions (southern Italy) and, finally, in the period 3-6 November intense gas exhalations happened near the Eolie islands (southern Tyrrhenian sea). The CLT radio-signal decreases we observed appear clearly related to the previous activities with some possible premonitory behaviour. The LF signals are characterised by the ground-wave and the sky-wave propagation modes. The decreases in CLT radio-signal we mentioned previously are related to a reduction of the electric field strength both of the ground wave and of the sky wave. Changes in the troposphere-ground boundary zone and in the lower non-ionized atmosphere seem to be the main candidates to justify the phenomenology we observed.
Variations in LF Radio Signal on the Occasion of the Recent Seismic and Volcanic Activity in Southern Italy
CAPOZZI, VITO GIACOMO;PERNA, GIUSEPPE;
2004-01-01
Abstract
Low Frequency (LF) radio signals lie in the band 30-300 kHz. The electric field of three LF broadcasting stations-CLT (f = 189 kHz, Sicily, Italy), MCO (f = 216 kHz, France) and CZE (f = 270 kHz, Czech Republic)-has been monitored since 1997 with a sampling frequency of ten minutes at a site named AS and located in central Italy. During September-November 2002, we observed significant decreases in the electric field strength of the CLT broadcasting station. A similar effect did not appear on the MCO and CZE radio signals. On September 6 an earthquake with M = 5.6 occurred offshore, about 40 kin far from Palermo city (Sicily), starting an intense seismic crisis for more than one month. On October 27, the Etna volcano (Sicily) started an eruption that in January 2003 was still active. On October 31, an earthquake with M = 5.4 occurred at the border between Molise and Puglia regions (southern Italy) and, finally, in the period 3-6 November intense gas exhalations happened near the Eolie islands (southern Tyrrhenian sea). The CLT radio-signal decreases we observed appear clearly related to the previous activities with some possible premonitory behaviour. The LF signals are characterised by the ground-wave and the sky-wave propagation modes. The decreases in CLT radio-signal we mentioned previously are related to a reduction of the electric field strength both of the ground wave and of the sky wave. Changes in the troposphere-ground boundary zone and in the lower non-ionized atmosphere seem to be the main candidates to justify the phenomenology we observed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
